boceltics17

I am starting a new post that is more descriptive. I have an 86 that has a bigger cam, long tube headers, intake and head work. I have owned it for over 10 years with no issues until recently. After accelerating hard, it started running rough. If you lean into the throttle, it coughs and hesitates. Under hard acceleration it runs closer to normal. It is running noticeably rich, dark smoke at the exhaust. So far I checked the plugs. They are black, consistent with running rich. Checked and replaced the throttle position sensor. Checked for vacuum leaks, none evident. I have read up quite a bit. If understand the o2 sensor operation, it is not providing into to the air/fuel mixture until the car it up to operating temp. If that is the case, I would say the o2 sensor is not the issue. The car has been covered to a heated o2 sensor.

So what do you think? Trying to use my brain before throwing a bunch of parts at it.

My guesses:
Weak spark, replace standard coil with HEI, new wires and hotter plugs
Some have said an ECM could cause the issue
Other than that I am struggling.

desertmike1

Have you checked the FPR for an internal leaking Diaphragm, by removing the Vacuum hose and looking for evidence of fuel.

DanielRicany

What I would do first is look at scan tool data.

I would let it warm up and go into closed loop and check the BLMs. If the BLMs are below 128 it is running richer than the ECM's calibration. If it is at 108 is extremely rich and the ECM cannot remove any more fuel. This would tell me if it was rich and if the computer recognized the problem.

Fouled plugs can be caused by too much fuel, oil consumption, retarded timing, incorrect heat range, or a misfire.

A misfire on an oxygen sensor will show up lean, so your BLMs should be higher than 128 in this instance.

Next I would check fuel pressure. And I would also ohm the injectors. I had 3 bad injectors on my '91 Camaro, caused the BLMs to be 108 and it was so bad that after driving for a while I could barely keep it at speed. Acceleration from stops was incredibly slow and I could go no more than 1/8th throttle. No power anywhere on the car. This leads me to my next question. Are all the plugs fouled or only a few?

The only time I would be driving this car right now is for diagnostic purposes. Running rich enough to produce black smoke is enough to cause ring wash.

Was this car ever tuned?

kcbc

block learn -->BLM
this looks like OBD1 .....it aint that easy to obtain OBD1 scanner for most car owner unless he is auto repair related
2nd ---> injectors can pass resistant test but fail on current ramp .....
noid light is also a waste of time cause it only show a circuit and turn on but not seeing the integrity of the solenoid

Cliff Harris

A bad coolant temperature sensor or wiring problem (corroded connector pins) can cause the ECM to think the coolant is very cold and it will run very rich.

You really need a scanner or (better) an ALDL cable and laptop with scanner software to find out what the ECM is seeing.

kcbc

any aftermarket OBD1 will do but not the cheapy in auto zone ..all my snap on from modis to veraz have the adaptor for OBD1 GM factory enhanced mode to view block learn,coolant sensor and others main parameters....haven't heard of any laptop emulator can do the old OBD1 ...maybe the new GM MDI that is use for global car and its replacing tech2

Vett1990

Big cam, long tube headers and intake / head work.... my first stop would be with tuner. With the changes made you need to look at a new ECM program? IMO, dyno time which maybe expense is worth every dime when it comes to figuring out A/F ratio and performance.

boceltics17

I wanted to provide an update for the good of the community. I took it in for service at a local shop. They determined the fuel delivery timing was off. It took them quite a bit of time to diagnosis. For good measure, the replaced the ignition control module. That didn't help. After testing many parts, they looked at the ECM. After a "tap test", they found that by tapping on the computer the idle would fluctuate by several hundred RPM. Since everything else had checked out, we went ahead and replaced the ECM. After replacing the plugs from being fouled, the car seemed to run better when in close loop. But when it would be in open loop, it appeared to be the same condition, incorrect fuel timing. So, they went back found that the gasket on the throttle body was leaking. Additionally, they saw the idle air control was not sealing properly. Both were replaced, but it still was not running right. They then started over diagnosing every component. This time around, the mass air showed its true colors as being failed. It was replaced and all is right now. I figure some guys will be skeptical, that the guy was just swapping parts until he found the right part. I understand, and I certainly don't know everything. At the same time, I know enough see through BS. I have faith in the tech. I believe him in his thinking that the blown throttle body gasket was the cause the mass air checked out ok initially.

At any rate, thanks for everyone's help. This forum is amazing. There are some serious sharp guys. I hope this can help the next guy.

kcbc

if idle air is not sealing properly and also blown gasket on the throttle body then who tested it as passing vacuum leak?...either equipments and test are not up to standard or testing was wrong.. tech acts and replace parts base on test result ....similar repeated action was taken earlier as you mentioned about replacing the computer ,whats kinda of test had been done to justify the replacement of the pcm ? u never mentioned the reason why but only stating --> thorough diagnosis ....