Started out with a few problems. #1 started running rough at an idle. Smelled a little bit of rotten egg smell. Nothing had ever been touched on vehicle. 115,000 miles. Changed spark plugs and cleaned coil boots. No change. Started losing power very bad. Pulled converter, plugged. Changed that. Runs much better, but still idels very rough. Now I have a mis-fire code on 4 and 6. I went ahead and changed the coils on 4 and 6. Runs better, but still rough. When code is cleared, it runs at its best. Once code appears, it losses power. Also when no codes appear, vehicle is turning just over 2500 rpms at 60mph. even with coverter changes, heavy exhaust smell and poor gas mileage. Not sure what the next step is. Any one have some ideas? No other codes are being given.

 

All you are getting are Random Misfire codes?
Could be injector, plugs, wire to coil. But it will probably kill your cat again if it keeps up.

 

Raw gas getting into the cat converter will eventually kill it,like stated above. When one of my coil packs went, my mechanic told me to take of it asap because of that. In other words, don't be riding around with the engine mis-firing.

 

Good point guys. Well i have changed all coil packs, all spark plugs. No change. When I clear the engine light, it runs better, but it is still misfireing. Plus I have the heavy exhaust. But does not throw any codes. Drive around to get light to come on. Once light comes on, it runs alot worse. I guess I'm going to have to break down and head to the dealership . I did look at all the wires going away from the coils, they all look good. If anyone else has any ideas, I'm willing to give it one last try tonight. I am going to check out the injectors tonight.

 

It could be a cam/crank sensor (not sure which these have) but that should throw a specific code.

Good luck and keep us posted. It's always good to hear the causes in case this happens to more later on.

 

one of the very first codes I got was a crank sensor code. Changed the plugs, cat, and made sure all sensors were plugged in tight and never got that code again. You are on track though

 

Some thing to do start engine and spray starting fluid around the intake where it bolts down to the manifold see if idle changes.Mine thru a 303 code which is a misfire in cyl.3 took the intake off and put lower and upper gaskets along with a new coil pack also found the vacuum line that goes down to the pvc valve on the back of intake was bad.Replaced it with a piece of 5/8 heater hose.Last week I coded a 304 put the coil pack in that I pulled back then and its been running fine for more then 2 weeks.I think the lower intake gaskets was my issue.

 

If you did plugs, did you change upper intake manifold gaskets? If not I would look at changing those gaskets. Once you split the intake manifold, the gaskets usually won't seal back up correct. You can check for leaks by spraying carb or throttle body cleaner at seam and see if car stalls or revs up.

 

Yup no intake leak. I did change gaskets when I changed plugs.

 

Not sure how you made out, but did you change all 3 converters or just the inline one? they have converters on each manifold and one inline wich may explain why you are getting misfires in just 4 & 6 as it may be the fron manifold converter thats pluged. Also sometimes the conveter stuff blows back into the muffler and plugs the muffler.

 

I would check the MAF, as it regulates fuel flow based on 'calculated' air flow. If the MAF gets a bit of dirt on it, it may miscalculate, and send the wrong amount of fuel. You can take them apart and inspect them for 'schmutz' on the wire(s).
Fuel pressure can also be incorrectly regulated, leading to the catalytic meltdown. I would also check for a vacuum leak on the manifold and all vacuum lines under the hood.
tom

 

I had a problem like that with mine. Random misfires and would run in safe mode only 3 cylinders or so. Tried plugs, gaskets, coils, crank sensor none of that worked. Turned out to be a faulty coil driver in the pcm computer. Got new computer installed and all my problems went away.