TeamSwift

I've got an 1988 Suzuki forsa (same as chevy sprint) that has a tachometer that goes kuckoo at about 4000 rpm. Below 4000rpm the engine accelerates just fine, then at about 4000 rpm the tachometer goes crazy and fluctuates rapidly around 6500-7000 RPM (just the needle, not the actual engine speed) and the engine power bogs slightly. This continues for 5-25 seconds before the needle settles back down to 4000rpm and increases accordingly with how much throttle I give it (as one would expect it to) and the power returns. It is like it has a healthy power curve, but there is this long static pause in the middle of accelerating at 4000rpm. It isn't a show stopping problem, the car runs great other than that.

Here's my hypothesis:

Whatever sensor feeds the engine speed information to the instrument cluster probably feeds the same information to the ECM which confuses the computer into mishandling its instructions to the carb. I am supposing if I can track down which sensor actually collects the information about the engine speed I may be able to fix the problem. Basically I am assuming if I can get the tachometer to register the correct engine speed, the power bogging issue will go away since the two issues always occur simultaneously.

I've check my Haynes manual and come up empty. Does anybody know what the doohicky I am looking for is actually called so I can research it on google? Hard to research without knowing the technical name of the part that I am looking for information on. Extra points if you can tell me where on the engine it is located~!

Thanks for reading...

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1988 Suzuki Forsa
1988 Chevy Sprint

If I'm right, and I think I am, that sensor you speak of would be the negative side of the ignition coil.
Start with a good tune up, plugs, wires, cap, rotor, etc, and go from there.

I've got a new rotor and cap when I installed the new distributer, but my spark plug wires are a mixn' match from different sources so that would be the easiest first line of attack on this issue to replace those with a fresh set. Are there any other sensors that feed the carb that may be out of whack and causing this kind of isolated disturbance? I already replaced the O2. There are also so many friggen' vacuum hoses that control actuators on this sucker.

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1988 Suzuki Forsa
1988 Chevy Sprint

Id also look at your ground wires on the car. do the lights or anything else flicker around the same time?

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1992 geo metro the perpetual project car
1986 suzuki samurai LWB aka beth
1994 suzuki sidekick 4 door

i have the same problem but mine is an aftermarket tach and it does it when ever it wants not an a especific rpm like yours

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suzuki forsa 1985 (SA310)
g13bb swap
GTi flywheel
clutchnet 3 solid puck clutch
clutchnet red pressure plate
honda short shifter> back to stock shifter
short ram intake
baleno 1.6 ecu
custom header with 2" exhaust
GTi front hub and calipers swap
soon mk1 GTi exterior coversion

The lights don't flicker, but the dashboard clock and radio are intermittently powered on any given day.

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1988 Suzuki Forsa
1988 Chevy Sprint

Already had new plugs, but I added new wires and a new coil. That made a big difference. Also my alternator was shot so I may not have been getting the voltage necessary to make the coil sing the proper tune. Also my EGR valve was not only completely blocked with soot, but also leaking vacuum pressure. Replaced that one. Its running MUCH MUCH better now, but the tach is still flakey

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1988 Suzuki Forsa
1988 Chevy Sprint