Hi folks,
I have a 2002 F-150 Supercrew with a 5.4L Triton and she has 94350 miles. Never had a problem until a couple of months ago. The truck acted as is the transmission was slipping, but it wasn't a trans problem. I took it to my mechanic, and he said he could not get any codes to show up even though he felt the lag when he would make a turn, go up a hill, etc. He said it might be the catalytic converter going bad, but wasn't sure. He changed out a vacuum line and it ran much better. He also said if the cat was going out, it would be easier to tell when it finally just laid down and died. The truck ran fine until about 2 weeks ago. I was traveling down the freeway, and it started running "washboard" rough. Felt like I was going down a bad gravel road, then suddenly the SES light came on. It would burn steady, then flash for a few minutes, then back to steady. I took it to my mechanic again. He put it on the computer and got a reading that the number 6 coil pak did not even exist. After a few more tests he ordered a new computer module. When the computer came in, he drove the truck to the Ford dealership (where he used to work) to get the computer programmed. The truck ran perfectly without a single miss. He did not put the new computer in. He put the truck back on the diagnostic computer again, no errors. He even pulled hoses, etc, trying to get an error and never did get one. He told me that he had absolutely no idea what was wrong with the truck. I got in to drive it home, and a few miles down the road, it started the "missing" again. No SES, but it still is running rough. I can't take it back to him because he is retiring at the end of this month. My next stop will be the Ford dealership, but I know it will be big $$$. Does anyone have any idea what could be wrong. I have trusted this mechanic for years because he worked on all our fire trucks and ambulances, and I know very little about vehicles. Appreciate any advice or solutions.

 

Even though he is retiring, he shoukd try tio make it right before he does. He should take it back to his old dealer for help or refund you money since he didn't fix it. Sounds like the new PCM is bad or you have a problem with your wiring harness and/or plug at the PCM.

 

Well, the good thing is he didn't charge me either time. He said that he gets paid to fix it, not just check it. So I wasn't out any money. But I still have the frustration. Thanks for the info. I'll get those things checked out.

 

If you are experiencing a light throttle miss in OD, chances are that there is one bad coil.
This peticular fault does not set a code because it is intemittant and load sensitive.
Have the tech stress test all the coils looking for one with low output.
Good luck.

 

Appreciate it. I'll tell him.

 

It may just need new coil boots. They can cause arcing if they get hard and brittle.

 

We have looked at them and they appear to be in good shape. What is throwing us off is the fact that the SES light won't come on, even when my tech unplugs things that should make the light come on. The light comes on when you turn on the truck, but while it is missing so bad, no light appears.

 

Ford doesn't use misfire counts to set DTCs the way other manufacturers do. Why? You have to ask them. Misfires are one of the few CONTINUOUS Monitors for most manufacturers whereas other systems in the vehicle only get tested once in a while(NON CONTINUOUS Monitors). Misfires are important because they can cause so many problems and can be caused by a lot of different things. If #6 got lost why didn't you look closers at #6 rather than replace the ECM. If the ECM was bad it couldn't tell you that #6 went bye-bye. As far as the cats. You should do an Exhaust Gas Backpressure Test. If the Cat is blocked(bad, shot, defective) it will INCREASE backpressure and the vehicle will run like it is having an asthma attack. You do the test at the pre and post cat sensor bungs. 1.5 is max on pre cat. If it goes up at post cat you have a partial blockage. If it is 0 at post cat you are completely blocked(DEAD). The pressure has to get out somewhere and if it can't go out the exhaust where else can it go? That's right it goes back out the INTAKE of another nearby cylinder. Not good at all.

 

I don't know what the other mfgers do but on these motors designs, Ford actually measures crank rotation time, compares it to a 'running' average that can also account for wear and updates over time.
When there is an absolute failure and it last for a predetermined amount of revolutions a code is set and a lamp lighted.
All the ways a cylinder can go down is therefore handled by this method because the contributuion to the total of 8 cylinders to the crank revolution time can be detected.
The only exception to this is a temporary missfire such as when the motor is running in OD at light throttle. If a coil developes low output such that it cannot fire extreme lean mixtures when the EGR is called, then you feel the missfire.
But as soon as you apply more throttle and the mix goes back to more normal rich, the coil can again fire it so the miss goes away and the record in software is canelled.
They didnt catch up with this one as far as it setting a code or a lamp.
Just something that has to be learned by experience.

 

I'll pass this info along to the mechanic. The ECM was NOT replaced. When the mechanic was taking it to get programmed, he had to put the old one back in to drive it to the dealer. It was during this drive that the engine ran as if nothing were wrong at all. The only thing that has been replaced is the #6 coil. And the truck doesn't run any better at 75 than when it does at 25. Doesn't make any difference with speed nor if OD is off or on.

 

Ford has a lot of COP failures. This case is just one example of it happening with no DTC going set. The manufacturers establish their own criteria of when they want to set a DTC and illuminate the MIL, but why should you have to wait for an "absolute failure" for the MIL to lite? Better to set the DTC early on rather than waiting for major driveability issues to develop. In this case the owner knew he had a problem, but the DTC was never set. What sense does that make? You might be able to detect the problem with Mode 6, but the customer doesn't come into the shop to have Mode 6 data scanned. You only see them when the SES lite is "ON" or he has driveability issues.

 

Usually seems that when one coil fails, others will soon follow because they are the same age and from the same lot number. Just hard to tell which one without the CEL.
Driving it with a good data logger may catch the culprit.

 

Thanks for the information. I am taking it to another mechanic tomorrow who is going to change the plugs and check the coil paks. I'm hoping it is something as simple as that.