LBZ: New Pump & Injectors - same low rail pressure (P0087)

[Bikey]

'07 LBZ dually. 165k miles.
AD II 100 lift pump with Baldwin WS and Donaldson 3 micron filter
Nicktane filter with Cat 750 filter
New fuel lines (from tank to OEM filter block to junction block and then back to the fuel cooler)
lift pump is supplying 11psi as measured post-OEM filter block

I was getting p0087 codes - started on a hot summer day (accelerating onto a highway, road was flat) and I drove around it/shifted around it/reset the CEL all summer (prob around 100 times). I shimmed the FPRV, seemed to work for about 300 miles but then it reverted to throwing a CEL whenever accelerating or going up hill with the trailer (but not when unloaded). I got around it by barely pressing the gas pedal and also shifting religiously to keep rpms up when under load. I put in a race plug and no improvement, behavior was exactly the same.
Before the recent swapping of the injectors and pump, it started to throw a P0087 code without towing (eg, under hard acceleration or very occasionally when climbing a hill). I initially just swapped 4 injectors (driver's side), it still threw the P0087 code and max rail pressure was still around 13k psi.
With the original injectors and pump, it would only push out a max of ~13k psi of rail pressure at idle (desired was 23k). Same result with the new pump and injectors (genuine GM reman'd injectors and pump directly from Bosch). Same result with OEM tune or Idaho Rob heavy tow or 80hp tunes.
When doing the parts swap, I used compressed air to blow out all the injector high pressure lines and the high pressure line from the CP3 to the rail. I did not blow out the rail-to-rail line (doh) or the low pressure feed line that has the junction block. I did install fancy Aeroquip hose at the CP3 and 100R3 hose to/from the filter block.
My thought it that the sealing area for the FPRV/race plug on the driver's side fuel rail was the problem all along. I'm going to do a bottle test with the plug in place, while commanding max rail pressure, and see if there is a leak.
Anyone have any other suggestions or tests to run to determine the root cause of the low rail pressure, which I believe might be a leak of some sort? Do the hard lines accumulate crap/wax/cholesterol? Worth it to replace both rails?
As for tests and logging, I have EFI Live at my disposal. I just put everything back together (also did the water pump), so I'd love to limit the wrenching as I've OD'd a bit.

Thanks

 

[slipclutchms]

Bottle test and go from there for sure

 

[56taskforce]

Good plan got to be a leak somewhere.:thumb:

 

[DIESELMAFIAPER.LB7]

Put a race plug in and eliminate the fprv all together. If you have 8 new injectors and a new pump and the lift pump has positive pressure I would really suspect the fprv even shimmed

 

[56taskforce]

His post says it has a race valve but suspects it is leaking by @ the seat.

 

[slipclutchms]

Problem is if it has had a race valve for awhile and wasn't seated well or had some crud on it during install the fuel leaking past can mess up the sealing surface of the rail to the point it won't seal again.

 

[Bikey]

Thanks all.
It was (and still is) my fear that the plug/rail seating surface is damaged. In fact, when I swapped out the shimmed FPRV, the FPRV was in less than ideal shape (the dark finish on the sealing surface was missing in a spot or two, so it seems the seal was not perfect). Here is an update with a happy ending, though there seems to be a bit of luck involved:

1 - replaced injectors and blew out injector hard lines
2 - replaced CP3
3 - [replaced water pump while I was doing the CP3; also replaced CAT filter and WS100 filters @ Air Dog II 100 w/Baldwin BF1275 and Donaldson P551315; installed mechanical fuel gauge post-filter, set pressure to 11psi @ the lift pump]
4 - unplugged CP3, could only get 13k psi at idle; same result when commanding 160kPA w/EFI Live
5 - removed fuel rail plug, inspected it and reinstalled it with only a single wrench setup (ie, less tq than a double box wrench tug). The sealing surface of the plug seemed to have a slight imperfection, looked like a tiny hair width line running diagonally across the surface. Otherwise looked perfect.
6 - did a bottle test w/CP3 unplugged, which it miserably failed as the bottle quickly filled with pretty warm fuel (~30F deg ambient temp), maxed out at the familiar 13k psi
7 - swapped in OEM tune, drove it, was magically able to generate 26k psi; commanded 23k psi with EFI Live while idling and actual pressure was 23k psi
8 - swapped back to the Idaho Rob tunes, used the 80hp tune on the drive home (350 miles), no issues when hammering it for a bit going up hills

I have no idea how it could fail a bottle test and then generate 26k psi while driving and later while idling. I'm guessing that maybe I re-torqued the plug (lots of late night holiday wrenching involved and things were looking bleak) after the bottle test and that re-torq did the trick, because otherwise it seems like a spontaneous healing. Clearly seems like there was a leak in the system after the pump and injectors were installed.
Maybe when the problem initially surfaced (over the summer, while towing on a 95deg sunny day), the FPRV spring was weakened. Perhaps I got a poor seal on the rail when I shimmed the FPRV and again when I installed the plug. We'll see what happens when I start towing again and the fuel system starts spending significant time @ 26kpsi when lugging up hills etc. In the early stages of this problem, I was able to hammer it w/o the trailer it would not throw the MIL - the difference of course being that the system spends significant and continuous time above 20k psi while towing a 16k lb trailer. Just before I swapped the injectors an pump, I could easily generate a MIL in the +80hp tune w/o the trailer. I was thinking the pump or injectors were dying/getting worse, but it could also be that the plug seal went from bad to worse when driving around and through the issue (800 mile trip to Road Atlanta started ok - no codes for 300 miles, then moderate codes; trip back was near constant codes). I wouldn't be surprise to see the code return when towing once I start towing again, though hopefully before then I'll have time to swap in a new driver's rail and new shimmed FPRV...but after that I'm out of ideas.
I do think a bottle test is mandatory whenever reinstalling the FPRV (eg after shimming) or after installing a plug, to ensure that the seal is good. It seems like unplugging the CP3 is the quickest/easiest/best way to do the bottle test, unless I am missing something.

Anyway - for future reference - can anyone confirm whether the FPRV is included with a new driver's rail (Delco p/n 2172433)?

Thanks again.

 

[Harbin_22]

I'm not sure on the part number you gave but I got a new drivers side rail from the dealer and it had the fprv in it.

I fought a similar battle with towing with an LBZ. It would get low rp pulling campers on hot days. I did a lot of testing and trial and error. The best thing I did for it was add a fuel cooler before the cp3. The fuel twmps would get up to 190°+ and it would start the low rail pressure stuff from than on out.

 

[Bikey]

Thanks, and sounds like a good idea. Was there anything else that you did that might be helpful?
I was thinking of adding a cooler a while ago but didn't have an EFI Live at the time (to see fuel temps) and I was thinking that if I could fix the FPRV issue then the fuel temps would be helped. In retrospect it seems necessary -- the only two times I've been able to tow through hilly terrain w/o codes were in the winter (ambient air temp was <35deg).
But, easy enough to add a cooler (I think) as I have them all over my race car.
What size / btu/hr cooler did you use as a fuel cooler? I was thinking of using a 25 or 34 row Setrab cooler but the LBZ trans cooler seems like a good option and hard to argue with the price. If anyone has used the LBZ cooler - it takes 7/8"-14 O-Ring adapter fittings? The OEM return cooler seems marginal at best, and adding another cooler (fan cooled) in the return loop is also tempting.