dave_n_s

Tim,

I'm a pragmatic troubleshooter and fixer, and as I wasn't going on any road trips, I decided not to fix what was apparently a bad LP fuel pump in one side (confirmed by trying to start with each LP fuse pulled in turn) and just keep the gas level a good way off empty. That appears to have cured itself as it happens.

The HP fuel pump is easier to diagnose with live data on your Durametric - if fuel pressure follows throttle, the pump is OK, if it doesn't it isn't and if you've been through my priming saga, you'll already have a good idea. The vehicle will actually run on only the LP pumps, but not awfully well! So there is no chance that the original fault was an LP pump - they have no ability to respond to increased demand.

Note that you do need to "like" working blind or with the aid of a mirror and don't forget the extra plastic part.

tbo_cruiser

Thanks so much for the quick response. I did not look at the actual values for the HPFP, I'll do that next (I am also dealing with leaking sunroof drains at the moment). As to the working blind part, I don't see that well anymore so it will be what I am used to. Climbing up on top of the engine, however, might be a little more daunting.

tbo_cruiser

Finally got around to doing some more work on this. I hooked up the durametric and saw the previous fault codes,1026 and 1023. I erased these and started the car. Same symptoms as before, 3 sec crank then very poor idling. Checked the fault codes and this time got 1023 and another code related to idling (forgot to write it down). Checked the actual values. Set point was at 40 bar and the actual value was about 5800 mBar. I don't remember if I revved the engine or not, but the values were certainly quite different.

Then to check the low pressure pumps, I turned off the engine, pulled fuse 13, then started again. I ran for a full minute until I shut it off. Repeated and it did the same thing. Reinstalled fuse 13 and pulled fuse 14. Started the car and it ran for about 10 seconds then stalled. Repeated procedures and it did the same thing. Reinstalled fuse 13, and the engine starts and runs. Pulled 14 again, and runs for 10 seconds and stalls. So is this the indication that the right side pump is bad?

Do you think I have 2 problems, HPFP and the right side low pressure pumps?

Another question. If I have fuse 14 pulled and run the car until it dies, how was it able to start again?

dave_n_s

The fuel pressure difference between set point and actual is pointing at the HP pump. You only need one good LP pump, assuming you're not racing round a corner with a low fuel level and the fuel has not sloshed over to the side of the bad pump.

I'll admit to being a shade nervous when I ordered my pump, given the cost, but I'm a professional troubleshooter of much more complicated things (not internal combustion engines though) and I trusted my ability to use the data presented to me.

From researching the LP pump issue, I concluded that a lot of them fail and you will never know unless you drive in a way that will expose a bad LP pump AND you run the fuel level right down.

The fuse test is a good one. The car will run with a bad HP pump (but not very well), providing there is an LP pump working that is submerged in fuel. It is certainly telling you that the pump on 14 (rt?) is bad. Once you sort out the HP pump, see how it runs on interesting roads. LP pump replacement involves rather more taking things apart than swapping the HP pump, which just requires the ability to work using a mirror in a confined space and a good set of metric tools.

Usual disclaimer - all information provided in good faith. I am not an automotive professional and the reader makes their own decision on how to proceed.

TRINITONY

When I had my P1026 it was the HPFP. Now there is a thread on here someplace where all the symptoms was pointing to the HPFP, but after tons of diagnosis it was found to be vacuum leak that was the problem. He spent a lot to time troubleshooting, but save himself the cost of a pump.

See https://rennlist.com/forums/cayenne-...etric-log.html

dave_n_s

That was an outstanding piece of troubleshooting to find that vacuum leak, but with the difference that in that case the HP fuel pressure was tracking the set point. In this case it was not.

tbo_cruiser

I had some issues with the Durametric working (low battery I think), so I fully charged the battery and tried this again. This time, I remembered to throttle the engine a few times. And very clearly, the set point is going up and down and the actual high pressure value stays low and unchanging. Seems pretty clear that the HPFP is bad. So, I ordered one on FCP Euro (lifetime guarantee on every thing). Should take about 10 days to arrive. In the meantime, I am ordering some ratcheting combination wrenches and getting ready to climb up on top of the engine.
Thanks so much for all the help.

dave_n_s

Looks pretty clear now. Note that I did all the work from the drivers side of the engine, on a step, leaning in, with all the appropriate trim removed.

Did you get the expensive piece of plastic needed to align the shafts?

tbo_cruiser

While I am waiting for my new (rebuilt) HPFP to arrive, I have been reviewing the DIY threads on the replacement. Multiple people have posted about the plastic plug that holds the coupler into the crankshaft, and how these are often noted to be disintegrated when the replacement occurs. For those who have looked at this when putting it together, is it possible that these fuel pump issues are due to this plug going bad rather than the pump itself?

dave_n_s

These pumps have an internal pressure regulating valve to ensure that the injectors get the right pressure, regardless of supply pressure or engine RPM - the pump itself will typically produce fuel pressure that tracks RPM, but that's not what is actually needed.

My suspicion is that these pumps fail with the pressure regulating value wide open (i.e. output pressure = input pressure approximately).

Whether that failure is electrical or mechanical, I don't know, but it is very unlikely to involve that plastic sleeve.

tbo_cruiser

I got delayed a bit by Hurricane Ian (I'm in Tampa), but put the HPFP in yesterday then spent the night obsessing about the fuel line connections. I was able to use a crowfoot on my torque wrench to tighten the low pressure line, but I could not figure out a way to get a torque wrench on the high pressure fitting. I paid attention when I took it loose and noticed that it took very little loosening (about 20-30 degrees) to get to the point where it was easily loosened by hand. So I just tightened as much as I could by hand and then snugged it up about 20-30 degrees. Since I am starting to develop cataracts, there is no chance I would be able to see a fuel leak down in that space so I took a bunch of toilet tissue and completely wrapped the 2 fittings before putting the LP fuses back in or starting the car. Once I did that, I cleared the fault codes with the Durametric and set up to track the actual values. The car started OK and the values tracked as they should -- both the set point and actual pressure were about 40 bar, went up when throttled and back down when I let off the throttle. Shut the engine off and checked for fault codes -- there were none. Pulled the tissue out and I could neither see nor smell any fuel on those. I think it is fixed!!

The write up that was linked in Dorkiphus.net was truly excellent. Just a couple of observations. The fuel line fittings are different sizes. The HP fitting is 14 mm, whereas the LP fitting is 17 mm. I found it easier to get the pump out of and into position behind the cylinder head if I tipped it with the drive shaft facing down first. After seeing how the stopper and coupling fit together, it is pretty clear that the only purpose of the ($$$70!!!!) stopper is to hold the coupling in place during assembly. Incidentally, when I took my pump out, the coupling fell out like usual. When I tried to install it with the stopper it wouldn't go in. After close inspection I found that part of the old stopper was still in the hole in the camshaft. I used a 10d nail and inserted it head first into the hole, slipped the head over the back end of the old stopper and pulled it out. I still could not get the new one to go all the way in, but it looked like it was about as far is as the picture showed in the Dorkiphus thread. I assume it got pushed the rest of the way in when I put the pump in and tightened it down. To get the bolts out, I bought a 10 mm ratcheting combination wrench that has the swivel head. I think it would have been really difficult without the swivel head.