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PostPosted: Sat Sep 24, 2011 8:51 am 
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DWELL Ignition/Air fuel ratio

In the old days of point type ignitions, there was as setting referred to as Ignition Dwell. This was an adjustment that varied the amount of time (in degrees) that the contact points stayed open. Adjusting Dwell went the way of the dodo when the HEI and breakerless points igntions became more common.

In the MK1 Sprints, NA/Carbureted we find that the term DWELL, is once again used but in reference to the initial setting of the air/fuel mixture screw at the base of the carburetor. According to both OEM and aftermarket manuals is tells one to set the value at 21-27. By plugging in either an old style or new style Dwell meter into the capped test port adjacent to the battery, one then adjusts the air/fuel mixture screw to obtain this setting. Furthermore, the GM OEM manual states to set the dwell meter to the 6cyl mode to take these readings. The more modern meters now have a 3 cyl mode, which should one use? I'm thinking use the 6 cyl for this adjustment as that is what the OEM values are based on. That, or do math to obtain a proper 3 cyl value.

My question? as there is no time base of points on an electronic ignition, What is it that we are adjusting? Does anyone really know? Is it possible the duty cycle of the MCS?

Tech minds that KNOW, please enlighten us.

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


Last edited by mkc1962 on Mon Sep 26, 2011 3:57 pm, edited 1 time in total.

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PostPosted: Mon Sep 26, 2011 3:56 pm 
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Thanks to a tip from a local friend that frequently still rebuild carburetors....the following info was found on the topic.

This is a description of the procedure I've used to diagnose air/fuel mixture problems in computer controlled carbureted engines; the outlined procedure can also be used to set the idle air/fuel mixture without resorting to infrared exhaust gas analysis. The procedure is based on the General Motors "System Performance Test" which was developed for diagnosing problems in GM's carbureted engines. This procedure will not work with carburetors which use a stepping motor to control the a/f mixture.

Theory

The a/f mixture is controlled by a MIXTURE CONTROL SOLENOID (MC solenoid). This is a valve which operates at a fixed frequency (typically, 10 Hz) and whose duty cycle (valve's ON time divided by period) is varied. That is, the valve is pulse width modulated. When the valve is turned on, the incoming a/f mixture is fully leaned; when off, fully enrichened. The former is called a "lean command" whereas the latter is called a "rich command." By varying the duty cycle of the MC solenoid, the AVERAGE a/f mixture can be varied. In GM products, this valve directly varies the incoming fuel and air flow. In Fords, only the incoming air is directly varied. In Chryslers, only the incoming fuel flow is directly varied.
The valve has a two wires electrical connector. One wire is connected to switched battery voltage whereas the other is connected to a power transistor in the computer and is a source of switched ground.

During closed-loop operation the following will occur (assume the oxygen sensor is sensing a lean condition -- its voltage will be low):
The computer gradually decreases the MC solenoid's duty cycle.
The exhaust eventually becomes rich enough that the oxygen sensor's output will swing high (about 1 volt).
The computer gradually increases the MC solenoid's duty cycle.
The exhaust eventually becomes lean enough that the oxygen sensor's output will swing low (about 0 volt)
.
The cycle now repeats. A device for monitoring the solenoid's duty cycle (such as a dwell meter will show a constantly varying duty cycle. The frequency of the oscillations will depend on the how fast the computer varies the duty cycle and the engine's RPM. An AVERAGE duty cycle of 50% corresponds to, on the average, NO average a/f correction. Stated differently, everything is operating correctly. An average duty cycle of LESS THAN 50% corresponds to, on the average, a rich command (the computer is compensating for a lean condition). An average duty cycle GREATER THAN 50% corresponds to, on the average, a lean command.

DIAGNOSIS AND SETTING IDLE A/F MIXTURE

Monitoring the MC solenoid's average duty requires (for most people) the use of high impedance dwell meter. A low impedance dwell meter may be used unless it affects engine operation; my recommendation is to not use a low impedance dwell meter (that is, stay away from self-powered dwell meters). Following the GM procedure, set the dwell meter to the six cylinders scale REGARDLESS of the number of cylinders in the engine. At this setting, 30 degrees will correspond to a 50% duty cycle, 60 to a 100% duty cycle, and 0 to a 0% duty cycle. Run the engine until closed loop operation is present; this will be indicated by a varying dwell (see footnote 1 for deviations from this procedure). Once the engine is hot, not the average dwell -- the reading should vary equally above 30 degrees and equally below 30 degrees. The following is a brief trouble listing:

DWELL NOT VARYING: system is operating in open loop.

DWELL STUCK AT 10 DEGREES OR LOWER: full rich command is present; the computer is compensating for WHAT APPEARS TO BE a massive fuel flow reduction (check for dirt in carburetor, air injection system stuck in upstream position, vacuum leaks, improper a/f mixture setting...)
.
DWELL STUCK AT 50 DEGREES OR HIGHER: full lean command is present (check for float stuck low, valve seat damage, oxygen sensor's sense lead shorted to battery voltage, etc.)

DWELL OSCILLATING, BUT AVERAGE READING IS BELOW 30 DEGREES: average rich command is present (check for vacuum leaks, dirt in carburetor's jets, improperly set a/f mixture...)

DWELL OSCILLATING, BUT AVERAGE READING IS ABOVE 30 DEGREES: average lean command is present. Check for incorrectly set a/f mixture, float stuck low, valve seat damage, clogged air filter, etc...).

Based on the above descriptions, it should be fairly clear on how to set the idle a/f mixture: merely set the mixture so that the average dwell is 30 degrees. Now, suppose the system's dwell is not varying, but the sensors are working properly, the upper radiator hose is hot...
Several cars with small engines have the oxygen sensor mounted fairly far away from the engines. Indeed, during idle conditions, the sensor may cool off to the point that it will not operate (I had this experience in a 1986 Mustang with 2.3 liters engine and EEC-IV system). My recommendation is that all electrical accessories be turned off (so as to provide a minimal load on the engine) and use the idle stop screw on the carburetor to gradually increase the idle rpm until the sensor begins oscillating. Ensuring a negligible load on the engine guarantees that the carburetor will be operating mostly on its idle circuit. Now, set the a/f mixture so that the average dwell is 30 degrees. On the Mustang, this was done at about 1500 rpm.
Note that the a/f mixture setting procedure assumes that NO fuel delivery problems (vacuum leaks, clogged carburetor, etc.) are present.

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Mon Sep 26, 2011 6:31 pm 
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Thanks for that, Mike.
This deserves a 'sticky' in the MK1 section, as I've never seen the GM procedure mentioned anywhere in the site.
Were you able to get the oxygen sensor to work fine at warm idle?

_________________
DIY Broken Bolt Removal: viewtopic.php?f=22&t=41042
DIY Clutch Adjustment: viewtopic.php?f=9&t=48281
DIY Wheel Bearings: viewtopic.php?f=2&t=29003
DIY Shocks: viewtopic.php?f=10&t=45483
DIY Wheel Align: viewtopic.php?f=2&t=42479
Once you get the cars dialed-in (compression, leaks, bearings, alignment, brakes) swap in new rubber and glass, you've got something which should last for years!


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PostPosted: Mon Sep 26, 2011 9:00 pm 
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Phil N Ed wrote:
Thanks for that, Mike.
This deserves a 'sticky' in the MK1 section, as I've never seen the GM procedure mentioned anywhere in the site.

Were you able to get the oxygen sensor to work fine at warm idle?

I assume it is, based on these found instructions on this topic, my dwell readings reflect proper mixture. I still would like to do a temporary install of my afr guage and do actual 02 readings .

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Mon Sep 26, 2011 10:25 pm 
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Location: Palm Springs: Too hot from June to Oct.!
Well, over 40 miles per gallon is certainly respectable.
Which part of it is the cam grind?
MCS?
Technician who assembled it?
Ha!

_________________
DIY Broken Bolt Removal: viewtopic.php?f=22&t=41042
DIY Clutch Adjustment: viewtopic.php?f=9&t=48281
DIY Wheel Bearings: viewtopic.php?f=2&t=29003
DIY Shocks: viewtopic.php?f=10&t=45483
DIY Wheel Align: viewtopic.php?f=2&t=42479
Once you get the cars dialed-in (compression, leaks, bearings, alignment, brakes) swap in new rubber and glass, you've got something which should last for years!


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PostPosted: Tue Sep 27, 2011 8:40 pm 
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Phil N Ed wrote:
Well, over 40 miles per gallon is certainly respectable.
Which part of it is the cam grind?
MCS?
Technician who assembled it?
Ha!


Well probably a bit of all of it....but we both know without a working MCS she aint going anywhere.

As for your question on the 02 sensor above...today after a short trip to town, using my dvm I checked the output voltages on the 02 at idle. The readings fluctuated between .1 and 1 volt. I then pulled that vacuum line that goes to the base of the air cleaner to create a temp lean environment and the voltage dropped to between 0 and .5 . After that I grabbed my propane torch (unlit) and placed it into the aircleaner snorkle, slight rich condition. the voltage fluxuations were then between .4 and 1. After that back to normal ilde condtions and the meter went back to the .1 to 1.0 fluxuating.

While at it went ahead and re connected the dwell to check to see if it was still where I last set it, and it was.

I think that between the Dwell testing and the above 02 testing it is safe to say the 02 is working great at idle. Of course a safe assumption is also the fact that I put in a new one as part of the rebuild. :roll:

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Tue Sep 27, 2011 11:15 pm 
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All the more reason to at least have some kind of bookmark of this thread in the MK1 section.
This has important diagnostic techniques for the carburetor version not found elsewhere.
The O2 readings should be noted by those with MK1s who are having problems.
Before posting a 'what's wrong' thread, take those readings and include them.


You've mentioned the effect of the O2 sensor on the MCS, but this question is regarding the effect of the O2 sensor on the IUA.If your air/fuel mixture is not right, or during periods of warm up, would you expect the O2 sensor to give signals to the ECM which in turn would send signals to the IUA causing a 'cycling' of the idle?
viewtopic.php?f=31&t=47750


Concerning the 'extended range' MK1 cam grind -
-are you satisfied with the grind?
-do you notice a shift of the power band to the lower range of the RPMs?
-have you compared the ER grind with the non-ER cam?

_________________
DIY Broken Bolt Removal: viewtopic.php?f=22&t=41042
DIY Clutch Adjustment: viewtopic.php?f=9&t=48281
DIY Wheel Bearings: viewtopic.php?f=2&t=29003
DIY Shocks: viewtopic.php?f=10&t=45483
DIY Wheel Align: viewtopic.php?f=2&t=42479
Once you get the cars dialed-in (compression, leaks, bearings, alignment, brakes) swap in new rubber and glass, you've got something which should last for years!


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PostPosted: Wed Sep 28, 2011 5:30 am 
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[quote="Phil N Ed"]All the more reason to at least have some kind of bookmark of this thread in the MK1 section.

Is that something a moderator must do?
This has important diagnostic techniques for the carburetor version not found elsewhere.
The O2 readings should be noted by those with MK1s who are having problems.
Before posting a 'what's wrong' thread, take those readings and include them.


You've mentioned the effect of the O2 sensor on the MCS, but this question is regarding the effect of the O2 sensor on the IUA.If your air/fuel mixture is not right, or during periods of warm up, would you expect the O2 sensor to give signals to the ECM which in turn would send signals to the IUA causing a 'cycling' of the idle?
http://teamswift.net/viewtopic.php?f=31&t=47750

Yes Ive read that post...I can say this much about the 02 and the readings. Ive tested many 02 sensors in my day, read many articles on the testing of 02 sensors, and even written a few similar posts on other forums about how properly working 02 sensors act. For those voltages to swing like that is a normal fact of life. For it to effect the IUA in relationship to that swing to me would make no sense. As for how the ECM sees that, I can tell you it see's that swing as normal and should not adjust anything. If that voltage were to stay constant either low (o) or high (1.0) or for that matter constant at any in between say like (.5) then the ECM might react. Firsly it would trigger a sensro fault in our older mk1's and in the newer ones it would trip a code.
As for the IUA, I myself am not 100% in the know as to what all issues might make it swing. I do know in the case of automatic transmissions, the minute the shift selector goes into anything other than drive or Neutral, 12v are sent to the vac solenoid valve for the IUA and in turn has the IUA do its thing.



Concerning the 'extended range' MK1 cam grind -
-are you satisfied with the grind?
I am satsified with the way the cam is doing its job. As it has been a very long time since I drove one with a std grind, I could not honestly give a judement of difference between the 2 various grinds.

-do you notice a shift of the power band to the lower range of the RPMs?
read above answer.

-have you compared the ER grind with the non-ER cam?
If you mean lobe measurement, then yes I did measure my lobes prior to install and they were different than std. But, I did not compare those to documented ER values.[/quote]

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Thu Sep 29, 2011 1:54 am 
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Mike, best post ever; that answers a lot of questions I had on my Sprint carb system. Can you still find dwell meters though? I haven't seen one for years, I always used feeler gages for setting points. I think I might have a Bad MCS, and hear they are very expensive. can they be disassembled and repaired? I rewound the resistance coils on a bad fuel gage sender once.


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PostPosted: Thu Sep 29, 2011 5:43 am 
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Thanks, they are still avail all over the web. I personally obtained mine through amazon.com for $29.

On the MCS. They are no more expensive than most parts for a proper restoration. If thats your goal. Try pricing a fully rebuilt carb. I would PM Phil above. He keeps several on hand, as well as having a source for replacments. My searches over the web found very few sources that actaully had them, even though claiming to. Most offered to rebuild yours if you sent it in. Phil has had good results with his units, owning several mk1 carbed cars himself. That is where mine came from. I am sure you know that without a good running mcs that carb will not give you the performance or MPG that it was desinged to do.

I too would like to learn to rebuild one, but to date have not had the opportunity. If I come across a spare carb that has a bad one I may try and teach myself.

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Thu Sep 29, 2011 9:36 am 
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mkc1962 wrote:

Is that something a moderator must do?
Yes.


You've mentioned the effect of the O2 sensor on the MCS, but this question is regarding the effect of the O2 sensor on the IUA.If your air/fuel mixture is not right, or during periods of warm up, would you expect the O2 sensor to give signals to the ECM which in turn would send signals to the IUA causing a 'cycling' of the idle?
viewtopic.php?f=31&t=47750

Yes Ive read that post...I can say this much about the 02 and the readings. Ive tested many 02 sensors in my day, read many articles on the testing of 02 sensors, and even written a few similar posts on other forums about how properly working 02 sensors act. For those voltages to swing like that is a normal fact of life. For it to effect the IUA in relationship to that swing to me would make no sense. As for how the ECM sees that, I can tell you it see's that swing as normal and should not adjust anything. If that voltage were to stay constant either low (o) or high (1.0) or for that matter constant at any in between say like (.5) then the ECM might react. Firsly it would trigger a sensro fault in our older mk1's and in the newer ones it would trip a code.
As for the IUA, I myself am not 100% in the know as to what all issues might make it swing. I do know in the case of automatic transmissions, the minute the shift selector goes into anything other than drive or Neutral, 12v are sent to the vac solenoid valve for the IUA and in turn has the IUA do its thing.

I think this is the part which 'economizer' feels is your 'best post ever'.
If, indeed, you are correct and the oxygen sensor has no effect on the IUA I would owe an apology to the original poster (Naftroz) who was complaining about his IUA cycling.
When you go back and read that thread, you will see:
-he rebuilt his carburetor using a freshly acquired (not mine) MCS
-after installing his carburetor, the IUA 'cycled' so he posted for help
-I explained it was normal; he hadn't finished properly adjusting his carburetor
-after adjusting the duty cycle as directed, his IUA didn't 'cycle' anymore.
Although Naftroz corrected the situation, 'normal' for a misadjusted carburetor, he maintained it was an 'anomaly', and the adjustment of the air/fuel mixture screw could not have possibly been related to his IUA 'cycling' problem, (further insult).

Since you considered the situation where the carburetor was adjusted properly, and the engine was warmed up to normal operating temperature, you mentioned the oxygen sensor would not normally affect the IUA.
(I agree; perhaps I should have let him figure it out himself.)

You left yourself a little 'wiggle room' for situations where the IUA COULD be affected by the oxygen sensor, and that is good.
If there are no instances where a completely good, new, functioning oxygen sensor will cause a IUA to 'cycle', then I promise to give a full and complete apology to Naftroz in the thread...but WAIT!!!

Since I've seen MANY IUAs 'cycle' just as he described,
Naftroz will
-buy an MCS from me
-get his degree using 'home study'
-become a millionaire working from bed
-put 4 daughters through College
-pay for their weddings
-continue sniffing exhaust with no affects to his brain
-be able to walk 30 feet without a wheelchair and EXCRUCIATING pain :roll: :roll: :roll:
...before any apology comes from me.

Concerning the 'extended range' MK1 cam grind -
-are you satisfied with the grind?
I am satsified with the way the cam is doing its job. As it has been a very long time since I drove one with a std grind, I could not honestly give a judement of difference between the 2 various grinds.
My question was more about the workmanship, surface areas, condition the cam arrived, ability of the reground cam to replace the original (fit).
-do you notice a shift of the power band to the lower range of the RPMs?
read above answer.
Perhaps with an automatic transmission, it is not a fair question.

-have you compared the ER grind with the non-ER cam?
If you mean lobe measurement, then yes I did measure my lobes prior to install and they were different than std. But, I did not compare those to documented ER values.
My question was not really a technical one about the duration and lift of the lobes, with measurements and degrees. My question was more about 'gas mileage before' vs. 'gas mileage after' and you have answered it adequately.
Thank you for taking the time to answer my questions.
Some people considering changing a stock cam to an ER grind would wonder.

As they say, back to the grind.

_________________
DIY Broken Bolt Removal: viewtopic.php?f=22&t=41042
DIY Clutch Adjustment: viewtopic.php?f=9&t=48281
DIY Wheel Bearings: viewtopic.php?f=2&t=29003
DIY Shocks: viewtopic.php?f=10&t=45483
DIY Wheel Align: viewtopic.php?f=2&t=42479
Once you get the cars dialed-in (compression, leaks, bearings, alignment, brakes) swap in new rubber and glass, you've got something which should last for years!


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PostPosted: Fri Oct 07, 2011 11:06 pm 
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Phil N Ed wrote:
mkc1962 wrote:




You've mentioned the effect of the O2 sensor on the MCS, but this question is regarding the effect of the O2 sensor on the IUA.If your air/fuel mixture is not right, or during periods of warm up, would you expect the O2 sensor to give signals to the ECM which in turn would send signals to the IUA causing a 'cycling' of the idle?
http://teamswift.net/viewtopic.php?f=31&t=47750

Yes Ive read that post...I can say this much about the 02 and the readings. Ive tested many 02 sensors in my day, read many articles on the testing of 02 sensors, and even written a few similar posts on other forums about how properly working 02 sensors act. For those voltages to swing like that is a normal fact of life. For it to effect the IUA in relationship to that swing to me would make no sense. As for how the ECM sees that, I can tell you it see's that swing as normal and should not adjust anything. If that voltage were to stay constant either low (o) or high (1.0) or for that matter constant at any in between say like (.5) then the ECM might react. Firsly it would trigger a sensro fault in our older mk1's and in the newer ones it would trip a code.
As for the IUA, I myself am not 100% in the know as to what all issues might make it swing. I do know in the case of automatic transmissions, the minute the shift selector goes into anything other than drive or Neutral, 12v are sent to the vac solenoid valve for the IUA and in turn has the IUA do its thing.


I think this is the part which 'economizer' feels is your 'best post ever'.
If, indeed, you are correct and the oxygen sensor has no effect on the IUA I would owe an apology to the original poster (Naftroz) who was complaining about his IUA cycling.
After going back and studying on this a bit more, and to also quote the Chevrolet OEM Manual. The IUA can pulse as stated during initial cold engine warm up even IF A new, perfectly working 02 sensor is in place. However Idle up is being handled by the thermowax element at this time and any movment of the IUA should not be detected (unless improperly adjusted down too far)

As for pulsing after warmup? It stand to reason that if the ecm detects a rich condition while the 02 sensor is warming up, and sends a signal to the IUA....then...if the 02 sensor were bad, or the MCS were bad, or the mixture is way off, then it might also effect the IUA.

When it comes to any part of the engine that is controled by a VSV (vac solenoid valve) one might also want to keep in mind that each of these vsv's has a filter element in its bleed side. If said filter gets clogged, and they will, all kind of weird things might could also happen.


When you go back and read that thread, you will see:
-he rebuilt his carburetor using a freshly acquired (not mine) MCS
-after installing his carburetor, the IUA 'cycled' so he posted for help
-I explained it was normal; he hadn't finished properly adjusting his carburetor
-after adjusting the duty cycle as directed, his IUA didn't 'cycle' anymore.
Although Naftroz corrected the situation, 'normal' for a misadjusted carburetor, he maintained it was an 'anomaly', and the adjustment of the air/fuel mixture screw could not have possibly been related to his IUA 'cycling' problem, (further insult).

After some recent expereinces of my own. I can safely say that a mis-adjusted mixture screw (mcs duty cycle/dwell) can causee all sorts of wierd idle situations.



Since you considered the situation where the carburetor was adjusted properly, and the engine was warmed up to normal operating temperature, you mentioned the oxygen sensor would not normally affect the IUA.
(I agree; perhaps I should have let him figure it out himself.)

You left yourself a little 'wiggle room' for situations where the IUA COULD be affected by the oxygen sensor, and that is good.
If there are no instances where a completely good, new, functioning oxygen sensor will cause a IUA to 'cycle', then I promise to give a full and complete apology to Naftroz in the thread...but WAIT!!!

Since I've seen MANY IUAs 'cycle' just as he described,
Naftroz will
-buy an MCS from me
-get his degree using 'home study'
-become a millionaire working from bed
-put 4 daughters through College
-pay for their weddings
-continue sniffing exhaust with no affects to his brain
-be able to walk 30 feet without a wheelchair and EXCRUCIATING pain :roll: :roll: :roll:
...before any apology comes from me.

Concerning the 'extended range' MK1 cam grind -
-are you satisfied with the grind?
I am satsified with the way the cam is doing its job. As it has been a very long time since I drove one with a std grind, I could not honestly give a judement of difference between the 2 various grinds.
My question was more about the workmanship, surface areas, condition the cam arrived, ability of the reground cam to replace the original (fit).
What Arrived, looked like new and fit perfectly.

-do you notice a shift of the power band to the lower range of the RPMs?
read above answer.
Perhaps with an automatic transmission, it is not a fair question.

-have you compared the ER grind with the non-ER cam?
If you mean lobe measurement, then yes I did measure my lobes prior to install and they were different than std. But, I did not compare those to documented ER values.
My question was not really a technical one about the duration and lift of the lobes, with measurements and degrees. My question was more about 'gas mileage before' vs. 'gas mileage after' and you have answered it adequately.
Thank you for taking the time to answer my questions.
Some people considering changing a stock cam to an ER grind would wonder.
I too wish I could have done a before and after comparison. But the car was not running when I bought it.


As they say, back to the grind.

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Mon Nov 07, 2011 8:40 pm 
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***UPDATE on the DWELL info***

If one references the FSM, the FSM states to set the dwell at 21-27. However, the follow up article that I found on line references more in the range of 30. some might ask "Whats the big difference"

I recently added an AFR meter to my car only for testing purposes. Mind you, all of my test readings are based on the fact I have a fresh rebuilt carburetor with a new MCS, as well as a new 02 sensor. Here is what I found after a few tanks of fuel and various dwell setups.

Keep in mind, as you adjust the dwell you will NOT get the meter to read an exact number, but rather it will bounce slightly on both sides of your desired goal. For ex...bouncing between 29-32 usually has it hitting 30.5 on avg.

Using the FSM recommedations of 21-27 dwell, the AFR meter showed both at idle and at road speed that the car was running too much on the rich side, especially around the 21 but even at the setting of 27. I then set that dwell so that it bounces between 29 at its lowest and 31-32 at the highest, I obtained the best AFR readings for both idle and road speeds at this setting. "Whats the big Difference?". For those into these cars for what they were originally designed for, that being economy, 21-27 dwell netted on avg about 34-36 mpg. 29-32 dwell range brought my avg's back in the 38-42 mpg range. Build your carb right, then tune it right if you want its optimum fuel economy performance. FYI during these tests I have my timing set at factory spec of 6 BTDC (for an automatic)

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Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


Last edited by mkc1962 on Tue Dec 27, 2011 2:09 pm, edited 1 time in total.

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PostPosted: Tue Dec 27, 2011 10:58 am 
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Bump to have this stickied either in this section or the carbs set up section.
Good information not readily available.
:thumb2: :thumb2: :thumb2:

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PostPosted: Fri Dec 30, 2011 1:58 am 
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I aplaud your test work. Having tested dwell settings at both published ranges, and finding that the higher range, worked better, I would be curious to see if it could be further improved by trying a still higher setting. I am sure this has crossed your mind as well. What do you think?


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PostPosted: Fri Dec 30, 2011 11:26 pm 
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Thank you,

I thought exactly as you did. That is why I conducted the above tests. If you will note on my latest UPDATE above. I installed an AFR guage ( Air Fuel Ratio) to test actual running conditions of the car at the various settings of dwell. The goal was to have the car run as lean as possible but not cause any damage that TOO lean might cause. The ranges I noted, had me running just on the edge of too lean. Another thing you have to consider is, IF the engine is running proper, with a new 02 sensor and a prefectly working MCS, IF you take it too lean, the 02 will pick this up and alter the duty cycle (Dwell) of the mcs hence dumping more fuel. The only way you will tune a carb for leaner (less fuel) running condition is to have a carb that has zero feedback at all. Even then I would want to run and AFR to make sure I am not pushing the lean burn damage zone. In the old days of leaded fuels, and even the unleaded days prior to this darn ethanol enrichement crap, one could tweek a carb by ear, and then after a healthy run read the color of the plugs.
One can still buy basic carbs and tweek by ear, but the plugs just dont color up the way they used to. :(

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Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Sat Dec 31, 2011 3:47 am 
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Ok, that makes sense. I had my Honda powered Mini on the dyno recently, and asked the tech to pull some more fuel out of the map at 3800 RPM (high vacuum cruise mode), he kept pulling fuel out, but AFR stayed at 14.7, so I guess the O2 was just putting the fuel back in. I think these engines can probably go up to as high as 19 to one without hurtng anything; Honda has a type of VTEC system on some super economy engine models, that run in this AF range during light load operation, so am considering modifying the signal from the O2 with a resistor, so it will let me make closed loop leaner,(where I do most of my freeway driving), and see if my MPG increases. How hot could valves get hot making only around 8 horse power? And if they could, how does Honda get away with it in their lean burn motors? Titanium valves? if so, no reason why I can't use them too, if I can get better economy. Any way, my Dyno Tech guy just shrugs his shoulders, I think I am the first guy he has ever seen in his shop, that cares about fuel economy. He has an 850 HP CRX with a turbo as big as my bathroom toilet.
BTW, I am already getting 41 MPG with my B-16 VTEC powered Mini, (when I try), and it makes 185 WHP on that Dyno. :-P


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PostPosted: Sat Dec 31, 2011 6:34 am 
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Yes Honda has or had what is referred to as a lean burn engine. I am not exactly sure how they electronically get away with it unless they have their ecms programmed to tolerate higher than the norm of 14.7. I personally know of an individual that is running in the 17.5 range with an eldebrock fuel injection system that one can set the limits at whatever they want. He is doing this on a 396 chevy avg 23 mpg. He's been doing it for years with no ill effects.

As for your resistor idea that wont work. Unless you could constantly vary that resistance, the ecm will just readjust to make up the diff. However, there is a device that will allow you to do what you are wanting to do. This device is known as an EFIE ( electronic fuel injection enhancer) this is a device commonly used by folks that dabble with hydrogen injection or the like. The most reliabel source I Know of is, http://www.eagle-research.com/cms/node/216. Basically what they do is take the signal , no matter what it is from the 02 and send a normal signal to the ecm. They are not very effective on the more modern engine control systems, but will work on the sprints old simple systems. However, I would still want to keep a constant AFR going to monitor things, that or be willing to pay the consequenses if I didnt.

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Sun Jan 01, 2012 1:41 am 
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mkc1962 wrote:
Yes Honda has or had what is referred to as a lean burn engine. I am not exactly sure how they electronically get away with it unless they have their ecms programmed to tolerate higher than the norm of 14.7. I personally know of an individual that is running in the 17.5 range with an eldebrock fuel injection system that one can set the limits at whatever they want. He is doing this on a 396 chevy avg 23 mpg. He's been doing it for years with no ill effects.

If I can piggyback on to that...
Do you remember the late '80's/early '90's? GM put out the Grand Prix and other vehicles (W body???) with the 2.8L and 3.1L. For a few years, 89 thru 91, the ECU's had a "highway mode" programmed in them.
It went something like this:
If the engine was warmed up, and the speed was above 50mph, and the tps was below a certain value...the ECU would drift towards very lean mix, hold it there for a bit, snap back to stoich to make sure the O2 sensor was still working and not much else had chance, then start the whole thing over again.
In mid-late 91, the EPA found out about this little trick to get great highway fuel mileage, and made GM issue a recall (or was it a TSB?) to reprogram the ECUs, which basically, the only thing the reprogram did was to change the 50mph value up to 255mph, so the highway mode would never get a chance to kick in.
I had an '89 Grand Prix with a 2.8 that did NOT have the recall reprogram performed, got great highway mileage, pulled a dump of the ECU and found the 50mph byte value...and totaled the car a week later :) It's all documented out there somewhere.
Jist of the story...I'm guessing it's relatively easy for an ECU to command a leaner than stoich mix as long as the conditions that allowed the engine to run at stoich haven't changed...up to a point.
As far as the Honda lean burn (and other 'lean burn' systems), there are a few different types of them out there. Most of them are of the variety that starts the burn in a smaller richer pre-chamber area which then spread the flame front to the leaner larger combustion chamber. So, overall, they burn leaner, but they don't burn the whole thing leaner. Chrysler's system was a disaster of epic proportions (go figure).
But I digress...


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PostPosted: Sun Jan 01, 2012 7:59 pm 
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skimask wrote:
mkc1962 wrote:
Yes Honda has or had what is referred to as a lean burn engine. I am not exactly sure how they electronically get away with it unless they have their ecms programmed to tolerate higher than the norm of 14.7. I personally know of an individual that is running in the 17.5 range with an eldebrock fuel injection system that one can set the limits at whatever they want. He is doing this on a 396 chevy avg 23 mpg. He's been doing it for years with no ill effects.

If I can piggyback on to that...
Please do...thats what were here for

Do you remember the late '80's/early '90's? GM put out the Grand Prix and other vehicles (W body???) with the 2.8L and 3.1L. For a few years, 89 thru 91, the ECU's had a "highway mode" programmed in them.
It went something like this:
If the engine was warmed up, and the speed was above 50mph, and the tps was below a certain value...the ECU would drift towards very lean mix, hold it there for a bit, snap back to stoich to make sure the O2 sensor was still working and not much else had chance, then start the whole thing over again.
In mid-late 91, the EPA found out about this little trick to get great highway fuel mileage, and made GM issue a recall (or was it a TSB?) to reprogram the ECUs, which basically, the only thing the reprogram did was to change the 50mph value up to 255mph, so the highway mode would never get a chance to kick in.
Ive heard the story a time or two myself, But couldnt remember the model line. Coincidentally I had an 89 Gmc Jimmy 4x4, this was the smaller s10 version with the 2.8 v6, around town 18-20, but out on the highway always got near 30-32 mpg. I had guys at work that insisted I was FOS, that it was not possible. To shut things up I used it as a car pool vehicle for a short period. My carpooler seeing the results with his own eyes finally shut up the masses. I hate I ever sold that thing was a great SUV.

I had an '89 Grand Prix with a 2.8 that did NOT have the recall reprogram performed, got great highway mileage, pulled a dump of the ECU and found the 50mph byte value...and totaled the car a week later :) It's all documented out there somewhere.
Jist of the story...I'm guessing it's relatively easy for an ECU to command a leaner than stoich mix as long as the conditions that allowed the engine to run at stoich haven't changed...up to a point.
I would have to agree, but like the above I also feel that most cars manufactured these days probably wont let that happen by much. The older ones still on the road probably will.

As far as the Honda lean burn (and other 'lean burn' systems), there are a few different types of them out there. Most of them are of the variety that starts the burn in a smaller richer pre-chamber area which then spread the flame front to the leaner larger combustion chamber. So, overall, they burn leaner, but they don't burn the whole thing leaner. Chrysler's system was a disaster of epic proportions (go figure).
But I digress...

_________________
Mike
Valley Grande, AL
1986 Sprint plus

Do you maintain a personal fleet like I do?
Why do we do it?
Because it's what we enjoy and because we CAN.
2011 camaro, 2005 Vibe, 2004 camry, 06 Expedition, 87 porsche 911, 86 Sprint plus, 73 gmc 4x4, 69 camaro, 99 Gl1500 Goldwing, 12 Kawasaki klr650, 2012 Kubota L3200, and we wont even go into the small stuff.


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PostPosted: Mon Jan 02, 2012 2:21 am 
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With a lot of vehicles using wide-band O2 sensors, more engines using variable valve timing for EGR (not to mention pumping loss reduction), and now G.D.I., I'm sure a lot of them are running a lot leaner than stoich under cruise conditions. But at the same time, I'd be willing to bet those "cruise conditions" involve a very narrow set of parameters...and you have to hold your tongue just right.


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