Hi everyone,

I was having some trouble with my 85 Sunbird (1.8 Turbo) -- volts light came on and died at idle. The alternator tested 11v so I rebuilt it, which solved that problem. The car still died at idle and would not restart at all, so I replaced the ignition control module, which helped alot! No more dying at idle, and the car runs much smoother at idle.

However, when out for the test drive, there is pretty extreme hesitation and stuttering, violent lurching at the turbo kicks in and out, or has no power. When revving the engine in neutral, there appears to be no misfire or turbo problems. Only when in gear under power does it lurch. The PSI on the turbo maxes out (15+ psi) and jumps around. I checked my plugs and wires, replaced one of the wires and the plugs look great. Put in a new rotor cap. Normal at idle. This is a manual transmission.

What is strange is that before I replaced the ICM, it did not do this at all, and seemed to run normally (it would die at idle and not restart, that's it).

There is no vacuum hose from the waste gate valve on the turbo (to?), not sure if that matters.

This has a relatively new turbo on it (the old one blew out, and probably threw some pieces into the catalytic converter -- so that could be somewhat plugged). But the stuttering happened only after the ICM was switched out, so I doubt that is it. Any ideas on what to check? Oxygen sensor? other sensors?

Thanks for your help! This is such a great group.
James

I think there should be a vacuum hose from the wastegate valve. check to see what happened to it. If it is off, you could be loosing vacuum under acceleration. That will cause problems.

Vacuum hose runs from the wastegate to the map sensor. Stuttering may be caused by many things... but get your vacuum lines squared away and retest. Usually stuttering could be caused by:

1. Overboost condition... lack of the v-line

2. Low or loss of oil pressure causing fuel pump shut-off.

3. Loose or loss of electrical contact-connection in the ignition circuit.

Sorry to hear you are having problems, that was a new turbo with 1 hour idle time on her.

Alan

Hi Alan! The turbo works great -- the car was saved, thanks to you.

After fumbling around, it turns out the exhaust manifold had melted the housing on the spark wire going to the furthest cylinder, and a small arc was jumping to the air intake tube sporadically. I only noticed this when working on the car after hours, and saw a faint blue spark on the red hot manifold. I taped the wire temporarily and that solved the lurching and stuttering, until I can get a new wire today to replace it.

I also found the vacuum line that had been disconnected from the wastegate valve. That seemed to calm things down a little bit more and make it smoother.

Oddly the turbo really launches at 3500 RPM with a violent, sudden blast of energy; it is slow coming off of idle and between gears at low RPM, then at 3500 it launches to hyperspace. Can this be adjusted? Is this normal?

I checked the air filter and intake for a restriction and it's good. One other idea is a plugged catalytic converter, which might explain the power loss and the glowing red-hot exhaust manifold?

Thanks for the help!
James

James.... first check to see if the wastegate is totally closed with the engine off. Many times the "gate" sits off of its seat and exhaust just bleeds right on through. The arm on actuator can be adjusted so it sits in the closed position properly. Then take her for a spin... see how much boost you are making. Boost is addicting so try to keep it below 10psi... yeah I know, it just feels so much better @ 15psi...BOOM ! If the boost needs to come up higher or lower a bit you can adjust the preload on wastegate diaphragm-linkage to fix that when running.

Have fun and don't burn those arms-hands of yours adjusting that linkage :>

Alan

Well, guess what. I've discovered all sorts of broken things this time around! Fixed the vacuum line, fixed ICM, replaced a cracked spark cable that was arcing, even replaced the thermostat sensor cap that had a bad gasket and was leaking. Because the wacky acceleration was still happening, I checked the air intake, then I toyed with the wastegate linkage, also replaced the rotor and distributor cap... still had the wacky violent acceleration...

I thought back about how the problem only started occurring after I replaced the ICM. So I went back to make sure my three connections were all good and what did I find? One wire going to the ICM had been pinched between the distributor cap and the ignition assembly, exposing bare wire and shorting out the connection! I taped the wire, put everything back carefully, started the car up, and immediately a difference (RPMs back to 2000 during warm up, whereas before it did not do this). Tomorrow is the test drive and either I discover a few new problems or hopefully get to cruise happily.

Thanks for your help!

James-

Glad to hear it is coming together.

That solved it! Car is running like a champ. Thanks for all the help and support from this group.