Experiencing intermittent misfire in my 2002 F-150, 5.4L V-8. No engine check light on, but acts like a bad coil pack. Was told by my mechanic that on Fords, unless the engine check light is on, it's difficult to narrow down which is defective. Is this true?

 

True.

How many miles on the spark plugs and what brand are they?

 

Probably about 50,000 on the plugs. Not sure of the brand, since I didn't install them.

 

No, it's not true.

If it's misfiring, all you have to do is use a scan tool to look at the misfire counts in the PC's memory. Mode $06, TID $53 for an 02.

An Android smartphone, a $20 BT OBDII adapter, and a $5 app will get you into the ballpark.

 

I've had that before. No CEL. But it was obviously misfiring. A scan tool will tell you which cylinder. If you don't have one, you can go to any auto parts place and have it scanned for free. If the misfire is bad enough that you don't want to drive it there, you can sometimes find it by unplugging each fuel injector and listening for a change in engine running. When the engine doesn't change, the cylinder to which you unplugged the injector is the one with the misfire. You can swap coil packs and check if misfire moves with it. If so, it's the coil pack. If not, it could be in the wiring harness (what happened to me). If you do decide to drive it somewhere with a bad misfire (i.e. totally non-functional ignition), you might want to unplug that injector and run it as a V7. Otherwise, the un-burnt fuel could wash the rings out. Finally, a Ford dealer has a much more sophisticated scan tool, which can isolate a misfire more thoroughly than an aftermarket one. I ended up having them repair a fault in my ignition wiring harness, after a new coil pack didn't solve my problem.

 

Thanks very much. I do have a basic Innova OB2D code reader (Model 3030F). Would this work for narrowing down the misfires?

 

Yes. It will give you the code number. But you'll have to look up what the code means, either in a service manual or online. I don't know if that reader will tell you which cylinder. But why not try it and see?

 

There may not be any codes if the CEL never came on. That's why you would need an advanced scan tool.

 

When I had a misfire (2002 5.4L), there was no CEL. A simple scan tool showed a misfire code had been set, but didn't specify which cylinder. It took about 10 minutes to figure out which one, by unplugging injectors.

 

Then there was a code stored in the KAM. It may have been blinking and you just didnt see it. That is not the case for everyone. It never hurts to scan it just in case it is there though. But, most of the time, if the CEL is not on, you will find nothing. Your must have been a P0300, random misfire if it did not specify a cylinder.


Typically a low grade misfire will show up near the OD shift around 45mph. Or under load. So, if you can... find that sweet spot where it is misfiring the most noticeable and hold it there as long as you can. It took me about 2 days of driving like that for mine to finally trip the CEL and show a code for which cylinder it was.

 

Thanks again for all the helpful suggestions. Will plug in the code reader and see what's what...

 

Here's the code reading: Odtc

 

That means no stored codes.

 

So, in other words, no detected problems from the code reader?

 

IOW, you need a more advanced scan tool. Go back and read post #4. I specifically told you what needs to be checked when there's no MIL or DTC.