Fuel pressure sensor.

[Silver 03 Cobra]

Does anyone know what causes the diaphragm in the fuel pressure sensor to fail?

 

[predator]

I can't give you any of the technical verbage, but I know there was a discussion with Dana, MJ and a few others in recent past on the subject. Hope fully they will chime in or somebody can point you to a thread.

Look forward to catching up with you in Richmond in June!

 

[Swervedriver]

The theory I've read is that when you over-rev & bounce off the limiter the ECU cuts signal to the injectors but not to the pumps so the rail pressure shoots up to >80.

Supposedly there is an updated part that doesn't blow out as easily. My car was built 1/03 and I've hit the rev limit hard at least 5 times and haven't had a problem yet...

 

[TRBO VNM]

i won't cross link, but MJ has a a thread about this on the modular ford board.

 

[02yellowgt]

so what would be the effects of the car if the diaphragm in the fuel pressure sensor failed? Is this something easily replaced?

 

[ShelbyGuy]

is it just me or does this part tend to fail the most for people running 55# injectors

 

[TRBO VNM]

Originally posted by StevePoe
so what would be the effects of the car if the diaphragm in the fuel pressure sensor failed? Is this something easily replaced?

I believe the car basically dies since it is starved for fuel. Go read the thread and MJ explains exactly what happened. It is easily replaced. He did it with a flash light on the side of the road I believe.

 

[racerat]

Originally posted by ShelbyGuy
is it just me or does this part tend to fail the most for people running 55# injectors

I had two fail with stock injectors, before the KB.

 

[predator]

Most people seem to have the problem after hitting the rev limiter with higher boost levels. There are exceptions. When the diaphram goes then fuel is sucked into the vacuum lines and into the crankcase. Two problems then....loss of fuel where it is suppose to be going......fuel mixing with oil in your oil pan. Both very bad. The part number for the new fuel pressure sensor is #3R3Z-9F972-AA and is around $50. Easy to replace. Racerat reminded me that MJ did post about it in another forum.

 

[Swervedriver]

Originally posted by predator
Most people seem to have the problem after hitting the rev limiter with higher boost levels. There are exceptions. When the diaphram goes then fuel is sucked into the vacuum lines and into the crankcase. Two problems then....loss of fuel where it is suppose to be going......fuel mixing with oil in your oil pan. Both very bad. The part number for the new fuel pressure sensor is #3R3Z-9F972-AA and is around $50. Easy to replace. Racerat reminded me that MJ did post about it in another forum.

The only thing I would add/correct to the above post is that there is no vacuum/pressure in the crank case (in theory). The way the fuel gets into the crank case is by flooding the intake & compression chamber, washing down the cylinder walls, then falling to the bottom end.

Not good for the rings either I would think.

 

[mike79]

I had one fail on me, when the car was bone stock, and I never got near the rev limiter, at all prior to that.

 

[Silver 03 Cobra]

Originally posted by Swervedriver
The only thing I would add/correct to the above post is that there is no vacuum/pressure in the crank case (in theory). The way the fuel gets into the crank case is by flooding the intake & compression chamber, washing down the cylinder walls, then falling to the bottom end.

Not good for the rings either I would think.

It's true. It happened three times on a buddies 03. It filled the TB with gas.

Is it possible the chip can be building too much fuel pressure under WOT conditions? I find it hard to believe this could happen since the returnless system is starved on high powered engines but I'm no expert.

 

[Swervedriver]

Originally posted by Silver03Snake
It's true. It happened three times on a buddies 03. It filled the TB with gas.

Is it possible the chip can be building too much fuel pressure under WOT conditions? I find it hard to believe this could happen since the returnless system is starved on high powered engines but I'm no expert.

All of the logs that I've pulled on my own car shows 39PSI differential all the way up to ~6K. Once I clutch I'd get a spike in differential to 59ish. I've never logged a pull to fuel cut, but I wouldn't be surprised to see an even higher pressure result.

I don't think the stock pumps being in over their heads effects this one way or another. You've got 55-60PSI at 200&something LPH. Plug the end of that line & the pressure will shoot up since pressure and flow are inversely proportional reguarless of what the pumps ratings are. In other words even if the line pressure is falling off due to over the rated flow, the pumps are still operating at a max flow condition. Once the injectors shut down the flow demand is cut in half (at least, possibly more) but the pumps are still spinning at the same RPM.

Mikes was obviously just a bad part.