Hello all, I'm new to the forum, I have an '08 F250 FX4 w/ a 6.8 V10, over 150,000 miles on it now.

It's getting the usual age related issues.

First off, a couple of guys on here mentioned they were having one problem similar to mine and I ended up finding a loose spark plug and solved one problem.

So, that leaves me with another problem that has me and everybody else I've talked to stumped.

Between 65 and 75mph and 3500 or so RPM, I get a flashing check engine light, which normally clears after a few seconds or occasionally goes to a steady check engine light that eventually clears itself if I don't get the engine in that range again.

I've pulled the codes a couple of times, using my generic scanner (Ease) and I had the local dealership pull it with their tool and I get a 0300 (random misfire) and nothing else. The guy at the dealer said there wasn't any freeze frame data either.

So, I've done some troubleshooting with it to try and figure out what might be going on.

When I get the flashing light, I don't feel or hear anything that's remotely like a misfire, there is no stumble, no lag, nothing, the only thing I've consistently noticed is what sounds like detonation just before the light starts flashing.

So, here's the weird part. I can drive at WOT, up to 4500 right through 3500 rpm and no light. I can go through 65 mph at around 2500 - 300 rpm and no light.

It only happens around 3500 rpm at maybe 3/4 throttle and 65 - 75mph and I only hear the noise that sounds like detonation right before the light starts flashing.

I thought maybe the loose spark plug might have been the cause (and I had the plugs changed about 6 months ago, so I know they're good). I changed the fuel filter and ran a bunch of injector cleaner through it and no change.

The only other thing I can think of is that the truck had been sitting for about 2 months while I was deployed and the problem started about 2 weeks after I got back (and I was driving the truck for the two weeks with no problems).

So, if anybody has any ideas, I'd greatly appreciate them.

Thanks.

 

sounds like a cracked/weak spark plug coil...

to high of rpm for a vacuum leak.
fuel pump not likely. to rpm limited.

other stuff would trigger a code.

 

When was the last time the boots were changed?
Denso 671-0001 boots (Rock Auto - $30/set of 10) work well.
I change the boots and plugs at 50k.
Our 2003 Exped has the OEM coils with 175k.
Here's an article on testing for a P0300 -
https://www.obd-codes.com/p0300

 

What are your short and long term fuel trim numbers when driving down the road?

 

Chuck - it doesn't feel like a coil, I had another car lose a coil while I was driving and this is nothing like it, the engine doesn't hiccup, stumble or anything. And every time I pull the code, it's showing up as a random misfire, it's not showing a specific cylinder. Since I tightened up the one spark plug, off-idle response is good and power is good and consistent, so I agree on the vacuum.

R&T Babich, boots were changed with the plugs, so about 6 months or so ago and they all looked good when I was checking for the loose plug.

redford, haven't run it with the scanner on it yet, I also need to see if the version of Ease I'm using will show my the trims (I'm using a generic version, so it doesn't show everything).

Thanks guys

 

Just throwing this out there since you are at a loss trying to fix your issue. I had a similar issue with my 97 escort that turned out to be an intermittently, only briefly stuck lash adjuster. My problem mostly happened at low rpm, but I can see how the sound in made could be mistaken for detonation. I fixed it with some cheap motor flush and an oil additive. (It's a POS get me to work car)

I know it may be far fetched, and that the engines aren't the same, but thought I would mention it.

 

If I was there, I would connect my cheap $6 Bluetooth dongle to Torque Pro (@ $5) and watch live misfire counts while you drive it.

It is showing or showed a P0300 code.
It IS a misfire.
That may not be THE problem but it is A problem.
https://www.ford-trucks.com/forums/5...t-come-on.html

A V10 does not sound or feel quite the same as a V8. A very slight misfire may not even be felt or heard at all.

 

i know you said yours was the V10.. but you also mentioned the truck sat for awhile when you were deployed.. my grandfathers 5.4 had similar problem whenever it was under power.. shops were telling him it was plugs or the COP.. problem was actually a result from the truck sitting so much. when my uncle got a hold of the truck he found some site that mentioned problems of the catalytic converters and O2 sensors getting found if not driven frequently or long enough distances. he drove it around for a couple months since he works quite a ways from where he lived and problem went away.. hasnt had the miss since.. i know the problem can be annoying to drive through but may work for you as well..