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Help misfire rough running girl

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Hello friends Cadillac Enthusiast I have a 99 Eldorado that has 49,000 miles I have the thing sitting for about five years due to the fact that was stolen and I went  and rebuilt the front clip  rebuild the body etc etc with a Northstar being sitting as long as it has I noticed when I started it up and drove it a little while a few years back that the water pump went out and it started to get a little hot so I got that replaced right away well anyway but the car is ran really great after an oil change and mice chew through the fuel injector wires on a couple of cylinders but beyond that everything is just fine for about 2 months with under 50000 miles and a fresh oil change I let it sit for about a week and when I went to start it back up it started running like dog crap so I took it to the local mechanic and he put the Diagnostics on it and told me that it would cost around $1,200 to replace the intake manifold plugs and wires and I thought what he said I had a cracked manifold intake manifold so I just searching around found me a used manifold put it on and I can't seem to find the crack on the old manifold and ask for the renewable intake manifold gaskets I bought new ones because I did not like the look of the old ones I did everything to the tee! plugged in all the sensors back to normal and it is doing the exact same thing it was doing? It does though seem that when I'm running the car for a few minutes or so it'll run really really smooth and the only other thing that I have had to do to the car as somebody stole and cut out the catalytic converter when it was sitting in storage  so I had it straight piped with new 44's as exhaust and I welded in bung and a oxygen sensor.  so after replacing the manifold gaskets plugs and wires that still has a misfire I tried the starting fluid trick under the hood with all that and I had no increase in RPMs or anything like that nature that would cause me to believe that there was a vacuum leak I don't believe coil packs go bad or are intermittent but maybe they are??? Thank you any help would be greatly appreciated TT Tucker 247 at gmail.com all lowercase

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Can you run the diagnostic trouble codes (DTCs) on it and share which ones are current and history?  Your Cadillac has onboard diagnostics, and will show you the current codes.  Please refer to this article on how to pull the codes: http://www.caddyinfo.com/readingcodes.html

When you say it is running 'like dog crag' do you feel that one or multiple cylinders are misfiring?

If you have removed the catalytic converter and not replaced it, you probably have a permanent DTC for that as the system will detect the catalytic converter as failing and not be able to use the O2 sensor info to advise the fuel mix.


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