350 TPI Vortec.....Fuel pressure before start is about 20lbs, after start(while running)with vaccum connected to regulator is about 38lbs...Recently changed the fuel filter. Now the problem is this while driving it the car will drive fine with about1/4 of the throttle depressed, but when I go to give it full throttle it hesitates for a few seconds, then suddenly feels alright and then goes back to hesitating again, Ive searched and searched but could not find anyone with a similar problem. Do my fuel pressure numbers look right? I was concerned with the key on/enging off fuel pressure. Any help would be greatly appreciated...thanks!!

 

Can you check the fuel pressure while the problem is happening? That would really help diagnose the true problem. If the fuel pressure looks steady at greater than 42psi at full throttle, then it's likely not the problem. If it cuts out or whatever at a steady high throttle, then yeah, your pump or even maybe the relay + oil pressure switch is likely the culprit.

The key on fuel pressure should spike to 43 ish while the pump is on, then when the pump stops after 2 seconds, it should hold above 40. It seems to be going to 20 from your post, but that doesn't necessarily indicate what the problem is, and whether it could be causing your symptoms. What happens if you cycle the key on and off a few times? Does it take a lot of cranking in the morning to get it started?

 

The car is not my daily driver, but when starting for the first time it does take a few cranks. I also drove it with the fuel pressure guage conncected and the pressure was steady at about 40psi even when the problem was occuring, so I'm guessing that it is not fuel related. The oil pressure switch and fuel pump relay are brand new parts by the way. But the problem still persists. If I floor it, it will feel powerful up to about 3000RPM, then flatten out until 3500RPM and then have full power again. I also noticed that the engine does not sound like it is loosing power while I am experiencing this loss in power.(Sounds strong all the way through RPM band) Perhaps the problem could be in my drivetrain?? Clutch or rear end related?? I'm still lost here, this has been the worst mystery problem yet with these cars and I've had 7 of them, lol. Any help is greatly appreciated, thanks again

 

Does the symptom "If I floor it, it will feel powerful up to about 3000RPM, then flatten out until 3500RPM and then have full power again always happen the exact same way ? I was just trying to find out if it was an intermident problem or not . You ever toss a code or anything ?

 

No codes at all, problem does not occur intermitently, but only seems to happen in closed loop. Also Idle is unstable/surging in closed loop from 800RPM to 1000RPM in which it will eventually cut off/stall the engine. I checked for vaccum leaks and found none, sprayed the inatke with carb cleaner to see if the intake was leaking, I even unplugged the IAC with the motor running, and it didnt even toss a code or turn on the SES light. Still lost over here, lol. Thanks again.

 

I am just tossing out stuff mow but , I had my car do that and the vacuume lines were split on the TB ( the one big fat one)

also I hear ( noooo idea why ) that a MAF burnoff relay does this to our cars . But it would be ncie to check somehow befroe tossing parts at it .

 

Now I have replaced the fuel pump since it took a crap on me, my headers and Y-pipe(got new ones for B-day Present) and installed a new O2 sensor to go with the new headers, and the idle is till surging from 700-1100RPM. I have tried to pull codes, there are none to be found. I have adjusted my minimum air as per the tech article and still no change. I have checked for vaccum leaks-none found. Anyone else have any ideas besides what I have listed. Thanks

 

check teh MAF buroff relay . Or the wires to it . Mine were , for some reason kinda yanked out fo the connector. I had the surgeing you pseak of.

 

do you think that by just disconecting that relay, not permenantly, would stop the surging immediately? Basically I'm looking for a way to test it. Thanks.

 

Ok so I went out to the car and tried unplugging the MAF sensor and bamm the idle stedied up. No more surging.Do youthink this could still be a bad relay? All of the relays in the uper drivers corner of the engine compartment are oval shaped except for the fuel pump relay. So i'm not sure which relay is for the burnoff. Thanks.

 

MAF burnoff relay is only used during power off. It cleans the MAF. Do a diagnostic on it (check for volts getting to the MAF during burnoff mode). I don't remember off had which relay is burnoff. Do a search or look in a book.

I'm going to guess that it's just a bad MAF, but troubleshoot the relay first.