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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29427
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Lb7 duramax intermittent split second engine cutting out

Customer Question

lb7 duramax intermittent split second engine cutting out
Submitted: 2 months ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 2 months ago.

Hi there, I am Cam.
Does your truck set any codes?
Any aftermarket power up devices like a chip installed?

Customer: replied 2 months ago.
it has a 540 air intake heater code that pops up now and then, no tuners installed
Customer: replied 2 months ago.
2000 miles on new injectors, balance rates good, runs and sounds great except when this intermittent problem pops up
Expert:  GM Tech (Cam) replied 2 months ago.

OK, This could be a pain to find, but I do have a couple places for you to check.

First the 2 large connectors on the drivers side valve cover. those are common for wiring or connection issues in or near the connectors that could under the right circumstances cause this.
Second is the temp sensor top middle beside the upper rad hose . On your year of truck I have run into poor connections at the connector and intermittent sensor readings that caused a momentary change in reading which caused a reaction much like what you describe.
Third is wiring hitting the side of the power steering pulley and chaffing.

Customer: replied 2 months ago.
temp connector looks clean and tight, no wires hitting steering pump pulley, large connectors on drivers valve cover seem tight how would I check them
Expert:  GM Tech (Cam) replied 2 months ago.

I do a pin drag test. That is where we take a new terminal and push it in each terminal, then pull it back out to feel how much resistance there is. If its loose it will make a poor contact.

Customer: replied 2 months ago.
I have the complete factory manual and tech 2 scanner but don't know where to start, ok I will do a pin drag test on all the pins.
It's been suggested to me possible intermtent crank sensor problem
Expert:  GM Tech (Cam) replied 2 months ago.

That is another option as well, but given the intermittent nature of the issue it will be hard to trace down. What I would do after the pin test is graph each sensor with the scanner and see if during the issue any of the readings drop out. then from there, determine which sensors drop out and find a common point. If its isolated then its likely the sensor or wiring to the sensor. IF its systemic then possibly a ground or ecm.

Customer: replied 2 months ago.
like I said rev the engine in neutral no problem put it in gear hold the brake, apply power and it will skip but not all the time. ECM meaning the main engine computer? How often do they fail?
Expert:  GM Tech (Cam) replied 2 months ago.

yes engine computer, and they do fail, not often but its not unheard of.

If you can make it skip that easily then I really would look for loose wiring. I would even move the wiring around while idling to see if you can make the issue happen.

Customer: replied 2 months ago.
Ok thanks for the advice I knew this was going to be a pain to diagnose. I had an 08 work truck with duramax that just died on the interstate, after a long stay at the dealers was a chaffed wire by drivers wheel well.
Expert:  GM Tech (Cam) replied 2 months ago.

It can be a very small needle in that haystack, but thats why watching and knowing which sensor drops out is the key.

Customer: replied 2 months ago.
Can I continue to ask qeustions on this problem or is ther a charge every time I come back.
Expert:  GM Tech (Cam) replied 2 months ago.

WE can keep chatting on this thread about this issue at no additional cost. I will say up front that I am also a paramedic and sometimes get called out, so if I don't reply, its because I am likely busy.

Customer: replied 2 months ago.
Ok thanks Cam I' sure I will be back before this is over.
Expert:  GM Tech (Cam) replied 2 months ago.

OK, thanks, ***** ***** at some point provide a rating. Its the rating process that I get paid from as experts are third party to the website.

Customer: replied 2 months ago.
Will do.
Expert:  GM Tech (Cam) replied 2 months ago.

Thanks

Customer: replied 2 months ago.
May have found the problem, took the truck for a ride ran great no surprise, started wiggling wires and connectors. pushed on the wires where they go into the lower large connector on the injector control module and the motor stumbled and knocked. Outside the wires were pretty dirty, cleaned them up with some brake clean. don't see any issues there. must be the connector pins on the inside. how would I make a better connection with those? I don't see any obvious corrosion.
Expert:  GM Tech (Cam) replied 2 months ago.

That or there is a break in the wires behind the connectors. I have seen broken wires on both sides. What I do is open the harness and pull gently on each wire. See if it stretches or gives. Otherwise that pin drag test will narrow it down for you.

Customer: replied 2 months ago.
Is dielectric grease a good or bad idea in those connections I see there is something on the female ends
Customer: replied 2 months ago.
Wires all seem tight they move a little but the brass connector moves with it. doing the pin drag I found one that may be little loose How do I remedy that it's pretty small
Expert:  GM Tech (Cam) replied 2 months ago.

Yes, grease works, If you can bend the terminal back, otherwise you replace the pin connector.

Customer: replied 2 months ago.
It is not the connector at all. a few inches up from the connector two wires are worn right through and grounding out on an aluminum bracket that is supoosed to hold them away from the alternator. I actually found a bulletin from gm about it with a little more searching. Would you like a picture.
Expert:  GM Tech (Cam) replied 2 months ago.

Sure if you have a picture of yours, that would be good. I know about the bulletins and had those in mind when I sent you looking there.

Customer: replied 2 months ago.
When I searched it came back to this site with another gm tech from five years ago
Expert:  GM Tech (Cam) replied 2 months ago.

Oh that one is on the FICM bracket.

Customer: replied 2 months ago.
Expert:  GM Tech (Cam) replied 2 months ago.

Thats typical. Tape each wire then put a section of rubber hose to insulate that area and prevent it from happening again.