Mechanics

FUEL PUMP

1998 Pontiac Trans Am

Engine Performance problem
1998 Pontiac Trans Am V8 Two Wheel Drive Manual 280000 miles

History of fuel pumps:
Orig - 235,000 mi - no problem
#2 - 500 mi - gas gauge didn't work
#3 - 3500 mi - pump failed on interstate
#4 - 33,000 mi - over time car lost gas milage (25%), lost power and didn't start right. Found pump puting out 35lbs of pressure instead of 60. Service engine lite on and off indicating problem with fuel system.
#4 - 9,800 mi - same as #4.

Can't believe I could get that many bad pumps (NAPA). Could it be electrical?
Avatar
Robert P Moore
May 14, 2010.




Hi Robert P Moore. Welcome to the forum. Two things GM fuel pumps are noted for are low pressure and noise. Chrysler pumps are extremely quiet but the trade-off is the impellers tend to lock up from microscopic debris in the tank. The typical story goes like this. The original pump failed at very high mileage. It failed to start up resulting in a no-start condition. Banging on the bottom of the tank while a helper cranked the engine would eventually jar it enough that it would start to run, and once it was running, it would continue to run. They almost never stop working while driving.

Replacement pump is purchased from NAPA and fails in a short time, usually within a few months. Two or three more pumps do the same thing. Gee, those NAPA pumps must be junk. Give up and buy a new pump from the dealer and don't have any more problems. This is such a common scenario that most mechanics are aware of the problem, and it isn't NAPA pumps. The dealer has the same problem with repeat failures. I can't say for sure about GM pumps, but NAPA buys their Chrysler pumps from the same supplier that sells them to Chrysler. That's why NAPA pumps are just as quiet. It has to do with tight tolerances and very little clearance between the impeller and body.

Microscopic debris becomes lodged between the impeller and body causing it to lock up. The clue is there is still electrical continuity through the motor, but it won't run. By the time you're on the second or third pump, the debris has been collected and trapped sufficiently that the next pump runs with no problem, and often that is the dealer's pump. The solution many mechanics have found is to take the tank to a radiator shop and have it steam cleaned before installing the new pump.

If NAPA's supplier for GM pumps is building them to tighter tolerances, they will be quieter than the original pump and I would expect them to suffer less from the low pressure problem, and more from locked up impellers. I have never heard of a Chrysler product having a running problem due to low pressure, but that is REAL common on GM products. The only difference is in the pumps. If you have another pump failure, do a continuity test on it before removing it to see if it is an electrical issue. If it has continuity but won't run, have the tank cleaned before installing the new pump.

Caradiodoc

Caradiodoc
May 14, 2010.


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