HPFP Question

[thegriffen]

Greetings!

I have an N54 that we don't really know the history of. Yesterday, we fired it up for the first time in our build and it seems the HPFP is completely dead. And by dead I mean the rail pressure was no higher than the low side pressure, at idle. From what I've read online, people with bad HPFPs usually still have at least a couple hundred PSI rail pressure. Is this the expected failure mode, or should I be looking elsewhere? Maybe a wiring issue? The engine starts just fine and seems to idle fine, which seems odd to me with only 70 PSI of rail pressure. Maybe the pressure sensor is bad?

If anybody has any thoughts on this or has any ideas on how to troubleshoot this further, hearing them would be much appreciated.

 

[NoQuarter]

The engine will idle without the HPFP

No codes to report?

 

[thegriffen]

The engine will idle without the HPFP

No codes to report?

We did get a 29DC after idling for a minute or so.

I was hoping the issue would be something cheaper than a new HPFP, but it's looking like that's not going to be the case.

Do you know if no pressure buildup at all is a common, or at least a known, failure mode?

Thanks

 

[NoQuarter]

I don't think I have ever read any posts about a total failure. Only ones going bad.

I would be more suspicious of the electrical connection first. Check the plug, wiring at the junction box, etc

If you know anyone with an automotive oscilloscope you can get a look at the signal driving the pump

 

[thegriffen]

I did run across one post saying the pump can go into a bypass mode, but I couldn't find anything else to confirm that.

I'll double check the electrical connections next weekend. I'll also hook up a scope to look at the signal. What should the signal look like? I'm assuming some sort of PWM?

I appreciate your input!

 

[NoQuarter]

It should look like a pretty simple square wave (PWM) on the scope at idle.

The only thing I can say about what you calling a bypass mode may be the same as I described. A failed pump, or even a pump that is disconnected will allow fuel to flow through. This is when you will see 75PSI rail pressure

 

[doublespaces]

If you have another n54 just swap the pump. But don't put the bad pump on your car, I've seen them leaking so bad fuel could get into areas it shouldn't.

 

[rac]

very small changes in duty cycle to the pressure control valve have huge impact on rail pressure. Its quite easy for the valve to be open enough to prevent the HPFP from adding any pressure to the rail. the first place to start hunting around is the electrical control side of this valve. Yes it will be pwm controlled.

 

[thegriffen]

Went through all the wiring, verified it was getting a signal and everything seemed to be in check. Then I had one of those "this will never work" ideas, and lo and behold, I now have full rail pressure. Just needed a little percussive maintenance It's been sitting for over a year now, so it kind of makes sense that something could have gotten a little stuck.

 

[Lawrencerc14]

Went through all the wiring, verified it was getting a signal and everything seemed to be in check. Then I had one of those "this will never work" ideas, and lo and behold, I now have full rail pressure. Just needed a little percussive maintenance It's been sitting for over a year now, so it kind of makes sense that something could have gotten a little stuck.

Hey man I’m having same problems what did it end up being

 

[doublespaces]

Hey man I’m having same problems what did it end up being

He hit it with a hammer by the sounds of it.

 

[martymil]

Works for starter motors, stranger things have happened

 

[NoQuarter]

That solinoid valve can be removed and cleaned, and put back. No reason to have to just whack it and hope.

I could see it getting gummed up and stuck if it sits around too long.

 

[Al Gor]

That solinoid valve can be removed and cleaned, and put back. No reason to have to just whack it and hope.

I could see it getting gummed up and stuck if it sits around too long.

I was under the impression that these pumps were unserviceable. Could you please confirm you are taking about the hpfp, or did you mean the low pressure pump assembly under the rear seats.

 

[NoQuarter]

Definitely talking about removing the solinoid valve on the HPFP.

 

[NoQuarter]

This is pretty cool... that is the stock solinoid stuck in an experimental adapter Filippo @fmorelli made for me.