2004 Cadillac Deville P0300 code

Tiny
CHRIS2363
  • MEMBER
  • 2004 CADILLAC DEVILLE
  • V8
  • FWD
  • AUTOMATIC
  • 120,000 MILES
I have a 2004 Cadillac deville that has the P0300 code and flashing check engine light on it was missing and sputtering. I narrowed it down to what I thought was spark plugs and 2 bad coils, changed them and it helped for awhile (about two miles). Now it is missing again and has the flashing check engine light and po300 code again I checked for vacuum leaks and didnt find any. I checked for bad connections and didnt find any. I checked the EGR valve to see if it was stuck or blocked and it is fine also. And the exhaust smells rich, but not like rotten eggs. I also had a new fuel pump and filters installed about 6000 miles ago. I also narrowed it down to cylinder #7 on the scan tool and the cylinder seems to be dead and completlely misfiring, I then swapped fuel injectors on #7 with 6 and #7 still is misfiring. I put a new ignition coil on # 7 cylinder also. I also checked compression and it was fine. I checked for spark and it was good, Any Ideas? Ignition module? Crank sensor? Cam sensor? Bad wiring harness? It is running very rich also.
Sunday, May 16th, 2010 AT 2:31 PM

4 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
A random misfire P0300 normally is caused by vacuum leaks and bad fuel
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Sunday, May 16th, 2010 AT 3:57 PM
Tiny
CHRIS2363
  • MEMBER
  • 3 POSTS
I sprayed carb cleaner everywhere, all around the hoses, boots, intake and fuel injectors, checked all the hoses, and nothing changed. Does water work better for checking for vacuum leaks?
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Sunday, May 16th, 2010 AT 4:40 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
It sounds like you have some experience perhaps since you are using a scan tool to ID the misfire.. I just want to be sure you are actually working on cylinder 7, you said that you swapped the injector for 6 and its on the opposite side of the engine. If this you are on the correct cyl you will need to test for injector pulse and pulse at the coil to be sure they are being old to fire. Sometimes the connectors have issue where the wire is crimped inside them or the connector just isn't making good contact

See the guides/diagrams below and let us know what you find

https://www.2carpros.com/articles/engine-misfires-or-runs-rough
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Sunday, May 16th, 2010 AT 4:50 PM
Tiny
TJAYPHILLY
  • MEMBER
  • 1 POST
Im having the same problem right now and I would be interested in what you find Chris im getting a rich exhaust smell and I currently drive a 2004 cadillac deville with 67k miles and i've checked for leaks and pressure and nothing yet I got the same code p0300 and it doesn't seem to be misfiring im thinking it could be one of my spark plugs I found a bit of moisture by one of them but I cant be sure any advice?
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Wednesday, November 9th, 2011 AT 12:32 AM

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