P0087 fuel rail pressure low limp under high loads

[JohnC]

Its definately fuel temp related, unless 180-190F fuel temps are considered normal...

Or you can't get enough fuel through the system to control the temps...

Whack!

[Mark Rinker]

Or you can't get enough fuel through the system to control the temps...

Whack!

If I were short on fuel, I'd be short on power. Power is normal - even when turned up with JK's tune. Yesterday on a few hills, I downshifted to 4th and stood on it. My pump can maintain 24k requested and 24k actual fuel rail pressures, indefinately. Try that with a plugged/plugging filter, crimped fuel delivery hose, or plugged tank sock.

Sure looks like injectors to me, but I won't be replacing them until there are more driveability related problems than I am experiencing right now. Todays issue is the ECMs, and a theoretical one for members of TDP to digest. (No white smoke, no power loss, no knock, no oil dilution, etc...)

I am not concerned, under extreme circumstances, that my Requested and Actual FRP vary by >10%. In fact, this whole issue could be programmatically eliminated through a few tweaks with EFI-Live...there are probably many LB7 trucks out there running around with the same issue, but the ECM doesn't detect the variance and set a code. That is why an LB7 with restricted fuel filter will run until power is down, with no check engine light. LBZs with same filter restrictions will complain of low FRP...

[JohnC]

If I were short on fuel, I'd be short on power.

My comment was based on the assumption that excess fuel flow is required to keep temps in check, like cooling the PMD. You may have enough fuel to produce the power, but nothing left over to carry the heat. Also, heat of "compression" likely contributes more the fuel temps than heat conducted away from engine components, but I could be wrong...

[DmaxMaverick]

I don't think it's injector(s). The possible return rate for an individual injector is minimal, and not of consequence compared to the return rate of the remainder of the system in regard to heat. If all 8 injectors were returning excess fuel to the point your fuel temp increases to the rate you are seeing, AND the rail pressure can't maintain, you would have a noticeable condition not limited to the conditions you are seeing. The PCM would be throwing a fit and you would have DTC's across the board. The injector parameters are monitored very closely. No way I can see it could return enough fuel to cause the issue and go unnoticed. It is a matter of likelihood, and I don't see it as likely. What's the likelihood of all 8 (or enough injectors) to fail in the same manner at the same time? Your odds are better at winning the lottery.

I'm still thinking pump or FRP regulator. The conditions you create may very well be pushing the fuel flow rate beyond what the system can maintain, while just under the envelope is sustainable. Pumps do not make pressure. They ONLY provide flow. A restriction is what causes pressure to develop, and pressure is maintained or limited by the amount of restriction. If the FRP or pump is bypassing, not by design, the maximum pressure attainable will be less. Fuel flow is friction, and friction is heat. At 24K PSI, this can be substantial. In any case (during your episodes), the pump is unable to develop sufficient flow to maintain desired pressure. This is either a failed pump, or a component responsible for maintain restriction. IMO, the FRP is the only component capable of flowing enough fuel to cause all the conditions you are seeing, assuming the pump is able to provide sufficient flow otherwise.

[Kennedy]

Cause-effect as Dmax Mav stated is my inclination.

It goes like this:

High loads due to head wind causes you to run deep into the tables and at a higher fuel pressure. Higher fuel pressure with ball seat issues will mean more flow and when the fuel passes it gets HOT.

The restriction gauge IS handy to verify the filter condition. This can change in one fill up or less. It will generally show at idle, but I have had guys add a hose to my gauge and clip iunder the wiper to observe.

[Kennedy]

I have fielded 4 calls from LBZ owners already today and it's not even noon.

1) Had P0087 codes and others. Replaced pump no cure. Replaced injectors and his fuel pressure issues went away. Now he's chasing boost codes. Totally stock truck

2) Has 4 Dmax trucks pulling RV's 2) 2007 LBZ, 1) 2005 LLY and 1) 2004 LB7. The 2007 LBZ's are the only ones giving grief. P0087 both trucks, sudden onset. Totally stock I believe

3) 350k and no fuel pressure problems. Running TS MP-8 (jacks fuel pressure) and called regarding different issues.

4) 2006 LLY (actually LBZ) 300k+ hauling RV's now getting P0087. Has Edge with monitor and uses it to clear codes.


I'm thinking this is still injector related (caller #1 supports this, BUT I also think this may be one of those things like the 2001 where we can do some programming changes to address this. Unfortunately not enough of the fuel psi info is available to do this at this time.