I'm back working on the 1991 D350 with the 360 gas motor. quick back story, it ran, then parked in 2009, in 2018 mice moved in and 2019 I towed it home from inlaws property. somebody stole the distributor, so new distributor, intake gasket, water pump, radiator, plug wires, plugs, oil change, valve cover gaskets etc...

There was some questionable repairs to the fusible links, and it would barely start, then run for 5 seconds then shut off.

I bought a 1991 W250 donor that I drove on and off the trailer, had messed up brakes but the motor definitely ran, rich, but it ran. I just yanked the whole harness from SMEC to firewall bulkhead connector out and swapped it in, pretty easy job actually...I previously removed the engine end of the harness and cleaned, checked and rewrapped it so I'm pretty certain everything is in order there.

The problem seems to be spark. the coil only has 1.5-4 volts at the + terminal. that is also the voltage at the ASD relay, but the ASD has 12.6 going into it at the 30 terminal. why wouldn't the switched accessories get the same voltage? I've tried multiple relays and they all do the same thing. I've also used both SMEC brains, no change...

I did the test yesterday on the hall effect pickup where I detached the coil wire from the distributor and jumped the 2&3 terminal and there was a spark present. There was only 10v at the terminal 1, the manual states it should be within 1 volt of battery voltage which is 12.6, so I'm a little out of spec there.

I have cleaned and checked the grounds. Battery to engine block with 4 ga, battery to core support with 10ga, harness to core support with 12ga maybe, then engine block to firewall with a strap and wiring harness has two grounds on one ring connector at center of firewall too.

any insight into why the ASD would only be shelling out 4volts through the relay and underpowering the coil?

 

Don't usually comment on things I don't understand, that's for the parrots. My experience is limited to 1Gens with carburetors, 73'-74's and and an '85.
You have no spark at all? Does TBI still use a ballast resistor? If it is open the ECU is not sending battery voltage. What happens if you jump the relay wiring with battery voltage. TBI have a crank sensor? Then you should have a reference voltage at the crank sensor when cranking to see if the SBEC is awake and functioning, closing the ASD or providing coil ground. That is as much as I will guess. You need a DODGE service manual, EBAY is the place, maybe 50.00USD. Maybe Mitchell, they used to be pretty solid, not some Haynes junk. There are a couple pretty smart guys here, hang in there.

 

I've got a Haynes, it isn't too bad any opinion.

There is no ballast on the 89 and up and the crank sensor didnt come until the module in 92.

The fusible link setup is stupid, there is no way to tell what is blown or about to blow, I'm not a fan...

I just jumped the +coil terminal to the battery, engine fired right up, ran for 3 seconds and quit. Now I've got no power anywhere, not sure what blew, I'm guessing one of the links.

I'm about down trying to chase unknown problems in the harness... I've got a spare one so my last effort may be to open up original harness and really trace each wire and do the good upgrade to the fusible links.

knowing the engine runs is comforting, I do have another complete motor but this seems all electrical, not fuel or air related.

 

Did you happen to swap out the asd relay? The asd relay is controlled by the pcm, Positive 12v+ comes from the ignition switch and the pcm gives it the ground. If it's dropping out i would say it's a pcm issue.