After searching around I have a problem similar to this thread...https://www.f150online.com/forums/v8...-no-codes.html

I tried forcing the code via jbrew suggestion about WOT but no dice. I had a logger on it and was watching the misfire counts. and can't help but wonder how many misfires is needed to force a code or CEL? I was hoping I could just go right to the cylinder misfiring and replace the COP for an educated guess at a fix. Now I got to look at every one of them. and last time I tried changing plugs it took 3 hours and I had to remove the fuel rail Not looking forward to that again. I don't pretend to know a lot about engine parameters so I'm looking at data labeled as:

MISCNTL (Low Counter of Cumulative Misfires (Unitless) -Hit 1705 by the time I got home (about half hour drive)
MISCNTH (High Counter of Cumulative Misfires (Unitless) - Stayed at 0 Anyone know what the difference of low and high counters are?

 

Short version,-

Calculated from a percentage.

Misfires are counted over a continuous 200(A) and 1000(B) revolution period.

Type A - Catalyst Damaging misfire threshold (software table) is an rpm/load table varying from 40% misfire rate at Idle to 4% at high rpm and loads.

Type B - Threshold rate is 2% to 4%.

Don't hold @ WOT necessarily. You hold @ misfire point to increase count.

 

Well here's where I'm at so far (supper time). I'm inclined to replace that number 6 and see what happens before I get em all out. resistance matches on all of them but I didn't expect that to be off considering it's intermittant (load related).

 

If you can check the individual cylinder's miscount values, you can identify the problem cylinder(s).

Understanding the H and L suffixes requires a bit of understanding of digital math. Most likely, each value is a 16 bit binary value held in one register. When the low order word rolls over from it's maximum value, probably 65535 to zero, the high order word then increments by one. This permits a total accumulated count of 2 to the 32nd power counts before both words roll back over to zero.

Resistance checks of mildly misfiring COPS is a waste of time.

 

Unfortunately I couldn't find the individual counts. I'm using http://www.obd-2.com stuff. But I suspected the counts worked the way you describe. But when the low counter rolled past 255 and didn't set the high up 1, I didn't know what the high was for. I did see the Total Cylinder events did reset around 65K. I would have to take a really long trip to get a count of 1 on the high side for misfires cause the counts reset when starting the truck again.

So jbrew... does that (Type B) translate to 20 to 40 counts per minute at 1000 rpm?

It's hard to hold at misfire cause it's so violent, it feels like you damaging something. Will try it though if I don't find anything tonight with the coils.

 

Percentage is used because revolution count is ever changing above idle.

As projectSHO89 posts above, you can compare cylinder miscount values with the correct scanner. Mode 6/ for cylinder history.

 

You could be. Well, it's like this, -when they miss, unburned fuel and air mixture is pumped by the exhaust stoke into the catalyst, where it washes over the advanced coating on the catalyst honeycomb.
The next blast of hot gas then ignites the mixture, driving up the catalyst temperature by as much as 1500 degrees Fahrenheit (800 C/1472 F documented) and causing a marked deterioration in the catalyst, so that severe catalyst damage can occur very quickly.
With a low grade misfire, you can get away with pushing for a DTC in that way because it's not spitting as much fuel over the catalyst. BUT! -That fuel can add up pushing for a DTC over and over again.

Yea, just be aware of that.

 

Could just purchase a set of Visteon/Motorcraft coils and be done with it. Since they can be had cheaply now. 180 for a set on ebay I believe. So far, 0 short term failure/0 DOA out of the box. I haven't heard anything derogatory about THESE particular sets so far.

 

Shoot, slipped my mind, - Also note, the Misfire Monitor is disabled at a high rate of change with torque (flooring, accelerator hard or lifting off suddenly). As well as closed throttle deceleration, (negative torque).

Keep that in mind when going for a DTC. Usually they won't miss when you floor it anyway. Unless you have a dead hole. I realize , I use to suggest giving it hell, but that's not totally correct.... Not that kind of hell anyway lol.

 

Well, guess I'm gonna call it a night. Couldn't get number 7 and 4 out tonight. figured I just quit before I break something. #4's plug boot got stuck and I can't figure out out to get at that #7 under the FPR.

I had replaced all coils (with ones recommended from here on ebay I think) about 3 years ago as well as a bunch of other stuff looking for a CEL lean problem. Doesn't mean I won't do it again, but at this point I'm leaning toward a loose plug on 3 and 6. 3 was finger tight at best and I think 6 was actually backed out a bit (1/16) turn maybe. and the plug insulaters show signs of combustion getting by.

 

You have to torque the plugs to 28 ft/lb or they will loosen and blow out!

The Ebay coils that we were recommending 3 years ago have not had a very good track record - hence the current recommendation for Visteons.

 

Bummer! As I just found out.

Took all coils and plugs out. Put it all back together in this scorching heat only to find out that the problem was still there. But when I put it back together I switched coils around that I thought might be a problem based on how they look (I know not very scientific). Took her for a drive. Fail! Still intermittent miss. So I set the throttle on an up hill that gave a constant miss and bingo the CEL started flashing. (That takes a lot of missing to get that dang code) Got home and got the code out. P301. Cool That was the one I thought was bad (visually) and switched over to #1 for easy access. About 3 minutes later (including getting tools out and putting them away) and using an old OEM coil...I was off for another test run. Tada. It worked. Wish it would have just given me a P306 code days ago.... would have saved me a pile of time.

 

You were lucky. Yea, it is a PITA. To bad we can't adjust the misfire monitor.