This is a two part question. I had a no start and heard my fuel pump turn on which was replaced about nine months ago. I replaced the fuel filter and tested the pressure after reading all the posts on here about pumps going bad. I was only getting 10 psi, but it held at 10 psi. Luckily the pump was still under warrenty and I replaced it and had to put on a new wiring harness with the pump. After replacing it the truck fired right up like it always has, after a day or so I noticed a little hesitation in starting so I hooked up the pressure guage again. When the pump is on the pressure goes to about 60 psi, as soon as the pump turns off without the engine running it drops to zero and fast. With the engine running it is steady at about 52-54 psi and I can't find a fuel leak. I don't know what to do next or why the pressure is not holding.

The second part is my fuel guage started fluctuating between E and F with the original pump. When I replaced to the other pump that failed it did not fix the problem, it is still doing it with this third pump. I know the sending unit is in the pump but cant figure that all three were bad and two never worked from the get go. Is there a common short to look for or a fuse or something to check out????

2000 4.3 L

 

Couple things.
Your fuel pump will push more fuel then your engine can possible use, even at WOT. All the excess fuel is routed back into the gas tank. It would be normal for the pressure to drop becuae it has an open line back to the gas tank. This constant circulation is what gools the fuel. If the fuel were allowed to maintain 60psi next to the engine it would get hot fast and thuse performance would suffer. Not too mention so would fuel economy.

I suspect you got the wrong fuel pump assemble. There are several different versions for the '00 Blazers. There is a tag on top of the fuel pump, this is the unit you want. The fuel pump is designed for the engine fuel injection system. Changing the wiring harness is not a typical modification on a fuel pump replacement. At least not the last time I replaced my '00 fuel pump. I suggest you contact the dealer and find out which pump you need and verify you have the right unit.

Having said all that, I would also double check your wiring connections, you may have a loose connection and thus faulty readings.

 

Tim,
I'm going to have to disagree with you... Pressure should be maintained at 55-60psi and should not drop, especially not fast. That is the function of the fuel pressure regulator. Any pressure in excess of 60psi will be diverted back to the tank, yes. Even after shutting down the engine, fuel line pressure should hold steady. If you were reading pressure on the return line I would say you are correct, but the supply line should always maintain 55-60psi unless there is something leaking.

 

Sounds like hte FPR then?

 

When you say the pressure should hold steady do you mean no change in pressure at all over 5-10 minutes or slight drop (1-2 psi) after the pump stops, engine off and key on?

 

A slight drop should be expected, but over a half hour, it shouldn't drop more than 3-5psi... This would indicated a slow leak somewhere, but shouldn't affect the performance of the system other than possibly extended cranking as the fuel system primes itself. If that is the case, turning the key to the 'RUN' position and waiting for the fuel pump to shut off, back to the 'OFF' position, and back to 'RUN' again waiting for the fuel pump to shut off, then 'START'. If that allows the vehicle to start, then you have a leak that is bleeding off pressure.

On my old Bravada, I had a slow leak that would bleed the pressure to zero in a few hours. I later replaced my injection spider due to a random multiple misfire code. After that the truck would hold 55psi over a weekend and started up instantly every time.