View Full Version : Misfire and Catalytic Converter Problems

12-17-2010, 01:48 PM
First off the car is a '98.5 2.8. I recently had the timing belt/water pump replaced and right after the car started misfiring. It is a intermittent misfire. It will do it in all conditions (cruising, aggressive driving, engine at running temp.), it will happen at any random time. I've noticed that if it starts misfiring if I pull over and park for about 5-10 minutes it will go away. Now the oddest part about it is that it is also throwing a code for the cat (bank 1). I just replaced the cats back in May and when it does misfire I always pull over immediately (I know that driving with a misfire for a long period of time can ruin the cats) so I don't think it would have done that already. So could a bad cat cause a misfire?

Here are the codes that came up:
P0422-Main Catalyst: Bank 1: Efficiently Below Threshold
P0300-Random/Multiple Cylinder Misfire Detected
P0301-Cylinder 1 misfire
P0306-Cylinder 6 misfire
P0303-Cylinder 3 misfire
Also I've replaced ignition wires, spark plugs, coilpack (twice now, once under warranty after the first replacement one went bad within a month), both Cat. Converters, and fuel injectors; all within about 9 months. My mechanic also checked the MAF and its fine.

Could a bad cat cause this? Or possibly the rear o2 sensor be malfunctioning and be causing the car to adjust and be making it run bad? Or could it just be another bad coilpack?

12-17-2010, 01:55 PM
looks like you need new coil packs in cylinder 1, 6, 3 and a new cat

12-17-2010, 02:24 PM
if it started immediately after the timing belt, i suspect its off by a tooth and cause random misfires

12-17-2010, 02:55 PM
Thanks guy. I'm gonna see how long the warranty is for the coil pack (its one pack for all the cylinders in the 2.8 unlike the 1.8). Either that or it could be the timing belt is one tooth off (would the car run more rough if it was that though?)

12-17-2010, 03:02 PM
What kind of catalysts did you go with? Ive seen lots of short lives on the cheaper aftermarket ones as opposed to OEM. Some only make it 2 months past their warranty!! The timing belt would also be throwing codes for cam position sensors, it tries to correct but cant and figures one or both sensor is faulty.