2004-ish Isuzu FRR. Early common rail. Truck would run fine, then drop three cylinders. Code 0158, short to B+ on something something injector something. Instant limp mode, cut three cylinders off. Those three were on a common B+ leg. There was power at both branches of that leg, the grounds for each of those injectors were good, each injector was good, the wiring harness tested good, the injector harness tested good, even the pass-through in the rocker box tested good. I hate diagnosing it as a bad ECU, but I ran out of stuff to blame. Put in an ecu. It ran for five minutes then dropped three cylinders.
.
Took valve cover off. Poked around with a multimeter. The injector harness on these is laid out on a plastic platform, so even if a wire were to chafe, it won't ground to chassis. Maybe two would get tangled up, somehow, but that would be very easy to spot. However, there was a 1k ohm connection between the ground leg on the harness and chassis. Unscrewing the leads from the injector removed this connection. The rear three cylinders, so far unaffected, had a 1M ohm connection. Weird.
I stared at it for a while. It's like the motor oil is conducting electricity. Actually, something in the motor oil WAS conducting electricity. This poor truck had the snot kicked out of it, and it had very irregular maintenance. It had a recent oil change, and that revealed the layer of carbon sludge adhered to the top of each injector and around all of the wires. Removing the carbon with a copious amount of contact cleaner and some scrubbing also removed the slight electrical connection, and the ECU no longer interpreted this as a fault-worthy event.
The moral of this story: Change your oil before it solidifies.
.Took valve cover off. Poked around with a multimeter. The injector harness on these is laid out on a plastic platform, so even if a wire were to chafe, it won't ground to chassis. Maybe two would get tangled up, somehow, but that would be very easy to spot. However, there was a 1k ohm connection between the ground leg on the harness and chassis. Unscrewing the leads from the injector removed this connection. The rear three cylinders, so far unaffected, had a 1M ohm connection. Weird.
I stared at it for a while. It's like the motor oil is conducting electricity. Actually, something in the motor oil WAS conducting electricity. This poor truck had the snot kicked out of it, and it had very irregular maintenance. It had a recent oil change, and that revealed the layer of carbon sludge adhered to the top of each injector and around all of the wires. Removing the carbon with a copious amount of contact cleaner and some scrubbing also removed the slight electrical connection, and the ECU no longer interpreted this as a fault-worthy event.
The moral of this story: Change your oil before it solidifies.
