92 deville no acceleration when hot

wiskerbizkit · #1 (**permalink**) 05-29-09, 12:57 AM

I'm chasing this gremlin as best as i can. after about 30 mins of straight driving, highway or city, i can put about quarter throttle to it before it acts like its idling. I'm not getting any error codes. I've cleaned my throttle body real good and changed my fuel filter, seafoamed it. I still have yet to clean my EGR valve or change the TPS.

It never stalls but like you push the throttle down a little and it picks up, then a little more and its like I'm not even pressing it. then when you let up it goes again. I hollowed the cat last week and thought i fixed it but i guess not. Now this problem only happens after it gets real hot i guess.

I've owned the car for a month now and i love it but i traded a perfectly good running truck for it. Also when it hits 6-7 gallons left it bucks like a bronco. I don't know if thats related. Any help would be greatly appreciated guys.

cadillac_al · #2 (**permalink**) 05-29-09, 10:34 AM

I would have suspected the catalytic but you ruled that out. You should clean the EGR tubes inside the throttle body and follow the sticky at the top of this forum and check your codes. My car quits running at 6-7 gal. I thought the gauge was mistaken but I later learned it is not picking up all the fuel. I had the tank out once for another issue and I inspected the pump and baffles etc at that time and didn't notice anything obviously wrong, but I guess I need a new pickup. It sounds like you have the same problem there. It could just be a failing fuel pump too. You might want to invest in a fuel pressure gauge.

**Ranger** · #3 (**permalink**) 05-29-09, 09:13 PM

Tape a fuel pressure gauge to the windshield and see what you're pressure is when this happens. I suspect a failing fuel pump.

wiskerbizkit · #4 (**permalink**) 05-29-09, 10:56 PM

I'm going to try and get my hands on a pressure gauge. I'm going to manually inspect the regulator.

steelybill · #5 (**permalink**) 05-30-09, 11:50 PM

I believe the manual calls that "sag", when it seems to not accelerate after a certain throttle opening.. The fuel pump is one of the items mentioned as a possible problem. The fuel pressure is supposed to be constant through the RPM range. Also, the vacuum hose to the MAP sensor, TPS for binding or sticking, the ground for the HEI ignition, a bad plug wire, etc, etc.

If that is a fuel-rail type injector arrangement, could be a bad or leaking injector. That was in a thread here a short time back.

AMENCADDY · #6 (**permalink**) 05-31-09, 03:57 AM

Here is an interesting tidbit from my FSM for the 92 Deville.
"Insufficient Fuel Flow Complaint
Many times a "starving-out" condition is actually due to a weakness in the ignition system, and ignition and fuel flow troubles are very hard to differentiate. Even when an engine is starving for fuel, the cause is more likely to be a plugged fuel filter or a restricted fuel pipe than a malfunctioning fuel pump."

Just to mention the ignition module in the distributor does have a known frailty that is heat related. Maybe it is dying from the heat. I know just how it feels. Just my $.02

wiskerbizkit · #7 (**permalink**) 05-31-09, 07:39 PM

replaced the module and filter. I'm just gonna replace the pump on tuesday to fix my 6 gallons bucking anyways. I cant seem to get my hands on a fuel pressure gauge. Regulator is not leaking any gas. I could see a bad ground but it was so hot today that anything more than a touch on the throttle was like shutting the engine off.

steelybill · #8 (**permalink**) 05-31-09, 10:13 PM

I picked up a small fuel pressure gauge at Autozone the other day. It's just a little plastic housing type, with a tee fitting. The gauge has a 1/8 NPT (pipe) thread though, and I figure on putting together a set-up for the fuel pressure tap in the line near the throttle body. I believe the gauge goes to only 15 or 20 psi.
Summit Racing has some small fuel pressure gauges also, which would work for test purposes. A 15 PSI gauge for $13.95 would tell if the pump is keeping up.

Ignition could still be a problem. Cylinder pressure comes up when accelerating, and weak spark from the system may cause a sag.

**Ranger** · #9 (**permalink**) 05-31-09, 11:06 PM

You're gonna need a larger gauge than that, Bill. 4.9 fuel pressure runs 45-50 psi.

AMENCADDY · #10 (**permalink**) 05-31-09, 11:10 PM

The 92 4.9L should have between 40-50 PSI so a different gauge would be needed that hooks up to the fuel rail at the port with the Schrader valve. on the RH end of the front bank.

cadillac_al · #11 (**permalink**) 06-01-09, 09:09 AM

I guess my post from yesterday disappeared but you can buy a decent gauge at a parts store for around $25-30; very handy to have.

steelybill · #12 (**permalink**) 06-01-09, 11:48 AM

Oh yeah, sorry about that. I was affected by the 4.1 syndrome

Anyway. I see Summit has those for up to 100 PSI if one can't be found locally, and they are liquid filled for damping the movement. They are not expensive, like $16.95 for all the liquid filled types.

wiskerbizkit · #13 (**permalink**) 06-01-09, 01:18 PM

im minutes away from dropping the tank. for all the research I've done it sounds like my pump is "overheating" because its on its way out, it makes sense. when the tank gets low enough that its not getting cooled (6 gallons) it starts bucking. when I replaced the fuel filter it was a rusty AC Delco so im not even sure it had been replaced. I've only owned this car about 5 weeks now.

AMENCADDY · #14 (**permalink**) 06-01-09, 01:41 PM

I agree with you on this one. Go for it!

wiskerbizkit · #15 (**permalink**) 06-02-09, 03:25 AM

I did the fuel pump today and its running like a champ. drove for an hour and a half with no probs. smooth acceleration throughout the RPMs now. thanks guys. now to fix my AC clutch hub spacing