P0087 fuel rail pressure low limp under high loads

[Mark Rinker]

Only 4500 miles!!!

A genunie Delco filter plugged up that quick in the middle of summer - so I know its not full of ice crystals from water in fuel... That must have been one crappy tankful, last tank was purchased in Moorhead, MN just off I94. Maybe some rancid bio-diesel blend, or a crusty underground tank?

Just my luck. 99K mile on the odometer, and I'll probably hang an injector next...just out of warranty.

[trbankii]

All it takes is one tank of the wrong stuff.

[Mark Rinker]

Well, the second time this happened - only 1,500 miles into a fresh OEM Delco fuel filter - I knew there had to be something more going on, than just bad fuel.

No smoke at idle, none under load, but watching requested and actual fuel rail pressure showed exactly what was happening...when requested gets to 22k# the actual begins to fall behind, and when it peaks at 24K# or more, the ECM catches the variance and sets the code.

A helpful and knowledeable diesel tech at www.whitesmountainchevy.com of Casper, Wyoming verified that he has seen this before (P0087 with new fuel filter that is flowing properly) with trucks used to pull heavy equipment in the Wyoming oil fields. Said that unlike classic injector failure symptoms such as smoke at idle, this one initially had him 'scratching his head' until it became apparent that the weak injectors and/or weak high pressure pump caused the low fuel rail pressure code to be set due to their combined high return rates, rather than due to a restricted filter, which is usually the culprit.

In my case, it took a loaded trailer, Wyoming mountains, and hot engine temperatures.

They documented my situation at 101,500 miles - and I used my own ability to reset the code to continue the trip on to Salt Lake City. Code was reset about 12 times, total - always while climbing grades. Unloaded (empty) trip home was no problem.

[Duramaster]

Here is something to your P0087. We had a few trucks come in with the P0087 and went through the fuel filter routine and come to find out the P0087 would set 350 mile or so later. These particular vehicles were "HAULERS" as well. Come to find out, the flexible fuel lines at the engine and under the vehicle near the transmission would kink and cause the P0087.

Here is the bulletin.



2008)


Subject: Diesel Engine Fuel Line Repairs


Models: 2001-2007 Chevrolet Silverado Classic

2001-2007 GMC Sierra Classic

2007-2009 Chevrolet Silverado

2007-2009 GMC Sierra

Equipped with the 6.6L Diesel Engine RPO codes LB7 LBZ LLY LMM




--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A dealer may need to perform a repair on the rubber portion of the fuel supply (suction) lines. The rubber section of the line could become kinked or collapse. Fuel lines that kink or collapse may induce a fuel system restriction (high vacuum gauge readings) or DTCs P0087, P0093, and/or P1093 to set.

If a technician was to suspect the rubber portion of the fuel feed line collapsing or kinking, replacement of only the rubber line is acceptable.

Recommendation/Instructions:
Complete the steps below to repair the rubber section of fuel supply line:

•Carefully cut, split, and remove the OEM crimp from both ends of the flexible hose. These crimps can be cut with a small cut-off wheel. Split the crimp into two pieces (use your discretion on first cut location, then cut directly across from, or 180 degrees from first cut). Special care must be taken not to damage the flare on the end of the steel pipe that will be reused.
•Remove the OEM crimps and flexible portion of hose from the existing supply line.
•If replacing the rubber section of the supply line, a 1/2 ID hose meeting SAE specification 100R3 is suggested. Dealers may be able to find a local supplier for this hose, or can contact the manufacturer Parker Hannifin. The replacement hose would be a 1/2" diameter Parker part number 601-8 or H017-8. To find a local distributor the Parker website can be accessed at www.parker.com
•Use worm type hose clamps (use double clamps on each end) to attach the replacement hose to the existing pipe.
The locations of the flexible hoses are pictured below.





Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

[Mark Rinker]

Tech did a suction test while I was standing there. If fuel lines were crimped (much like a plugged filter) I believe that test would have shown the restriction.

There are clearly three injectors out of range, indicating high return rates. I failed to mention clearly that the tech wrote up his findings, and recommended replacement of all eight injectors...

Thanks for the TSB. I'll check those lines, anyway - just in case!!!

[Duramaster]

Those lines won't show much of a obstruction at idle or even at 3000 rpm's in the shop. It's more of a load thing (trailer, hill, WOT, PULL BABY PULL!)

[Mark Rinker]

Hmmm...duely noted.

I would sure like to get a fresh set of eight sprays, if possible, since the return rates indicate that as necessary, but...

The truck will certainly be up on the hoist looking into the other possiblity.

Thanks for taking the time to post. Possibly its the combination of the two.

[Mark Rinker]

(A quick update on a previous thread that I will merge with this final installment.)

Received final decision from GM customer assistance on my injector warranty claim. Denied. They were very polite, and did a fair job of collecting information on the claim, but it was also very clear that two factors weighed heavily in their decision NOT to goodwill the repairs:

• Vehicle was diagnosed at 101,500 miles with high return rates on three injectors, GM tech recommended 8 new sprays.
• Vehicle was not purchased new from a GM dealer, was purchased from a private party. (Two GM customer assistance reps asked me this same question, both of the Service Managers I worked with also asked as well.)

Truck runs fine under 95% of daily use, but will set a P0087 low fuel rail pressure code when towing heavy and in the hills. It is repeatable, under these conditions.

If you read the entire thread , you can see how the scenario unfolded - first P0087 was assumed to be a fuel filter at 99K. Next P0087 was at 101500 and I paid to have a GM dealer diagnose and document as I was on the road.

Make sure you get any oddities DOCUMENTED by a GM dealer BEFORE the 100K cutoff...they aren't as charitable as they once were...

[Mark Rinker]

Those lines won't show much of a obstruction at idle or even at 3000 rpm's in the shop. It's more of a load thing (trailer, hill, WOT, PULL BABY PULL!)

I also inspected the supply line with the truck on a hoist, it appears fine (no obvious damage or kinks) but may replace entire supply line anyway, to rule out the possibility of an intermittent collapse... which would be nearly impossible to see unless you are under the truck when the high fuel request was happening!!!

(BTW it doesn't take WOT to trigger my P0087. It does take a fair load (12K#), warm/hot engine temps, and a reasonable climb - one that would put the %LOAD at 95% or better on the OBDII data...)

[DmaxMaverick]

Have you given thought to a lift pump setup? Certainly not a complete solution, but could edge you across the threshold causing the fault. What's JK think about it?

[Mark Rinker]

Had thought about that ... hadn't taken it any further. I still have a NIB Delco inline lift pump from the 6.5L days, would that provide enough flow?

[DmaxMaverick]

It should, at OEM to moderate fueling levels. It should work, at least, for test purposes. JK has the stuff, though (on my Christmas list). A test shouldn't be too difficult, and you wouldn't have to hard-wire or fail-safe it for the testing. If it doesn't help, you're only out some time and a little change for wiring and line coupling. If it does work, you're well ahead.

[Mark Rinker]

The p0087s were all produced at stock fueling levels, and a 6.6L doesn't use much more fuel than a 6.5L, right - if your loaded mileage is the same?

[DmaxMaverick]

Technically, correct. However, not all the fuel pumped actually finds a cylinder. Both engines use the fuel for lubricant and coolant, and return a significant portion to the tank. I don't know which returns more. I don't know which carries more heat, but my truck, even in Winter, will show a hot running fuel temp of 140°+. I've never observed the fuel temp or return rates of a 6.5 system, so I can't compare. I don't know if it even matters, one way or another. I do know several folks who have installed, and are currently running, a 6.5 OEM pump, or similar aftermarket, successfully on LB7's.

[Mark Rinker]

Started out with a fresh OEM Delco fuel filter before this trip. (The old filter lasted all winter - even through the December snap of -25F cold, without plugging. Thats a first.) Fuel level full to 1/2 tank during episodes described below, no blockage of OEM tank mounted fuel cooler/radiator.

About 1500 miles into the trip, I noticed the check engine light on. Checked and reset a 'low fuel rail pressure' code. Started watching the requested vs actual fuel rail pressures on the Edge.

Sure enough, with a stiff and gusty head wind working against the tall, shrinkwrapped boat - any hill ascended with even a medium heavy foot to maintain 60mph would predictably set the code. All of this happened while running the stock OEM tune, water temps were never over 200F, trans temps 200-220 max the whole time.

Hmmm...pulled over and looked at injector return rates at idle...nothing looked out of range, nice quiet idle, and the truck is otherwise running fine by all 'seat of the pants' measurements, until the code is set and the truck then starts running 'lopey' and low on power. When I started back at it, began watching fuel temperature. Normally it runs about 130F-150F, but today for some reason it was in the 160-170 range? All this on a sunny 75-80F spring day, Wisconsin rolling hills, with about 15K# of boat and trailer in tow...nothing out of the ordinary, really - except for the headwind.

When running the next hill, I kept my foot moderately into the throttle, watching fuel temperature...when it went past 170F and about when it hit 180F, the requested vs. actual pressures began to separate, and then *BING* the check engine light would illuminate, and the truck would start running badly. I repeated this cycle a half dozen times. There appeared to be a direct relationship between high fuel temp, and low fuel rail pressure. At one time, really pushing it - I saw fuel temperatures of 190F...that doesn't sound good!!!

Later that afternoon, it began to rain, the outside temperatures dropped to 60F, and the headwind and hills went away. No more codes, power felt better, and I could again easily hold 65mph with 160F fuel temps, no codes...

Whats making my fuel get so hot? Is my injection pump on its way out?

[CoyleJR]

Mark,
Have you ever crawled under your truck and cleaned your fuel cooler? About every 10k milles I spray my fuel cooler with Gunk degreaser and pressure wash it. I am always surprised by the amount of road grime that comes off of it. If your fuel cooler hasn't been cleaned recently, it could be causing high-fuel temperatures under high-power applications.

Good Luck,
John

[Mark Rinker]

No visible obstructions, but have never cleaned it. Great idea, I'll do this tomorrow!

[JohnC]

Have you ever watched the fuel temp this closely before? Maybe the temp is normal and the pump can't keep up with the thin fuel...

[DmaxMaverick]

Curious....How are you reading "fuel return rates" on the roadside? Perhaps injector balance rates or PWM, but return rates?

Anyway, start looking for the cause of the fuel temp increase. A couple possibilities come to mind....HP pump bypassing internally (failing), or failed/failing FPR/sensor. Friction = Heat. This applies to all states of matter, including liquids. Either the pump or FPR/sensor can cause this condition, which increases fuel temperature. This can also cause a snowball effect, regardless of the suspect component: Component bypasses excess fuel at high pressure -> fuel temp increases -> fuel returns to component at a lower viscosity -> fuel bypass increases (due to lower viscosity) -> fuel bypass increases fuel temp -> lower fuel viscosity and progressively increased bypass condition push the pump's ability to develop pressure -> PCM unable to maintain desired fuel pressure -> DTC set.

This condition is not likely a restriction issue. Generally, a restriction rate will decrease as viscosity decreases. This is opposite the condition you describe.

The later lower temps and less load demand doesn't help much with the diagnosis. The lower ambient temp helps prevent higher fuel temps (increases the system's ability to shed heat), and the lesser engine load reduces the fuel volume demand (less foot-feed required). The condition may still exist under this condition, but doesn't exceed the pump/FPR ability to maintain the desired fuel pressure range. Because of this, you won't likely get a dealership or garage able to duplicate the issue. You'll have to get the tech with you on the road with a load on, or on a dyno.

[Mark Rinker]

>>> Curious....How are you reading "fuel return rates" on the roadside? Perhaps injector balance rates or PWM, but return rates? >>>

Sorry, wrong terminology. Reading injector balance rates, using Edge Evolution...

Today, completed boat delivery to Walker, MN with no further codes or issues. Fuel temps averaged 130-140 all morning... (Have NOT yet cleaned the fuel cooler, but plan to.)

REQUEST FOR ASSISTANCE: To any of you that haul trailers, 5'ers, etc. and have the Edge Evolution, Predator, etc. where you can monitor fuel temps - would you give me your averages for 60mph level cruise? Please include ambiant (outside) temps during your readings. Interested to know what you are seeing...thanks in advance!