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1978 Eldorado vacuum hose routing question

Started by bill06447, June 01, 2016, 06:47:46 PM

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bill06447

I'm hoping someone with a 1978 425 carbureted could help me verify where the vacuum hose coming from the fuel economy minder connects to. The yellow jewel on the dash stays lit all the time and I want to confirm it's connected properly. I have a diagram in the shop manual but the thick lines blend together where they intersect and its difficult for me to decipher.

Thanks, Bill

R Schroeder

#1
Bill, this is the only diagram in the manual that shows it. 425 engine , for 78. It is the blue line. This diagram was for my 78 DeVille.
Roy

TJ Hopland

Looking at the diagram it sort of looks like the distributor is tapped into that line, its not.  The distributor connects to its own port on the intake manifold.   At least on a federal emissions car that is, if yours is CA there may be a different diagram. 

I see that its in the EFE circuit.  EFE is the 'heat riser' valve at the end if the right exhaust manifold.   I believe the EFE thermal vacuum switch is sticking out the side of the timing chain area on the right side of the block sort of under the alternator.   If its not there then it would be sticking out the front of the engine sort of near the base of the distributor.   There are 3 ports on the EFE switch.  One is the vacuum in from the carb (the circuit your monitor is tapped into).  One goes to the EFE actuator.  The 3rd likely is a vent.   So in 'cold' mode the valve connects the carb to the actuator.  When coolant warms up the valve operates blocking the carb line and connecting the actuator to the open port which lets it retract to its normal position.    If those lines are hooked up wrong you could be venting vacuum all the time so the economy sensor never 'sees' high vacuum which is what would make the light go green.   Its also possible that the actuator is bad so its a constant vacuum leak and the valve is stuck or hooked up wrong. 

If you have a hand vacuum pump you could try hooking the sensor line and see if that will make the light change.  If you don't you could try disconnecting the EFE circuit and see if that makes it work.   You could also try tapping into the distributor line, that for sure should show full vac at idle so should show a green light.   It may be that the proper port in the carb is plugged up so its never seeing vacuum. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

R Schroeder

Like I said. This was the only one in the book that showed the economy switch in the diagram. All other diagrams seem to eliminate the switch.

Like you said, he should be able to T into just about any vacuum line that is in the manifold.

bill06447

Thanks for the input. I'll check the routing this weekend and report back

Bill