All Things Mk5 > Performance Modifications

Fuel pressure deficiency...

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ROH ECHT:
Hello all...I have a 2007 GTI. Everything is in fine shape. Recently I switched back to my GIAC K04 HO(HO=RS4 fprv and a 140 BAR request for rail pressure) from a trial period with a DriverMotorsport K04 tune. My GIAC tune was fine a few years ago...but not the case when it was reloaded last year. The rail pressure request should be 140 BAR but only hits 110 BAR specified even though the actual exceeds that. 

I have a USP High Flow lpfp(in-tank pump) and the mentioned condition is present with either the USP or OEM pumps...with the OEM pump currently installed. I cannot believe that both of these lpfp's are failing but cannot figure out what the problem is. Again, there are no fault codes and the filter and follower are nearly new. Additionally, with both lpfp's, the actual low pressure will drop below specified nearly 0.5 BAR each time I collect data for group 231 in the upper revs...6k to redline mostly. Earlier the pressure will match requested low pressure.

I've had recommendations to replace nearly everything like: cam follower, filter, hpfp, lpfp, fuel pressure relief valve, and the controller. But I think everything is in good shape other than the controller which I haven't heard of being the culprit to this. Only I haven't heard of anything being at fault for this, so....any others here ever experienced this? "This" being, everything runs fine...it is just that the high fuel pressure request is the stock 110 BAR rather than the tune limit of 140 BAR...

pudding:
Sounds like either the fuel flow isn't there to support the higher rpms, or the software is commanding a lower pressure.

You've been through the mill with this haven't you!  Have you got S3 injectors to support your K04 conversion?

If I were in your shoes,  I would do this:

Refit a new standard OEM LPFP & controller, latest revision. Early ones overheated.
Fit a Loba HPFP.
Refit standard frpv.
Fit a new OEM fuel filter.

Get a new tune for that and see where you are.  You should hit 300hp easily with a 120bar relief valve and the Loba.  My ED30 does about 310hp with 115 bar request.

If all that holds the right pressure / flow and makes the expected numbers, consider the slate wiped clean and slowly increase things again.  One thing at a time so you don't lose track of what's been done.   The trouble with your situation is you've been changing hardware and software together, so it seems like resetting things back to a known good baseline again would be wise.

Dan_FR:
ECU/software issue. Hardware won't affect the ECU HPFP request so swapping parts out will not help

pudding:
I don't think it's solely software related because he said the actual exceeds the requested anyway.  The OEM parts have a tight grip on the pressure differentials.

ROH ECHT:
I have S3 injectors...RS4 fprv....and the tune for this.
"S3inj_FMIC_TBE_HPFP_140BARreg"

The 6.6 BAR fuel filter is nearly new...CF has less than 2k on it. The actual is below specified from the lpfp and above the specified from the hpfp.

GIAC said it could be readings from a sensor but had no help determining how to locate which one. I've recently replaced the fuel pressure, MAF, and MAP sensors except for the pressure regulator on the hpfp itself. All of my adaptations are done and the tests look to show all is working properly.

My APR-hpfp is believed to be fine as it's actual pressure always exceeds specified by 2 to 10 BAR. Lambda readings looked good in their opinion and the only thing they think it may be is the tune or the lpfp. The lpfp doesn't make sense to me because the ECM doesn't see the lpfp deficiency until late in the revs as actual matches specified up to 6k rpm.

I have been through enough with attempting to solve this and just wish it solved at this point without spending any more unless I have to.

Driveability is normal and I only want to know why the high pressure request of 110 BAR when it used to work at a 140 BAR request. I was at 285 hp at the wheels with this tune before and I am taking it step by step. I think it wouldn't hurt to try another controller...maybe a new oem hpfp and upgrade...last would be the lpfp because I have two and neither correct it.

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