Fuel pressure oscillations

[azgolfrat]

Hey guys,
Took my Marauder on its 1st road trip yesterday. I went 173 miles in one direction, from Chandler AZ to Show Low AZ.
The rebuilt engine, etc., had only 200 miles on it prior to the trip, so still in the shake down phase.
Everything went good until about mile 140. Then the engine stalled. As it stalled I saw the fuel pressure (AutoMeter gauge) had dropped to near zero. I got the car over on the side of the road, opened the hood and looked for anything obvious. Nothing. I attempted a restart, and the car started and I completed the trip. Yay. However...

The fuel pressure reading would oscillate very widely from 100 to near zero if the car was idling and my foot was off the gas. If I gave it a teeny bit of gas with the accel pedal, the pressure would normalize at the steady state level, which appears to be 40 psi on the gauge.

When I arrived, I pulled into the garage, took my foot off the gas. The gauge oscillated again and the car stalled.

The car has never done this in the prior couple hundred miles of running; all of my other trips were relatively short.

There is a high volume fuel pump I put on the car while it was in rebuild. The pump is powered, essentially, directly from the battery , with that power going through a relay , then the FPDM. There is a 40amp fuse on the line in. This is a wiring set up that was found on this site, and recommended by Chris at ADTR.

There was no check engine light, no codes.

After a night in the garage, the car runs/idles very normal, albeit the stable fuel pressure is at 30 rather than 40.. so maybe the problem is temp driven?

Any ideas what was causing the wild oscillations in gauge fuel pressure?

Thanks guys

[azgolfrat]

guys, sorry - I did get 2 codes
P0190 & P0442





Hey guys,
Took my Marauder on its 1st road trip yesterday. I went 173 miles in one direction, from Chandler AZ to Show Low AZ.
The rebuilt engine, etc., had only 200 miles on it prior to the trip, so still in the shake down phase.
Everything went good until about mile 140. Then the engine stalled. As it stalled I saw the fuel pressure (AutoMeter gauge) had dropped to near zero. I got the car over on the side of the road, opened the hood and looked for anything obvious. Nothing. I attempted a restart, and the car started and I completed the trip. Yay. However...

The fuel pressure reading would oscillate very widely from 100 to near zero if the car was idling and my foot was off the gas. If I gave it a teeny bit of gas with the accel pedal, the pressure would normalize at the steady state level, which appears to be 40 psi on the gauge.

When I arrived, I pulled into the garage, took my foot off the gas. The gauge oscillated again and the car stalled.

The car has never done this in the prior couple hundred miles of running; all of my other trips were relatively short.

There is a high volume fuel pump I put on the car while it was in rebuild. The pump is powered, essentially, directly from the battery , with that power going through a relay , then the FPDM. There is a 40amp fuse on the line in. This is a wiring set up that was found on this site, and recommended by Chris at ADTR.

There was no check engine light, no codes.

After a night in the garage, the car runs/idles very normal, albeit the stable fuel pressure is at 30 rather than 40.. so maybe the problem is temp driven?

Any ideas what was causing the wild oscillations in gauge fuel pressure?

Thanks guys

[gdmjoe]

azgolfrat... P0190 & P0442


P0190 - fuel rail pressure sensor circut malfunction
P0442 - EVAP leak

[blazen71]

Pull the vacuum line off of the fuel rail pressure sensor and smell for gas. Replace if you smell gas. P0442 is a small evap leak and will not affect the drivability of the car. I would also check for a large vacuum leak.

[azgolfrat]

Pull the vacuum line off of the fuel rail pressure sensor and smell for gas. Replace if you smell gas. P0442 is a small evap leak and will not affect the drivability of the car. I would also check for a large vacuum leak.


I think the 0442 was from starting the car without gas cap back on (ooops),
I will check that doggone vac line as well. I've had problems with it before.

[azgolfrat]

Blazen,
The item to be replaced, if there is a gas smell, is the frps, correct?
Does the frps work based on differential pressure on either side of a diaphragm?
There was a gas odor. The only location to easily disconnect was at the upper manifold connection.



Pull the vacuum line off of the fuel rail pressure sensor and smell for gas. Replace if you smell gas. P0442 is a small evap leak and will not affect the drivability of the car. I would also check for a large vacuum leak.

[blazen71]

Yes, the FRPS. There is a diaphragm inside it that can rip.

[azgolfrat]

Thanks Blazen
So that raises a good question ...is the oem frps ok for a boost/vacuum environment that will produced with the supercharger in place? Or are there compatible frps units that are designed for use with a supercharged system? Thanks again!
-KK


Yes, the FRPS. There is a diaphragm inside it that can rip.

[justbob]

Thanks Blazen
So that raises a good question ...is the oem frps ok for a boost/vacuum environment that will produced with the supercharger in place? Or are there compatible frps units that are designed for use with a supercharged system? Thanks again!
-KK

Kenne Bell makes a disc that goes in under the FRPS to help with fuel spikes. I bought one probably 12 years ago now and never even used it LOL.

If it’s not on my tool box in the original envelope then it’s long gone, but if it is I’ll donate it. I’ll check this afternoon.


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[justbob]

Wow I actually remembered a date LOL!

2010….

Anyways PM me your address.

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[azgolfrat]

JB,
PM sent, thanks very much!

[azgolfrat]

Hey guys,
I took the fuel rail pressure sensor and the fuel pressure gauge sensor off the fuel rail (the gauge sensor allen bolts right on top of the frps) in prep for replacing the frps and found a small black oring one of two) on the gauge sensor was ripped. Maybe this was the source of instability. I will replace the oring (but neither sensor), put the new (smaller) belt on with new oem tensioner and see what happens. Thanks for the help.

[justbob]

FYI I sent it out Monday 5AM.

Sounds like you found your issue!


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[azgolfrat]

FYI I sent it out Monday 5AM.

Sounds like you found your issue!


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JB, got the part and installed.
Thank you sir!


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[BLACKMARAUDER04]

I’ve been able to pull 2 good units of these at the junk yard just in case I need one.


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