Questions and Answers

Cadillac Backfires Q. Hi Vincent, I have an 1989 Cadillac Deville that has the 4.5 liter engine, automatic transmission, 150,000 miles DFI fuel injection and no ABS. P/S, A/C and rack and pinion steering, I bought the car used with 131,000 miles. After, 6 months and 8,000 miles it started to backfire through the TBI unit.

Since this has started I have replaced the fuel pump and filter, put a used TBI unit on it off a car that ran fine, replaced the spark plugs, wires, distributor cap, coil, module, and the pick up coil checks within specs, and the coolant fan temperature light has been coming on intermittently too. Any ideas?

Thank you for any help in advance.
Tom

A. If it's a constant backfire that is in time with a cylinder that's firing, it sounds like a broken valve spring or worn camshaft lobe. You can unplug spark plugs one at a time to isolate the bad cylinder. Then you can pull that valve cover to see what you have going on.

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