1975 Eldorado Stalling

Stalling has been a recurrent problem with this factory stock 1975 Eldorado with 500 cubic inch (4BBL) V8 for five years. It runs normally for between 2 and 3 hours at normal highway speeds and then simply quits with little warning other than a slight surge. After being allowed to sit for about 3 hours, the car will start and run normally for another period of from 2 to 3 hours. The following cures have been tried:

1. Fuel pump replaced along with fuel filters.
2. Major tuneup including plugs, wires, distributor cap and electronic ignition components.
3. HEI ignition module replaced.
4. Factory rebuilt carburetor installed.
5. Distributor Vacuum Advance Rebuilt.
6. New 4-row Heavy Duty Radiator Core.
7. New dual exhaust including dual converters.
8. Auxilliary Transmission Oil Cooler Installed.
9. Variety of Fuels have been tried including regular and premium grades as well as gasohol blends with almost no difference noted.

The problem persists. Any suggestions as to what we may be overlooking? I am planning a long vacation trip in this vehicle next summer so would like to get it running properly this summer.

Your symptoms sound like a classic case of the ignition module overheating. The kicker is that you've replaced it. The only other culprit would be an excessive current limit on your ignition module. 7 to 8 amps is the limit. Any higher causes the power FET that controls the firing of the coil to overheat and saturate. I can't remember if there is a ballast resistor or resitor wire on a 1975 HEI system. But without either one, your ignition module is getting too much juice.

Problem Solved - - !!!

After more than five years and at least seven mechanics, an independent mechanic in the town where I moved two years ago found the elusive culprit of the stalling problem. What he did find:

1. The resistor in the ignition circuit was either missing or faulty (thanks delamothe for the suggestion).

2. The secondary issue was the VERY elusive part of the problem. Just 60 miles after having the iginition system repaired, the car stalled again - - this time less than six blocks from my mechanic. He sent a tow truck to pick-up the car - - ignition good but no fuel (tank had just been filled with 20+ gallons of gasoline). The car went into the shop immediately - - fuel pump tested as good but no fuel - - removed fuel line near tank and used air hose to check for obstruction (none discovered) - - then was asked for permission to drop the fuel tank - - removed the fuel pickup/guage unit and it was clogged with what looked like a piece of white fabric - - conclusion:

The tank had been replaced by the previous owner less than 30 days before I purchased the car in 1995. My mechanics theory is that the two pieces of fabric had covered the opening for the filler and the fuel pickup/guage opening and had been punched into the tank by the installer rather than removed. These pieces of fabric were floating around in the tank and would be periodically pulled into the fuel pickup blocking fuel flow - - then would dislodge when the gasoline was sloshed around while being towed in behind the tow truck. The solution was to purge the fuel tank and then install a new in-tank filter sock (the previous owner's mechanic had omitted this part when the replacement was completed.)

This problem was diagnosed in March, and I have now driven the car enough to have confidence in its reliability. It will be going to my Vintage Airstream Club Rallys over the next month.

Kevin
http://www.airstreamphotos.com/photos/data/500/827streetside_cadillac.jpg

1975 Cadillac Eldorado Convertible with 1964 Airstream Overlander International Land Yacht

I have a similar problem , where I go through ignition modules about every 4to6 months.Ruled out heat transfer grease , alwaysed used new corect modules , low ohm res. plug wires , gapped plugs at 040 , problem still persists .
Ground is clean between the dist. and block.
Dist. is a Mallory HEI out of the box.
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