Help diagnose RPM gauge bouncing and finally stalling at slow speed... (Page 1/1)
a_bartle JUL 08, 07:42 AM
Trying to determine what's is the issue with my '86 Fiero GT / 2.8 V6 with 56,000 miles on it. When the car is cold, it runs fine and going down the road at around 60 mph the RPM gauge is rock solid. However, after about 15 to 20 miles and everything in the engine bay is nice and warm, at 60 mph I begin to see the RPM gauge starting to bounce slightly. The gauge starts getting a little more aggressive, and then I can begin to feel a little jerking/hesitations. It's never quit on the road, but when I slow down in the driveway/heading into the garage, it stalls. It struggles to start (but I've always been able to get it running again) but I limp it back into the garage (sometimes stalling a few times). Thus far no check engine light.

Then after a day or two when I go to use it, it fires right up, acts fine, but the cycle repeats....

Any suggestions what I need to check................?

[This message has been edited by a_bartle (edited 07-08-2019).]

flimbob JUL 08, 08:55 AM
ICM bad or missing heatsink paste
a_bartle JUL 08, 03:34 PM
I was kind of wondering about that. However, I recently replaced the Distributor (which includes an Ignition Control Module) with a Richporter #GM17. Before installing, I put on a big heat sink on it.



Then not long after installing, the common "oil leak" started, so it had to come out again and replaced the seal with one of the really good ones (from RodneyDickman.com I believe). Anyway, it's all still pretty new, do you think the ignition control module could still be the issue? I wonder if ICM that Richporter uses in their mfg process is a quality product....?

Is there an easy way to check them?

[This message has been edited by a_bartle (edited 07-08-2019).]

Patrick JUL 08, 04:12 PM

quote
Originally posted by a_bartle:

I wonder if ICM that Richporter uses in their mfg process is a quality product....?



I suspect it's some cheap no-name ICM. It seems that the ACDelco ICMs are much more robust/durable.

Adding a heat sink is a great mod (as long as the proper thermal compound is used between the heat sink, the distributor base and the ICM), but it's possible the ICM used by Richporter is of such low quality that it's failed quickly despite adding the heat sink.

I've heard that ICMs can be tested at places like AutoZone etc, but it's critical that the test be run over and over to really heat up the ICM.
a_bartle JUL 08, 04:52 PM
I used the proper thermal compound, however, as you said, it still might be a cheap/poor ICM. I think I have a spare, but I "hope" I can change it without having to pull the distributor (especially due to the bolt used to hold the heat sink).

Upon reading & doing some research, it "might" also be a faulty fuel pressure regulator (when it stalled in my garage, the exhaust smelled very rich)??? Can a leaking fuel pressure regulator be exacerbated after the engine has been running for a while? Someone said pull the vacuum hose and check for fuel; I know it's under the upper intake plenum, is it accessible without removing it?
Patrick JUL 08, 06:38 PM

quote
Originally posted by a_bartle:

Someone said pull the vacuum hose and check for fuel; I know it's under the upper intake plenum, is it accessible without removing it?



Check the other end of the hose. It's a lot easier.

You should be able to figure out which hose by looking at the image in This thread.
a_bartle JUL 09, 08:02 AM
I believe I found the correct vacuum hose for the fuel pressure regulator, I didn't notice any gas (and when I pulled it off, the engine RPM's went way up).

I checked my "Fiero Spare Parts Bin" and found that I had a new AC Delco ICM still in the box. So I removed the Richporter ICM (which was stamped "Made in Canada"... false since of quality? ) but in doing so, I had to remove my heat sink (it was fastened on using the same mounting bolts for the ICM). Pretty much impossible to put it back on without pulling the entire Distributor, and I wasn't going to do that. So it's back to the way it came from the factory.

However, I decided to hot wire the coil/alternator cooling fan so it runs all the time, thought it might help. I was also thinking about getting a short piece 1/2" of metal tubing and place it in front of the pipe opening that cools the coil and bend it to perhaps re-direct a little air directly to the ICM... has anybody done that?

So I drove the car into work today, seems ok, but I'm not saying my issue is solved (I drove the car to work last week just fine, it was when I got back home when it stalled in the driveway). I'll keep you posted...

[This message has been edited by a_bartle (edited 07-09-2019).]

a_bartle JUL 12, 09:09 AM
Just wanted to report back in, I'm pretty sure the new ICM was the issue. I've driven the car into work a few times now, and it's been fine... no hesitation/jerking at road speeds and it has not stalled again. Thanks for the help/suggestions, much appreciated.

Disappointments: the Richporter Distributor (with ICM)... thought it was a quality product, replaced my old one to eliminate future problems. It ended up having a poor seal and ICM, both of which failed! Now that I've replaced the ICM with a ACDelco, I do not have a heat sink under it (and I do not want to pull the distributor again to re-install) so I hope having the coil/alternator cooling fan on all the time will compensate (although I wonder how long the fan will last if it's running all the time...).

[This message has been edited by a_bartle (edited 07-12-2019).]