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I am coming hat in hand looking for insight and helpful opinions about a P0087 Low Fuel Rail Pressure code and a solution “I think” I have. I’m a long-time lurker with a below average post count. I scour the pages to learn. Because of this very valuable resource I have been able to solve most issues I have run into owning diesels. I have done my research across various platforms. I think I have a path forward……just need input before I head down a rabbit hole only to back out 3 days later.

I use this truck as my daily driver for work and play. I bought the truck in Nov 2019 with 179, xxx miles and now has 309, xxx. Probably a little light on miles it could/should have due to COVID and reduced driving during that period. Still gives you an idea of yearly miles. I do not tow anything but a flatbed trailer or a boat. Hauled about 8,000lbs of landscaping rock 3 times…...other than that it is a boat only or a dump run. The Appalachian Mountains dead head in the area I live in North Alabama so there can be some long hills and 6% grades from time to time.
Its only happened twice. Both times pulling a 19’ fiberglass center console. Axle is rated for 3500lbs. I think I remember reading one time it should weigh about 3200lbs loaded with fuel.
The first time was a trip to Grenada Lake in December 2021. About 2/3rds of the way there it started. Continued for the rest of that drive and the drive back. It’s a long flat drive west of me. Any hills I encounter would have been leaving Alabama. There is rises in the road but not hills past that. Got home put a fuel filter in it. Immediately started to leak fuel back to the tank overnight and needed to pump it up in the morning, Rebuilt the head, still done it so I replaced the head. Never saw the issue again based on driving habits till last weekend.
Second time it done it I was pulling the boat again. I pulled the boat about two hours south. Started out about 3am. Never saw it once. Coming back home outside air temp was high 90’s. Stopped for diesel half way home. Put ¾ of a tank in it. Pulled out to a four way. My direction was up a hill (probably a 100’ rise over a quarter mile). Limp mode half way up. Nursed it the rest of the way home doing the usual resets along the way.

What I have done
1. Ordered an Edge CTS3. Will be in Monday for install that night. While waiting on that I have also done the following
2. Ordered a Kennedy fuel port gauge. Tested before I replaced the filter at 2.5 in hg. Replaced fuel filter and tested at 1.75 in hg. Picture is post-filter change. Something interesting to me is that even while revving the engine it may have risen .25 in hg but I feel it did not rise at all. Pinching the supply off the filter head to the CP3 it drew into a vacuum and I quit at about 15 in hg.

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3. Looked the engine over. Fixed a loose turbo inlet horn and what looked like a leak at the turbo intercooler inlet because of the oil build up around the clamp area.
4. Bottle tested the FRP. No fuel in the bottle at idle. In park revving the engine. Nor while driving a 10’ish mile circle with WOT 10-12 times.
5. Cleaned the fuel cooler
6. Imma call it a “***” bottle test of the injectors and CP3 pump. What I mean by that is nothing is calibrated equipment and I’m doing “large chunks” of testing to determine a direction. Heck the process I used may be all wrong. I have no way of increasing rail pressure other than through the accelerator. I pieced together several ideas from other users and research material to come up with this.
7. Bottle test

Step 1 - I removed the return line to the fuel cooler, pulled the two plugs in the engine compartment and started the truck for 15 seconds. I had almost 150 milliliters of diesel in a paint mixing cup the first time and I was just trying to make sure the lines were primed. The second time the results were identical.

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Step 2 - I then moved to the return rails of each bank of injectors and isolated them. Ran each of those lines in a paint mixing cup and left the return line to the fuel cooler in its own cup. Cranked it again for 15 seconds. Probably less than 2 ounces (prolly closer to 1 ounce) in each injector bank cup (the cup started at 50 milliliters and with it sitting flat it came nowhere near that). I would even call it the same amount in each injector bank cup. I ended up with just over 50 milliliters in the return line cup at the tank. Because these do not add up to what I had in the first step.... I am aware that to compare tests you have to remove any variables between tests. I did it twice to ensure full lines. These are pics from the second attempt. Thoughts!?!

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Step 3 - Next I put the two big plugs back together and started the truck and let it idle for 30 seconds. I had shy of 50 milliliters in the passenger and driver cups each (less than 100 milliliters added together). At the fuel cooler/tank return line I had close to 650 milliliters.

View attachment 652521

8. Buttoned it all back up

Now based on that I am starting to focus on the CP3 pump. Like the title says it takes a village.......I need you guys to bring me back from the ledge.

Questions I have are -
  • Is there any validity in the bottle test I performed on the fuel system?
  • Should only CP3 return be leaving the return line at the fuel cooler if the injector return lines are isolated at their respective return lines? Could anything else be contributing to the amount of fuel seen there?
  • What are the allowable return rates for injectors/banks of injectors and CP3 pump? I found info that said like 30 milliliters at each bank (4-5 per injector) and 1-2 ounces for the CP3. I am focusing on the CP3 based on the numbers I am seeing.
  • I had air bubbles in the return lines on both banks of injectors. It was not a stream of bubbles or aeration. It was 2-3 bubbles attached to each other intermittently. It surprised me. Should I be?
  • I have read the fuel line TSB and it appears it is for 2004.5 and older trucks. Should I be concerned about the fuel lines on an LBZ motor? I am currently trying to source the hose that is called for. I intend on doing it more because of age rather than the TSB. Just looking to prioritize and/or not overlook any issues that may affect the “***” test I have already done.
  • What else should/could I do to aid in nailing down or eliminating variables until the Edge arrives?
Questions or input you have -

I am asking for help. I have a lot of tools but I don't have every tool. What I lack in tools I like to think I make up for with an open mind and a great attitude.So nothing is off the table....I will try to provide info, answer questions and update info when I get it.

Next on the agenda –
  • The Edge is coming. Right or wrong I feel I have done all the things I can do without it. I intend to monitor fuel rail desired and actual before and while pulling the boat. I will update on what I have found.
  • Start pricing a CP3 unless I hear compelling reasons not to
  • EGR delete/up pipe/down pipe if I have to do a CP3.....or injectors for that matter. To me if I have to tear it down that far I may as well.
Thanks for reading, thanks for your time and thanks for your input!
Kennedy has a great write-up on the P0087 issue: https://kennedydiesel.com/docs/Duramax LBZ and LMM P0087 Low Fuel Pressure code.pdf
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22,315 Posts
Yep.....its outstanding. It talked me into buying the pressure gauge. I was fully prepared to verify injector issues. The results, to me, point to the CP3 pump though. That's not mentioned in the Kennedy write up.......other than a note that indicates "others that have replaced the CP3" may not have done their homework. That is why I need to others to put eyeballs on what I've done so far and either agree, disagree or suggest. Thanks for taking the time.
In Kennedy's write-up, he states " Simply put, the backflow or return rate is excessive so the pump does not keep up and rail pressure drops".

If the injectors are returning too much fuel then the CP3 won't keep up, making you think it may be the CP3.

22,315 Posts
Here is the write-up on return testing: LMM: - DIY injector replacement for LMM
IIRC, the CP3 return rate is no more than 2 ounces while cranking for 15 seconds and the CP3 is isolated from the rest of the system

22,315 Posts
EMSmotorhead - thanks for the input. I’m back right of center and leaning towards injectors. Almost pulled the trigger last night but man that’s gonna hurt….gotta do some more hand wringing first. When I do go that way imma put a lift pump in. Not immediately so as to see the benefits of the injectors but in the interim till I recover from the hit. If injectors don’t fix it….CP3 is coming but will probably be next year.
When you do decide to pull the trigger on Injectors I would highly recommend you contact Brent over at Lincoln Diesel Specialties: Diesel Injection, Parts and Services
LDS is one of our long-time supporting Vendors and Brent can set up exactly what you need.
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