Fuel Pressure question??

[JayRolla]

Ok im starting to think that fuel is not raising with boost. I have to add about +30% fuel just when boost hits and after that I can run about +20% with no knock. Does this sound like Im tuning around the FP not raising with boost?

 

[GVR4592]

Do you have a datalog you can post? How much boost are you running? Have you considered that you might be pushing the limits of the stock fuel system?

 

[romeen]

Have you considered that you might be pushing the limits of the stock fuel system?

Agreed, since your profile indicates that you are still on the stock FP.

Nonetheless, I wonder if it would work to use the FP check terminal to pressurize the system and then pressurize your intake using your boost leak tester (you will need to purchase a FP guage of course). That way you can see if the FP is rising as it's supposed to as you pressurize the intake. I just thought of this right now so if I am missing something that won't allow this to work someone let me know. But being as how the FPR is controlled mechanically by manifold pressure I don't see why it wouldn't work.

This won't tell you if you are flowing more air than the fuel system can keep up with but it might answer your original question about the FPR possibly not functioning as it should.

 

[JayRolla]

Here are the main mods:

16g@15psi
SAFC
550cc injectors
Desno 3000gt vr4 pump
rebuilt 6 bolt/2g pistons
2g maf

I have checked the lines and dont see any kinks. Fuel filter is about 6 months old. Swapped stock FPR with another one and no difference. My logs are inconsistant. One run can have 0 counts, the next can have 7-14 counts. My coolent temps are running around 214-216*. Could that be a problem?

 

[romeen]

That inconsistency is very strange. I agree with you that it sounds like a fuel problem but don't know why it would vary from one run to the next like that. Although your coolant temps are high and should be addressed I don't know if that would cause the inconsistent logs. Maybe a voltage problem causing the pump to decrease output at times. Have you noticed anything else that happens only on those runs when you are getting the knock? Whether it be some measurement (voltage, etc.) or something you feel the motor doing.

Usually when I see intermittent issues that happen randomly in an unpredictable manner I think of an electrical problem: loose connection, failing switch, sensor, etc. Just a thought.

 

[JayRolla]

The safc reads voltage and it doesnt drop at all. When it gets knock the timing pulls so yea its not as powerful. I also get a major misfire at 5k-6k rpm. Ive always had this problem but was not as bad at stock boost levels. Sometimes it wont do it but usually does. It gets worse the colder it gets outside. I mainly get the knock real bad right when boost hits.

Not to mention new knock and o2 sensors.

My next thing im going to do is pull out the new knock sensor and retighten it. I think it may be a little lose but its more than hand tight. Im also going to change the fuel filter and I have a FP gauge coming in. If that does not get me anywhere Im going to a shop that has a gauge I can hook up and sticks to the outside of the windshield so I can make sure FP is raising with boost.

After that I dont know what to do maybe swap the ecu.

 

[romeen]

Is the fuel pump rewired? I don't know what size the VR4 pump is, but if it's output is borderline for your setup and it is still on the stock wiring that may be enough to lean you out, especially when you are getting a denser air charge when it is cold.

Maybe a Wiseman can provide some input on whether the elevated coolant temps might be a cause. Have you tried running some high octane gas to see if that solves the issue.If it works it may at least rule out some other possibilities. I wish I could be more helpful but I'm out of ideas at the moment.

Good luck.

 

[JayRolla]

Thanks man, no its not rewired but will be doing that real soon. The vr4 pump pump runs about 180lph not rewired so that should not be the issue.