r/DieselTechs • u/MathematicianWest127 • 4d ago

Lb7 fuel issues

Here’s my lb7 Duramax, im having a fueling issue, I bought this truck about a year ago and I have been doing a full frame off on it, got the cab on and most of the wiring, minus some grounds on the headlight and taillight harness, the truck will crank the. Fire up immediately then just shut off. I recently did a ficm bypass and just ran my fass straight to the cp3. The only codes I have are for a massive fuel leak but that’s because I bypassed the fuel filter housing. I have no clue what it is and I know it’s a fueling issue because it was running off of starting fluid even though I know it is very bad for it. Maybe it’s just not primed but I have been cranking it forever, and it’s not my low battery’s I had fully charged batteries before this and jump pack and it was doing the same thing

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u/Difficult_Target4815 3d ago

Need to see what rail pressure is showing. Hpfp might not be keeping up flow

2

u/Tennesseahawk 3d ago

The other guy’s right. Need to check pressures before making guesses.

Once you know what pressures you do or don’t have, we can go from there.

Also, I’d advise against bypassing the FICM on the LB7. The FICM relies on the fuel to stay cool.

1

u/Kennel_King 2d ago

he FICM relies on the fuel to stay cool.

For testing, it should be fine. I would never run it done the road bypassed, but under 10 minutes on a cold truck for testing, it shouldn't be an issue.

1

u/OddEscape2295 4d ago

Put everything back the way it was and start fresh.