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Discussion Starter · #1 ·
I have a 07 LBZ that is throwing a code for low fuel rail pressure. It only does it when ambient temp is over 90’F and I’m towing at highway speeds.

I already replaced the fuel rail relief valve and the fuel filter and now I’m suspecting one or more injectors may be bad. I have noticed a chugging/loss of power condition before it faults that if it were in a gas engine would be a misfire. I’ve been resetting the codes but I need to identify the real problem.

My code reader shows a maximum fuel rail pressure of around 26,000 psi.
 

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More posts about this problem than any other. Use the search function for find hundreds of answers.
 

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There is a ton threads about P0087. The most common problem and unfortunately most expensive is that the injectors are returning to much fuel.
 
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FRP was at 20,105 psi when it threw P0087
Ok..... so I like to look at desired fuel pressure and actual fuel pressure to see if they match. I would like to back up for a second to a simple basic thing to check. How much vacuum are you pulling at an idle ? Kennedy Diesel sells a gauge that goes on the test port and you can find it at other places that is a very useful diagnostic tool. Kennedy Diesel. If that checks out good then you can move on to some other items. What are your fuel temps when this happens ?
 

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My 07 lbz was doing the same thing. Couldn't pinpoint the problem so I changed everything. Injectors, cp3 pump, fprv, ported fuel rail fitting, fuel lines, fuel pressure regulator, glow plugs, water pump. Lol, must've been one of the above. Runs like a new one now! No codes when towing.
 

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Discussion Starter · #9 ·
I have an appointment Monday with a recommended shop. I want the to do the fuel vacuum test, the fuel return test and the command 21,000psi at idle test.
There is a local shop that will bench test my injectors for $30 each if the tests point me in that direction. Anyone recommend changing all injectors due to mileage (190,000)?
 

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I have an appointment Monday with a recommended shop. I want the to do the fuel vacuum test, the fuel return test and the command 21,000psi at idle test.
There is a local shop that will bench test my injectors for $30 each if the tests point me in that direction. Anyone recommend changing all injectors due to mileage (190,000)?
If the fuel return test shows one or more failing there is no need to bench test the injectors. Just bite the bullet and replace all of the injectors and be done
 

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Also consider replacing the CP3 while you are in there because when it fails it can send metal to your injectors therefore having to replace them again.
 
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I have an appointment Monday with a recommended shop. I want the to do the fuel vacuum test, the fuel return test and the command 21,000psi at idle test.
There is a local shop that will bench test my injectors for $30 each if the tests point me in that direction. Anyone recommend changing all injectors due to mileage (190,000)?
My 07 lbz was doing the same thing. Couldn't pinpoint the problem so I changed everything. Injectors, cp3 pump, fprv, ported fuel rail fitting, fuel lines, fuel pressure regulator, glow plugs, water pump. Lol, must've been one of the above. Runs like a new one now! No codes when towing.
Your close on the price! My buddy is a certified gm mechanic that works at a dealership so that helped! My truck has 215000 miles reason I replaced everything an I plan on driving it till it won't go. Imo if I replaced injectors I would definitely replace pump or vice versa. My command fuel rail pressure would only hit about 18500 (pump) and it would haze raw fuel at idle (injectors) Didnt wast the time to bench test them cause I was gonna replace all if one was bad.
 

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Discussion Starter · #13 ·
So the description of the injectors says that it’s flow calibration number must be programmed into the PCM and the glow plug control module. The PCM I understand but what does do the glow Plugs have to do with anything?
BTW, while I was changing the fuel filter yesterday the truck started throwing a code for the #4 glow plug 😤
 

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So the description of the injectors says that it’s flow calibration number must be programmed into the PCM and the glow plug control module. The PCM I understand but what does do the glow Plugs have to do with anything?
BTW, while I was changing the fuel filter yesterday the truck started throwing a code for the #4 glow plug 😤
There are several computer systems that need to talk to each other and need to be sync'd. ie. PCM BCM. TCM etc..
 

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So the description of the injectors says that it’s flow calibration number must be programmed into the PCM and the glow plug control module. The PCM I understand but what does do the glow Plugs have to do with anything?
BTW, while I was changing the fuel filter yesterday the truck started throwing a code for the #4 glow plug 😤
The flow rate info is stored on both the ECM/GPCM so if one fails the info can be retrieved from either one.
 

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Ok. Thanks. So it dont actually have anything to do with the operation just storage? Correct? Thx
Correct, the GPCM is just for storage.
 

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I have a 07 LBZ that is throwing a code for low fuel rail pressure. It only does it when ambient temp is over 90’F and I’m towing at highway speeds.

I already replaced the fuel rail relief valve and the fuel filter and now I’m suspecting one or more injectors may be bad. I have noticed a chugging/loss of power condition before it faults that if it were in a gas engine would be a misfire. I’ve been resetting the codes but I need to identify the real problem.

My code reader shows a maximum fuel rail pressure of around 26,000 psi.
Have you looked at the rubber fuel supply line that goes from the hard lines on the chassis to the hard lines by the transmission? I started throwing the same code towing heavy only in high heat situations. I replaced it with the 601-8 / 601 Series Parker Hannifan line (GM bulletin recommends it) from partsgopher.com. Only towed in 90-ish since replaced not 118 like when it first happened but the problem has not returned. I could squeeze the factory line with my fingers. Know you will have to cut the old hose clamps off as part of this process.

GM tech details PIP4526
http://www.askatech.com/AskATechLive/forums/ResourceHandler.ashx?a=3446
 
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