Well, sorta. The project continues.
One point that may be helpful to someone another day is that the Fuel Pump Relay for the ‘98 AEL truck is housed in a multifunction relay box (the black relay between the evap canister and the washer fluid reservoir) that, according to RAVE has four distinct relays inside of it. Only two of which are used. On start-up, both the FPR, and an injector control relay are energized. The “clicking,” on application of ignition position II that I’ve been hearing, I have discovered to be the injector control relay, and NOT the FPR. (Pull the injector fuse in the engine bay box, and poof! No clicking on pos. II.) So, that has changed my bug-hunt somewhat.
I’ve bench-tested both the old and new relays, and they are both working properly. I’ve hunted continuity and resistance backwards and forwards, up and down. From the relay to the pump, from the pump to ground. From the supply side of the relay to the fuse box, from the fuse box to the battery. I’ve checked both the ignition side of the FPR control circuit and the ECM side of the FPR control circuit. I’ve checked, cleaned and lubricated every plug involved. I’ve checked every ground leaving the ECM, and cleaned and polished every ground that impacts the system, along with some that don’t. This leaves me with one conclusion: the electrons have a path to flow... but they aren’t flowing. That is to say, the ECM is not telling the FPR to close on application of position II. Now, before I consigned myself to whatever hellscape replacing an ECM (my research doesn’t even seem to think it’s really possible?!) might bring, we went back and started combing the RAVE, the forums, and anywhere else we could think of to try to figure out what would cause the ECM to clam up on activating the FPR, but run the motor perfectly happily when the pump was jumped with battery power. The shop manuals are pretty specific when they indicate that most of the sensors on the engine will cause the ECM to interrupt spark on failure, not fuel, however, anecdotal evidence from forums seems to indicate that this is not totally true, and that the Crank Position Sensor may cause mis-fueling, erratic idle, stalling, etc. Those were the initial symptoms the first time the truck started acting up and nearly stranded us before coming to life and getting us home before conking out for good. So. We have a Crank Position Sensor (I forget if it is commonly abbreviated CKS or CPS off the top of my head) in the mail, hopefully arriving this week. I’ll get back from work over the weekend, and hopefully will be able to replace that, and we’ll go from there.
Hopefully, one of these days, I’ll have good news! In the meantime, my understanding is that the Crank Sensor is a total B***h to get at, and that an 18” ratchet extension and some double jointed appendages are the best solutions short of dropping the exhaust, which I have neither the space nor the inclination to do. Can anyone chime in with any tips?