lugnut87

Hi, I think this is the first time I've posted on this board, I've been floating around for a while, doing some reading and what-not. As for introductions I'm Keith, I own a 1987 TransAM GTA, 5.7L TPI, it has just over 100k miles on it. I have about 13 years of miscellaneous car/motorcycle experience under my belt, everything from restoring a 1930 Ford Model A, to sport tuners and everything in between. I'm not new to chevy small blocks, just un-familiar with TPI.

I'm having what I thought originally to be a common TPI problem, but the more I'm getting into it the more it's seeming like its a little bit more interesting.

When I got the car, it was having issues with a rough idle and lack of power. I replaced the cap, rotor, plugs, and wires. It was running better, but not quite right so I checked the timing, I re-set it to base timing of 0* with the electronic timing control plug un-plugged. This also vastly improved performance but its still not right.

I had a very high idle, 1000-1200RPM, (in neutral) So i checked and adjusted the TPS and the minimum air screw. This seems to have fixed the high idle, but makes the cold starts rougher.

Basically the symptoms are, on cold start up it sounds like its spark knocking really bad, if i raise the idle with my foot, it seems to smooth out, but if i rev it up and let off fast it starts knocking again. if I ease down the idle I can get it to idle smoothly. Once its warm it seems to run better, it stops knocking constantly at idle, but I can still induce it by reving it up and letting off fast. Once warm it has a slight miss, an off idle stumble and a labored rev.

The timing seems to be floating at idle when I have the timing light on it, especially with the electronic spark control hooked up. With the spark control unhooked, it doesn't seem to float as much, but from time to time it has a miss, which causes a small fluctuation.

I have a check engine light that refers to the fuel pump circuit.

I have done a few other random things, I installed an adjustable fuel pressure regulator, which is set at the stock 44psi, I have also resealed the upper intake manifold and runners with new gaskets when the adjustable FPR was installed. All vacuum lines have been replaced other then interior dash lines. The exhaust is stock except for the muffler, I have a slight gasket leak at the manifold on the passenger side. The smog pump belt has been removed but the pump and all the lines are still hooked up, this hasn't changed the way the car runs before or after belt removal, no check engine lights were the result of the belt removal. Then engine doesn't change when I tap on the MAF. I had the distributor pickup tested by advance auto(previous owner already replaced this part it was a wells brand part), they did the test about 15 times, and not once did it fail.

I'm not really sure what to check next or where to look at this point. the likely hood of mechanical problems seems small since I can get the timing to mostly stabilize with the spark control unhooked and the mileage is not terribly high, but I'm not claiming to be an expert by any means. I don't have a scanner, or much if any money to throw at anything expensive at this point, but if anyone has any ideas I'm open to any and all suggestions at this point, I just want my car to run like it should.

John 89 Formula

Base timing should be set at 6* before.
The floating timing is normal, thats the computer making adjustments according to the information from the various sensors

lugnut87

I apologize, I did set the base timing to 6*. I've been bouncing back and forth between a tbi truck project, I verified today and it is set at 6. I am aware that the timing is adjusted by the computer, and will float. The floating that I'm describing is irratic and seems to be causeing a knocking or stalling situation at low idle speeds, I'm also thinking it may have something to do with the lack of off idle power/stumble.

I'm having trouble pin pointing my problem and seem to be checking the same things a multiple of times only to verify they are ok and still the cars not running properly. Any advice at this point is appreciated.

lugnut87

I apologize, I did set the base timing to 6*. I've been bouncing back and forth between a tbi truck project, I verified today and it is set at 6. I am aware that the timing is adjusted by the computer, and will float. The floating that I'm describing is irratic and seems to be causeing a knocking or stalling situation at low idle speeds, I'm also thinking it may have something to do with the lack of off idle power/stumble.

I'm having trouble pin pointing my problem and seem to be checking the same things a multiple of times only to verify they are ok and still the cars not running properly. Any advice at this point is appreciated.

John 89 Formula

check for proper operation of the egr valve

lugnut87

I had the egr off while doing the afpr install, replaced the gasket, it seemed to move alright, I'll double check it tho.

Anything else to check?

Chevy8588

iTrader: (1)

knock sensor?

lugnut87

I thought about the knock sensor, but it never threw an engine code, so i dismissed it.

is there a way to check it other then to just replace it?

John 89 Formula

with the engine running, tap on the block with a hammer if the idle changes then the knock sensor is working.

lugnut87

Well I'm going to revive this thread from the dead with the solution to my problem. Albeit an odd solution.

I started with the TPI tune up article that I sourced from this forum, originally from either Hot Rod, or Chevy Power magazine can't remember which at this point. I went through the entire article, checking every sensor setting, base timing, min air setting, etc(except fuel pressure, just found my gauge tonight) to be 100% sure that everything was correct, and as I found out it was, other then the TPS sensor that I had out of whack messing with it before I knew how to use my DVOM correctly, and the min air setting was too low.

Once those were solved it ran better but still had the floating timing and knock sound.

On a whim, I remembered something my dad told me about a long time ago, he broke a flywheel on a K5 blazer one time and it had made a rattle/knocking sound. So I jacked it up and slid under the car. My trans inspection cover is missing so all I had to do was shine a light up there and the problem made itself quite clear.

All three torque converter bolts were loose, one of which i could see two threads on the engine side of the flywheel! I went around and tightened all the bolts back up, nice and snug.

when I started the car it instantly felt better, throttle response was there, and the knocking noise was gone.

The loose torque converter was rattling on the flywheel sending a false "knock" into the engine, which the knock sensor picked up on and was pulling timing to remove the knock.

Funny how fast I/we are to blame the electronics(which are responding perfectly) when all that was wrong this whole time was Previous Owner Hillbilly Engineering.

The only slight problem left is that it seems to be lacking in low end yet a little, and if I goose the throttle either at idle or driving, I get a rough idle situation, don't smell fuel or anything, but I can solve the problem by reving the engine back up and slowly letting it back down to idle.

I installed an AFPR in my attempts to fix the car and its either not working properly, or I have fuel pressure to high. Also, I don't know if my torque converter is the correct stall since its been removed at one point it seems, which this would have nothing to do with the rough idle situation only with the feeling of bad low end torque.

I don't have datalog capabilities yet, or a scanner so I'm kinda going at this old school for now. If anyone has any suggestions, throw em at me. I'm verifying FP tonight before I head in.

gregorydtatum

Hello Lugnut 87
I too have had the same problem before with my 87 TA. I noticed you mentioned a slight exhaust leak in your earlier post. My advice FIX THAT. I had an tiny chuffing leak and for the life of me I couldn't set the dang thang right to save my life. But, I repaired the exhaust leak and once I did that THEN I made sure all my sensors were good to go. And it made an amazing difference. Believe it or not, that slight sucking back in of air once you goose the throttle can really screw with these TA's.
Once you repair that then you want to check and adjust your valve lash (if needed) you know as well as I do that improper valve lash can be to blame for tailpipe backfires and throttle response problems. What I normally do it try to set them all to the same torque (only after ive removed all freeplay in the pushrod vs. rocker arm connection)
Then, once that is done you may want to adjust your TV cable (Transmission shift control) slightly inward (tighter) those 700r4 trannies are notorious for funky downshifting. Once you do those things you may see a monster improvement in the low end torque.
Mine for example, if I nail it from dead stop, it climbs up to about 4700rpm and then scratches second gear pretty hard. And on the highway I've cracked 152 mph with the vehicle speed govenor disabled. Not bad for a 305 (yes 305) TPI Huh?