I have been working on a TPI swap in a 1971 Nova for about 3 months now and have finally got it to running decent. well very good considering it wasn't running period about 2 months ago.

Anyways. the problem. the car starts up fine, idles, and revs; but here is the problem. when the idle slows down it develops a pop in the exhaust something like the timing is off and when it starts this you can not give it a good rev without it back firing. I have checked all that i know to check at the moment. the timing is set at 6 degrees is there a certain rpm it has to be set cause i set it at idle speed. I change the plugs, wires, cap, rotor, modle, everything put the reluctor. i have checked the TPS just to make sure i was getting the right readings and it is good. I also readjusted the valves to just make sure that they were not to tight caust i had a similiar problem before ant the valves were to tight, but it did not help it. I have not checked the fuel pressure, but previose test had showed it to be good. i do know that i have a few leaking injectors, but the fuel pressure does not drop below 40 psi overnight so i figure it would not be that big of a deal. any help would be apriceated. PS: the system uses a stock 730 ecm with vats deleted.

 

I would like to see your vacuum situation. Have you plugged the line going to the booster and checked this?

 

BUMP, I am having the SAME problem in my 91 t/a L98. I am in the process of tearing the engine down due to a blown headgasket, not sure if this is the problem, we will see though.

 

No i havent checked the vaccum yet, but i will give it a shot.
----------
sdtrans am what all did you do before determining that the headgasket was blown?

 

My TPI was doing something like this a while ago. It would run fine for a while, then when I gave it gas it would start backfiring like crazy. Couldn't go anywhere, had to play with the throttle and hope it would get going again.

What happened was my ignition module was installed with tune-up grease and not that heat-sink stuff. (my fault, got bad advice) I put the right stuff under the module and the problem went away. You could also check your exhaust for a leak. My car pops a bit on decel but I think it sounds kind of cool.

 

yeah figured it out just a while ago....... them darn crossed spark plug wires will do the darndest things.....

 

Pat yourself on the back , I've been there with a swap and it's pretty overwhelming .

 

Well, I did new plug wires, and was messing around with the car, and noticed every time I shut it off, it would boil over, It started running ok with the new wires, but never ran right. I only drove it twice since I bought it. I am still in the process of tearing it down, I HOPE the headgaskets are blown, I am gonna do some head work anyways, my dad runs a machine shop. I am gonna put new injectors in also, 'cause it has a miss matched set by the looks of it.

 

You wouldnt happen to live in Clyde would you? Ive got a few ideas on how to work on those if you do....LOL.. Mine did the same thing. Did you disconnect the electronic advance when you timed it? Vacuum leaks as well as exhaust leaks can cause it as well.