Are the plugs & wires AC Delco??? A lot of people have reported problems with other brands. Yes, do replace the coil. You might try misting the wires at night and looking very closely for any sparking that might be occuring.
Automobile(s): Cadillac 78 Seville, 78 Coupe de Ville, 92 Sedan de Ville
Re: Coupe Deville 4.5 Rough Running
It's got a fairly recent tune up, and hesitates or weak on power and smells like sulfer.........hmmm............I wonder if that catalytic converter is original? It's starting to sound like the cat is clogging. If it's the cat, it may gradually get worse but you could keep driving it until it starts glowing or something. A clogged cat will alter your vacuum but I can't remember if it makes it way high or way low. You could take out a couple of the easy spark plugs to see what they look like. Keep us posted and good luck.
I am going to try and make it into a muffler shop tonight. They will do a test on it. I think its original - looks like it.. but of course that does not say much. It it requires replacement. The person quoted me 189 for the complete job (labor and all) so we shall see.
If they say it's not clogged, I'd really check that coil if your plugs/wires are new. It sounds like your car is running rich. If the temp sensor isn't reading too cold, and the MAP is reading vacuum correctly, there's really no reason for it to run rich.
So folks, I drove my car out there tonight to get the estimate done. He put it up in the air... He did not conn. anything to it, but claims based on how it started and the condition of the cat. it WAS bad and was causing the backlow, etc.
I thought they might have done a slightly more thorough inspection but I don't do exhaust so I could tell ya less.
He quoted me a price of 290.00
Does this sound right? I might call another place tomorrow for a 2nd quote.
I doubt that your CAT is causing your engine to miss. But before you spend all that money, do a back pressure test first. Or if the mufflers guys are so sure that your CAT is the problem, draft an agreement and have them sign it that you won't owe them anything except the cost of parts if installing a new CAT doesn't fix the problem.
I called another muffler place and they gave me a quote of 189 for the complete (+ Labor) replacement of the cat. I asked them if this WAS the price, since the last place - one guy on the phone gave me the same quote.. but when I went in - with nothing extra - quoted me 110 extra. I told this shop they just looked at it, etc.
This place recommended I bring it in. Cost will be 189 AND they will do a pressure test, etc... so I feel more comfortable about spending the dough if I need to. Will let you know what I find out.