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I know these engines like to run well, but mine wouldn't shut off about a year ago, and I never quite fixed the problem. It'd run fine, but when I went to turn off the engine the key would turn off, but the engine continued to run! This is very disconcerting.
After a little probing around I found I could pull a relay in the LF electrical box, but the electricity was still hot. I eventually lost both batteries and $1200 to the dealer, who tore a lot of things apart and cleaned some of it, eventually telling me that I should either buy a new vehicle, replace all the chassis wiring ($10k fix) or install a master cutoff switch.
Needless to say, I bought a red isolator switch, a cheap pair of jumper cables, and installed a quick mod in the front dash to control power to the main circuit box.
I now turn off the master cutoff switch as a part of my everyday shutoff routine.
It hasn't tried to stay on since then, but I often wonder what happend. Anyone ever had this experience?
If that doesn't beat all...sounds almost like alchemy - how could an accessory feed back through to power up the PCM?? It sure blindsided the dealer!
I was 600 miles from home in March and was thankful that I had family in Anchorage willing to put me up for another week because I was an "out-of-towner" and got second priority to local clients.
Add that one to the memory banks.
how could an accessory feed back through to power up the PCM?? It sure blindsided the dealer!
The _coil_ circuit (small terminals) of the relay is powered by the same fuse as the PCM, through the red/green wire. Sometimes when the relay fails internally, some piece of metal inside comes loose and bridges between the always-on terminal of the _contact_ circuit (big terminals) and the switched-power terminal (red/green wire) of the coil circuit. This feeds power back into the PCM, which continues to run the engine.
This is pretty basic stuff to anyone who's owned one of these for a while. Not too surprising that the dealer biffed it, though. They're equipped and trained mostly to work on much newer vehicles, and of course, whenever they encounter something that stumps them, they're not likely to do the kind of research on it that a long-time owner would. They'd rather throw a lot of your money at it, which either makes them big $$$ in the shop, or hopes to push you over the edge to go back to the showroom and buy a new vehicle.
I took voltage readings at the GPR secondaries (the fat ones). Voltage at the unswitched is 12V (always hot, I suppose) and the switched one gets about 9V when the key is turned on and the cycle begins.
Know the correct way of analyzing glow plugs using the valve cover plugs?
The problem has never showed itself since it happened a year ago.
Since I was in ANC I had the dealer look at it. They replaced batteries and blew the dirt out of things (the vehicle was dusty - had operated on the gravel "haul road" N of Fbks). They told me the simplest thing would be to install a cutoff switch before the main fuse box. Though it worked without it when I left the dealer I still installed one.
The GPR it had at the time seems is still in - seems to measure up voltage-wise, and the wiring seems to be OK. I don't have a complete closure to the shut-off issue, but I do have the cutoff switch in case it happens again.