p0090 - failing HPFP? or something else?

[points]

Had about a half dozen times in the last 10 days where the car failed to start. Would go through the crank process but fail. After letting it sit for 5-10 min it would then start. Have not had any driveability issues otherwise. Scanned it and found code p0090 Valve for Fuel Metering open circuit. I didn't see any info on this related to our engines, only to TDI engines and they seem to point to a problem with the HPFP. I did check fuel pressures via VCDS and they at least appear to match what the ECU is requesting, didn't see anything that pointed to one being way out of range. I checked the connection and wires at the HPFP but didnt see anything that would indicate a failure there or at least none visible. Anyone have a good place to start diagnosing this? Is there a way to test the n290 valve?

Appreciate the help.

[points]

For anyone interested, p0090 for me ended up being the ECM power relay. The ECM, engine harness, secondary air pump and fuel pump relays all share a common ground and the strut tower right next to the ecm box. My relay tested fine with a multimeter but must have been failing when it got hot. Anyhow, replaced all three 645 relays that are in the under hood fuse panel and problem has been solved.

[Loe]

Hi there,

would you happen to have a picture of the location you are speaking of? I may have an actual mechanical failure of my HPFP.

Today, I keep getting a bearing-like noise, followed by a CEL for the N290 fuel metering valve (6559/P0090). I can clear it, but as soon as the noise comes back, the CEL comes back on. Fuel rail pressures are 100% normal, I wonder if my Autotech HPFP is clogged?

[points]

This is the diagram I used. The relays are in the same box as the ECU at the base of the windshield on the drivers side. It takes a little fiddling but you can remove the cover without taking off the wiper like a lot of the DIY writeups say. My car only had relays F,E,D,C installed and relay E us actually different than the other 3, it was 2 smaller relays in mine. Dont recall the numbers off the top of my head and its going to be -15 out tonight so I probably wont be working on the car for a few days. As for the N290, in the pic I attached of my spare pump its the 90 degree plug, the brass plug is the low pressure side pressure sensor. As far as I can tell, Audi or VW do not sell the n290 separately from the pump in the US, and its tough to find in Europe although the pump itself is pretty cheap. If you need one, I'll sell you the extra I have.

[Loe]

sent you a PM, my N290 valve is making some noises so it's like that I just need a new pump altogether. I ordered a replacement ebay LPFP as well just in case, my golly these are cheap used.

My fuel rail pressures jump from 3500kPa at idle to 14000kPa randomly when it makes the bearing-like grinding noise from the HPFP. I don't think my issue is a relay issue like yours, my car starts 100% fine and operates 100% fine, I just think the N290 (valve for fuel metering) is getting old or grimy so I'll likely just need a new HPFP and swap the Autotech internals.

[Loe]

I'm going to start documenting this as we get higher and higher mileage on our cars and more and more people run ethanol (which could potentially cause issues with our fuel systems, could, not will...)

I have a few logs to share about my N290 valve failure experience. What it is is basically a metering valve on the HPFP side that's not a serviceable part, you have to buy a new HPFP unfortunately in our case (or score a used on on the internet/ebay). It's controlled via PWM with a scale of 0-100%, 100% signal which dials back completely on the fuel rail pressures, and 0% signal which gives full pressure on the fuel rail, which I found out is about 17100kPa (well above what most tunes ask for, to give you an idea of how much more headroom we could potential have in our HPFP, at least with the Autotech rod).

I'm having my local shop disassemble my HPFP this Saturday, and install the new HPFP & and course transplant the Autotech rod in there. I'll take pictures of my old HPFP and its N290 valve. I have lots of logs so hopefully this will help those down the line.

symptoms:
unusual noises from HPFP area (aside from the normal tick tick tick). There is a metal-on-metal rotating grind-like noise, some knock knock knock (sometimes just knock knock) that goes in cycles at idle. When these noises occure, fuel rail pressures spike to beyond WOT levels from a tuned file
P0090/6559 CEL or stored code

the car will still drive fine, at least until the entire N290 valve fails. Another way to dx this is if you can start your engine with the N290 sensor unplugged, then the sensor is not working.

[pedro sr.]

It's a fairly common issue on the HPFP, in 2.0 and 1.8 tfsi too. The mecahanical sound you hear is excessive pressure in the rail/injectors and the regulator-valve protesting. Never tried a separate replacement, only complete pumps. Starting problems may or may not occur, it's random. I dont think E85 is a cause, it happens on stock cars too (max e10).
Not a bad thing to change or upgrade after a few miles on it or heavily tued

[RWD2quattro]

I'm going to start documenting this as we get higher and higher mileage on our cars and more and more people run ethanol (which could potentially cause issues with our fuel systems, could, not will...)
symptoms:
unusual noises from HPFP area (aside from the normal tick tick tick). There is a metal-on-metal rotating grind-like noise, some knock knock knock (sometimes just knock knock) that goes in cycles at idle. When these noises occure, fuel rail pressures spike to beyond WOT levels from a tuned file
P0090/6559 CEL or stored code.

Hey Loe, can you record the noise? That might be helpful for the rest of us. I've noticed the tick tick tick noise on my car has gotten a bit louder but so far all is normal.

[Loe]

yeah for sure.

My regulator valve hPa values are all over the map, even at idle jumping from -2000hPa to 4000hPa with every number in between despite a fairly steady PWM signal at 17-18% to the N290 sensor. At idle it should register around 100-200hPa give or take a few hundred, and it may or may not trigger a P0090/6559 N290 valve CEL.

My idle seems lumpier than normal given that the metering (aka regulator) valve jumps around. I have a replacement HPFP on the way, it should resolve it. Seems to either be rare on the 3.0t, or the threshold isn't great enough for those that may be failing to trigger any hidden or active CEL's

[Loe]

I did, but ended up deleting it off my phone. I can get another recording. The tick-tick-tick is the HPFP fuel rod, it's normal. The regulator valve is more of a sound of a rotating metal and metal noise or like when you drag some chains across a concrete floor like noise.

The N290 regulator is "serviceable" per say on the 2.0t/2.0tdi models, you can unscrew out the assembly and just check for metal shavings in it. It seems more rare on the 3.0t, I really had to go deep in a google search, but I found a few instances of N290 failures on Q7 3.0t's.

[RWD2quattro]

I did, but ended up deleting it off my phone. I can get another recording. The tick-tick-tick is the HPFP fuel rod, it's normal. The regulator valve is more of a sound of a rotating metal and metal noise or like when you drag some chains across a concrete floor like noise.

The N290 regulator is "serviceable" per say on the 2.0t/2.0tdi models, you can unscrew out the assembly and just check for metal shavings in it. It seems more rare on the 3.0t, I really had to go deep in a google search, but I found a few instances of N290 failures on Q7 3.0t's.

Got it, thanks for describing it. I don't have anything that sounds like metal on metal.

[points]

I did see somewhere that it was possible at least for a time to order the n290 direct from bosch in Europe. I'd be curious to know if the n290 is the same across all audi HPFPs but since the pumps are pretty cheap it may not be a big deal. Which also makes me question why the upgraded rod costs more than the entire stock pump.