Fuel pump colamity

1,455

Asked by Oct 03, 2012 at 05:24 PM about the Pontiac Firebird

Question type: Maintenance & Repair

I have a 1999 Pontiac Firebird with the 3.8 v 6. Im haveing fuel pump issues. this will make the third time swaping the fuel pump/sending unit.   The unit keep burning up and im not letting it get below a quarter of a tank. The engine is also missfiring heavly at idle but smooth out mostly at high way speeds. At idle it  the exhaust smells raw fuel. I have changed the battery, altenator (which was checked and inspected), coil packs, spark plugs, and wires. Im running out of options on diagnoseing the issue and a certified mechanic tells me its your altenator. I dont know if it is the computer gone haywire or fuel injectors, loss of compression or what, All i can tell you is the day this started i was sitting at mcds  on the internet for a while with the car running  and it started hesitating and died on the way home and this will make the third time with the fuel pump/ sending unit and second time with trans seeing that the engine was acting up and cause the trans to shift hard and lose two bands in the trans for second and overdrive. anyyyy takers on helping me diagnose this would greatly be appreciatedddddddd

3 Answers

35,675

#1 what is the voltage coming out of the TPS with the key on engine off? Should be .5V +-.05. The TPS could flood the engine thinking the gas pedal is pushed down further requiring more gas, it will also make the car shift super hard. #2 what is the fuel pressure with the key on engine off? Should 50-60PSI. Apply 15 inches of vacuum to the fuel pressure regulator and the fuel pressure should drop to about 40 PSI +-5. There are so many possibilities. As for the alternator I'm guessing someone is really trying to sell an alternator.

35,675

Ohh and a bad regulator will keep the pump under strain because excess pressure can't be let off. BTW its excellent that you know about the fact that the gas IS what keeps the pump cool and prolongs its life. Make sure your friends and family know.

1,655

In regards to what fuel level you're keeping in the tank, interesting point is that the shape of the tank means that 1/4 tank is closer to the 1/2 mark on the gauge, 1/2 tank is 3/4 mark on gauge, 3/4 tank is at the full mark. Case in point, when my needle was on E, I put in 3.5 gallons and the needle jumped to 1/2 on the gauge. When the needle was a bit between the 1/2 and 3/4 mark, closer to the latter, I filled up the tank and it took about 8 gallons.

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