Mk5 GTi stage 1 fuel pressure problems

[Lassebongo]

Hi!
Im new here so if the thread is posted in the wrong section let me know.

Ive got a 2008 Gti mk5 stage 1 with fuel pressure problems.
On hard pulls it jerks and in the VCDS logs the pressure drops from 110 bar to 7(with the new HPFP, the old one went up to 129 bar and dropped)
A local company loaned me a HPFP which is swapped but didnt solve the problem.
Fuel filter swapped last year.
The cam follower is also new, doublechecked and its in pristine condition.
There are no leaks from what i can see, atleast around the visible fuel rails and HPFP.

So whats left is the in tank pump and im pulling it out today but i dont know what to look for 

Could there be anything else causing this problem or can i just swap out the in tank pump and the problem should be solved ?
Can the in tank be repaired ?
Is a 4 bar pump enough?

[ZoliWorks]

Check the part number of your old pump and buy based off of that. IIRC you need a 6 bar pump and a 6.6 bar filter.

Log the low pressure side with vcds next time you go for a drive so you can check what the pump is doing. Could be the pump, could be the controller or could be a worn out HPFP lobe. Even just a slight bit ow wear on th elobe can mess with the regulator open/close times and in turn mess up your fuel pressure.

[Lassebongo]

Ty for the reply
I did the filter swap myself last year and did check the pressure requirements beforehand so the filter is the correct one.
Here are the logs:
https://log.tunezilla.com/s/bbQzxooI

I'm doing tests on the n80 today and checking if the charcoal canister is clogged because there is a hiss when opening the fuel cap.

How do I test the controller on the fuel tank lid?

[ZoliWorks]

Holy, yeah look at your low-pressure side, that's basically dead. I'd say in-tank pump, controller or maybe the filter but unlikely. Your low pressure side is basically starving your engine completely. It should never really drop under 4.5 bar on full WOT.



Try logging the in-tank pump duty cycle as well. I forgot the exact VCDS param for it. Auxiliary fuel pump or electric fuel pump? something like that.

If you're going to replace it, there are a few threads here with people and the pumps they used.

[Lassebongo]

Yea as I feared I ordered a new pump and controller. The new pump will have a newer revision, 1t0 DB i think it was, same with the controller. It's weird though because its a low milage for its age. 130k
Yea I did log the duty cycle att some point, lost the file, it did max out at 95% if I remember correctly.
Thanks for the insight, I'll post the results after the swap!

[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.

[Lassebongo]

Swapped to my old pump and the problem is identical. Yup 6.6 bar filter, from googling a bit and looking at new filters i saw that the filter has a regulator which also can fail so ill be swapping the filter next. I have been running the car for more than a year on stage 1 without any issues, the problem started right after i did a carbon clean and swapped out all the seals on the injectors. If the problem persists after filter swap the company that tuned my car will take it in and look at the map.
Cool good to know, haha nicely made tool!

[ZoliWorks]

Well, if it started with a carbon clean and injector service, your best bet is to look there. You can long a few more things to get an idea of what's happening.

I think the misfire counter per cylinder and the lambda correction are the go to values here. Misfire counter will tell you if the car is experiencing any major misfires during load, which would prompt the ecu to reduce power by cutting fuel/air. Lambda control tells you how much the ECU is compensating for the correct air-fuel ratio. If it's positive, it's adding more fuel, so the car is running lean now and if it's negative, it's reducing fuel because the car is running rich. Another 2 values that are worth looking at is the lambda requested and actual. The ECU will try to maintain a specific lambda value (air fuel ratio) at all times but if the 2 values differ too much, there's a problem. I forgot the exact value but I think I'm running a 0.8 actual under WOT and as close to 1 as possible during idle.

Also check that all hoses and bolts have been tightened properly. I forgot to tighten the pressure release on my hpfp and while it was bubbling fuel out of it, the uprated pump internals were able to compensate. I ran the car like that for 3 days before someone mentioned how much it smells of fuel. I didnt even notice.. Honestly surprised it didnt catch fire cause of how hot these engines get


Edit: Get a MANN filter or a UFI. Dont go OEM because they are literally UFI filters with the OEM emblem on them instead..

[Lassebongo]

Alright I'll check these values. It does misfire on cylinder 4 but nothing excessive under load, mostly on idle.
Now that you mention it, I did see a fault code for slow lambda a while back but didn't think much of it.
I did the injector reseal three times and triple checked the valves for debris that could have stuck in the openings but nothing.
Yup I've checked for leakage as well , couldn't find anything. The current filter is a  Mann filter and I intend to buy the same brand yes.
The car does smell of fuel on cold start yes but only from the tailpipe fumes.