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Duramax 6.6 liter stops/limits at 1800 RPM's

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bczoom

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My neighbor was driving his truck last Thursday and all of a sudden, the engine dropped to 1800 RPM's and would go no higher.

He was towing at the time. He pulled over, put it in neutral and floored it. It still wouldn't go past 1800 RPM's.

He limped it home, disconnected the trailer and took it to the dealer. Once they got in it, (of course), it worked fine and would go past 1800 RPM's.

Any ideas of what caused this?

Thanks
 
Dargo

Dargo

Like a bad penny...
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Did he shut if off for over 10 minutes between the time it played it's trick on him and worked fine for the dealer? If so, it could have reset the ECM.

I'm sure most of you know that your transmission has a mode that is actually called "limp home mode". Some diesel engines have a similar feature that is controlled by the engine control module. If it senses that there could be impending danger of blowing a head gasket, turbo failure, etc., it could 'de-fuel' at a preset point. Since the Duramax diesels have been known for popping heads, I wonder if Isuzu or GM has a sensor that senses excessive pressure head pressure and limits the fueling process, therefore, the RPM?
 
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HGM

New member
I'm not really familliar with the Duramax, but on a PowerStroke there is a limp home mode for failures.. If it were to overheat(sometimes:pat: ) or even run low on fuel you would likely get a lack of power to save the engine from excessive damage.. Regardless, the dealer should have found a code or something to give an idea where to go..:confused:
 
Dargo

Dargo

Like a bad penny...
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HGM said:
Regardless, the dealer should have found a code or something to give an idea where to go..:confused:
Click to expand...

Duh! I intended to add that line. Thanks HGM. :tiphat:
 
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bczoom

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HGM said:
Regardless, the dealer should have found a code or something to give an idea where to go..:confused:
Click to expand...
That's what we expected as well.

I haven't spoken with him since he picked it up but I was with him when he called to see what's up and they said to come pick it up as they couldn't find anything. There was no mention of a code. I don't know if they checked for a code or checked and there wasn't one...
 
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HGM

New member
Unfortunatly, as much as I prefer a dealer over an independant shop, you dont always get the most qualified guy to work on it.. If the concern isnt present and they have more work to do the helper may drive it and say the vehicle is fine, NPF.....Maybe your freind is sweet on someone there and just pretended to have a problem with his truck:pat:
 
BigAl

BigAl

Gone But Not Forgotten
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Check with the : dieselplace.com . If anyone knows ,these guys will . There has also been a recall by GM for a Glow Plug problem . I wonder if this may be part of the problem . I would'nt think so but who knows anymore .
 
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bczoom

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He did get a code:

I didn't get the number but it was "major fuel leak".

Am I wrong in guessing his fuel cap isn't/wasn't on tight?
 
A

Av8r3400

Gone Flyin'
Very possible.

These do have (God only knows why) a sealed fuel system like a gas motor. It should have given a "check engine" light, before it went to "limp" mode, though. Unless there is another sensor glitching on him too...
 
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bczoom

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He did get a check engine light, right before it happened.

Think he fuel cap was on loose?
 
A

Av8r3400

Gone Flyin'
They need to be tightened untill they "click" or the seal will leak and not allow the emmission system to do whatever it does.

(I sold Chevies in a former life. Yeah, I'm not proud of everything I've done for a living. :( )
 
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bczoom

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Follow-up.

The resolution was a clogged fuel filter. A filter replacement corrected the issue.

Don't know how/why GM has it coded as a "major fuel leak" as I would have expected a clogged filter to register "no damn fuel getting to the engine"...
 
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HGM

New member
Some fuel delivery systems just assume fuel presence by what is needed for each situation. If the PCM is programed to recognize a larger than normal demand as a fuel leak, then it would make sense that a lack of fuel can be seen as the same.. Sometimes we give computers a little too much credit, they are just dumb boxes that interpret numbers.. The technician(not mechanic anymore) must be able to interpret what the PCM tells him... Apparently the first guy missed that part in the diesel performance class:pat: ..
 
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