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1990 Cadillac Seville, 4.5L engine

this vehicle is running extremely rich, and back firing. It recently blew up the muffler due to excess fuel in the exhaust. It also runs rough. I thought it might have a stuck valve so i performed a compression test and found all cylinders to have 175 psi of compression. Next i checked the timing and it was on. I tried adjusting the distributor and that helped a little, but after a few minutes it went back to missfiring and running rough,

When i first started to look at the car it had a dead battery so i jumped it with my car, the wierdest part is: With jumper cables on the vehicle it runs fine, no backfiring and a smooth idle. as soon as i take the cables off it starts to stumble and backfire.


ANY IDEAS??????

You should clean and tighten the electrical grounds. They did have problems with grounds being loose or dirty causing all kinds of weird problems. I think that some of the grounds, like the one for the engine controller, are on the transaxle to engine bell housing bolts. Remove and clean them really good. If you see any other grounds, clean them up too.

malek79,

Discrete is right. I see this alot in your particular car. Use one part water and one part baking soda to clean the connections.

Thank you so much for the help. You were right it was a bad ground. i really appreciate it.

Good call Discrete.....you are "Da man"