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1985 Eldorado, no start...no fuel pressure

Started by danjarrett1, January 21, 2020, 09:40:09 PM

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danjarrett1

As a project, a bought a super clean 1985 Eldorado. Car hasn’t run in months. Discovered that fuel pump was not working, replaced fuel pump relay, check power to pump, still nothing. Removed fuel tank....was a mess, full of crud and rust. Considered ordering a new fuel tank but decided on a little experiment instead. Soaked fuel tank in solution of vinegar for 4 days.....power washed and tank look new inside. Replace fuel sending unit and pump with new, blew out the fuel line, return line and the vents lines. Cleaned and rebuilt TB with new gaskets. Checked tank pump ground.....still...pump is not being activated. Checked wiring diagrams, replaced oil pressure switch as it is tied to the fuel pump relay, still no pressure. I ran 12 volts directly to the pump to confirm pump is working, What’s next? Considering jumping around the fuel relay, concerned that ECM is not triggering control signal to fuel pump relay. What are my options on testing ECM or replacing ECM If necessary?
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”
1985 Cadillac Eldorado

cadillacmike68

Check the schematics and verify that you have voltage going to and coming out of  the fuel pump relay or whatever is supposed to be sending voltage to the fuel pump. If you have voltage both into and out of the relay, check for an open in the circuit from that point to the fuel pump. If you don't have voltage then the problem is in the ECM (if no voltage going to the relay) or pump relay (if there is voltage going to the relay but not coming out of it).
Regards,
"Cadillac" Mike

danjarrett1

Thanks for the suggestion. I hope I don’t have to get into replacing the ECM. I understand the PROM can be removed from the factory installed ECM and placed into a remanufactured unit, but there is no “flashing “ of the replacement ECM that I’m aware of. It is my understanding that the PROM carries all the data that is relevant to this particular car, are the ECM’s otherwise generic in function? Does anyone have a referral for success for a  remanufactured ECM?
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”
1985 Cadillac Eldorado

cadillacmike68

There are sources for refurbished ECMs / PCMs etc. I'm not sure what has to be done with one for 1985 to get VIN, mileage, etc. info onto the replacement ECM.

I highly doubt that it is the ECM though, these were pretty robust units. check for voltage going to the pump relay and after. You will probably have it going to the relay, but maybe not out of it. then yu would check for an open.
Regards,
"Cadillac" Mike

danjarrett1

I hope you are right about the ECM’s being robust. I’ve also been told to check for proper ground. I plan on confirming a signal from the ECM to the relay and the relay to to the pump. I also understand that, on some models, GM would have a connector in the engine Bay Area that would allow or a direct connection to the fuel pump so 12 v could be supplied to confirm pump operation....don’t where where that pigtail might be located though
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”
1985 Cadillac Eldorado

cadillacmike68

The service manual should have the location of any pigtail to supply voltage to the fuel pump but I don't have that year's manuals.
Regards,
"Cadillac" Mike

danjarrett1

I do have the shop manual but there’s no reference that I can find to that particular pigtail. Was hoping someone might know where to look for it
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”
1985 Cadillac Eldorado

bcroe

Make sure you have a good ground connected to the tank unit.  Bruce Roe

danjarrett1

Will do, I did replace the connector from the fuel pump sending unit to the existing ground, put 12v to the pump...at the pump...and pump worked. Going to recheck light blue wire which is the power feed from the fuse box to the pump for continuity. I’m still concerned that I’m not getting a command from the ECM to trigger the fuel pump relay. Weather has been crappy here for the past several days, going to check tomorrow
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”
1985 Cadillac Eldorado

danjarrett1

Problem solved!,,  bad ground at the tank, I missed it in reassembly.
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”
1985 Cadillac Eldorado