2000 V8 Losing Fuel Pressure at WOT

[2000StreetRod]

defective fuel pressure damper

99sportx has a thread for an issue similar to this one, and the culprit was indeed the fuel pressure dampner on the 99 up fuel rail. Just a heads up.

Thanks for reminding me about his problem and the solution. There is a diaphragm in the damper just like the one in the pre 1999 rail mounted fuel pressure regulator. If the diaphragm leaks then fuel will be sucked into the vacuum line. However, the symptoms in this case don't match well with that as the source of the problem. Vacuum is max at idle and min at WOT. Therefore (in theory) the fuel pressure would be least at idle and max at WOT.

 

[JTrent]

Well, I played around with it earlier today after I got out of work.

Fuel pressure at idle is now 50 psi from the schrader valve on the rail. When I crack the throttle the fuel pressure acts as if it's a vacuum gauge, dropping the instant it's opened.

I also disconnected the vacuum line to the fuel damper and revved it to see if was leaking fuel and it wasn't, at least a far as I could tell. Also noticed that the disconnected vac line didn't affect the fuel pressure reading at all.

Crawled under it to check for a ground wire on the frame but didn't find one.

I was feeling lazy tonight, first day back to work after a long weekend and all and didn't really feel like dinking with it.

Anyways, I really appreciate your help guys. It's probably one of the things already brought up, just checking the easiest things first to count them out.

 

[2000StreetRod]

fuel pump ground

I'm home from vacation. According to my wiring diagrams the ground for the fuel pump is G204. It is located under left side of instrument panel behind the kick panel. The power door locks, power windows, rear park/stop lamps, power side mirrors and numerous other items use the same ground. Unless you're also having problems with them I doubt that a bad ground is the problem. However, if you want to check continuity from one of the two fuel pump connectors it is inboard of the driver side frame rail and in front of the fuel tank. The BK wire goes to G204. The other fuel pump connector is only accessible after lowering the fuel tank.

I was wrong about the wire color from the fuel pump relay to the inertia fuel shutoff switch. It is DG/YE and changes to PK/BK after the switch.

 

[JTrent]

I suspect something is restricting the flow of fuel to the rail. Check the fuel line from the pump to the fuel rail for kinks.

You were right Mr. 2000StreetRod!

Long story short, the braided line going to the rail was kinked. I half ass checked it the first time and after banging my head against wall checking voltages and replacing the damper, looked at it again and it stuck out like a sore thumb!

THANKS ALL FOR YOUR HELP! YOU GUYS ARE AWSOME!
:biggthump:bdrunk: