Idle fuel pressure cut out?!

[Joshlc1988]

Hey guys I need some help diagnosing a stumbling in my 06 2.0t. Been chasing this for a while now. When I start the car an let it warm up it'll start to stumble briefly every minute or so. Only happens after it's been idling over 5 minutes. Looking at the lpfp at idle, duty% is at 55% on startup but will slowly climb to low 60s after getting warm. Lp requested varies between 5 and 6 bar, as does actual, but every time duty% gets back down to high 50s the rail pressure will drop out to 20 bar or so. Also I'm seeing mid 90% duty cycles on a wot run from the lpfp.

This happens while driving also but I haven't been able to log it driving. Seems lpfp is supplying requested pressure at all times. This cut seems more duty cycle dependent. Once warm my rail pressure will cut out to mid 20 bar every time the lpfp gets around 58% duty. What's weird is it's still supplying requested pressure!? Could my pump just be dying and not giving the volume? Or the controller possibly dying?

Car is jhm stg2 93 hpfp, brand new jhm upgraded hpfp, new cam/ chain/ and tensioner, new fuel filter, o2 sensors, n80
Any help would be great!

[Denio24]

Check your ltft and stft values at idle, and wot.

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[Joshlc1988]

I reset everything yesterday and replaced the vc an gasket. Checked all my cc lines and vacuum tested everything. Let it run for 30 mins then took a drive. No change. Block 31 holds almost spot on with requested while block 32 reads 0.3 / 9.8. Maf reads 2.20 to 2.40 at idle but low 180s at wot. Lpfp pressure ranges from 4.5 to 5 bar on a wot run still.

I'm I'm starting to wonder if my lp fuel sensors is reading wrong as I noticed 11 bar yesterday on prime and a max of 118 bar WOT.

[blakefife]

lpfp seems like its going bad? 90% duty cycle? i dont think its supposed to go up that high even under extreme demand. i thought anything over 54-60% indicates suspicion.... have you checked your high pressure fuel relief valve? its located on the fuel rail, its a brass fitting thing that screws into the fuel rail on one side and then the stainless fuel line on the other side. it bleeds off excess gas, maybe yours is stuck open or closed? open not creating enough back pressure or closed not allowing enough fuel to return to the tank? idk just my two cents

[Denio24]

I'm I'm starting to wonder if my lp fuel sensors is reading wrong as I noticed 11 bar yesterday on prime and a max of 118 bar WOT.

Usually if it's something wrong with the controller isn't it short to ground? That would usually throw a code. So I wouldn't look at the LPFP controller unless you see that the you see any codes related to it. I would look into the thrust sensor before trying to mess around with the lpfp controller or the lpfp.

Again to be clear, what exact issues are you feeling at idle and wot?

[Denio24]

lpfp seems like its going bad? 90% duty cycle? i dont think its supposed to go up that high even under extreme demand. i thought anything over 54-60% indicates suspicion.... have you checked your high pressure fuel relief valve? its located on the fuel rail, its a brass fitting thing that screws into the fuel rail on one side and then the stainless fuel line on the other side. it bleeds off excess gas, maybe yours is stuck open or closed? open not creating enough back pressure or closed not allowing enough fuel to return to the tank? idk just my two cents

These fuel issues are tricky to diagnose. I wonder what his duty cycle at idle is.

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[Joshlc1988]

It has a stutter at idle and inconsistent power delivery. Car has no codes. Also +10 to +15 ltft. At idle my lpfp is at about 55% duty. Last night i took the pump out and cleaned out the basket and sock filter. Also blew out the fuel lines. So far duty cycle hasnt hit 90s again, just mid 80s wot so I'm thinking I either had a restriction or line clogged. I did find some nasty stuff in the pump basket. I'm gonna do some logging this evening

[Denio24]

55 is normal at idle. I was reading up on this for a bit today and found a thread somewhere saying that a lean condition could be attributed to the rail pressure sensor (thrust sensor)

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[Joshlc1988]

Well overall I think cleaning out the fuel pump basket was a success, as duty cycle at idle is down to 50%, and I've yet to get above 80% WOT. The car seems to run better but fuel trims didn't show a change. There was a lot of trash and bits clogging the sock filter and what looks like carbon sediment.

That leads me to to this morning. Warm her up an head thru town an light comes on. Hook up vcds an got evap small leak. So I kept it hooked up to log my o2 trims. Got on the interstate an leaned on her and threw another cel for evap large leak. I checked over everything an suprisingly block 32 has came down lol. Idle -1.1% / partial 8.2%.
I'm starting to think I've had a slowly developing evap issue that's letting junk get into my gas tank.?.

[Denio24]

Well overall I think cleaning out the fuel pump basket was a success, as duty cycle at idle is down to 50%, and I've yet to get above 80% WOT. The car seems to run better but fuel trims didn't show a change. There was a lot of trash and bits clogging the sock filter and what looks like carbon sediment.

That leads me to to this morning. Warm her up an head thru town an light comes on. Hook up vcds an got evap small leak. So I kept it hooked up to log my o2 trims. Got on the interstate an leaned on her and threw another cel for evap large leak. I checked over everything an suprisingly block 32 has came down lol. Idle -1.1% / partial 8.2%.
I'm starting to think I've had a slowly developing evap issue that's letting junk get into my gas tank.?.

Whats the code youre getting?

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[Joshlc1988]

P0455. The only thing I can think of is that the orange gasket that seals in the lpfp was in rough shape. I'd assume that if it don't seal it would cause an evap leak? That code just started since I cleaned the lpfp.

Also just for shits and giggles I just blocked off the rear pcv vent tube from the turbo to vc. Right now I'm just venting my cc to air. I didn't drive it far maybe 2 miles but so far my partial trim is +0.4, however idle trim has risen to +2.2, I'm guessing because of the evap leak letting the n80 suck air instead of fuel vapors.

It's too soon to say but I'm curious if the vc I got from edstoy also has an internal leak, since blocking the rear breather seems to be helping the fuel trims off idle.

[Denio24]

An EVAP leak would have anything to do with vapors coming from the gas tank. It's a sealed system that was designed that way. Did you install the N80 in the correct direction? It could also be from the gasket you mentioned.

[Joshlc1988]

Yeah the n80 is right. I'd say its the pump seal as it was all cut up.

[Denio24]

The n80 is OEM? not aftermarket? Perform some basic settings tests in groups 70 & 71 (try blocking off the n80, redoing the gasket on the fuel pump, checking for loose lines, etc)

[Joshlc1988]

It's OEM. The problem I got now is I gotta go on a 10hr trip this weekend with the car. I don't know what that leak will do to the drivability? I'm gonna pull the pump lock ring an try to seal it better in a bit

[Denio24]

10 hr trip?! Quite a bit away.

[Joshlc1988]

Yeah well 5hrs there then back. I'm in the national guard an use the Audi for traveling there.

[Denio24]

Yeah I'm going to have to prep my car soon for storage I'm actually headed out myself to cape may uscg in a few months. I still have a high multiplicative fuel trim. Ultimately I think this is due to contamination or some part of the fuel system not being able to keep up with the tune under load.

[Joshlc1988]

UPDATE: so I deff didn't put the fuel pump seal on right. Pulled it again an got it right and bam! No more evap leak. It took it out for lunch about 6 miles after clearing codes and got a block 32 reading of +2.2 idle/ +2.0 partial. It's still sol but that's already much better than it was! I believe I had a vc leak somewhere since the partial went down so much after venting to atmosphere an blocking the turbo vent. Car seems much happier than before, pulling no more than 4.5* timing.

Car still has a randomly low maf readings and block 3 timing still wanders between 2 and 12 btdc. Maf will read 2.50gs then randomly drop to 1.90gs for a min then go back. Every now and then I see a cyl 2 misfire on the counter. I swapped plugs and coils and it still happens on cyl 2. I believe I may have a intake manifold leak or injector seal leak on cyl 2. I remember #2 injector coming right out when I did the carbon clean so I hope that's the issue. But overall it's much better than it was.

[Denio24]

As long as you don't go over +10 combined for the idle and partial trims then you're good.