Just today, I very carefully replaced my Fiero's original (severely corroded) distributor with a new Spectra GM17 distributor. I did my best to line everything up in the same orientation as the old distributor, but I must have been off somewhere. I need some help!
The car started up no problem, but it idled a little rougher than usual. When I took it for a 20 minute drive on the highway, it seemed OK at higher speeds, however, whenever I drove at a lower speed, slowed down, or came to a stop, it got really, really rough. Whenever I stopped at a red light, it started hunting wildly from 600 to 1400 RPM and it sounded like it would stall. It did stall on me once when I finally parked it in my driveway.
I am thinking that the distributor is messing up the timing. Is that likely the case? Is this easy to solve? Do I try to spin the distributor a few degrees and see if the roughness goes away? How do I fine-tune this engine?
I would love to get some advice before trying anything else...
Thank you and God bless.
David
------------------ "He is no fool who gives up what he cannot keep in order to gain what he cannot lose."-Jim Elliot
I am thinking that the distributor is messing up the timing. Is that likely the case? Is this easy to solve? Do I try to spin the distributor a few degrees and see if the roughness goes away? How do I fine-tune this engine?
Use a timing light. Pages 1-22 and 1-23 in the Haynes repair book.
I usually just connect to spark plug #1 and set to 10 degrees BTDC.
I purchased a timing light and I adjusted the timing to 10 degrees. It had been around 16 degrees, so obviously that was a problem!
However, I still have an issue.
It seems to be running smoothly when I am driving up over 60 km/h (35 mph). The RPMs are good and solid. Below this, it is a little rough - and it gets rougher the slower I go. And whenever I come to a stop, it stalls out after 10 or 20 seconds.
I would check out the spark plug wire location assignments again. It could also be an ignition module. Be advised that aftermarket modules do not work much of the time. Only the AC Delco modules seem to be able to take the high heat location and if you installed one did you use thermal grease? Are the heat shields back in place?
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
It sounds like you're saying it ran perfectly fine before you changed distributor.
That's why the emphasis is on timing, making sure plug wires are correct, and checking anything that may have been disturbed or disconnected when changing distributor.
[This message has been edited by fierosound (edited 10-27-2019).]
With the old (original) distributor, old spark plugs, and old plug wires, the engine was running OK, but not perfectly. It would hunt at idle and it seemed sluggish.
A few months back I had changed the EGR valve, which made it a little less sluggish.
Last week I replaced all the spark plugs and plug wires and made sure the engine ran, which it did. Then I changed out the distributor the same day.
After that, the hunting was worse than ever, and it was running REALLY rough. I thought this might just be a timing issue.
Now, just today I was able to set the timing at 10 degrees. (However, I have no idea what the timing was set at before I changed everything. Maybe it was at some "custom" setting?)
It still runs rough (though maybe slightly better than before I set the timing), and it is actually stalling when stopped for 10-20 seconds.
Is it possible that some other issue is now being exposed? Can this roughness be caused by the old ICM (ignition control module) and/or ignition coil (which are probably original)? Or is this definitely a problem with the new distributor?
I will note that there are NO engine codes present.
Next step then is determining if the outer ring of the harmonic balancer might've spun on the inner hub... as if it has, the ignition timing will be all off. This is not an uncommon occurrence.
The main timing mark needs to line up with the actual TDC of cylinder #1.
[This message has been edited by Patrick (edited 10-27-2019).]
This morning, I decided to try (gently, slowly) rotating the distributor while the car was running normally (not in diagnostic mode) while I listened carefully to the engine. With my ear I could hear what sounded like a more optimal position. At that point, I put the computer in diagnostic mode and then got out my timing light. I could see that I was now on the right track. What I had previously thought was the timing groove was obviously some other mark on the balancer. NOW I could see a very obvious, noticeable groove all along the edge of the balancer, and it was lining up closer to where it should (around 14 degrees). I rotated the distributor a touch more, and I was at the 10 degree mark (more or less).
I guess that the timing had been SO far off before that I couldn't even see the right groove!
I then exited diagnostic mode and took the car for a good long spin on the highway. It never drove better! At idle, the RPMs fluctuate only from 900 to 1,000. No roughness at all. It was simply a timing issue - or more honestly, a human error issue.
Thank you, gents. Problem solved! God Bless.
David
[This message has been edited by CookesForChrist (edited 10-28-2019).]
What I had previously thought was the timing groove was obviously some other mark on the balancer. NOW I could see a very obvious, noticeable groove all along the edge of the balancer...
There are three timing grooves/marks on the balancer. Two narrow ones and a wider one for cylinders 1 & 4. If you had used one of the narrow grooves for your ignition timing, I doubt the engine would even run... unless the outer ring of the balancer has spun, thus negating all efforts to correctly time the ignition with a timing light.
quote
Originally posted by Patrick:
Next step then is determining if the outer ring of the harmonic balancer might've spun on the inner hub... as if it has, the ignition timing will be all off. This is not an uncommon occurrence.
The main timing mark needs to line up with the actual TDC of cylinder #1.
for solving the problem. Persistence pays. 
