I have a 98 f-150 which has been acting up the last couple weeks. Always seems to happen while hwy driving not around town. Truck begins serious hesitation, check engine light comes on. I will pull over turn engine off and restart, truck runs better. The code says truck miss firing on cyclinders 1 and 6. The local ford gargage as replaced the coil pack and two oxygen sensors and also found a wire that had worn thru. Problem still exist. A different mechanic suggest disconnecting erg (egr) don't remember correct term. We did, truck seemed to run smoother but still acts up. Anybody have a clue.

 

What engine? 4.2L?

 

Yes its a 4.2

 

I'd change the plugs and go from there. In my opinion, if a shop replaces some components and still doesn't fix the problem, I would not go back. It is very easy to troubleshoot the ignition system without REPLACING EVERYTHING. If your O2 sensor is bad, normally the computer would give you a code for bad 02 sensor. THIS WOULD NOT CAUSE A MISFIRE!!!!!!!!! This would cause a slightly incorrect mixture for the current conditions, but it would affect all cylinders equally. Try some fuel injector cleaner and see if that works. You pour a bottle of the stuff in your tank when you fill up, and it will clean the injectors.

I don't mean to sound dogmatic, but if a shop can't troubleshoot a problem without having you replace half the ignition components, they probably shouldn't be fixing cars.

 

Crazy, I'm in no way mechcanic but it seems to me that if you turn the engine off and the skipping stops my problem might be something a little complicated. If it were plugs and wires wouldn't hesitate all the time, and I understand that cyclinders 1and 6 misfiring at the same time is not common. I do agree that the shop is lacking but the mechanic that usually helps me suggest a ford garage thinking they only work on ford product they would find the problem before he would and suggest I stick with them till the end. Thanks for the reply

 

Normally, yes, a spark plug problem would be continuous regardless as to if you restart the engine or not.

Here's my best guess:

As you drive your truck, the PCM constantly makes changes and corrections to ignition timing, the timing of the fuel injection, fuel mixture, etc. On most vehicles when you start the vehicle up, it uses factory set defaults. Then, as the PCM gathers information, it makes corrections based on that information.

So, when you restart and it runs fine, it is more than likely running off of factory set defaults. As it gets information from the sensors, it's trying to correct itself and is ending up causing a misfire. If the problem is only with cylinders 1 and 6, there may be a problem with the ignition timing or fuel injection that does not occur when the PCM is running on factory defaults. This could be maybe a problem with the injectors themselves, but more likely a problem with one of the sensors that tells the PCM what is happening. Maybe a crank sensor?

I'd try running some fuel injector cleaner through on your next fill-up and see if there's any improvement, and if that doesn't work, I would guess it's a timing issue.

I'm sorry I couldn't be more helpful!

 

Crazy, I will note your last response and pass it along to the garage. Thanks for your help

 

Great, let me know how it works out!

 

The mechanic that suggested disconnecting the EGR (exhaust gas recirculation) valve was trying to determine if the ports were stopped up. The 4.2L uses runners in the lower intake with individual discharge ports at each intake runner to inject the exhaust gases, and these ports can clog causing EGR flow to the unclogged ports only, this can lead to an overly lean condition on the unclogged ones and may cause a fuel mixture so diluted they don't fire correctly. If running without EGR connected helps your passages may indeed be clogged. Hope this helps narrow down the problem, but keep in mind as Crazy001 said, the computer is going to "see" the EGR isn't working at all and adjust to compensate rather quickly.

 

fordtech1 thats excatly what my mechanic friend explained to me concerning the egr. Unfortunately this didn't seem to be the problem either, truck acted up three times in about an 80 mile trip. Thanks to you and crazy for taking the time to respond. Truck is currently in garage and last time talked to them they were still trying to figure it out, leaning towards them computer or a wire that leads from the coil to the computer I believe.