1995 cad dev wont start


Asked by Jul 30, 2015 at 08:30 PM about the 1995 Cadillac DeVille Concours Sedan FWD

Question type: Maintenance & Repair

Lost pcm voltage to fuel pump relay. Volt meter reads 8.5v with no relay in fuel pump socket. Drops to .2v with relay in socket. Also lost fuel injector drive signal . Have 11 volts on injector wire plug but injectors don't fire. Changed pcu and no improvement. suspect loss of ground or voltage to pcu. fuses and relays checked ok. Dash display reads (no pcu data). Need PCU diagram to continue trouble shooting. Any suggestions!

7 Answers


Hi nice to meet you. What is th voltage for the batt?.


Check under the driver's side dash for a hidden ECM fuse. Some GMs use them. HTH. -Jim

1 people found this helpful.

Hello folks. Bat volts was 11.5v. Will check under dash for fuse. Does sound like ground open or no voltage. working on getting pcm schematic.


You need too verify if you have injector ground pulsation. If you have B+ in the ignition coil and spark. You need 3 things for operation. 1. Coil spark. 2. Fuel 3. Compression in engine.

2 people found this helpful.

Got compression, spark plugs firing, pressure on fuel rail. Can't feel or hear injectors firing. Need an Oscope. Pulse is to short to read on digital volt meter. Will try a small amount of starting fluid in the intake next time I visit my brother (his car). If it just hits on 1 cylinder I'll know the injectors aren't firing. Thanks guys. Still look for the scismo on the pcu.

1 people found this helpful.

Ok first thanks for give me the oportuniti to help you. You can verify the injector signal with a test light. I prefer one bipolar test light because have more impedance and is more secure for the pcm in this test. Put your test light in B+ and try to start the car meanwhile someone try to start the car you touch with the test light the conector pin of the injectors. You have two pins, one have B+ and the other have pulsating ground. If the car is cranking and you touch with the test light conected in B+ you can see the test light flashing but you need to be fast. You have compression in the engine thats mean the engine is in good shape. You have firing in spark plugs that mean you have one good and working cam sensor because the cams control the firing time. You have a good fuel pressure. Ok you have firing and fuel pressure thats mean maybe the pcm is not the problem because the pcm control the drivers for the coil and the activation of the fuel pump relay maybe MAYBE you have problem with the B+ of the fuel injectors or crank sensor because the cranck sensor control the injectors operation oooor you have the theft system activated, when the theft system is active the pcm don't send the pulsating ground signal for the injectors. The theft system neutralize only the starter motor (GM, Ford, Chrysler) fuel pump (Ford,Chrysler, Asian, European) injectors ( GM, Asian, few Ford).


Well folks I found one problem after getting partial schematics. Open B+ wires feeding pcm. Replaced wire from pcm fuse in engine compartment to 2 battery voltage feed pins on pcu. The schematic shows a direct connection from the fuse to the pins on the pcm but the car wouldn't start until I jumpered the old wire back in at the fuse block still with the adde feeder wires. So this line from the fuse is not a direct connection and there could be hidden fuse some where. Now car starts fine but has fast idle and a/c (which was the orignal problem) still not working. I can jumper across a/c compressor relay and it works. I also jumpered the high and low pressure sensors with no success. A factory wiring diagram would make this so much easier. Searching for a/c control wiring now. I will responde when I get a final fix. Thanks guys!

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