2000 V8 Losing Fuel Pressure at WOT

[JTrent]

Hi Guys!

This is my first post and am looking for some help as to why my Explorer is losing fuel pressure. It's a 2000 XLT V8 2WD.

I replaced the fuel filter and installed a new Delphi fuel pump assembly and its still doing the same thing and I don't know what else it could be.

Had a friend hook a fuel pressure gauge up to it while driving and it drops to 10-15psi when WOT. Its about 62-65psi at idle. I understand it's suppose to be 65 psi all the time. It seems to run fine until I get on it, it just bogs down.

I don't see any leaks in the line or smell raw fuel anywhere.

Pulled the plugs and they all look scorched (lean).

I'm guessing it's a bad ground. Is there certain spots that are more likely to go bad than others?

Can a vacuum leak cause this?

Does anyone happen to have any other ideas what is causing this?

This is my only vehicle and would really appreciate any help anyone could give me.

THANK YOU in advance!

 

[jremington59]

It doesn't happen often but it wouldn't be the first time a part was bad from the factory. The last starter I bought was crap out of the box.

 

[JTrent]

Thanks for the reply jremington59.

The reason I don't think that's the problem is because it's giving the same fuel pressure reading/acting the same with the new pump as it did with the old pump.

Besides, dropping the tank again is the last thing I want to do!

What a PITA to do in the driveway with hand tools!

Might have to do it anyways to check what the voltage is going to the pump though...

 

[jremington59]

Did you replace the pump and strainer?

 

[JTrent]

Did you replace the pump and strainer?

Yes, it came as one complete assembly.

This is what I installed:

Delphi HP10135 Fuel Pump and Sender Assembly
http://www.ebay.com/itm/DELPHI-HP10...Parts_Accessories&hash=item232cc9d4b0&vxp=mtr

 

[bill06447]

Have you checked the fuel pressure regulator? It is partly controlled by engine vacuum, which drops at WOT.

Bill

 

[SoNic67]

Strainer is attached to the pump suction port.

I did bought just the pump motor and the strainer and replaced them into the assembly.

 

[jremington59]

Have you tried changing the fuel pump relay with another?

 

[2000StreetRod]

returnless fuel system

Have you checked the fuel pressure regulator? It is partly controlled by engine vacuum, which drops at WOT.

Bill

The 2000 has a returnless fuel system. The fuel pressure regulator (FPR) is part of the intank fuel pump assembly. The part on the fuel rail with the vacuum hose is just a fuel pressure damper.

JTrent, the Delphi assembly you purchased appears to be appropriate for your model. 62 psi is what my stock pump supplied. I think the pump normally runs at a constant speed and the excess is just returned to the tank via the intank FPR output (corrugated tube).

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. Make sure the direction arrow on the fuel filter points toward the engine.

 

[JTrent]

Thanks for the ideas!

Swapped the relay out with one from a 1999 at the junk yard. Same thing.

Checked the lines again, No damage or kinks. Fuel filter is on right.

I did think there could be something jammed in the line, but there is no way something that big could pass the fuel pump sock and the fuel filter.

Do these trucks have a fuel pump driver module (FPDM)? Could a bad MAP or TPS cause this?

 

[bill06447]

Is there a voltage drop at the fuel pump during WOT? You mentioned a ground issue but not whether you corrected the issue.

Bill

PS next time you need parts try Rock Auto. For example, your pump assembly is $156.79 for identical manufacturer/part number

 

[2000StreetRod]

fuel pump driver module

The fuel pump driver module and fuel rail mounted pressure/temperature sensor was not implemented until the 3rd Generation Explorer. The PCM has no control over the fuel pressure other than shutting off the fuel pump when there is no signal from the crankshaft (CKP) position sensor. Try cleaning the CKP sensor connector contacts by disconnecting and reconnecting the connector a few times. Maybe the CKP sensor/connector/wiring is defective causing loss of signal to the PCM. As bill06447 suggested monitor the voltage to the fuel pump during WOT. If it drops to zero at WOT then there is a bad connection or the fuel pump relay is being de-energized by the PCM.

 

[JTrent]

Thanks for the heads-up Bill. And thank you 2000streetrod for you insight!

Haven't checked voltage yet but that's next. Is there a way to check it without dropping the tank? Would like to see what it is while driving...

 

[jremington59]

Your check engine light does illuminate in the key on position doesn't it? I'd think you should register a lean code with 10 pounds of fuel pressure at WOT.

You might want to run this by the others with more experience, but I believe the fuel pump runs constant with the engine running. You'd have to drop the tank but if you went directly to the fuel pump with power through a toggle you'd know if the problem is in the line or related to something else.

You may be an expert at dropping the tank before you figure this one out.

 

[2000StreetRod]

monitor at Inertia Fuel Shutoff switch

I'm on vacation and don't have my wiring diagrams with me but as I recall the output of the fuel pump relay is routed to the Inertia Fuel Shutoff switch before going to the fuel pump. I don't remember the wire colors but I'm guessing pink/black for the hot and black for the ground.

EDIT: This thread I posted confirms the above wire colors: Fuel pump replacement - 2000 Explorer Sport

 

[SoNic67]

Fuel Inertia Switch is in series with the positive going to the pump. Because is normally closed, you would have +12V on both pins of the switch (measured to ground). Switch is low in passenger pillar.
Ground for pump is somewhere under truck, close to the tank, on driver side frame.

PS: @2000StreetRod: Nice clean garage there. I had to replace the pump with the truck on side of street, where towing truck left it (my driveway is uphill)

 

[JTrent]

Thanks guys! Very informative. I'll let you know what I find!

 

[2000StreetRod]

pink/black wire

Fuel Inertia Switch is in series with the positive going to the pump. Because is normally closed, you would have +12V on both pins of the switch (measured to ground). Switch is low in passenger pillar.
Ground for pump is somewhere under truck, close to the tank, on driver side frame.

I agree that the pink/black wire would go from the fuel pump relay to a normally closed series switched connection in the fuel inertia switch and then continue to the fuel pump. If I'm correct about the faulty CKP sensor at WOT, the PCM would de-energize the fuel pump relay and no power would be available at the fuel inertia switch.

PS: @2000StreetRod: Nice clean garage there. I had to replace the pump with the truck on side of street, where towing truck left it (my driveway is uphill)

Thanks for the kind comment about the garage. My subdivision covenants prohibit working on vehicles but I get away with working on them in the garage. I just assembled a shelf unit for storing all of the supercharger related components so I won't lose track of them.

 

[Turdle]

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.

 

[JTrent]

Thank You Turtle!