Ignition/radio Interference capacitor

MCKEE1

MEMBER
1998 LINCOLN NAVIGATOR
230,000 MILES

Vehicle will only crank and not start.

Radio Ignition Interference Capacitor #F6AZ-18801-A.

I can get it to start by taking a single jumper wire and connecting it from the battery to the one red wire going to this capacitor and then it will start and run. This truck has two of these capacitors on each side and the opposite one reads back battery voltage while the car is running when probed from the back.

The capacitor in question will not allow the truck to run when it is plugged in normally.

1 Reply

STEVE W.

MECHANIC
13,556 POSTS

Sounds like the capacitor has failed, most likely opened inside if it prevents it from running. A capacitor is designed to allow a DC voltage through (battery voltage) but it will prevent AC and spikes of DC from getting through. Its job is to filter out noise on the battery feed that is generated by the alternator, ignition, fuel injection and any other relays or solenoids in the system. When connected in the circuit you should find the same voltage on both sides with the key on. If you find voltage on one side and not the other it has failed open. If you find the same voltage on both sides but you hear whining, ticking or other strange sounds in the audio system (especially on AM) then it has shorted internally.
Replacement should take care of the problem.