I'm a long time (guest) lurker, first time poster. I apologize for the length of this post, but I've done a bunch of diagnosing and want to make sure I give as much information as possible. I'm looking for something I may have missed.
As per the subject, I'm working on a 1986 GT w/ 63k mi for a friend and I'm stuck. I've had the car for about 5 weeks. It was brought to me with several symptoms:
1. Horrible exhaust odor 2. Exhaust rattle 3. Poor mpg 4. Idle varies, lopes, wanders 5. In drive or reverse, engine RPM drops from 900 to 400 and often stalls. Triggers a check engine light...sometimes (CODE 33). If it recovers, the RPMS shoot up to 2k before settling down. Car ALWAYS restarts after stalling. Otherwise, the car wants to idle around 1000-1200.
He gave me a new Cardone distributor to install. tested coil and module. Both ok. Substituted known-good coils and modules for fun. No difference. I was unable to set timing accurately, as the timing pointer was all over the place (yes, I did ground the ALDL). More on that later.
Did a smoke test. Found no leaks. All vacuum lines and connectors look good. The lower exhaust manifold bolt at cyl #3 is broken. There's definitely an exhaust leak there, but not severe. No other issues seen with the exhaust other than the rattling cat.
I did a compression test and also installed new plugs, wires, cap, and rotor. Before installing the plugs, I did a compression test and the lowest cylinder was around 130psi and the highest was 155psi. Most were around 145psi. Not bad, not great. New delco O2 sensor. New coolant temp sensor. EGR tested ok per FSM. I ran the car without it, not much difference.
Checked evap canister. Looks good. Not saturated with fuel. I blocked it off to test. No difference. Air filter ok. Changed PCV valve. It snaps back when engine runs.
I scanned the ECM and discovered that the integrator was well below the desired 128. It was anywhere from 30-80. Pig rich. Fuel pressure is about 42 psi running. All sensor data looked good. TPS around 0.52V. Nothing out of the ordinary other than the MAP voltage increased (~2.5V) due to low vacuum.
At best, this engine puts out about 12-13" of vacuum, which will certainly increase fuel pressure and signal the MAP to add fuel. Substituted a known-good MAP. No difference.
I removed the plenum and ohm tested the injectors. Most were around 12, one was at 10. I lifted up the rail and primed the system. Two injectors were dripping. I replaced all 6 with new SMP injectors and a very slightly leaky regulator diaphragm with a Delco unit. Put it all back together. Blocked off the cold start valve and replaced fuel filter with a Delco unit. Car ran only slightly better.
Next up was to investigate the jumpy timing pointer. I checked the timing chain slack and found 12 degrees! Hurray! After installing the new timing chain, the car runs better, but definitely not fixed. I managed to drive it around, but it frequently stalled in gear. Always restarts immediately. At speed, it was ok. A little surging, but not horrible. I'm absolutely certain the chain was installed correctly. I brought the engine to TDC and the marks lined up at 12 o'clock. Balancer was dead on 0 BTDC. Hasn't slipped. Triple checked the marks at 12 before reinstalling timing cover, etc.
I reset the IAC (also substituted a known-good unit. Made no difference in stalling, etc). Rechecked timing. Still all over the placed with ALDL grounded. Varies from 10 to about 18 BTDC.
I also installed a new battery and cleaned all battery cable connections. I cleaned all the ground strap connections. Ground strap looks good.
I was seriously hoping to have solved the problem at this point. No dice. I decided to check the catalytic converter with a USB endoscope through the O2 sensor hole. Melted/broken. I unbolted the exhaust. Runs better, and the surge at cruise is gone, but the car still runs the same. Rich condition likely destroyed the converter.
I reset the IAC and substituted a known-good TPS as well. Also unplugged the TCC. No difference. Left EGR vacuum hose off, too. Nope.
This car has 63k miles. Oil pressure is good. Coolant temp looks good on the scan tool.
I have a couple of spare ECMs I will try, but I doubt that will help.
I spoke to the local Guru last night and he suggested I recheck distributor endplay and shim, if needed. He also suggested I check the EGR tube for cracks. I'll be doing those today and attempting to datalog the stalling condition. I'm kicking myself as I could have done those things while they were apart.
He also said that there is a cam plate? behind the timing gear that can wear out on the 2.8s and can cause erratic timing as the cam walks back and forth.
I'm about at the end of my rope here. I feel I've been very thorough with diagnosis and followed the FSM. I could use some suggestions.
With all the work you have done, You have not fixed the exhaust leak.....I wonder why. It can mess up the O2 sensor reading without tripping a code....and make your car run 'pig-rich'.
With all the work you have done, You have not fixed the exhaust leak.....I wonder why. It can mess up the O2 sensor reading without tripping a code....and make your car run 'pig-rich'.
Hello and thank you! Good to be here. In my experience with OBD1 cars, the exhaust leaks will cause a false lean condition. Definitely not the case here. This car is rich right off the bat whether in open or closed loop.
I haven't fixed it because it looks like the only way is by dropping the cradle. Unfortunately, that's is beyond my means (space and equipment). I don't see another way to get in there. I can take a pic. Maybe there's a trick? 90 degree drill?
What is the fuel pressure while running, and how quickly does it drop when the engine is turned off.
Hi Patrick. Fuel pressure, is about 42 psi at idle. Seems a bit high to me. If you wing the throttle it increases. Stock regulator. When you shut off, it slowly drops down to about 25 psi (takes about 10 mins), then stays there for hours.
After replacing all the injectors and the regulator diaphragm, I'm convinced that there would have been a significant difference in running condition, better or worse. The fact that it's basically the same after the injector swap tells me something else is likely wrong.
Hello and thank you! Good to be here. In my experience with OBD1 cars, the exhaust leaks will cause a false lean condition. Definitely not the case here.
Absolutely. However, on the scan tool, this would show Block learn and Integrator values above 128. In this case, the block learn is at 120 and the integrator varies between 30-80. That means the ECM is trying to pull fuel.
[This message has been edited by backtod80s (edited 11-17-2017).]
When you checked the engine vacuum, did you do it right off of the MAP/FPR port on the manifold, with nothing else hooked up? If not do so. You may have a vacuum leak or blockage in the tubes.
When you checked the engine vacuum, did you do it right off of the MAP/FPR port on the manifold, with nothing else hooked up? If not do so. You may have a vacuum leak or blockage in the tubes.
Is the vacuum steady or does it pulse?
I checked it off both the MAP/FPR port and the port on the front closest to the distributor. Same reading. I used different gauges.
The gauge was usually steady, but would randomly drop from 12-10 and sometimes much further. Around 1500 RPM, it produces 15"
A local Fiero guru suggested I check the EGR tube. I just did. Sure enough, it has a hairline fracture on the EGR side. I have a new one and stainless steel vacuum lines on order. With the fiberglass cover on the tube, a smoke test wouldn't be very helpful. Hopefully that's it!
I'm definitely interested in other ideas and I'll keep everyone posted.
[This message has been edited by backtod80s (edited 11-18-2017).]
Cracked Fiero EGR tubes are relatively common, but normally all it causes is a raised idle speed.
As in the side of the EGR tube where it bolts to the EGR valve. It likes to idle around 1100-1200. Anything less than that and it's not happy. IAC counts are usually near 0 in neutral or park. It's around 50-60 in drive.
As in the side of the EGR tube where it bolts to the EGR valve.
The point I'm making is that it's all the same tube, and it makes no difference which "side" or end of the EGR tube is cracked. The air that gets sucked through the crack all ends up in the same place... into the intake manifold.
Howdy!! My first concern would be that the timing is still jumping around. With the ALDL grounded it should be completely a mechanical function, with no variation. Since the chain and tensioners should be good, I would be looking at the cam and dist gears. Possible slop in the "new" distributor (bushings springs, weights, etc.) None of the electricals are going to function correctly until the mechanicals are correct. As to the rich condition, have you checked the return line to the tank??? A kink or collapsed hose might be restricting flow from the regulator back to the tank. Does it have the correct pump?? Pressure seems high (I think it should top out around 36) to me and once again, you can't fix the "rich" until the mechanical aspect of the fuel pressure regulator system is correct. Hope this gives you some ideas. Good luck.
Howdy!! My first concern would be that the timing is still jumping around. With the ALDL grounded it should be completely a mechanical function, with no variation. Since the chain and tensioners should be good, I would be looking at the cam and dist gears. Possible slop in the "new" distributor (bushings springs, weights, etc.) None of the electricals are going to function correctly until the mechanicals are correct. As to the rich condition, have you checked the return line to the tank??? A kink or collapsed hose might be restricting flow from the regulator back to the tank. Does it have the correct pump?? Pressure seems high (I think it should top out around 36) to me and once again, you can't fix the "rich" until the mechanical aspect of the fuel pressure regulator system is correct. Hope this gives you some ideas. Good luck.
These are very good suggestions and I appreciate them. Since so few threads actually have a resolution, I figured I'd put it in. The EGR was stuck open. It was replaced along with all the vacuum lines (stainless) and the EGR tube. All is well now. Classic stuck EGR symptoms.
Glad you got it figured out. I worked at dealerships and independent shops years ago, and I can't recall ever having that happen on a GM, however, it was "common" on Ford models.
I'll have to take your word on that analysis........having never owned a scan tool. Maybe someone else can offer some insight.
A little surprising.
