Hey guys...Im stumped...'91 Formula LB9 with a T-5...Car was sitting for about 2 years...Was only driven about 100 miles in the 2 years...I picked up the car last Monday and noticed a stumble/hesitation when cruising and the car felt kinda flat when ya gave it gas...Idles at about 750 but shakes and rattles...When you let off the gas in gear you can hear popping and backfireing from the exhaust...The previous owner had a remand computer and a new fuel injector (cylinder #2) installed at the dealer april '05...He took the car to them cause it was "stumbling above 2500 rpm"...The first day i got to work on the car im fiddleing for about 3 hours and go to start the car and it wont start...Then i get the "mysterious" start whenever it wants syndrome...I've had this on other third gens and was positive it was the ecu...Replaced it with another remand unit and start problem gone...Of course i was hoping this would help the stumble/backfire but noooo...The car is running rich...Quite rich...Took out the plugs and cleaned them about 5 days ago...Took em out today and they are carboned up a little...I syphoned the gas tank and removed all the gas that was in the tank when i got it along with a new fuel filter...Since then ive done---plugs, wires, cap, rotor, another fuel filter, ICM, CTS, O2 sensor is a year old...I used about half a can of throttle body cleaner...Car has 40 psi fuel pressure off and about 38 when running( fuel pressure was bouncing a little when running...Between 36 and 38 )...Hooked a vacuum gauge to the car and had about 17 on the gauge...The computer is showing no codes...Nothing i have done has done anything...Still acting the same as the day i got it...The only thing left i can think of is the EGR and seeing as how nothing else has worked im assuming cleaning the egr wont help( not to mention not looking forward to removing most of the intake to get to it )...Am i missing something that you all can think of...Broke down and took it to the dealer and they "reset" the prom and said they think its the prom/ecu and proceded to give me a price of $650...Well the ecu didnt help...And ive got a Hypertech stage 2 chip on its way...I ordered it the day i picked up the car...I'm assuming it wouldnt help...But im kinda looking forward to put it in and see if it does help ( basing this on the dealer "thinking" the prom is bad )...Any ideas...Thanks in advance
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BTW car has 135,000 miles and is in excellent overall condition

 

Forgot...Adjusted TPS to .54

 

Non start problem is back now...Car is now dieing out for about 2 seconds then fireing back up as im driving...When i park it it wont start for about an hour and doesnt wanna run if it does start...I ordered a new prom from Pontiac...I'm hoping its the problem

 

Have you checked the ohms on your injectors? I was having a very similar problem, and checked the resistance at the injectors. Most of them were way below spec. Replaced the injectors, and everything is fine. somebody on here told me there is a driver in the ecm for the injectors that will overheat and and cause a no start if the ohms are bad. At least its easy to check. The injector change is another story.

 

hmmm...https://www.thirdgen.org/forums/dfi-...injectors.html ...seems i am having issues with the injectors...when i disconnect #3 injector the car starts...and runs like its on 7 cylinders...plug it back in and it dies and wont start

 

geese when I had 1 bad injector . The car would BARELY I meanbarely run . One touch of the gas and it would stall out on me.