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Duramax Third Generation: 2006-2007.5 (LBZ & LLY) Discuss the third generation (2006-2007.5 LBZ & LLY) of the 6.6L Duramax diesel engine & associated components. 2006 LLY engine discussion also belongs in this forum due to the similarities of the 2006 LBZ and the 2006 LLY. Engine related discussion ONLY.

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Old 04-01-2018, 10:41 PM   #1 (permalink)
KTMHauler
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Goes rich when pulling hot, cools off then fine

Hey guys,

I've got a COMPLETELY stock 2007 Classic LBZ. 165,000 miles. Daily driver. I pull a 9000 lbs. toy hauler 6 times a year. I drive like a grandpa 90% of the time. The truck runs like a swiss watch. Replaced the hydroboost, a few glow plugs, Trans coolant line, just maintenance.

I live at 100' elevation. For the past 3 trips going over a 4,000 pass; it pulls fine for an hour; motor running at 210 degrees, 50mph. Totally even throttle. All of a sudden, loose power and starts blowing black smoke; I get off the throttle and then moderately come back on, same condition (very low power, lots of black smoke). (I had the same condition when I tried a PRE-oiled K & N filter that clogged the MAS, cleaned it and have used a stock air filter since. 5 years ago.) I pull over, let the truck cool down at idle for a few minutes, then it runs like normal. No codes. No other situations make it happen. Even the shorter pulls coming home don't cause the problem to happen.

I have cleaned the MAS and MAF sensors. My best guess is the prolonged pressure is forcing the EGR to come open and it sticks open, or there is something wrong with the turbo vanes where I loose boost when it's hot for a prolonged time.

I don't want a race truck (I ride motorcycles for that). I need a reliable hauler.

Any thoughts?

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Old 04-01-2018, 11:04 PM   #2 (permalink)
KTMHauler
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Edit: By MAS, I meant the manifold absolute pressure (MAP) sensor.

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Old 04-02-2018, 09:30 AM   #3 (permalink)
G2GBY
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Exhaust leaks or Boost leaks, you can usually hear a boost leak as a high pitched squeal under load.
EGR and or MAF problems or intake leaks after the MAF sensor.
With no codes you need a way to monitor what's the cause.

Last edited by G2GBY; 04-02-2018 at 09:37 AM.
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Old 04-02-2018, 08:19 PM   #4 (permalink)
KTMHauler
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G2GBY,

No squeal at any time.

No other times does it just loose power (boost pressure?).

I've looked for leaks on the intake side. Is there a way to check for intake leaks using a chemical? (I.e. spray something around the intake joints while idling, listening for changes in RPM?)

Thank you for the info.
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Old 04-02-2018, 10:19 PM   #5 (permalink)
heymccall
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How old is that PowerCore air filter? Sounds like it only acts up under high airflow demands.
By design, they can't be easily examined.
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Old 04-02-2018, 11:13 PM   #6 (permalink)
KTMHauler
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Since the oily filter gummed the MAF sensor, I have only used AC Delco paper filters. I change them fairly often.

Yes, it only goes rich after sustained high airflow demands. Almost at the same place on the grade, after an hour of climbing.
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Old 04-03-2018, 08:21 PM   #7 (permalink)
IGO1320
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Is the check engine light coming on? It's possible you have a P0087 code, rail fuel pressure is not keeping up with demanded fuel pressure. When P0087 is set engine goes into a reduced power mode. Shutting off the engine clears the code. I installed a PPE Dual fueler to extend the useful injector life, got 600,000 miles out of the original injectors with a 100hp tune.
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Old 04-03-2018, 10:57 PM   #8 (permalink)
KTMHauler
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No CEL and no codes on my cheap code reader. I don't shut down the engine, I just let it idle with the hood open to cool down.

Could this be from built up PCV oil (from daily driving), that migrates during a long pull?

Thanks for the replies.
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Old 04-04-2018, 10:09 AM   #9 (permalink)
Rvn4me
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Might be something in this.
https://www.dieselplace.com/forum/63-...ack-smoke.html
They always say “Black smoke means too much fuel not enough air.“
What are your balance rates?
Your EGR stuck open will casue low power, but you shouldn't see smoke because of it.
You should have an EGR code for this.
Google “duramax LBZ lost power and starts blowing black smoke during a long pull”

Last edited by Rvn4me; 04-04-2018 at 10:23 AM.
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Old 04-04-2018, 04:24 PM   #10 (permalink)
Ron Nielson
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I would be suspicious of the performance of the MAF sensor or the connectors or wiring for the MAF, especially since you've experienced this condition previously with your K&N filter. Apparently it works OK when not hot, but when hot it gives an incorrect reading causing ECM to adjust fuel mixture. Another thing to possibly check would be the Coolant Temp sensor, connector and wiring. Engine gets hot, but CTS sends low temp message to ECM and engine goes rich.

Would be nice to have a better engine scanner to see what's going on when conditions cause the problem. May be cheapest and least frustrating way to solve the problem. Investigate, test, THEN buy ONLY the necessary parts.

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