2001 6.8 Misfire
 

Ok i'll preface this buy saying I've posted alot of this over the last year on the Excursion facebook group, but now im gonna post here to see if i can get some more helpful info. I will try and simplify the entire story real quick to bring it up to date.


Truck ran great from the day I bought it and for about a yr or so after. Suddenly got a misfire and a code to go along with it. Ended up buying coils and plugs. Changed the coils first, Misfire went away. Drove the truck with zero issues for about a month and developed another miss. this time with no code. Swapped the plugs, still a misfire. Doesnt seem to miss in Park at idle or revving, only seems to happen in gear and its also intermittent. Fast forward to now, I buy a scanner and a FORScan license. I get into mode6 and run the tests. Not a single cylinder is showing a miss and not a single injector is showing a fault. Yet it is still misfiring. Pull the gauge page up and it shows no misfire being recognized by sensors yet it is counting misfires as they happen. Im pulling my hair out here. I had a bunch of Ford techs that almost guaranteed mode6 would reveal the issue. It has not. Does anybody have any other ideas for a seemingly intermittent misfire? Vacuum leak? Intake gasket? PCM? I need help as I am at a brick wall with this thing.

Any help is truly appreciated.

Moved to the V10 forum for you

The first thing I gotta ask - Is it really misfiring? Could it be the torque converter lockup clutch slipping?

Can you explain this a bit more: "Pull the gauge page up and it shows no misfire being recognized by sensors yet it is counting misfires as they happen"

Random misfires? Random misfires can be counted but not individual cylinders.

What do the fuel trims look like? Pegged all the way one way? Or somewhere in the middle?

Cleaned the MAF yet? And yes, a vacuum leak can cause a random misfire.

Also, gotta ask, does it say OBD-II on a sticker under the hood? If it's not OBD-II, it won't throw codes for certain things like misfires.

(Side note: Facebook groups are definitely not the way to diagnose things. I belong to a couple, and the jokesters on there are a huge pain)

https://cimg3.ibsrv.net/gimg/www.for...078025cdd6.jpg
As you can see here, no misfires detected
https://cimg7.ibsrv.net/gimg/www.for...a59d7f061c.jpg
No injector faults, no misfire detected yet NM or number of misfires was constantly raising as the truck was running.

This article goes into some interesting stuff about the difference between Type A (catalyst damaging misfires) and Type B. https://www.motor.com/magazine-summa...y-august-2018/

Maybe that's the difference?

I only use torque pro, cause I'm cheap and it's free.

Torque pro shows misfire counts on each cylinder......somehow.

What brand of coils did you put in?
Coils can be ok when at idle or when cool but react poorly when they heat up and have to fire faster.

Also check coil and injector clips to make sure none are broken and have poor or bad connections.

Pull injector plugs off one at a time and listen for a misfire. I'm suspecting a poor preforming injector or two.

This would be my approach too---especially the question what brand COP's were used. Were new boots part of that swap?

And we can't discount the transmission issue either regardless what's been experienced in the past---if you're able able to isolate a suspected misfire to something electrical it might be time to look at other parts of the drivetrain.

IMHO anyway. :)

First set of coils were cheap, but a name i recognized. I cant recall at the moment. They did come with new boots as well. Ive checked over all the clips and wiring for the injectors as well. I get that cheap coils can be ok at idle but not when they heat up, but that doesnt explain the 1000 or so miles i put on it after i put those coils in that it ran perfectly normal. I do have another set of brand new Denso coils that i have yet to install. In the code section of the FORScan the codes for the OSS and VSS are coming up. Now ive changed the OSS once before. I believe these are coming up due to improper drive cycles from me not driving it and having the battery disconnected for 3 months. Im just tired of throwing money at this thing and getting no closer to anything. Its hard to isolate as its random and seems to be diff cylinders all the time. But i'd hate to gamble at a new PCM just to get one and have the issue still be there. People have mentioned vacuum, but ive never heard of a vacuum leak fixing itself for a month lol This is one of the hardest diagnosis' i have ever been a part of in my 12 yrs of being a tech and all my garage wrenching since those yrs.

You're getting OSS and VSS DTCs?

That can be related to two things: Bad alternator causing a lot of "noise" in the battery voltage, OR - a COP arcing to ground, or not arcing at all, causing feedback into the electrical system.

Get a digital volt meter, set it to AC volts, and right at the battery, or better yet, at the cigarette lighter/power-point, check the voltage with the engine running, and report back.

Seriously, over the years, quite a few people reported OSS and VSS codes and it turned out to be an alternator with a bad diode or two causing noise on the battery voltage, or a COP arcing basically causing the same type of "noise".

That's completely believable because as I understand those sensors are inductive devices--a failed alternator would indeed inject errant currents into the entire electrical that might confuse such sensors. They could be "seeing" something similar to a bad signal generated due a failing sensor or tone ring.

We've had a few people here report they were getting misfires, and OSS/VSS codes, and fixing the misfire cured the other issues. And I'm pretty sure at least one person reported an alternator problem with OSS/VSS codes, so ... it's worth a shot investigating.

I gotta see if I can locate my multimeter. I will report back as soon as I find it or go buy one lol

13.7v while running in park, 13.4v while running in gear. Thats from a 12v source in the cab. Alternator reads 13.9v. Also the o/d light is blinking now. Lovely.

Set your meter to AC and check right at the alternator, ground to case and test big output wire.
If you get an AC reading, it is a sine of a failing alternator.

Now that's downright clever! :-X22 :-X22