1997 Chevy Malibu Help verify a faulty fuel pump please?

AREDECOM

MEMBER
1997 CHEVROLET MALIBU
6 CYL
FWD
AUTOMATIC
10,600 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.

1 Reply

MERLIN2021

EXPERT

Fuel Pressure Check 1. Relieve fuel pressure. See FUEL PRESSURE RELIEF. Connect Fuel Pressure Gauge (J- 34730-1) to fuel pressure fitting on fuel rail. Turn ignition on with engine off. Fuel pressure should be within specification. See FUEL PRESSURE table. If no fuel pressure is present, go to step 5). 2. Start engine. Fuel pressure should drop 3-10 psi (.2-.7 kg/cm 2 ). Turn ignition off. Pressure should hold. If fuel pressure does not hold, check for leaking injectors or fittings. If injectors or fittings are not leaking, replace fuel pressure regulator. 3. If fuel pressure is less than specified, check for restricted fuel line or fuel filter. Repair as necessary. If no restriction is evident, apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. For location of fuel pump test connector, see COMPONENT LOCATIONS in the SYSTEM/COMPONENT TESTS article. 4. Gradually pinch off fuel return line between gauge and fuel tank. If fuel pressure increases to within specification, replace fuel pressure regulator. If fuel pressure does not increase with line pinched, check for faulty in-tank fuel pump or partially blocked fuel strainer. 5. Using a 10-amp fused jumper wire, apply battery voltage to fuel pump test connector. For location of fuel pump test connector, see COMPONENT LOCATIONS in the SYSTEM/COMPONENT TESTS article. Observe fuel pressure reading. If fuel pressure is still not present, check wiring between test connector and fuel pump. If wiring is okay, replace fuel pump. 6. If fuel pressure is present with voltage applied to test connector, test fuel pump relay and voltage supply to relay. See the SYSTEM/COMPONENT TESTS article.
Some systems also use oil leve/pressure to control fuel, test this way.
ENGINE OIL LEVEL SENSOR 1. Ensure engine oil level is up to the full mark on oil dipstick. Verify that all fuses and fusible links are okay. Disconnect oil level sensor harness connector. 2. Turn ignition on, with engine off. Using a jumper wire, jumper sensor harness connector terminals. If LOW OIL LEVEL light turns off, check for faulty connection or faulty oil level sensor. If LOW OIL LEVEL light does not turn off, go to next step. 3. Connect a test light between battery voltage and oil level sensor harness connector Black/White wire terminal. If test light illuminates, check for open in Brown wire to PCM or faulty PCM connection. If circuit or connection is okay, replace PCM. If test light does not illuminate, check for open in ground circuit Black/White wire.
41-47 is spec for pump pressure.
Fuel System 1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. After performing OBD system check, go to next step. 2. Turn ignition off. Install fuel pressure gauge to fuel pressure test port. Remove fuel pump relay. Using a fused jumper wire, jumper fuel pump feed circuit at fuel pump relay connector to battery voltage. See the WIRING DIAGRAMS article. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 10). 3. Disconnect jumper from fuel pump relay connector. Connect test light between fuel pump relay connector terminals for ignition feed circuit and ground circuit. See the WIRING DIAGRAMS article. Turn ignition on. If test light illuminates, go to next step. If test light does not illuminate, go to step 9). 4. Turn ignition off. Connect test light between fuel pump relay connector terminals for fuel pump relay driver circuit and ground circuit. See the WIRING DIAGRAMS article. Turn ignition on. Test light should illuminate for about 2 seconds. If test light illuminates, go to step 8). If test light does not illuminate, go to next step. 5. Turn ignition off. Disconnect PCM connector. Using a test light connected to battery voltage, probe fuel pump driver circuit at PCM connector. If test light illuminates, go to step 15). If test light does not illuminate, go to next step. 6. Check continuity between fuel pump relay driver circuit between PCM and fuel pump relay. See the WIRING DIAGRAMS article. If circuit is open, repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. If circuit is okay, go to next step. 7. Check fuel pump relay driver circuit for poor terminal connection at PCM. If connection is faulty, repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. If connection is okay, go to step 20). 8. Check for poor fuel pump relay terminal connection. If connection is faulty, repair as necessary. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. If connection is okay, go to step 18). 9. Using a test light connected to ground, probe ignition feed circuit at fuel pump relay connection. See the WIRING DIAGRAMS article. If test light illuminates, go to step 17). If test light does not illuminate, go to step 16). 10. Remove fuel filler cap and listen for fuel pump operation. If fuel pump is running, diagnose fuel system. See BASIC FUEL SYSTEM CHECKS. If fuel pump is not running, go to next step. 11. Using a fused jumper wire connected to battery voltage, jumper fuel pump feed circuit. See the WIRING DIAGRAMS article. Raise and support vehicle. Disconnect fuel sending unit connector at fuel tank. Using a test light, check circuit between fuel sending unit connector. If test light illuminates, go to step 19). If test light does not illuminate, go to next step. 12. Using a test light connected to ground, probe fuel pump feed circuit at fuel sending unit connector. See the WIRING DIAGRAMS article. If test light does not illuminate, go to next step. If test light illuminates, go to step 14). 13. Locate and repair open in fuel pump feed circuit. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. 14. Locate and repair open in fuel pump ground circuit. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. 15. Locate and repair short to ground in fuel pump relay driver circuit. After repairs, perform ON- BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. 16. Locate and repair open in ignition feed circuit to fuel pump relay. After repairs, perform ON- BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. 17. Locate and repair open in ground circuit to fuel pump relay. After repairs, perform ON- BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. 18. Replace fuel pump relay. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. 19. Replace fuel pump. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. 20. Replace PCM. Perform PCM relearn procedures. After repairs, perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK.