Fuel rail pressure still too low AFTER replacing sensor, fuel pump, PEM and filter Topic is solved

[oragex]

Also, more basic things like the spark plugs and timing belt in good condition. If you want to keep looking for what may cause the fuel pressure to be low - but I recommend using used parts otherwise it will get too costly, may also look at the bottom contacts of the ECM (I put a video showing how to remove the modules without the tool), the antenna ring can also cut the fuel delivery, may also look at the small connector to the starter (may get corroded), there is another wire that gets corroded at the top of the radiator fan if you have the large connector

[volvolugnut]

I understand your frustration. When things go bad, it is sometimes hard to get everything corrected again. In the case of the hard plastic fuel lines, once they are kinked, it is hard to get them round again. Perhaps some mild heat can get the kink out of the tube.
Maybe there is a replacement tube available, or use rubber hose with hose clamps on the ends?
volvolugnut

[jonesg]

The pump might be losing its prime. It should be submerged to get proper cooling from the gas.

[jimmy57]

Did the car run OK for at least part of a test drive immediately after new pump install?
I am asking because many times on P2 models when the pump is removed dirt gets into tank. Fine dust silty stuff that ends up on top of tank. There is a fine mesh cloth filter on bottom of pump inside that pump bucket. The cars with problem typically will run fine for a short distance and then the fuel stirs up the dust and it gets in the filter (the one directly on pump bottom) and stops up the pump. Oh, yes add fuel. The tank needs about 3 gallons minimum on the right side for that bucket to get fuel in it where the main pump will send some fuel through the ejector (venturi) pump on the bottom of the bucket. The fuel pump in the bucket does not have a direct suction to the bottom of tank. There is a little trap door with an orange rubber seal on that allows fuel to flow into bucket if the fuel level is high enough to get into bucket through trap door and be high enough in the bucket to let the mesh filter on bottom of pump to be covered and get into pump. If the hose is getting under bucket then the initial fill amount is even more. The bucket in on those flat spring bars and will yield upward to something being under the pump bucket. The fuel pump can be removed from bucket to see the mesh if you push inward on the three black plastic tabs that hold pump down. Be careful not to damage the fuel level sensor. It can be slid off the bucket to keep it safe during the pump removal from the bucket.

[jonnydrums]

Hello all-

Seeing as how either way the first replacement fuel pump was crappy/broken and either way the problem was not solved, I acquired and installed yet another new fuel pump. With everything I have learned so far the process went much smoother this time and I came up with a good way to do the install with much less pain, and I am sure this one went in right and I can hear it working well. However....the car is now only back to a state where it will start and it will run, but sometimes idle fails (not every time) and in all cases, it performs inconsistently and/or poorly under load. We added 5 gallons of fuel back into the tank to do these tests.

So at the recommendation of several posters and friends I got a tester to gauge fuel pressure at rail. Here are the results.

This first test was done with: new fuel pump, new PEM, and new fuel rail pressure sensor. Result was start and run but sometimes drops idle/dies and definitely not able to consistently handle driving under load.




This second test was: New Fuel pump, new PEM, but with the original fuel rail pressure sensor. It actually seemed to be a little better (see video) and was promising enough to induce a road test, but sadly again it just can't hack it at load conditions like driving uphill. So I'm still stuck spinning my wheels so to speak after weeks.



I also tried running it with the FRPS totally disconnected - no start, I even tried with the old PEM - no start. Just trying to rule stuff out. Connecting/disconnecting MAF sensor doesn't really fix anything either.

[jonesg]

maybe try testing fuel pressure at the tank outlet.
Need some hose and clamps to rig it but it will show where the problem is.

[jonnydrums]

maybe try testing fuel pressure at the tank outlet.
Need some hose and clamps to rig it but it will show where the problem is.

Do you mean at the Schrader valve just before the fuel filter? Or a different location?

[abscate]

Spec is 52 psi, I think?

Blockage in fuel lines, fuel tank sock, or in fuel rail?

Tough one.

Time to monitor the output wave forms on the PEM...these are referenced ina thread here

[jonesg]

maybe try testing fuel pressure at the tank outlet.
Need some hose and clamps to rig it but it will show where the problem is.

Do you mean at the Schrader valve just before the fuel filter? Or a different location?

At the fuel tank outlet.
Schrader valve is on the fuel rail, but you might have blockage somewhere between the tank and the injectors.

[jonnydrums]

Hi everyone-

I wanted to let everyone know I finally got it all the way fixed!

I finally decided one last try....I swapped out the brand new PEM that I had bought and installed (previous to the videos above) for one from an identical car at the junkyard, and it works. Flawlessly.

Turns out the brand new PEM I had bought and installed was enough to make the car start and run, but not well, and after trying a few more things, a lot of head scratching, and the onset of desperation, I made a last-ditch trip to a junkyard and grabbed a used PEM for $50.

Before anyone says "well why did you replace the fuel pump again first?" Well, besides the fact that the first new fuel pump was compromised right off the bat and that we had problems with the install, I also think it's fair to say that most people at that time at that stage would have thought, as I did, given all the evidence detailed above, "well a new PEM helped get from no start/no run, to will start and run just not perfectly" and reasoned as I did that there was yet another issue.

I returned the new PEM and shockingly they didn't fight me on it. Lesson learned I guess..junkyard part is preferable to new sometimes because even though they say "fits your car" that's not always the case (even though it looked like it should, checked all the boxes for "fitment" and improved the situation without fixing it).

Thank you SO MUCH to everyone that read, replied and tried to help out, you are all great and I truly appreciate all of your efforts! I am now an unintentional "expert" on every inch of XC70 fuel systems . I hope this thread helps someone else some day.