OK, Colin yelled at me for awhile, but I'd heard most of it before
His main point was that the system itself is pretty simple, and I should long ago have ferreted out the problem. Sheesh, just learnin' Colin...
So here's what I did before I ran out of light this evening:
Verified the Power Supply Relay (hereafter PSR) is receiving 12 volts at pin 85 from the ignition, and closing. Click is heard, all is good.
Verified the Fuel Pump Relay (hereafter FPR) is receiving 12 volts at pin 85 from the ignition, and not closing. No click, problem.
Verified continuity between:
FPR 86 to the Fuel Control Unit (hereafter FCU) at pin 20. Continuity is good.
PSR 86 to head. Continuity is good.
PSR 87 to FCU pin 13 continuity is good.
FCU pin 7 to ground on head, continuity is good.
FCU pin 25 to ground on head, continuity is good.
FCU to Temp II sensor. Continuity is good.
Temp II sensor ground to head. Continuity is there, but spotty (it was getting dark. I'm going to check again in the morning, but the reading was switching between "I" and a resistance value).
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Those last two seem immaterial to the starting issue ~ I just wanted to thorough and check everything I can. There are several points to be made:
1. The fuel pump wasn't running to start with
2. In attempting to troubleshoot the system, I shorted pin 30 on the relay to pin 86 on the relay
3. After shorting the relay, I fixed several wires including grounds.
4. The van runs with FPR 85 jumped to FPR 87
So either:
1. I had a wiring problem which I fixed, but shorted/killed the FCU
2. I had a wiring problem which remains, but shorted/killed the FCU
3. I had a wiring problem which remains, and the FCU is OK
My money is on 1, but there's one more thing I want to check in the morning.
Previously, I verified 12v in at FPR 85 and out at FPR 86. Since I know that wire has continuity, but the relay is NOT opening, I want to make sure that in fact we have 12v going to the pin out on the FCU (pin 20 on the FCU).
If in fact we're getting 12v all the way to the FCU, then there are two options, I would think:
1. The FCU pin and the little connector aren't connecting
2. The FCU is bad
Any problems with my logic here? Any checks/verifications I missed?
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Now for the bad news:
Even with the relay jumped for power, the engine was hiccuping/dying (on occasion). Driving along, the RPM indicator drops straight to zero (no bouncing around ~ straight fall) sits for a second, and picks up again. Sometimes the engine dies, sometimes it doesn't.
If the tach is going out, I'm wondering if the coil is dicey (since the tach draws directly off the coil) or if I need to be looking at several things. In any event, this suggests to me that there is another ghost in the machine, and simply replacing the FCU without attention to the electrical system broadly is likely to result in another dead FCU ~ or some other problem... fire, death, that sort of thing.
Best,
L.