1998 Ford F150 - 4.2L P0306 Misfire

[Mike W]

I have a 1998 Ford F150 4.2L V-6 Automatic that has a hard misfire (like a plugwire breaking down). With Genisys scanner comes up with 7 codes but most prevelent is the #6 cyl misfire P0306 and have swapped wires from 5 to 6 and replace coil pack. no change. Checked Identifix, of 34 posts -30 of which are EGR passage plugged have not found anything to help. Have tried the plug the EGR vacuum supply test, and it should show difference but to no avail. We did find a hole in the PCV hose elbow and plugged that but it didn't improve the running condition. Is there a fuel mixture memory that we need to reset the is componsating for old vacuum leak. Any help on this would be greatly appreciated.
Andy Coburn
Service Manager
CFS Auto and Truck Repair

[AndyC4G]

The other codes this had were P0136 O2 sensor Bank1 sensor 2
P0171 System too lean bank 1
Po174 Sytem too lean bank 2
P0303 Cylinder 3 Misfire
P1131 Lack of heated 02 sensor switch bank 1 sensor1
P1151 Heated O2 bank 2 sensr 1 switch point indicates lean
P1506 Idle air control overspeed malfunction.
Checked all wiring connectons at all the 02 sensors and checked TPS, MAF, CPS & CRPS also. Thanks in advance
Andy

[protraxrptr17]

Have you run a leakdown test yet? Had a 3.0 Ranger give me fits because I was overlooking the simple stuff. Had leaky valves. They were recessed badly. Another shop in town had supposedly reworked the heads 6 months prior. Found this out later. May not have anything to do with the other codes but may help you if the customer doesn't want to spend the money to fix the mechanical engine problems first.

[steven kiser]

the egr runners may be the issue. i've had a few where i had to take intake off and clear the egr port. they all were dead skip issues. check compression first just to be sure and if this is good i'd bet lunch when you yank off the intake you'll find a piece of carbon in the port. some of these that have been brought to me already had a major tune up and a couple had the major tune and injectors. all were the egr. on all of the ones that were brought to me that had been to other shops i boxed up all the parts that were installed prior and installed quality ones. we all know that since we were the last to work on it no matter what fails it's coming back to us. really, check basics then yank the intake. the first one i did i couldn't believe that the plugged port would cause the issue. the biggest tip is a fairly smooth idle but the dead skip comes just off idle under a load.

[ricmorin]

You have lean codes and an IAC code that all point to a vacuum leak. So this is likely a lean misfire. Check fuel trims at idle and at cruise after repairing anything you've found so far. I'm willing to bet that it is still lean. Check the Baro pid too. Contaminated MAF's can cause this condition. PID should be around 159 at sea level. MAF's can be cleaned but better replaced. You may have to smoke it if the Baro is good.

[steven kiser]

if we wait long enough the cat's will plug.