Our 1990 740 will die intermittently, usually at a stop light. The usual pattern is an occasion miss as I slow down followed by the engine dying while it idles. The engine will not restart after it dies. However, on most of these occasions I have been able to get it re-started before the tow truck arrived.

About 4 years ago when the problem became very frequent and after replacing the cap and rotor did not help, my son (a former mechanic) said this was typical of of bad ignition module so I replaced the "module" (the finned aluminum thing that sits under the coil) with a after market unit from Auto Value. About 3 weeks later the problem recurred and the car would not re-start. I took the module back and they gave me another one.

The car ran perfectly for over a year and then the problem recurred. I got another unit and the problem recurred on the second trip after replacing the module and putting the old unit in the trunk as a spare. This time the car died at a stop sign and would not restart with either the new module or the old one and we came home on the hook about 3 hours later. Again I took the module back to Auto Value and they replaced it and the car ran fine for several months. Again, it died and would not restart, so I got another module and put the old one in the trunk.

Again, a year or so later (about 2 months ago) the car died and would not restart. This time I replaced the module with one of the old units I had in the trunk and the car worked fine for several months before the next occurrence. This time the car would not restart and I did not have my tools with me, so I could not try the old modules. After a long cold wait, the tow truck arrived. Since the car was in a bad spot, he picked it up from the front and towed it to a nearby shopping center so he could set it down and pick it from the rear to tow it home. The next morning the car started immediately without changing anything. Since the only thing that happened to the car after it died was being tipped at a steep angle nose up and then nose down by the tow truck I thought maybe there was some debris in the fuel tank.

Last week the car misfired a couple of times as I slowed for a traffic light and then would not restart. While I was waiting for the tow truck, I put in one of the 2 old ignition modules from the trunk in and was able to restart the car. However, the car soon began to miss and died again. Just after I put in the second spare module and the car still would not restart the tow truck arrived and we came home on the hook. This did not seem to be a fuel supply or fuel injection problem since I could smell unburnt fuel when I was trying to re-start the car. I tried restarting it the car about once a day since the without any result. Yesterday I put in one the modules that was in the trunk and a new coil. I was able to restart the car and it ran for a few minutes and died. I waited a couple of minutes, re-started it and it died again. A few minutes later, I restarted it again and it ran for 20 minutes without missing.

Any suggestions as to what could be causing this? I am going to get a price for a new module from the dealer as I am becoming dubious about the aftermarket units. Apart from this ignition problem the car is running fine. The ignition system must be crank fired, since the only wire going to the distributor is the coil wire.

 

I'd look at the crank angle sensor. No way known all those modules are defective.

Regards, Andrew.

 

I'd also say that the Crank Pos Sensor is suspect, along with possibly bad ground connection somewhere...

 

The only thing I can contribute is to remove the distributor cap then the rotor button (Battery disconnected) and give it a visual inspection as well as checking for any play in the shaft. I had a distributor on an old cutlass that was burning out every set of points I put in it randomly, as it turns out the shaft in the distributor had alot of play in it and it would ground out the magnetic pickup and burn the condenser up.

 

This is a 1990 740, all the distributor does is distribute spark. They have a crank angle sensor on the flywheel and the computer does the rest.

Regards, Andrew.