Originally Posted by kitchenguy
Engine had been running a little rough after this 1999 F-150 4.6 had been sitting for a while. Local shop checked Obd and came up with Codes 304 & 401. This said I pulled plug #1 first to check what may be going on. The plug looked pretty good and the gap was almost spot on. Then I went for the gold and removed #4 which unlike #1 the boot was loaded with grease and the plug itself was vairly well fouled. This plug was thouroughly cleaned and regapped and torqued back into place. Started the engine which now appeared to be running quite well. I disconnected the battery for a while to get rid of the engine light and now curious to see if the engine light comes back on.
Need to find out what most likely caused # 4 to foul and missfire.
Thank You in advance for your help.
for the 401 code:
Check all of the vacuum tubing on the EGR system, for bad tubing or disconnected ones. Replace any bad vacuum lines in the EGR system.
The first test to do for the 401 code is the vacuum test on the egr. Id you have access to a hand held vacuum pump, connect directly to the EGR valve. With the engine idleing, pull bout 5 # of vacuum (no more than 5#), if it is working properly, it should stall or make the engine run very rough. If you hear or see the valve move but the engine does not stumble the EGR ports are probably stopped up..
If you don't have a vacuum pump, you can connect piece of vacuum tubing to it and suck on it very hard, if it is working right, it should make a notice stumble in the sound of the engine.
If the EGR system appears to be working right, the throttle body probably needs to be removed, and the EGR ports cleaned out.
If the EGR works right the problem could be with the DPFE.