1989 Cadillac Deville Backfiring/very rough idle.

CADDYJER

MEMBER
1989 CADILLAC DEVILLE
V8
FWD
AUTOMATIC
78,000 MILES

I own an 89 Deville. I have replaced the fuel pump, strainer, filter. The fuel pressure regulator, distributor cap, rotor, pickup coil, all spark plugs and wires. Battery is new, alternator has been tested and passed. Egr valve moves freely. It will run fine for about 15-20 minutes then start acting like its starving for fuel. It will sputter then surge and begin to backfire. I have read many of your messages to others with similar problems. The only things left I can think of are the MAP sensor and the ignition control module in the distributor. When I do the computer diagnostic check the codes I get are E21 and E 28. I'm just at the point where I'm throwing money at it. If you have any suggestions or advice on how to proceed from here I would be very greatful.

1 Reply

MERLIN2021

MECHANIC
17,250 POSTS

Well the E 21= shrted TPS circuit
28=open 3rd or 4th gear circuit.
Or quad driver #3 circuit fault.
Locate the black and blk/pink and dark blue wires at the tps, with key on engine off backprobe with a voltmeter, at closed position you should have.5 volt or less, at wide open it should be about 4.5 volts, if not unplug and test the two wires for continuity, should be none. If tps fails replace it.