I have a 1999 Ford F-150, regular cab XL with a 4.2l V-6. This afternoon when leaving work, the truck started idling extremely rough, almost as if it was missing a couple of cylinders. I drove to autozone and had them read the codes and was told that I had a missfire on 3 cylinders, #1, 4 and 5 I belive. In addition they stated that the system was running lean. I purchased sparkplugs, installed them and no success. I then got my can of carburator cleaner out and sprayed the vacuum lines and there seems to be no vaccum leaks. I am at a loss. I did remove wire 4 and 5 to see if there was a spard, and I do have an extremely good spard. At an idle, it acts as if it is going to die due to the rough idle. I am at a loss. Anybody have an idea?????

Thanks

German

 

Sounds like a carbon build up problem. Try doing the basic things first; clean the MAF sensor,clean the IAC valve,fuel filter,air filter. You might need a professional de-carbonizing process done. Add a bottle of Techron to the gas next fill up and run it till the tank is nearly empty. You might have to pull the upper intake and clean it. Good luck and keep us posted!

 

Well,
After some serious search and destroy, it turned out to be a bad intakevalve spring. Who would have figured??
I also found out that Ford recommends not using Bosh platinum plugs because they cause missfire codes in many motors. It is recommended to stick with Motorcraft plugs.

German

 

how and were did you take it to find this out. ? Mine is giving same codes , miss fire on 1 And4 , getting ready to put in new plugs, but i bought the AC Rapid fire for it. Hope they will work. Dont no what happened to mine loned it to a frind and light was on when i got it back. by the way how much did it cost to fix it?. Thanks Gil. by the way any thang else you could tell me about it would be appreceiated Thanks

 

I tried the AC-delco RapidFire plugs and developed a rough cold start and multiple cylinder misfires after about 5000 miles. I now have a set of bosch platinums installed and the rough cold start is still there! I think I'll take your advice and just go back to the Motorcraft plugs. Pete