ok truck runs and rives great but i get a cylinder missfire from several cylinders, my mechanic has checked them and the coil packs are new and new plugs, he says he thinks it might be a short in the wiring, is there a way to track down this problem, truck is 01 f250 superduty SCSB 4x4.

 

Are the cylinders next to each other? On the same side? Does it miss at idle but not on the highway? A vacuum leak could kill 2 cyls at idle possibly. I need to know more pls..


Dick

 

It's ok when over 2k rpm but has some hesitation at 50 mph till it reaches 70 but also has an odd idle, and I was receiving p0304 code was also receiving code for cylinder 8 missfire

 

First, P0304 means cylinder 4 misfire, and likewise the cylinder 8 code was likely P0308. Cylinders 8 and 4 are right next to each other in the firing order, so the PCM could think both are misfiring even if it's only one of them.

I had a misfire develop on me last week on the way to work. Once I got there I was able to determine that it was cylinder 7 by unplugging each fuel injector one at a time while it was idling. When I got to number 7 the engine didn't run any worse, which meant that this particular cylinder wasn't firing.

I would recommend doing the same; this will tell you if any of your cylinders is consistently missing at idle. My guess is that it will be one of the ones that was indicated by the trouble codes.

 

great advice

 

A short in the wiring? What wiring? The 12V signal to fire the COP? Unless the wiring harness to the COPs is frayed or damaged, I would rule that out.

A misfire is caused by a lack of ignition spark, or by a fuel/air mixture that is not "close enough" to start combustion, or a mechanical issue in that cylinder. I would start my search for the problem by concentrating on a spark issue, since that is the cause of most misfires.

First, do not make the mistake of assuming that a "new" part is a good part. All parts should be suspect. Pick a misfiring cylinder. In this example, we will use #4. Take the plug, COP and boot out of 4. Swap the spark plug with #3. Swap the COP with #2. Swap the boot with #5. Run the engine and see where the miss moved. It will follow the bad part.

If the miss does not move after moving the parts, then you can suspect either a wiring issue or a mechanical issue (such as a vacuum leak or a bad injector).

 

How do I track a vacuum leak