guza

I did some searching through the site and some checking but havent been able to find a problem like mine. I am having a problem with my 85 LG4 cc quad. The car has begun "bucking " when cruising and giving lite throttle. The Rpms jump and I am getting some popping through the exhaust. I get the popping on lite throttle and on deceleration. I have also felt popping through the carb as I give a little throttle. I have checked timing, set at 0. the TPS is showing .5 volts.

What really has me confused is. This only starts after the car warms up. Maybe going into closed loop? If this was a valve problem, wouldnt it do this cold also? Could the ICM be getting hot and causing this?

By the way, when I press hard on the gas, the car runs well!

Air_Adam

Sounds like its running lean, but 0* is too low for your timing, even if thats the factory setting. Try about 6* or so, and see if it helps.

I'd say its running lean though. Have you checked your fuel filter?

Stekman

ICM's typically fail when hot, so I would guess otherwise as far as that is concerned.

As already suggested, I would play with the timing a little bit, give it a little more base advance and see where that takes you.

What do you mean by the car only starts when warm? How do you start the car to get it warmed up, if it only starts when warm? Or is it a sluggish cold start?

sqzbox

Check your coil wires and see if their touching anything or each other. Might want to pull the cap and check for carbon tracks too.
A good trick is to pull your air filter assy. and check around in the dark. It's easy to see if wires are arking with each other. Being your RPM's are bouncing around, I would suspect a short somewhere. That usually causes the tach to go haywire.

guza

The problem only happens after the car warms up. Sorry for the confusion!! I can drive some without any problems, but as soon as the car warms up, or goes into closed loop, the problems arise.

I have checked for arcing in the dark but haven't seen anything. I will play with the timing tonight. I have Coil in the cap so I am not sure what wires may arc.

Replaced the paper fuel filter about 6 months ago but will do again, they are cheap enough!

Thanks for the input so far!

five7kid

iTrader: (14)

Ignition control module.

The tach gets its signal from it. They are known to fail. Along with the coil.

Replace both. If the cap & rotor haven't been changed lately, get them too.

guza

Ok I have an update. On the way to work today, I thought, "Hmm runs fine till the ecm kicks in?" I unplugged the ecm about halfway to work. Ran fine after that. No popping, no stuttering, just beautiful. At least I didn't spill my coffee on the way to work!

Now, I think, "What could it be? Post an update and pray for a quick answer."

Is the ECM at fault, or maybe the prom? Could a bad O2 sensor cause this?

five7kid

iTrader: (14)

Does your SES light work? Is it coming on?

guza

It wasn't on before. Now that the ECM is unplugged it is on.

five7kid

iTrader: (14)

The tach jumping when the popping occurs indicates the ICM. With the ECM disconnected, it goes into "limp home" mode, which is probably bypassing the faulty circuit in the ICM.

guza

I was kind of thinking ICM because it only did it after warming up. But I heard that ICM are either "go" or "no go" once they are overheated they are done and the car won't start. I will try a new ICM tonight and let you know. Is one brand of ICM better than another?

five7kid

iTrader: (14)

Now that's opening up a can of worms. . .

While almost everyone says the stock units are weak, some people say they won't put anything but genuine AC Delco back in their car. I've been running an Accel 7-pin ICM since Nov '01, some people say they'll never buy anything from Accel again.

So, get out the salt and take it. . .

guza

Well, I went to Advance and got a GP Sorensen. That will have to work. When I opened the distributor, one of the screws came out of the rotor. It was laying in the bottom. This time I used a little Loc-tite on it.

Put the ICM in and took it for a ride. It ran great. Thanks everyone for all the help.

csa000

Sorry to steal your post but how does one disconnect the ECM? I have a 89 Iroc that is doing about the same thing so I would like to give this a try. Thanks

guza

Mine has a single wire connection that comes off the the positive side of the battery. It runs along the right wheel well. I just unplugged that.