power loss injection pump circuit 984

[Lug]

Continuing saga of my 94 K2500 Suburban. Last year the old gal gave all the symptoms of a failed pmd. Has one of Heath's remote kits with a black Stanadyne pmd. Bill kindly sent me up a new pmd to trouble shoot with (Thanks again) and that didn't cure the issue. Sometimes it would start and idle for a while and then die like the key had been shut off. Ran thru the troubleshooting chart and found nothing conclusive. In discussing things with Bill I had installed the wrong chip for the current configuration so I got the proper chip. Still no joy. Winter came and no garage so there it sat. Found a used pump and finished installing it today. Primes fired up and idled great. Hooked up a vacuum/pressure gauge to monitor fuel pressure and have a nice 4 pounds idling in the driveway. Then it shuts itself off. This time running thru the troubleshooting chart I have less than 0.5 volt on pin A at the pmd. Pulled the pcm and have continuity from the pcm to the pmd. Tried a different pcm with the new chip and same results. So what other electronic widget is breaking down and making power go away? Wished it wasn't such a hassle to go mechanical because I would be there right now.
Justin

[DmaxMaverick]

Probably something simple, like the ignition switch. It wouldn't be uncommon.

[Lug]

I think it is fixed, and yes it was simple. After posting I got to wondering what the voltage into the pcm was. Probed the input to the pcm and it was 12.08, but 12.13 at the battery. Started trying to figure out which fuseable link went to the pcm and discovered one of the hot battery buss nuts not fully tight. Snugged it up and now full battery voltage to the computer. Ran it around the neighborhood and then a couple of speed runs down the Glenn. Need to dry up a seep around the injection pump fuel in port. Wished I had thought of that a year ago and I might not have missed moose season. GRRR!!
Justin

[Robyn]

Glad to hear you found the gremlin.

Bad connections and poor voltage can drive these things nuts.

Grounds are another real sore spot.

Got back through and check your voltage with the engine running and be sure that you have nearly equal voltage at both batteries.

Make sure that the voltage at the ECM is good. Hard to say what you will actually have. There are so many connections and the wires are small, so the voltage can vary a lot.

The condition of the connections and if the rig has seen any amount of SALT country can be a factor as well.

The 94 feeds the chassis off the RH battery and the alternator connects to the LH one, so be sure that your crossover is good and that voltage is up to snuff.

I have seen the crossover go south and the RH battery get short changed on voltage and all sorts of bad stuff happen.

Missy

[Lug]

A new alternator is on the short list of items to replace. The gauges except the tach and speedo will sometimes pulse after start especially when the turn signal is on. Kind of like the pulse caused by a strobe light if you have ever been around small airplanes like a Cessna 150. And last year there was a whine that was getting into the 2 meter fm transciever. So I still have a ways to go yet on the electrical aspect of the old buggy. Plus have to fit in new injectors and glow plugs sometime between fishing season, hunting season, and the start of winter.
Justin