Inconsistent LLY Defuel

[baileydirt27]

My LLY truck has been defueling randomly for a few months and haven't really had the time to check it til the other day. It usually occurs after having driven for a few minutes or even immediately after starting it some times. Basically anytime I go past around 50% throttle position it cuts the injection pulse width by 30-40%. Was wondering if my injection pump might be bad (kinda doubt since rail pressure seems fine), or if my Fuel Injection Control Module could be bad. Maybe even something going on with my tranny since I have limped it in the past. I have already replaced multiple fuel lines, added a lift pump, rebuilt filter housing, shimmed fuel rail, and changed my fuel pressure regulator.

Any thoughts?


I have attached a log of the truck doing this...

[GMC-2002-Dmax]

do you have the DTC codes all enabled or did you set a bunch to "not reported" ?

I suspect it is throwing a code and going into limp mode.

[baileydirt27]

do you have the DTC codes all enabled or did you set a bunch to "not reported" ?

I suspect it is throwing a code and going into limp mode.



No codes are set when this happens.

Does limp mode reduce pulse width's? If not are there any EFI-Live tables that would?

[GMC-2002-Dmax]

Did you disable any codes ? or is the DTC list stock ?

There are limit tables, but they will usually only come into play if there is an out of range sensor or code.

[baileydirt27]

No they are all stock. It seems really odd to me that there is no code. I wonder if there is anyway to test the FICM?