My DeVille went to craps a couple months ago. There was a code 19- dealing with fuel delivery. So I checked the pump, all wiring, fuses, and relays. Finally cleaned harness in engine comaprtment going to the fuel pump. It worked for one day, even though the car was getting gas and spark it still wasn't starting, and giving me code 20! Checked everything again. Cleared all codes and then 19 came back and 20 went away! I read some thing the other day though that got me to thinking, I read that magneseum based MMT gas additive's can cause harm to your car. I believe I did see a bottle of octane booster in the car that said "With MMT" on it.Could this be what happened? What could I do to fix this? I tried new computer, relays, fuses.Thanks
Your problem may be the oil pressure switch, near the bottom of the engine. There is a big red wire going from the conduit by the distributor, down to the bottom backside of the engine where you can't see it anymore. The wire coating can get brittle, and often strips, leaving an exposed wire to touch any nearby grounds from time to time. The oil pressure switch/harness itself should also probably be replaced.
The oil pressure switch has a wire going to it from the fuel pump/relay, making sure the fuel pump is powered when oil pressure exists. This 'safety feature' can become a problem if the exposed wires get brittle after 20 yrs.
I had mine done at the dealer a couple years ago. This took forever to track down on my '82 eldo (finally saw the bare wire at the bottom), but looks like a potentially common problem. They covered it with a plastic conduit, and I haven't had a problem since.