I diagnosed one wrong, and I don't even feel bad about it.

greasytshirt

Moderator
Staff member
Mechanic
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.

:censoredsign:.

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.
 

BobWolf

Veteran Expediter
Owner/Operator
This would be the customer who uses "mechanic in a can" and expects a permanent repair for the head gasket, oil seal, faulty oil pump, dirty or failing injectors, weak HPOP, slipping transmission, leaking or blown water pump, leak in the cooling system, tire that wont hold pressure, and wonders why he gets the major bill when he has a problem.

I have a friend whose drivers have managed to destroy 3 YES THREE pre 2003 non emission DT466E engines in six months on the same truck. When he asked me to work on the truck and started to hate on electronic engines, I told him its the drivers abusing the equipment, and lack of maintenance.
 
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