My Sc Just Started To Run Bad When Warm & In Boost

lilredstang

Registered User
I JUST GOT MY 89 SC ABOUT 2 MONTHS AGO. I GOT HER CHEEP CAUSE SHE WAS COOKED. I PLAINED AND REBUILT THE HEADS AND RESEALED THE REST OF THE TOP BACK UP. A BIT OF THIS AND THAT AND SHE WAS RUNNUNG GREAT. THEN ALL OF A SUDDEN, IT STARTS RUNNING LIKE CRAP! IT BARILY IDOLS, USUIALLY DIES. WHEN THE MOTOR IS COLD IT RUNS FINE, EXCEPT FOR THE BAD IDOL. ONCE IT HEATS UP THOUGHT IT SEEM AS IF IT GETS TICKED WHEN I PUSH IT INTO BOOST. ITS LIKE I GOT MY FOOT ON THE GAS AND THEN PUSH THE BRAKE TOO! I CLEANED THE I.A.C. AND INSTALLED A NEW T.P.S....NO LUCK. I USED SPECIAL CONTACT CLEANER ON THE CONECTORS FOR THE SENSORS AND STILL NOTHEING. I CHANGED THE FUEL FILTER..NOTHING. I RAN THE CODES AND WHILE I DONT REMEMBNER THE EXACT NUMBERS I REMEMBER THEY SAID SOMETHING ABOUT THE MASS AIR VOLTAGE AND THE TPS VOLTAGE BEING LOW. 2 CODES REFERED TO A LEAN CONDITION, AND ANOTHER WAS ABOUT THE FUEL PUMP. ANY HELP YOU HAVE WOULD BE GREAT.
 
First of all, PLEASE turn off our caps lock. One thing that jumped out to me was that you got a code related to the fuel pump? If you are not getting enough fuel, your car will sense a lean condition and trigger the knock sensor, and pull timing. This would cause a loss of power that you might be feeling. The fuel pressure is supposed to increase pound for pound with boost, and if it isn't, then it would cuase a lot of trouble. You also mention that it happens more when it is warmed up. This also leads me to think that it might be the fuel pump. If you can pull the codes again, and get the specific numbers, it would help out quite a bit.

Thomas
 
I would look at the vacuum line going to the fuel pressure regulator, might have come off or cracked. I would also consider looking at something with the ignition if it is stumbling or missing when it heats up.
 
ok first off my caps lock button works right 5% of the time. i know some people are ofended by caps for some reasion, but there was nothing i could do. it just was being a p.i.t.a. its just been one of those weeks! nothing can go right.

i unhooked the battery and cleared the codes, so i will go and drive her a bit and see what cades are in it now. if it is the fuel pump, is it a pain to change. i herd it down right sucks. true or not? i will check the vac line to the regulator too.

thanks guys...
 
ok, i took it for a drive and it was still doing it. i pulled the codes and here they are.

key on motor off... 11

key on motor running... 41, 72, 73 and 25

i checked the vac line on the fuel pressure regulator and it was not off. it is supposed to be the short one about 3-4 inches long, right?
 
so today i had a little time so i pulled off the vac line from the intake to the fuel press. regulator. i checked it over good and found it to be in good shape. just for the heck of it i replaced it with a new pice of line and went for a drive. it was still doing it. i then had the idea to just remove the line altogether and cap off the vac port in the intake, just to see what would happen. nothing....no change. there was no vac line on the fuel press. regulator..geezz shouldn't this have done something different?
 
Only when warm? I'd try first resealing the intercooler tubes, blower top and throttle body. Codes can run rampant with even just a tiny air leak that the computer cannot control. After that, I'd replace the o2 sensors if you haven't already. Do them both at the same time. Hitting a lean condition such as too much air in the engine from a vacuum leak will trigger an o2 sensor. Also, a worn out o2 sensor will act up as you describe. I can see from teh codes you didn't goose the throttle and press brake pedal during the key on-engine running test.
Next time, watch the check engine light. It will flash 3 times quickly. Goose the gas to get the motor over 2000 rpm. Turn the steering wheel side to side, and press the brake pedal all the way down. These are all required and explained in the SC EEC4 test procedure.
Code 41-right side o2 sensor. Possible bad. How long since you changed both?
Code 72,73. You didn't do the test correctly.
Code 25-knock sensor. Possible also bad, but also could be because you didn't do the test correctly.
There is a possibility your fuel pump is bad, but if it was, I'd think you'd get codes for both o2 sensors and the motor would not run cold or hot. Right now I"m leaning towards a vacuum leak and bad o2 sensors.
 
problem solved!!!!!!

I spent the $$$ and got a fuel pressure tester kit. to make a long story short I got lucky and barley herd a vac. leak. one of the hoses was cracked. that smoothed the idol a bit. and the fuel pressure regulator was holding 2psi in the rail and leaking gas into the vac. port on top of it. replaced the regulator and the vac. line and she runs fine.
 
Back
Top