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Jerry Newton
Jerry Newton, Cadillac Technician
Category: Cadillac
Satisfied Customers: 4628
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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I'm at a loss. I have a 2001 Deville it idle rough. I get a

Customer Question

I'm at a loss. I have a 2001 Deville it idle rough. I get a code of P0300 random miss fire. I've but in new plugs boots even changed the coils. I've dropped the converter due to it turning red thinking it was stopped up but still have a rough idle. I've
changed out the crank sensors and the PCM. Still no luck and im getting tired. I've also changed my fuel pump and filter. The only thing that I know for sure is the when I unplug the coil by the firewall there's no change in the car running. But if I unplugged
the front coil it dies. My father in law has a Cadillac also so I unplugged his coil at the firewall and his care started running just like mine.
Submitted: 2 years ago.
Category: Cadillac
Expert:  Jerry Newton replied 2 years ago.
I would be looking at the coil connector, making sure there is power on the pink wire and ground on the black wire per the schematic (see attached). It sounds like you are missing one of those circuits if the whole bank of cylinders is dead. It's not a fuse, since both coils are powered from the same fuse, but the wiring can absolutely be broken somewhere, or you may have a loose or broken ground connection.
Customer: replied 2 years ago.
Ok I take my lunch break at 12:30 and I'm going to run home and check it out. Then ill get back with the answers. This can be checked with just the key on or the car needs to be running. Never mind I just read the schematic
Expert:  Jerry Newton replied 2 years ago.
I'll be around, let me know what you find out. That schematic should be all you need to get this going, aside from a couple of tools.
Customer: replied 2 years ago.
Ok yes it has 12v at the pink and its grounded
Expert:  Jerry Newton replied 2 years ago.
And the engine is misfiring on all four of the rear cylinders?
Customer: replied 2 years ago.
IM not 100% sure but you can unplug the connector while its running and there's no difference
Customer: replied 2 years ago.
in how the car runs
Expert:  Jerry Newton replied 2 years ago.
Well, that seems to indicate that the rear cylinders are all misfiring. However, we don't know that it's due to a lack of spark. Fuel injectors are wired in two sets, but not 1-3-5-7 and 2-4-6-8.... they are grouped differently, so if there is no change when removing the coil, we just have to assume that there's no spark there. I only sent you part of the schematic, I didn't mean to do that, it came out that way due to a technical glitch. Let attach the whole thing for you. If there is power and ground and you aren't getting any spark (I would want to verify that there is no spark being produced), it seemingly points to a wiring issue or a faulty PCM. I've never seen a PCM fail in this fashion, but I never say anything is impossible.
Customer: replied 2 years ago.
Well I had an extra PMC due to an A/C problem I had before. and I changed it back out and it didn't help either.
Customer: replied 2 years ago.
so how can I verify if im setting spark
Expert:  Jerry Newton replied 2 years ago.
That takes us right down to wiring, then. If you have power and ground, the PCM is what triggers each coil. If this were in my shop, I'd be putting a lab scope to the trigger circuits to see if they are carrying a signal. I have never seen a signal fail to reach the coil of a Northstar engine, though.... you are in uncharted territory, and I have opened the hoods on thousands of these cars. It seems more likely that you have a terminal issue at the connector. Wires break inside the insulation sometimes, which can result in intermittent issues like "I checked for power and it was there, but when I plugged it in, the power disappeared." You can check for spark by simply leaving the coil plugged in and lifting it away from the engine while the engine is running. You should be able to hear and see the spark leaving the towers and finding ground. Even pull the coil all the way out and hold it next to a ground source.... it's just one of those things I would want to see before moving past it.

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