The vehicle runs great most of the time, however, sometimes at any speed the engine seems like it boggs down starving for fuel. Checked the fuel pressure 55 psi, replaced fuel pump. It seemed to help, then started doing it again.
The engine will not die, 1000 rpm, but will not accel. You can hear the engine backfiring. Turn the key off, it resets and the vehicle will run fine sometimes 50 yards sometimes 50 miles.
I suspect fuel pressure regulator.
Where is it located?
I had another guy say the regulator is in what is known as the spider? He says it is a real bear to replace? Any help would be appreciated.

 

The regulator is on the back of the fuel metering body (commonly referred to as the spider) under the upper intake plenum. It can be somewhat involving to replace. A fuel pressure leak down test will let you know if you have a leaking FPR. Check out the fuel pressure test thread in the Tech Article (DIY) Index linked to from my signature.

 

Thanks for the information. I want to be sure of something:

Step 3----if the pressure drops more than 5psi in 10 minutes, one of the five items listed is faulty. I simply turn the key on and leave it? Correct, because the pump will only run 2 seconds then shut off. If the pressure bleeds off will the pump come back on?

Of the five items listed I think it would only be the FPR. As I have put 2 pumps in it already. The first one I thought was bad from stock as it was reading around 55 psi.

My friends scanner said the injectors were good.

The problem is intermittent, it does occur evertime you drive the truck. With it being intermittent do you think it could be the FPR? As I am about to pull all the hair from my head, both of them.

 

The pump will not start back up. It has a preset prime cycle when you turn the key to the 'Run' position.

I doubt your problem is FPR related, but you could test the fuel pressure when you are experiencing the issue to see if there could be a problem in that respect.

It could be electrical or even sensor related as well. Every diagnosis has to start somewhere.

 

Again thank you for your insight.

Amplifying information:
----62 psi when key is turned on, when pump goes off--immediately drops to 56psi, then in 45 seconds to 50 psi and continues to decrease to zero.

-----driving conditions
normal 52 psi
when accelerating 60 psi

When acting up, it is at 50 psi, when starting to accell drops to 46 psi, engine levels out at 1000 rpm then the pressure surges to 60 psi and engine fall to 600 to 700 rpm.

when acting up I stopped put in nuetral, 50 psi, reved eng fell to 46 psi then starts to increase to 52 psi as the eng rpm increases to 2500. at 52 psi the eng starts to sputter, psi increases to 60 psi the eng completely falls to 600 to 800 rpm immediately.

I think it is fuel related, something other than the pump. As this is the 3rd pump including the original pump.

Correct me if I am wrong, but shouln't the pressure remain somewhat constant, not wildly swing from 45 to 60 psi? If the pressure drops off that quickly when the key is turned on, only 5 items could be the problem. Of which the check vlv should be elminated because of the new pump, injectors--read good on the computer, so I am down to pump flex line, FPR, or fuel pipe. I think the most logical item would be the FPR, again you thoughts would be appreciated.

A/M/G

 

I would definitely say that it is a fuel related issue. It should not drop below 50psi at any point in time.

What brand of pumps were you installing?

 

The first one was a Airtex, which after installing I learned was a no no.

The last was a Delphi.

I think the Airtex was prob ok because the truck acts the same with all three the original, airtex and delphi.

However, there is one thing I do not understand, after insatlling the two new pumps, the truck ran much better initially and then slowly reverted back to consistent poor performance.

The pump seems to be doing its job providing 62 psi on start up.
I cannot imagine all three pumps having a bad check vlv.

I think I am going to put a FPR in and hope for the best.

I will let you know the out come.

A/M/G

 

The FPR was bad. The valley under it was washed clean and it would not hold a vacuum. After replacing the FPR the fuel pressure increased. After the key was turned on the pressure did not decrease as before.

But, that did NOT correct the problem. The fuel pressure still fluxed 44 to 60 when the engine lost power. What the Hell?

Could it possibly be iginition related, as you said before?

Why would the pressure drop to 44, if it was iginition related.

I am at my witts end, about ready to commit SUICIDE, KIDDING!!!!!!!!!!! Really about ready to trade off this truck.

A/M/G

 

One other thing I thought of, the last time it went crazy:fuel pressure at 44::si acting crazy, I Turned the key off, the fuel pressure immediatly went to 62 psi, without turning the key back to the start position. The truck started again, ran for several miles and never faulted again.

I appreciated any info anyone can give.

I have a friend, her truck, 2002 blazer, 4.3 did the same thing ------never figured out the problem. She trade it. There has to be a common/simple solution. As I am sure the people on this board have seem this problem before.

A/M/G

 

The more I think about it, I think the pump is loosing current, causing the pressure to drop. It drops to 40 psi which is where the injector poppets close.

I am going to:
--check my ground wires for the pump
--swap relays for the fuel pump
--check Vehicle control module
--wire a L.E.D to the pump and route the LED inside the cabin with me.
If the LED goes out that means the current is loss to the pump. If need be I will put a multi-meter on the LED to see what the voltage is.
--If need be I will use the fuel pump prime connector to provide a constant power source to the pump.


What do you think about?