How to diagnose a dying HPFP?

[Jretal]

Hey all,

So I've gotten the dreaded P0087-008 code for low fuel rail pressure, and upon researching, it's pointing to the HPFP (not surprised).

Car has been taking longer to start in the mornings, and I get slight hesitations at low RPMs/light throttle load (b/n 2-3.5K RPM), and the occasional hard cut when flogging.

Is there any way to actually test the HPFPs? Or do I just replace both and be done with it? I'm pretty sure I know the answer, but figured I'd ask.

Also, part numbers? I'm finding 079127025C and 079127026 C on the online ETKAs, but also finding 079-127-025-AF instead. There been an update?

Thanks for the help! I've got a little over 13K miles on the new motor, and the car has been a blast. This has been the first major hiccup, but the HPFPs are original, so they have 114K miles on them.

-Justin

[ven0m]

You can manually check the Delta (difference) between the actual fuel-rail pressure and what the ECU is expecting from the HPFP with a VCDS cable. But if the P0087-008 has already been triggered then the delta-threshold has been exceeded in any case so the ECU already noticed the difference.

Not wise to play with low-rail pressure and running lean. Lean misfires are dangerous.

[Jretal]

You can manually check the Delta (difference) between the actual fuel-rail pressure and what the ECU is expecting from the HPFP with a VCDS cable. But if the P0087-008 has already been triggered then the delta-threshold has been exceeded in any case so the ECU already noticed the difference.

Not wise to play with low-rail pressure and running lean. Lean misfires are dangerous.

Agree on not playing with fire!

Is there a way to check between the two rails w/ VCDS? I was looking at fuel pressure measuring blocks, but didn't see a way to tell between banks. I'm very green when it comes to figuring out my way around VAG-COM though, so I might be missing something.

Just trying to figure out WHICH pump is dying.

Thanks!

[Chandler]

Agree on not playing with fire!

Is there a way to check between the two rails w/ VCDS? I was looking at fuel pressure measuring blocks, but didn't see a way to tell between banks. I'm very green when it comes to figuring out my way around VAG-COM though, so I might be missing something.

Just trying to figure out WHICH pump is dying.

Thanks!

Unfortunately only one rail has a HPFR sensor on it - why it was designed that way I am unsure. I am pretty sure it is the passenger rail. I will go through my photos to verify.

Ninja edit: Confirmed - passenger side only.

Part numbers:
Hitachi 079127026AB Driver
Hitachi 079127025AF Passenger

[ven0m]

Is there a way to check between the two rails w/ VCDS? I was looking at fuel pressure measuring blocks, but didn't see a way to tell between banks.

Unfortunately only one rail has a HPFR sensor on it - why it was designed that way I am unsure. I am pretty sure it is the passenger rail. I will go through my photos to verify.

Before Chandler's answer my idea would be to look at the 2nd ECU which you can find on module-11 (1st ecu is module-1). But if there is physically only 1 sensor, then both ECU's are displaying same data.

[Chandler]

Before Chandler's answer my idea would be to look at the 2nd ECU which you can find on module-11 (1st ecu is module-1). But if there is physically only 1 sensor, then both ECU's are displaying same data.

I went through this not too long ago, there definitely is only one sensor I just couldn't remember which rail. Technically the pressure and equalize too, making the one sensor even less accurate on a single rail if you have a failing pump.
What you can do is stick a screw driver up to the solenoid and with your ear on the other end, see if you can hear the same ticking. Maybe be hard to do since you will hear the buckets under the pump as well. I could not tell a real difference between mine and ended up sending both pumps to APR to bench test. Ironically, the second pump failed soon after :(

At the price point, and failure rate/ duty cycle - If you are sure it is the HPFP I would replace both before replacing one unless you are just strapped for cash. And if you are, there really isn't a good way to test the two without a bench test. Best I can do is say get a resistance reading between each pin (three pins, not sure on the pin out) for both pumps and I Will compare readings to mine if you would like. My bad pump did have a significant difference as it was the solenoid.

I'm not sure if the spring should be compress to active the solenoid or decompressed to get a proper reading, so keep that in mind.

[MugelloB7RS4]

At the price point, and failure rate/ duty cycle - If you are sure it is the HPFP I would replace both before replacing one unless you are just strapped for cash. And if you are, there really isn't a good way to test the two without a bench test. Best I can do is say get a resistance reading between each pin (three pins, not sure on the pin out) for both pumps and I Will compare readings to mine if you would like. My bad pump did have a significant difference as it was the solenoid.

The HPFP solenoid is pretty dumb, it's only 2 wires and the resistance between them should be 450-1000 ohms. You can start with that and see if there is a chance one/both soleniods are wonky. However you should also get a code for that if they were.

[Jretal]

I'm not positive it's the HPFP, but searching kinda pointed me that way.

Car takes a lot longer to start (i.e. cranking longer) than it used to from cold. Once car has run, it starts up fairly quickly/easily if you don't let it sit for a long period of time. Like it takes it a little bit to build pressure (and yes, LPFP does prime when I open the door to get in).

I've also been getting a very slight hesitation at like 2200 or 2800 or 3300 rpm and light throttle. Nothing hard, but you can feel it. It's been doing this since I put the new motor in (couldn't tell if this was occurring before since old motor was toast), but the frequency has increased.

I also def has moments of hesitating as if it's have a slight misfire (w/ heavier throttle). It's been getting progressively worse, and then w/ the long cranking to start - everything seems to be pointing that way.

I have been gentle on the car since figuring this out, but figure I will need to bite the bullet sooner rather than later at this point.

So if I read MugelloB7RS4's comment right - it's the solenoids that die on these? Other than knowing they're run off the cams, I am not too familiar w/ how they work.

Appreciate everyone's help!

- - - Updated - - -

And thanks for the part numbers, Chandler!

[Chandler]

I'm not positive it's the HPFP, but searching kinda pointed me that way.

Car takes a lot longer to start (i.e. cranking longer) than it used to from cold. Once car has run, it starts up fairly quickly/easily if you don't let it sit for a long period of time. Like it takes it a little bit to build pressure (and yes, LPFP does prime when I open the door to get in).

I've also been getting a very slight hesitation at like 2200 or 2800 or 3300 rpm and light throttle. Nothing hard, but you can feel it. It's been doing this since I put the new motor in (couldn't tell if this was occurring before since old motor was toast), but the frequency has increased.

I also def has moments of hesitating as if it's have a slight misfire (w/ heavier throttle). It's been getting progressively worse, and then w/ the long cranking to start - everything seems to be pointing that way.

I have been gentle on the car since figuring this out, but figure I will need to bite the bullet sooner rather than later at this point.

So if I read MugelloB7RS4's comment right - it's the solenoids that die on these? Other than knowing they're run off the cams, I am not too familiar w/ how they work.

Appreciate everyone's help!

- - - Updated - - -

And thanks for the part numbers, Chandler!

Yes the failure point is the solenoid. Unfortunately you can't buy just that part.
They do run off one of the cams, there is a bucket that sits between the actuator spring/ piston and the cam lobe.

If you have VCDS, I would log the pressure on the LPFP side when the door is open/ the pump is primed. Should be right at 6bar. HP side is all over the place depending on RPM range, load, etc.

If the car runs fine intermittently I would also be hesitant to point a finger at a HPFP, could be an injector as well. However, two HPFPs is going to be quick and easy compared to buying 8 injectors and doing a carbon cleaning service. Any the HPFP will go eventually. My OEM ones made it about 106K miles.

[JetG0ld]

Do folks usually replace with Hitachi pumps (I am guessing they produce the OEM pumps anyway) or is it the general consensus to go OEM?

[Datadatum]

On my car, only the passenger side began to have trouble, so that is all I had replaced using a new OEM part. My mechanic's experience is that they fail pretty randomly, and preventive replacement of a working part doesn't necessarily help.

[Jretal]

On my car, only the passenger side began to have trouble, so that is all I had replaced using a new OEM part. My mechanic's experience is that they fail pretty randomly, and preventive replacement of a working part doesn't necessarily help.

You have any idea how he diagnosed one being bad vs. the other? Just resistance perhaps?

Luckily, I still have the original injectors from the first motor, but they will need a cleaning/servicing, as they have 101k miles on them. That is an option at this point as well.

The HPFPs have just shy of 115k miles on them now, so not sure what's considered "borrowed time" on some of these components.

Appreciate the input all! I was eyeballing the Hitachi units from FCP Euro, as they were the ones w/ the best pricing.

[Datadatum]

IIRC, it was making noise. Kinda simple diagnosis. I'm not certain what the specific cause of failure was.

Regarding injectors, the mechanic I use recommends cleaning them regularly. I'm aligned with this, given that it appears to be one of the #1 reasons for RS4 motor failure.

[Chandler]

Do folks usually replace with Hitachi pumps (I am guessing they produce the OEM pumps anyway) or is it the general consensus to go OEM?

Hitachi is/ was the OEM. VW group would be OE.
Definitely save the buck and go OEM.

[Jretal]

Ok, so my LPFP is giving me a constant 6bar at start up and revving. At idle and revving (no lead), I'm seeing 20-30bar at the fuel rail.

When I went to do an OHM test across the solenoids, both are 2.5-3 ohms... which is a far cry from the 450-1000 mentioned by MugelloB7RS4. BUT, both are damn near the same. Are both on their way out?

What am I missing, folks? Is there a chart to show where the pressures at the fuel rail SHOULD be? I didn't get a chance to take it out for a drive, but also hesitant to really romp on it, as I don't want it to fuel starve and do damage.

Thanks!!

[WhatsATurbo]

I think I'm in the same boat as the OP. Did new pumps fix the issue for you? Similar symptoms and I got a real hard cutout last week at about 6200 rpm - scared me half to death.

Ryan

[Pyromatic177]

Time for me to chime in...

I have had the low fuel rail pressure code pop 3 times. All when doing a single gear pull. Once in 4th & twice in 6th. I replaced both HPFP and it still came back. But the weekend I changed the pumps the crank sensor failed too. I have to grab it from the shop i got it towed to and see if i get the code again...

I'm also replacing fuel filter, and upgrading the LPFP when I get it home regardless. But I will report back to see what's at least causing it on my car!

PS: Supercharged RS but don't think it makes a difference here

[WhatsATurbo]

Thanks, James. Must be contagious! I'm hopeful I'll have time to log with VCDS tonight. My OBD scanner showed pretty low rail pressure above about 5500 rpm, but I haven't had any codes/MIL light so I don't trust the measurement just yet. Need to see what the LPFP is doing before I get too carried away ordering parts.

How many have had the fuel pressure regulator fail and does it act the same as a bad pump/pumps? Do those need to be replaced along with the HP pumps?

Ryan

[Pyromatic177]

Thanks, James. Must be contagious! I'm hopeful I'll have time to log with VCDS tonight. My OBD scanner showed pretty low rail pressure above about 5500 rpm, but I haven't had any codes/MIL light so I don't trust the measurement just yet. Need to see what the LPFP is doing before I get too carried away ordering parts.

How many have had the fuel pressure regulator fail and does it act the same as a bad pump/pumps? Do those need to be replaced along with the HP pumps?

Ryan

The regulator is the only thing that really goes bad on the pumps. The rest is mechanical. But you can't buy them alone. They come with a new pump...

[nr103]

For what its worth, Id been feeling a hesitation or cutout around 2,500-3k rpms for the past few months but never had any codes/CEL. Then finally a few weeks ago I got an EPC light followed by the HPFP leaking and only then did I get a CEL for some sensors. Not exactly the same situation but I was also baffled with no codes being thrown. Ive installed new HPFPs and shes running great again

Sent from my SM-N950U using Tapatalk

[WhatsATurbo]

The regulator is the only thing that really goes bad on the pumps. The rest is mechanical. But you can't buy them alone. They come with a new pump...

Are we talking about the same part? https://jhmotorsports.com/products/e...-4-2l-fsi.html

Is that not serviceable? I haven't had this part of the car apart yet (yay for trying new things!).

[Pyromatic177]

Are we talking about the same part? https://jhmotorsports.com/products/e...-4-2l-fsi.html

Is that not serviceable? I haven't had this part of the car apart yet (yay for trying new things!).

That's the pressure relief valve. I was thinking the electronic part up top. I cleaned the valves but mine were fine

[WhatsATurbo]

Well, that was di$appointing. Logged rail pressure (actual vs demanded) and I’m only getting around 25-30 bar above about 6200-6300 rpm on a 2nd gear pull. The low pressure pump holds 4.4 to 6+ bar at all times, typically over 6 when the HPFP takes a dump.

I sat in the car reviewing the data log with the engine off and saw 110+ bar rail pressure after sitting close to 10 minutes. Unless this is abnormal, I believe this tells me the injectors and rail pressure regulators are working fine/not leaking. I’m going to log on my way to work in the morning to help confirm it’s the HPFPs that need replacing and nothing else. 140k miles on mine now but it’s unknown to me at the moment if these were changed already somewhere along the way. Both pumps are older ‘C’ revisions.

Ryan

[MugelloB7RS4]

That's the pressure relief valve. I was thinking the electronic part up top. I cleaned the valves but mine were fine

I've heard those called Solenoid valves or metering valves too, but I know the ones you mean, basically the part that you plug the electrical connector into. I've had a few of those fail and it throws a code which was easy for me to diagnose.

- - - Updated - - -

Well, that was di$appointing. Logged rail pressure (actual vs demanded) and I’m only getting around 25-30 bar above about 6200-6300 rpm on a 2nd gear pull. The low pressure pump holds 4.4 to 6+ bar at all times, typically over 6 when the HPFP takes a dump.

I sat in the car reviewing the data log with the engine off and saw 110+ bar rail pressure after sitting close to 10 minutes. Unless this is abnormal, I believe this tells me the injectors and rail pressure regulators are working fine/not leaking. I’m going to log on my way to work in the morning to help confirm it’s the HPFPs that need replacing and nothing else. 140k miles on mine now but it’s unknown to me at the moment if these were changed already somewhere along the way. Both pumps are older ‘C’ revisions.

Ryan

Do you have any codes? My car is acting similar. I have a VFIZ and I can watch the values in realtime. The low pressure side seems fine, but intermittently I have a drop of like 1000psi on the high pressure side. No codes, so it's likely a pump or sensor for me.

[Pyromatic177]

Man I really need to install my VFIZ lol. You can do so much with it

[MugelloB7RS4]

Man I really need to install my VFIZ lol. You can do so much with it

Its definitely really cool. The only things I will say is that customer support is not their strong suit. I've been emailing back and forth with the owner since May to have the units changed to metric and it's still not working right.

Also what I didn't realize when I installed it is that I can't seem to communicate to ECU1 via VCDS now. I think it has something to do with the VFIZ as you can check codes and all that with the VFIZ unit itself. Not the end of the world, but good to know going into it.

But the amount of info you can get is pretty awesome.

[WhatsATurbo]

Do you have any codes? My car is acting similar. I have a VFIZ and I can watch the values in realtime. The low pressure side seems fine, but intermittently I have a drop of like 1000psi on the high pressure side. No codes, so it's likely a pump or sensor for me.

No - no codes! I can't believe it given the huge delta from demanded pressure to actual pressure. Not even a pending code...



This is from a quick full throttle stab in 1st gear this morning. I backed off at around 6500. LPFP pressure is 4.17 bar at the lowest point shown here.

Ryan

[AA 954]

No - no codes! I can't believe it given the huge delta from demanded pressure to actual pressure. Not even a pending code...



This is from a quick full throttle stab in 1st gear this morning. I backed off at around 6500. LPFP pressure is 4.17 bar at the lowest point shown here.

Ryan

Thats also where my LPFP ranges under WOT ~4bar

[MugelloB7RS4]

That seems similar to mine.

My next step is high pressure pumps.

[WhatsATurbo]

That seems similar to mine.

My next step is high pressure pumps.

Me too. I've read in several places that 6 bar from the LPFP is normal under most conditions, down to ~4 bar with load. So that only leave the HP pump(s).

Ryan

[MugelloB7RS4]

Me too. I've read in several places that 6 bar from the LPFP is normal under most conditions, down to ~4 bar with load. So that only leave the HP pump(s).

Ryan

I believe that to be correct too

Weirdly enough, yesterday we went on a 300 mile trip and about half way the cars EPC light came on and it was for a P2294 in ECU1 which is pointing me to the passenger side HPFP solenoid valve.

This was after just straight highway driving didnt do anything crazy. We stopped for fuel and when I restarted the car the code had gone away. So it's an intermittent thing in that pump it appears for my car anyway.

[Pyromatic177]

I believe that to be correct too

Weirdly enough, yesterday we went on a 300 mile trip and about half way the cars EPC light came on and it was for a P2294 in ECU1 which is pointing me to the passenger side HPFP solenoid valve.

This was after just straight highway driving didnt do anything crazy. We stopped for fuel and when I restarted the car the code had gone away. So it's an intermittent thing in that pump it appears for my car anyway.

Had that code on my Muggy RS4. Happened to have another HPFP laying around so I threw a new solenoid on it and it was good

[MugelloB7RS4]

Had that code on my Muggy RS4. Happened to have another HPFP laying around so I threw a new solenoid on it and it was good

I've ordered replacement pumps, and I'm on the fence on upgrading their internals. I've read that the high pressure output helps ease the load on that solenoid which helps it last longer. So while I don't need the extra preasure, if it can help these damn things last longer, it would be worth it.

[AA 954]

I've ordered replacement pumps, and I'm on the fence on upgrading their internals. I've read that the high pressure output helps ease the load on that solenoid which helps it last longer. So while I don't need the extra preasure, if it can help these damn things last longer, it would be worth it.

Just get a supercharger and the kit will come with the upgraded internals

On a serious note did you get the hpfp from Rockauto? I’m thinking about pulling the trigger too and just change mine as part of a maintenance excuse even though they are ok

[MugelloB7RS4]

Just get a supercharger and the kit will come with the upgraded internals

On a serious note did you get the hpfp from Rockauto? I’m thinking about pulling the trigger too and just change mine as part of a maintenance excuse even though they are ok

Yes, I ordered both Hitachi pumps from rockauto. Hitachi is the OEM and I don't see any reason to think they are any different than the ones that were supplied to Audi originally.

[Chandler]

Thats also where my LPFP ranges under WOT ~4bar

4bar on LP side at WOT is acceptable.

[WhatsATurbo]

All better now - two new pumps:

[AA 954]

All better now - two new pumps:

So much better

[MugelloB7RS4]

Nice! Mine was similar. I would routinely see +- 50psi before. Now, its rarely a - number and if it is, it's like -7psi, its so much closer to the commanded. Not only that, but it runs so much better. I'm not sure why I'm surprised by that, but its totally changed the way the car drives.

[WhatsATurbo]

Nice! Mine was similar. I would routinely see +- 50psi before. Now, its rarely a - number and if it is, it's like -7psi, its so much closer to the commanded. Not only that, but it runs so much better. I'm not sure why I'm surprised by that, but its totally changed the way the car drives.

I only have my drive to work this morning with it so far, but yes - I thought the engine/cal had a couple of flat spots as the car did it since I bought it 2 years ago. But apparently that was bum fuel pressure, even in the mid-range. I'm very happy to have spent this money - it was a super fun drive in today.