Hello, I’ve not visited in some time. I’ve got a problem with my little truck. It’s an 02, 4.0L with about 110K miles. A while back I got a check engine light so I had it checked at the local auto parts store and they said it was the heated o2 sensor so after some time, the engine started idling a little rough almost like it was pulsing or surging. So I finely got around to replacing it as a matter of fact while I was at it I replaced the two before the catalytic converter and ordered a Actron reader and reset the computor. Anyway, It’s still surging and running rough at idle. The codes I’m getting is P0171- bank 1 too lean, P0174- bank 2 too lean, P0300- random multiple misfire, P0301- #1 cylinder misfire, P0302- #2 cylinder misfire, P0303- #3 cylinder misfire. I picked up some crc maf sensor cleaner and throttle body cleaner and did that bit put some injector cleaner in the tank with some high test gas just to kind of rule out the simple stuff. Sure could use some help figuring this out??? Anyone know what’s going on with this??????????? Oh is it possible that a very small exhaust leak could cause this and maybe make the o2 sensors read something odd. I don’t really know much about all the newer electronics give me the old simple stuff I can get to and work on.

 

You've been busy on this one. In short yes an exhaust leak can let air in & confuse the O2 sensors, but it's not likely to cause the cyl 1-2-3 misfires you've posted.

Seeing as how you have more than 100K miles on this puppy, it was probably a good idea to replace the upstream O2 sensors.

It's also time for the PCV valve to be replaced & it's rubber hose is known to crack & leak vacuum, so put that puppy on your suspect list.

On the mileage & misfire, the plugs & wires are due for replacement. Have you ever replaced the spark plugs & wires, or checked the plug gap????
The specified Motorcraft finewire plugs & wires are recommended for our waste spark ignition system. If your using other than double platinum or newer finewire iridium center electrode plugs, be sure to check the plug gap, as non platinum, or single platinum plugs spark gap will erode & open up fast on the waste spark system. Be sure to check the plug wires end to end resistance, as you wiggle them.

If all that checks out ok, raise the hood after dark & look for arcs & sparks in the secondary ignition, maybe use a spray bottle of 5% salt water from the coil pack to the plugs & see what happens.

If no joy, the coilpack is known to crack underneath & arc to ground unseen, so pull, raise & ground probe it & see what happens. If you come to suspect it, most autoparts stores can bench check it for output.

Some problems have been reported on intake manafold gasket leaks, so if you come to suspect that, maybe rig & do a sniff test around that area with an unlit propane bottle, with a piece or tubing & a sports needle attached as a probe. Look for an increase in idle speed when the leak sucks the propane in. It's plastic, & O2 sensor safe to use. If you find an intake leak, maybe try retorquing the fastners to spec & see how it goes.

A bunch of thoughts for consideration, let us know how it goes.

 

i would look for an intake leak. get a can of carb cleaner and spray around the intake and see if the idle changes.

 

I have a the same problem with my 2003 3.0 ranger. I've cleaned the MAF,Throttle body,injectors,Cam shaft sensor,checked the intake with cab cleaner, and all vaccum lines for leaks,replaced air cleaner,plugs,wires,ran all kinds of injector cleaner even the BG44K. It only misses at idle and not at a higher rpm,has 95k miles runs good except for the idle sounds likes its searching back and forth..I have not replaced the fuel filter but you would think that if the filter was plugged it would miss all the time. and does the crankshaft sensnor have a half of a horseshoe magnet because mine does not go half way around only maybe a quarter way around. should I take it to a shop and have fuel pressure tested? What do you think? Thanks Pinger