1992 4x4 3.0 auto pickup.
Think I've narrowed my fuel issue down to either the (square ) EFI relay or COR. Part store has neither in stock so I'll have to order. Can these be tested with multimeter? $40 for the EFI and $125 for COR new. May try used relays on ebay.

 

Yes they can be tested.

The simplest test is to listen/feel for the circuit to close (click).

You can check resistance but this could be misleading. A more accurate test is the loaded circuit voltage drop.

Have you tested voltage downstream of the relays?

Exactly what symptoms are you having and what led you to think you have a problem with one of these relays?

 

Replacing relays on a guess, without using a multimeter to actually locate the problem, is a sure path to bankruptcy (or madness, whichever comes first).

Actually, relays don't fail that often. Everything around them fails first. But your multimeter will give you the right answer almost immediately.

So, as co_94_PU asks, HOW did you narrow down your problem?

 

I haven't checked voltages but done lots of reading. Truck starts and runs a few seconds, dies. Jumper from B+ to Fp and runs fine, pump sounds good and even. EFI 15amp fuse test good. VAF ohms good, and I see the change at E1 -FC when I open/close vane. (THA - E2 seem a little high at 3.9k ohm dunno) I now understand that EFI relay must be good or I wouldn't get power to B+. Many with this run/die problem report corrosion of COR. I don't have a spare EFI relay but should be able to rob a COR off a 90 or 91 truck, I think those are compatible anyhow.
BTW, could the jumper B+ to Fp be used in a pinch to get home (probably not good if in accident I realize) and does fuel pump run continuously anyhow under normal operation? Just wonderin.

 

Okay, now you're getting somewhere!
Uh, why not? You're talking about spending $165 on a guess; is $6 too rich for your blood? https://www.harborfreight.com/7-func...ter-63604.html Get a multimeter; it's the first tool you need for any electrical problem (and most problems on powered vehicles are really electrical).
Correct. You still need to check voltage to ground from B+, but it is very unlikely you have a problem on the EFI side.
If that doesn't work, then what will you know? Spare COR is bad? Your wiring is bad? Something else?
Correct.

Testing the COR is pretty simple; you're just testing for continuity in the two coils. http://web.archive.org/web/201003261...96circuito.pdf

But look at the schematic. While you have he COR out, test for voltage with key-on at B+ on the relay socket (the drawing is looking the the relay, so you have to mentally flip it to get the terminals on the socket). Test for continuity to ground on the FC terminal when the VAF door is opened. You could have a good COR but a broken wire. You could have a COR with two good coils (it will pass the diagnostic), but where the contacts have been burned out (rare, but not hard to check for).

Be systematic. Your reading has lead you to do the right tests (using the jumper). Just keep it up.

 

COR failed the last coil test in FSM. Tested the "new" COR , installed, all is good! I could see a little rust around the cap on bad relay. Smacked it with screwdriver handle and got it to click but still had no continuity. Will have to figure out how to keep moisture out. Antenna is good n tight , maybe windshield is leaking. Will investigate. Thanks guys for all ya do!

 

Good work.