Engine Chugging with Modified Exhaust
I have a 98 Mustang GT. I've had her for 4 years now. I haven't had much problems until recently. about 2 months ago did a regular tuneup due to some rough running and chugging. That seemed to help for awhile. This last week the chugging got much worse on a daily basis. We found a couple of spark plugs fouled out due to the thermostat housing seal broke and some fluid leaking in the sparkplug wells. We cleaned it all up, replaced the bad seal and replaced the spark plugs. Still the chugging. We went to an auto parts store where they put on the diagnois machine. It showed the EGR valve to be bad. We bought a new one and replaced it. It runs worse than it did before. We went back to the store because we were at a lost of what was going on. I have modified exhaust on my car. I have H pipe with the cats removed totally. The guy said it's either my O2 sensors, but we don't see them, or the EGR valve is trying to make the engine run correctly but can't due to the illegal modified exhaust system. I bought the car this way. When going up any slight incline I have to downshift several times. If I'm on the freeway and have gotten up speed I do pretty good except when someone cuts me off or slows me down and then if I try to accelerate I hear like sputtering and almost sounds like it's misfiring. My daughter and I work on the car all the time and know it inside and out but this has totally baffled up. Would appreciate anyones help with this problem. The store says I need to replace the cats, sensors costing over 2K which it's quite a bit I think. Thanks for all your help.