Coolant and fuel temp reading negative

[Dante2795]

My buddies lb7 started running rough and random stalling with no codes. Went to log it and saw both coolant and fuel temp are reading the same and both negative. When giving it throttle they both max out at 12 degrees.

Swapped in new coolant temp sensor with no change, wires appear good. Any ideas?

 

[TheBac]

What year LB7? 01-02 electrical is different from 03-04.

 

[kidturbo]

Off top of my head, going with a low reference wire issue. Both reading identical show a linked supply line. And -40 being an open circuit reading, says there is crappy wire somewhere.

Wiggle the bail connectors while watching on EFI. Most wiring failures I've seen were located in that area.

 

[Dante2795]

What year LB7? 01-02 electrical is different from 03-04.

Sorry, 03

 

[Ron Nielson]

Off top of my head, going with a low reference wire issue. Both reading identical show a linked supply line. And -40 being an open circuit reading, says there is crappy wire somewhere.

Wiggle the bail connectors while watching on EFI. Most wiring failures I've seen were located in that area.

Concentrate on this solution.

 

[dndj]

Off top of my head, going with a low reference wire issue. Both reading identical show a linked supply line. And -40 being an open circuit reading, says there is crappy wire somewhere.

Wiggle the bail connectors while watching on EFI. Most wiring failures I've seen were located in that area.

This. The ECT and fuel temp sensors are negative temp coefficient resistors, negative temp values = open circuit. ECT sensor and fuel temp sensor both wire independently to the ECM. ECT is C1-74 and C1-80 (reference). Fuel temp sensor is C2-25 and C2-60 (reference). Both circuits go through C107, which is one of the bale connectors on the driver side. Unplug/replug this connector, inspect for bent pins.

 

[kidturbo]

This. The ECT and fuel temp sensors are negative temp coefficient resistors, negative temp values = open circuit. ECT sensor and fuel temp sensor both wire independently to the ECM. ECT is C1-74 and C1-80 (reference). Fuel temp sensor is C2-25 and C2-60 (reference). Both circuits go through C107, which is one of the bale connectors on the driver side. Unplug/replug this connector, inspect for bent pins.

Thanks for posting the pinouts. I had nothing saved from LB7. If it's not bail, it internal to ECM then.

I fought a crank sensor code on one my my stand alone setups a while back. First wrote it off to my swapping the 5v and low ref between crank/cam circuits. Ran ok, for a while, then got worse. Swapped out the ECM and quickly realized it was and internal ECM fault. Guessing this posters issue ends up being the same since two circuits / 4 wires are involved.