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Duramax 6600 Welcome to the Internet's first Duramax 6600 diesel discussion forum for the LB7, LLY, LBZ, LMM, LML, LGH & L5P RPO code engines. Tips on performance, fuel economy, troubleshooting and more.

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  #11  
Old 09-15-2009, 08:27 AM
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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?
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2011 Chevrolet Tahoe 5.3L daily driver
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW, '05 Denali
  • Total GM diesel miles to date : ~950K
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  #12  
Old 09-15-2009, 12:30 PM
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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.
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  #13  
Old 09-15-2009, 02:43 PM
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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?
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2011 Chevrolet Tahoe 5.3L daily driver
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW, '05 Denali
  • Total GM diesel miles to date : ~950K
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  #14  
Old 09-15-2009, 03:53 PM
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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.
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  #15  
Old 04-14-2010, 06:24 PM
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Default Low fuel rail pressure - searching for root cause

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?
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2011 Chevrolet Tahoe 5.3L daily driver
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW, '05 Denali
  • Total GM diesel miles to date : ~950K

Last edited by Mark Rinker; 04-14-2010 at 06:53 PM.
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  #16  
Old 04-14-2010, 07:30 PM
CoyleJR CoyleJR is offline
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Default Fuel Cooler

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
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Last edited by CoyleJR; 04-14-2010 at 11:17 PM.
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  #17  
Old 04-14-2010, 08:22 PM
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No visible obstructions, but have never cleaned it. Great idea, I'll do this tomorrow!
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2011 Chevrolet Tahoe 5.3L daily driver
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW, '05 Denali
  • Total GM diesel miles to date : ~950K
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  #18  
Old 04-15-2010, 07:48 AM
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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...
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  #19  
Old 04-15-2010, 09:58 AM
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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.
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  #20  
Old 04-15-2010, 03:38 PM
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Quote:
Originally Posted by DmaxMaverick View Post
>>> 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!
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2011 Chevrolet Tahoe 5.3L daily driver
  • Previous owner of two 1994 6.5L K3500s, '01, '02, and '05 6.6L K2500s, '04 C4500, '06 K3500 dually, '06 K3500 SRW, '09 K3500HD SRW, '05 Denali
  • Total GM diesel miles to date : ~950K
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