Engine Mechanical problem
1997 Chevy Malibu 6 cyl Front Wheel Drive Automatic 10600 miles
I replaced the fuel pump with a new Airtex unit from Advanced Auto. I think it might be fauty, but please let me know if there is anything else that would cause these symptoms.
The car runs fine for about 30-40 minutes, then the fuel pressure starts to drop from 35lbs to 25, down to 15 and it starts sputtering and dies. I can turn the key 2-3 times and prime the pump to get 41lbs of pressure and car starts and drives fine for another 10 minutes or so, and pressure starts to drop again, engine stumbles and dies.
When the pump was working at normal pressure I had checked the fuel pressure regulator. Running at 35lbs, I unhooked the vacuum line, pressure rises to 41lbs, there was no fuel at the vacuum line, and verified it was getting of vacuum (20inHG). Plugged vacuum back in and pressure returned to 35lbs. Swapped the fuel pump relay for the horn relay, horn still works, and fuel pump still has low pressure after 30-40 minutes of driving.
Besides the fuel pump- I have replace in the last month:
Fuel filter, air filter, plugs, wires, coil packs tested good, replaced the idle air control valve, and 7x crank position sensor, cleaned throttle body, fixed 2 bad ground wires, replaced PCV valve and boot, checked for additional vacuum leaks and there were none.
After all that I took it to a shop because the idle was low, and had it hooked up to a diagnostic computer. All reading were within specs, from the STFT and LTFT, MAF, IAC, TPS, o2 sensors, both crank position sensors, everything was good. Except RPM gauge was 250RPM below actual RPM, so there was no low idle, I thought I was done. It's my sons car and he took it to work 2 days (120mile round trip each day) and it ran sluggish the last 15 minutes of each trip, wouldn't go over 40, then by the time he got home it would barely drive at all and the check engine light for Catalytic system ineffeciency (P0420) Since I knew the 02 sensors were good, and the fuel pump was new(I checked pressure again but didn't let it run long enough to see the drop), figured it was the Cat, so he had a shop weld in a new convertor. But it still drove like a slug after 30-40 minutes. So I drove it till it started fouling out with a fuel pressure test gauge on it, and verified that the pressure is in fact dropping to below 15lbs when this stumbling and dying occurs.
From a cold start, it will run good for 30-40 minutes before the fuel pressure drops, after it's warm it peters out in less than 10 minutes. It will always start back up, especially if you give the key a few turns to prime the fuel pump up to normal pressure.
Before I go and yank out the fuel pump again and replace it under warranty, is there any other possible faulty part that would cause this? There are no exhaust restrictions, and with good pressure the car runs great. Seems like heat or electrical resistance is building up in the fuel pump and causing it to shut down, but could anything else cause it? I figured if the gas was bad, or filter was clogged it would be constant, or maybe not? Please give me your opinion.
Sunday, July 12th, 2009 AT 9:50 PM