stas101

Hi everyone. 957 2008 Cayenne S. Just got a dreaded p1023 error "Fuel high pressure too low during starting" and cyl 1-4-5-8 misfire on COLD start and starter spinning longer than usual.Cleared codes.Turned the engine off.Started again 1 min later and pig started just fine no codes thrown. Both pumps are new less than 8k miles. New fuel filter and fuel pressure regulator.New spark plugs. Its doing it only during cold start!.Just wanted to confirm that its time for knuckle stripper aka replacing High pressure fuel pump in the back of the engine driver side? Thank you everyone for help.

stas101

Anyone????

nodoors

Sounds like it!

stas101

Changed the high pressure fuel pump to a brand new one though not the actual part# for sale but previous generation (94811031507 is the current part# I got 94811031504 instead though it looks the same) Car started fine and drove fine for almost 2 month and now same thing again - long cranking and got p1023 error out of nowhere
Could be the bad pump? it was brand new with plastic caps on the houses. Thanks in advance.

deilenberger

I would want to read out the actual fuel pressure that's getting to the injectors. See if it remains within the correct range after the vehicle is shut down. If not - there is a leak - either a bad injector, or a bad HP fuel pump.

stas101

this thing really got me tired.Why would it work for over a month starting just fine no glitches, everything is well and all of a sudden same issue again? The pump was brand new I only got p1023 error no misfires on cylinders though. Ill check the actual pressure.Do you remember by any chance what should it be? thank you very much in advance.

deilenberger

Unfortunately I have no documentation for the 957 direct injection models. I can look up the 958 numbers and I'd expect them to be compatible..

Here is from the 958 factory manual:
I don't know if a Durametric can read the pressure value - I'm certain an iCarScan can since I've looked at it on my 2011 CTT.

stas101

Sorry for long delay was too busy.Ok got scanned with iCarsoft. Got those values
when ignition is ON and car is running.
Second pic when ignition is OFF

stas101

Here is an update. When i start the car it cranks longer starts though you can hear its realy trying hard. I run it for a few min shut off and turn on again and it starts immidiatly like it is supposed to, most likely because pressure is not releaved yet. As soon as i wait a few min after shutting car off it does the same long crank thing. Im thinking it is still the new high pressure pump i installed since its is not the current part# used but 3 generations lower 9( current part # is 07 at the end mine is 04) even though its new but bought on ebay from looks like chineese guys from New Jersey.
P.S. i tested the high pressure while driving and under load and actual value does keep up with set value though yesterday after 30 min of driving after i gave it a gas in sport mode got a p1026 error check engine pight and slight loss of power. Cleared the code and it has not come back only p1023 shows up all the time.Any suggestions will be greatly appreciated. Thanks in advance!

deilenberger

Sounds like a bad check valve in the HPFP.. too bad someone doesn't make something that could be put in-line, perhaps on the output of the HPFP to do the same thing. Wouldn't need to be very complicated, a simple spring/ball check valve would do it.

stas101

Thank you for your opinion! Appreciate that. Im also leaning towards s bad hpfp even though it was new, looks like an error p1023 99% of the time means your hpfp is bad

nodoors

I would check the wiring first before replacing the part again. On one of my other vehicles I had a wheel speed sensor with intermittent failures. After thoroughly testing the sensor, wiring and EBCM, in time I replaced the sensor and tested a borrowed EBCM. The failure came back. I was forced to trace all wiring at that point. It turns out there was a break in one of the wires inside of the protected loom in a protected place in the car. If it had ever been to a mechanic, I would have swore it was foul play. There was a partially clipped single wire which was twisted with another inside of the hard plastic and sealed loom. My best theory is that it was installed damaged at the factory and took 15 years for it break down enough to cause problems.

Testing for continuity and even resistance was not enough. It seems it only split apart just enough under certain conditions to trigger the signal error.

So with all that said. Perhaps the pump is fine, but it has a bad ground or damaged wire which is reducing the amperage it can draw for full performance and that may be exacerbated by temperature and/or vibration.

stas101

Thank you for your input but its a mechanical pump driven by camshaft connected to it with a clutch. So honestly i can not think of any wiring for it to check . Basicly it can not build a presure to start the car properly though keeps it more or less after car started. On the top of 1023 i get occasional p1026 while driving and accelerating fast in a sport modem. Looks like its a well known spread wide problem with bosch made hpfp that other Gernan brands experienced as well but porsche 4.8 engine in general.

nodoors

DOH! hehe Scary lapse in memory there. I just switched out the HPFP in my boat a few weeks ago and must have had that on the brain.

stas101

Yap.Just swapped the old HPFP back just to see the change in behavior and car starts a lot harder and you can hear the engine struggling to keep up the rev. Trying to contact the seller to exchange the pump since it does look like valve in the new one still can not hold or built the pressure for proper start.