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Q: My cadillac requires a catalytic convertor...How much will this cost me? on 1991 Cadillac DeVille

I have a 91 cadillac sedan deville with just 60,000 miles on it....recently had the battery changed, engine tune up and oil change done by a backyard mechanic...Car started misfiring, stalling and losing power...even my gas mileage fell drastically from 13 MPG to 4.5MPG....Utterly devastated I took it to the dealership to have the problems checked. First the technician stated that he had to do a compression test to find the problem which would cost me $350...after the compression test he stated that 4 cylinders were not firing and I needed replacement. Utterly devasted I asked him if he checked my spark plugs or for that matter the fuel injectors? At this he stated he will get back to me. The next day he called me and stated that there were 2 different set of spark plugs were used and some had oil foul etc etc...On further insisting him to diagonize the problem instead of offhandedly asking me to replace th engine...he stated that he would change the spark plugs and see if the cylinders fire....Today he called me and stated that the engine runs better than before but the spark plugs need to be changed, some cables connected to the spark plugs need replacement and some of the fuel injectors have leaks which need replacement. Then finally he stated that the catalytic convertor needs to be replaced as well since something fuzed and damaged the catalytic convertor. My predicament is the technician did not come up with any solution after the compression test and wants to charge me $350....and with all that he stated that the total will come to $1700.....Now should I proceed with the repairs since he was not honest in the first place. If not will be okay for me to find a wayside garage to get the job done? Someone please help me
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On later cars (1996 onwards)the computer monitors misfires and flags witch cylinders are misfiring and a scan tool will identify them reading data straight off a tool. On an older car you have to start with the basics. If an engine is running poorly and you are told it was recently "tuned up", you must then look at the basics. An engine misfire can be caused by engine mechanical isues, fuel issues, or ignition issues. You've got to start with the basics, check the engine is mechanically sound (good even compression, no vacuum leaks,valves are properly adjusted (in the case of shim or screw adjusted valve clearances), check the engine's ignition system is good (good spark plugs coils or plug wires where applicable) then the fuel system needs to be tested and inspected to make sure it is operating efficiently. A misfire can be caused by many things but basic diagnostic tests need to be done rather than just trying to guess what the problem is. A mis fire will eventually damage the catalytic converter. I'm not sure what the blue book value of your car is look at also think of what it would cost to replace your car with a comparable car and think do you repair or replace.
There are universal cats available at some parts stores...they have to be welded on...mechanics should charge no more than $250 to do this. The factory cat will probably be around $400-$500 to replace. Go with the universal one if you are on a works the same way, might be just a little bit louder.
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