I have a 1991 Trans Am that has poor acceleration/bogs down with anything more than very light throttle input when the engine/trans are cold. Only with very slight throttle input will the engine not bog down. Once the car does finally get moving, if given any type of 'normal' throttle input, the engine bogs down again. While 'bogging', the RPM's do not rise......it's as if the timing goes way off. The engine doesn't sound like it's sputtering due to fuel starvation, but it's definitely making the bogging sound (sorry I can't explain the sound better). Given the engine RPM won't rise, it makes me think the transmission isn't slipping so it isn't the culprit....but I could most certainly be wrong.


In Park/Neutral and in all temperature conditions, the engine revs normally and will hold whatever RPM the throttle position is calling for.


HOWEVER, when the engine/trans warm up after about 5-10 minutes of driving, I can gradually begin to take off from a full stop using normal throttle input and the engine will rev up normally and transmission shifts fine. It also begins to have better throttle response at all speeds with normal transmission shift points......nothing real stellar, but ok. I can floor it, the trans will downshift appropriately and RPM's rise normally. Again, this all takes some time driving but eventually it all starts to react normally.


When I first got the car at 107K miles, it ran fine and shifted fine, but it had a little blue exhaust smoke. I decided it was time for at least new rings, so I had the engine rebuilt at a local shop. The transmission was also 'gone though' to make sure it was ok. The TPI and fuel system weren't touched. Again, all worked normally prior to the engine rebuild/trans go through. This is where all my trouble really started. When I first got it back from the shop, it would idle and shift ok when the engine/trans were cold, but as soon as things warmed up, then engine would unexpectedly shut off. It would need to sit a while before it could be restarted. Back to the shop it went. I was told it wasn't holding it's timing. I'm sure no true root cause diagnosis was made, just parts thrown at it (distributor/cap/rotor/wires/plugs/ignition/ECM/fuel filter).


This fixed the stalling issue but when the 'bogging' began. The original shop hasn't been able to fix the problem after numerous attempts. They claimed the TV cable was misadjusted, but it never solved the issue. At this point, I have zero trust in them and I'll end up in Small Claims Court with them eventually.


I really need this Forum's help/experience so the issue can be diagnosed and FIXED!!! HELP!!!

 

 

makes me think a sensor is either bad or they ddint plug it back in or something.

if you could scan the car I bet your fueling would be either super rich or super lean during cold operation (open loop). when the engine warms up the ecm is able to partially compensate by trimming the fuel accordingly (closed loop), hence the improved operation.

the fact that you're not getting a lean backfire when flooring it when warm probably hints at rich. and the over rich condition is probably costing you some power, which may explain the lackluster performance.

 

 

Discovered what 'multecs' are......injectors. Not sure if they are original or not. The strange thing is the engine was fine right up until I had the ignition issue....and once that was fixed, the bogging started.

I thought of a better word to describe the engine bog sound.......it chugs. Think of a coal locomotive....that is the sound (minus all the black smoke).

 

Since the crappy engine rebuild place changed out the ECM (using my existing PROM) and the Ignition Control Module when fixing the stalling out issue, but that's what led to the bog/chug issue, I'm thinking one of those two parts is faulty. Maybe?

 

This fault description makes me wonder if two of the sparkplug wires got transposed during the repair of the original ignition issue ....

 

 

When I run a code check, the only thing I get is '12'.....nothing else. I'd think the ECM would tell me if the sensors were showing faults or if something else was wrong, but it's telling me nothing. Could the ECM be not storing the codes? I believe it would be showing a 42 or 43 if the ignition module were faulty. Could the ECM itself be faulty?

The fuel has been replaced with fresh 91 octane gas, so water/contaminants can be ruled out. The fuel filter was also replaced. Also given the car runs okay when warm, I'd think the entire fuel system could be eliminated as a root cause.......right/wrong?

Another question I have based on this 'journey' so far......is there a good tester that would give me diagnosis info and not just tell me codes? I've read about a few, but they are from many years ago. What do you recommend today?

Again, this is just me thinking out loud based on what I've researched so far. PLEASE keep the ideas/input coming.....all are highly appreciated!!

 

 

Anybody have any suggestions for me?

 

Apparently no one has much interest in this post , but I still wanted to follow up in case anyone else ever has this problem.

From what the repair place is telling me, the distributor was installed two teeth off where it should have been, and the timing was adjusted to compensate. Not sure if that all makes sense, but I'm being told it runs great now that they fixed it I'll find out tomorrow for sure when I go pick it up.

 

how did the car run when you got it back?

Funny because I have this same exact problem. Car runs great when warm, but when cold it makes an excessive noise as if it's struggling. Once warm it's fine.

I recently installed a Davis distributor and then turned the cap to bring the timing back in line. I bet you I installed it off a tooth or something.

thanks for following up too