Misfiring Problem...HELP!

[AceOnGuitar]

Hello everyone,

I have a '99 Explorer Sport with a 4.0 V6 and 183,000 miles. A few months ago I started having a misfire when I first started it up, but it went away after a few minutes. After a while, it misfired all the time. So I changed the plugs and wires, and it stopped the constant misfire, but still misfired on a cold start. Recently on a longer trip, it started misfiring off and on. It would run good then run bad. It never got hot, but it would misfire for a few minutes then run good for a few minutes. It still does it after two bottles of fuel cleaner. The check engine light came on and the codes were: 171, 174, and 303. I understand that the code 303 is a misfire, and the other two codes are system running lean. I have to note that I hit a deer in 2005 and the vacuum ball shattered, and so the lines are just spliced together. Could the misfire be caused by a vacuum problem?

There is no water in the oil, and it does not smoke. It hasn't used any water or oil.

Please help!

Thanks in advance,
Chris

 

[dogfriend]

Could the misfire be caused by a vacuum problem?

Yes, if you have vacuum leak(s), the fuel / air ratio will be too lean, it is more difficult to fire the plug in a lean mixture. I would try to find and resolve any vacuum leaks.

Another possibility is clogged injector(s), which would also lead to misfires.

Here is a complete list for P0171:

http://www.explorerforum.com/forums/showthread.php?t=145587&highlight=p0171