2002 Jeep Liberty 3.7 MISFIRE multiple cylinders

Question

2002 Jeep Liberty with approximately 130,000 miles.

Engine is misfiring on multiple cylinders.  Burnt wire smell and smoke coming from firewall area.  After troubleshooting, I believe the engine is running on only one cylinder.  Smell coming out of the exhaust is atrocious; does not smell like sulfur but instead unburnt fuel and/or stale gas.

Scanning the vehicle indicates all fuel injectors and all coil packs except for one are malfunctioning due to a circuit issue.

We pulled the coil packs off and looked at the spark.  At the end of the spark plug, there was a pale yellow spark. On the working cylinder, it was bright blue.  We swapped the two coil packs / plugs and ultimately nothing changed - meaning the originally working coil pack now was providing a pale yellow spark, and vice versa.

Things I have tried:
Replacing ECM; no change
Cleaning ground wires to ECM and applying conductive grease to the ground; no change

I am stumped and really not sure what the issue could be.  Any ideas on what to test next?

Thanks!

Spivonious · Answer

Great diagnostic work so far.

We know that it's not:

the plug
the coil pack
the wire between the pack and plug
the ECM

Something is interfering with the power levels between the ECM and the coil pack. I'd inspect the wiring harness and the wires themselves for any damage, or just replace them if the cost is low enough.

Zaid · Answer

This looks like a case of excessive voltage drop across the coil supply
... leading to poor spark.

The yellowish spark suggests that the coil circuit is complete but not at the right voltage level
The burnt-wire smell may explain the excessive voltage drop if the coil wire have partially burned. You will have to check both ground-side and power-side to see where the problem lies.

Note
There is no way that a six-cylinder engine can sustain itself running off just one cylinder. There is some combustion occurring in the other cylinders, albeit at sub-par levels.

2002 Jeep Liberty 3.7 MISFIRE multiple cylinders

2 Answers

This looks like a case of excessive voltage drop across the coil supply

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