Weird fueling issue, where to go from here?

[Kwakazaki]

Background, this 2006 A4 B7 2.0T manual (160k miles) has been owned by me since new, the car purchased to bring my son home from hospital at birth (we had an Aviator grey TT 2.0 coupe previously), and the A4 is now his daily driver.

We have been having fueling issues for a few months, initially identified via VCDS full scan and while trying to add a JHM stage 1 tune.

The low pressure codes we were getting were two instances of the same code starting this thread 008 and 004.

012555 - Low Pressure Fuel regulation
P310B - 008 - Fuel Pressure Outside Specification - Intermittent - MIL ON

012555 - Low Pressure Fuel regulation
P310B - 004 - Fuel Pressure Outside Specification - Intermittent

So we immediately changed the LPFP, and there the saga started.

It is clear to me now that we had multiple problems related simply to age and wear because, for example, changing the HPF rail sensor solved a ‘cut out’ problem, but not the basic low pressure codes.
To date all the following have been replaced…

LPFP (VDO)

HPFP (Hitachi)

Fuel filter (x2 Hengst then genuine)

HPF rail sensor

LPF sensor (genuine)

Fuel control unit (genuine)

I have been sharing with the guys at JHM, they asked for the full VCDS codes, and for logging, but we have been unable to find the source of the problem.

Over the course of attempting to solve these issues the car became increasingly more drivable, almost back to the beautifully smooth car we originally purchased, yet enhanced by JHM short shift and stage 1.

The problem was that we could never get the codes to go away, and when reading measuring block 106, the new LPFP duty cycle at idle has been slowly getting higher, till today it finally gave out altogether - poof!

At installation 54% (the upper end of acceptable)

Two or three weeks later, 67%

Another week later, 76%

Earlier this weekend, 83%

Today, non functioning.

I watched this happen wondering whether the numbers I was seeing were real, and how the duty cycle was calculated. I guess I got my answer to the first query, but still wonder about the second.

I have done things like check the voltages and ground at the sensors. I blew the fuel line through with compressed air while the ends were disconnected.

The high pressure rail is all new because I changed the intake manifold.

Summary - car has been running better and better as we added new parts (some made no difference), yet through the codes and measuring block 106 we watched the LPFPumps demise.
Note - if I hadn’t had the misfortune to experience this I’m not sure I would have believed it!

Exactly what I’m going to do now I do not know… suggestions would be very greatly appreciated.

[justincredible]

Since all of this is LPFP - It’s not a bad idea to go and get a fuel gauge and tap into the low pressure fuel line just before the rail. Also check the old fuel pump. At some point you might want to swap it back.

This isn’t just a you thing.

I’d manually inspect the fuel lines from the front to the back
Swap in a different fuel filter as the LPFP is controlled by the fuel filter and it’s not uncommon to have them fail out of the box.
Put a Mechanical gauge in to help have real time hard proof of what’s going on.

[Kwakazaki]

Thanks very much much Justincredible,

Agree with everything you said, just have a few more questions and information. My post was already very long, so there were a couple of bits missed out as less important. I’m including now, I have access to a pressure test gauge and after being stumped for a while tested pressure at idling (76% timeframe), the pressure averaged 50psi, but I was surprised to see it jump around from 40-60psi. Measuring block 106 was showing around 50psi, so didn’t think much more about it, also I have little experience of what I should be seeing.

On the final morning before LPFP failure, just because I couldn’t think what else to do or test, I hooked the pressure gauge up again (Shraeder valve on HPFP). And was very surprised to see 20psi, within mins failing to 15, then 10 psi, after which car would not run. It seems I caught the LPFP in the final throws of failure, although at the time I was thoroughly confused.

Questions or statements

• [ ] I was confirming the measuring block results manually (Snap on pressure gauge) and it didn’t seem to add much to my knowledge or understanding.
• [ ] Threw the old pump out, won’t do that again! I am trying to get a new pump via parts warranty.
• [ ] Looked back at my receipts and contrary to my original thoughts that the new LPFP was installed 6-8 weeks ago, it was actually 3rd week of October last year!
• [ ] I haven’t looked at the EVAP system is there anyway that could cause the pump to work harder than it should have to?

Inspecting and testing of all the fuel lines and wiring probably means dropping the tank at this point. Do you think I’m at that radical point? Or is there anything else I should try first?

[TheBoyDrewWonder]

I’m having the same problem I do believe it’s the fuel filter with the regualtor. JHM sell an upgrade of it for the s4 so start with that believe it’s located under rear passenger side door.

[TheBoyDrewWonder]

Or your gas pedal fuel sending unit could be a problem too

[Kwakazaki]

Thanks for the suggestions.
Right now it’s looking like a bad fuel pump, got it warrantee’d as only had it a couple of months.
Replaced again, along with revision K low pressure sensor.
So far, so good!

[TheBoyDrewWonder]

Nice I replaced my diverter with a pierburg and added the dv+ now it’s not detecting it. Pedal cuts out. Now i got the codes for the fuel regulator. I’ve been ripping around without a gas cap bc it runs better without, its killing me on gas tho especially running 91. Maybe I’ll look into my pump next. thanks !