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Mk5 GTi stage 1 fuel pressure problems

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ZoliWorks:
100k is about the expected lifetime of these pumps tbh. They will last more but can break at any moment.

95% is basically dead. IIRC even under WOT it should be around 65 max. I think I deleted my logs but I dont think I've ever seen it go above 70 and that was when when I was pushing it for 370hp

Lassebongo:
Alright good to know! Also found that cylinder 4 misfires, not much but still. How long does the injectors last you think? Recently replaced all the seals on the injectors but it didn't fix the misfires, so I'm suspecting they are on their way out as well.

ZoliWorks:
The injectors themselves have a general lifetime of no more than 100k km. They'll work more than this, but under 100k is when they still operate in factory params. Then again, you cant trust sh*t nowadays cause i installed 4 brand new oem injectors in mine and one failed after a month...

Injectors generally fail by leaking or getting stuck open/closed. They are engineered with very small tolerances so once they get dirty inside, that's the end of them. you also cant really clean petrol injectors because of mechanical wear. To get a matching set of 4 injectors that all spray in the same pattern and the same volume, you need to refurb about 14 injectors at least.

Another thing that fails about them is the filter at the top. It literally disintegrate and get's sucked into the injector. OEM filters last about 60k km or less so most people opt for mesh baskets instead.



Now regarding misfires, it could be caused by many things. My misfires under WOT were caused by a sticking injector while my current misfires at idle are caused by mechanical wear inside the engine. Specifically, my camshafts are rusted and pitted. During idle, cyl 3 misfires 90% of them time.

Other likely causes are spark plugs, ignition coils, valves that arent sealing properly, carbon buildup on the valves and in the intake, faulty pcv system, faulty maf, or a vacuum leak. Plus billion other things...

My advice is, as long as it runs and doesnt have issues during WOT, dont try to fix it lol

Lassebongo:
Ok pump and module swapped, problem persists. tried with new pump + old module and new pump + new module, no difference. The car felt a bit smoother during regular driving though.

Here are the new logs.
https://log.tunezilla.com/s/6a3soTxh

At this point im stumped, im thinking the borrowed HPFP may be faulty so im swapping it back to mine.
Is it the regulator ? fuel filter ?

ZoliWorks:
For some reason your low pressure side is still dropping. Are you using a 6.6 bar filter? I'd swap back to your own hpfp and check if the issue is still there. I dont think stage 1 would have any demand for more than 130 bar and even that is unneeded.

I've had issues with fuel pressure demand on my side cause of 2 things: Non-upgraded hpfp and stock fuel pressure release valve. The hpfp would cut out between 3k and 5k and pressure would dip because it could not move enough fuel volume for what the tune was demanding. Stock valve also opens at around 128 bars since these engines run on 120 bar stock. You need an RS4 valve which opens at a higher pressure, but I forgot exactly how much.

However, I dont think your issues are related to the valve but we'll see. Try your old pump, the one that was working fine and see what it does. If it works up to 130 bars, try the FPRV. You can get them new from the dealer for about 100 euros or buy it off of some marketplace group for half. You dont need to remove your intake when changing this.

The way I did mine, I cut a wrench in half, welded it into a 90 degree bend and used another wrench to apply turning force on it to loosen/tighten the valve.

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