Tach is bouncing and starts to bog down??

[killer1GDSM]

Okay, I am in need of some serious help. I looked at the very few threads that concerned bouncing tachs but nothing i could reed seamed to help or be for a 1st gen.

Just recently my car has started acting this way, at normal speed (we will say 5th gear, 65 mph, at 2900 rpm) my tach starts to bounce down to 23-2500 rpm then back up then down and so forth, after about a minute of that any gas i give it bogs itself down like i have a fouled plug or something, but those all check out okay.

then if i come to a stop ( say at a stop sign) and have to wait for a few, it will drop to below 300-500 rpm and lights go dim.

There has to be electrical explanation for this, right. Because mechanically speaking, my car is sound.

Thanks, Dustin.

 

[gusu]

Bad alternator or something isn't grounded properly is where I'd start first.

 

[killer1GDSM]

Any way to test alternator without taking it off? Oh boy checking grounds will be fun..... not. Any ideas on which ground to check first? haha
thanks though.

 

[WES_393]

Try testing the ignition control module.

 

[killer1GDSM]

Try testing the ignition control module.

pardon my derp moment. But, what and were is that?

 

[WES_393]

It should be on the intake manifold right behind the fuel rail if I'm not mistaken. Its ben a while since I owned a 1g. Its a black rectangle and says "power transistor" on it.

 

[killer1GDSM]

okay, i think i know what you are talking about. how do i go about testing it?

 

[WES_393]

If I wasn't on my Kindle I would have the link. Just search ICM testing. You just measure resistance with a Multimeter across certain pins. Many auto parts stores can do live ICM testing as well.

 

[killer1GDSM]

cool, thanks man.

 

[killer1GDSM]

Okay, so i still havent got around to checking the module but i have heard that its rare for it to go bad? also i threw a check engine light and my data logger said it is the coilpack?

 

[brianksm]

Bad alternator or something isn't grounded properly is where I'd start first.

i had the same problem, it's a bad alternator. Are you any other lights or just cel?

 

[killer1GDSM]

its just the CEL, and it only intermittently, takes about ten minutes of normal to mild driving then it has the symptoms i was talking about.

 

[gameover95]

People automatically always assume this is the alternator, could be your tps. My car had the same issue, bogged up and down. My car is in need of a tune, however, I tested that theory on mine, replaced the alternator, alt belt, and battery. Just trying to relate to your issue. I would def check the throttle position though.

Still a newb at this, just trying to help /:

 

[AngelOfPassion]

My car threw a check engine light at me for the TPS when my cars tachometer bounced like that. However replacing the alternator fixed the problem. I didn't even have to touch the TPS...

 

[bryanwheat]

Kind of sounds like what happens when the caps start to leak in the ecu. The engine will only fire on to coils intermittently. And the tach will drop to half the rpm's that the engine is running. I would check the board for damage around the caps.

 

[killer1GDSM]

The ecu is the first thing I checked,it had seals from motoguysgarage ecu repair but that has to be from years ago, anyways te caps look fine no leakage or anything, as for the tps were do I find it and how do I tell if it's bad or not? Also I had my alternator tested and it is fine.

 

[bryanwheat]

A bad tps won't case the tach to bounce around.

 

[killer1GDSM]

Kind of sounds like what happens when the caps start to leak in the ecu. The engine will only fire on to coils intermittently. And the tach will drop to half the rpm's that the engine is running. I would check the board for damage around the caps.

Doesn't the ignition module cause the same thing if it is bad?