6.4L with a hiccup misfire

[integritymechanicsbydavid]

Posted on a different forum and no one answered. I’ve got an 08 F250 with a 6.4L. Cold start just started a slight random misfire that I can’t pin down to a cylinder. I replaced all the injectors because I had 4 out of spec. I replaced the crank and cam sensor. No luck. After the engine reached optimal temp the misfire is gone.
I’ve ran live data and watched the fuel trim and I’ve done power balance and shut each cylinder off one at a time and the misfire never stopped no matter which cylinder injector was deactivated. I’m at my wits end and really could some help here.
The truck is deleted and tuned. The heads are studded. Under the valve covers looks brand new. Oil is fresh. New lift pump. New injectors.
Thanks for any help.

 

[6.0 Tech]

Could be the frp sensor, we’ve fought it on our 6.4 test truck. It gets a rolling miss at idle seems to go thru the firing order and then start over again. It will clean up for ten seconds or so randomly, and then start again. Changing the frp made it much better, but there is still something in the tune that does it as well. We’ve got twin pumps and 100s in that truck.


Sent from my iPhone using Tapatalk

 

[integritymechanicsbydavid]

Could be the frp sensor, we’ve fought it on our 6.4 test truck. It gets a rolling miss at idle seems to go thru the firing order and then start over again. It will clean up for ten seconds or so randomly, and then start again. Changing the frp made it much better, but there is still something in the tune that does it as well. We’ve got twin pumps and 100s in that truck.


Sent from my iPhone using Tapatalk

Heard something new today. Cold start and tiny bump bump noise coming from intake box. I’m starting to lean towards a sticky valve. Gonna take the valve covers off Sunday and look at rockers and bridges then do a compression test on all cylinders. While I’m there I’m replacing both injector harnesses. Might as well replace the pressure sensor. I’ll also be adding 60oz Hot Shots Secret Stiction Eliminator. The heads were done 60,000 miles ago and still look new. I’m not going to be happy if it’s a failure.

 

[integritymechanicsbydavid]

Could be the frp sensor, we’ve fought it on our 6.4 test truck. It gets a rolling miss at idle seems to go thru the firing order and then start over again. It will clean up for ten seconds or so randomly, and then start again. Changing the frp made it much better, but there is still something in the tune that does it as well. We’ve got twin pumps and 100s in that truck.


Sent from my iPhone using Tapatalk

Heard something new today. Cold start and tiny bump bump noise coming from intake box. I’m starting to lean towards a sticky valve. Gonna take the valve covers off Sunday and look at rockers and bridges then do a compression test on all cylinders. While I’m there I’m replacing both injector harnesses. Might as well replace the pressure sensor. I’ll also be adding 60oz Hot shots secret stiction eliminator.

 

[DEEZUZ]

You've got cam/lifter failure, imo.

Cut open oil filter... Should be a disco ball

 

[integritymechanicsbydavid]

I did. No metal. Did an oil change when I replaced my injectors. Filter was dirty but no metal. Magnetic oil drain plug had very small amount of micro shavings. I’m compression testing it Sunday because I’m replacing the injector harnesses. Also going to measure rocket arm travel to hopefully rule out your suggestion. Honestly it sounds like a sticky valve. If it’s a cam or lifter I’ll buy a Choate.

 

[DEEZUZ]

You cut the top/bottom off filter and spread it out? Let it dry over night. I'm suspecting flat spot on a roller.

 

[integritymechanicsbydavid]

I’ll let you know tomorrow what I find after compression test.

 

[DEEZUZ]

In for #2 being lower than the others #typical6.4things

 

[integritymechanicsbydavid]

I feel like it’s #7. This is a rebuilt “bulletproofed” engine. I scoped cylinders 1,3,5,7 when I replaced the injectors. The pistons looked good but prior to replacing the injectors, #7 was dipping out on power balance. After the injector replacement #7 was still dipping out.
Someone told me that the wiring harness can go bad and present a misfire type issue and then go away when warm. As if the wiring harness when hot conducts electricity better.
I’m replacing the harnesses tomorrow anyways but really hoping there’s no mechanical issue found.

 

[integritymechanicsbydavid]

 

[integritymechanicsbydavid]

Compression test came back 345 to 350 every cylinder. No sticking valves, no broken bridges, no missing rocker balls. I recently replaced my crank sensor and after thinking about when my issue started, it started after I replaced my crank sensor. I bought one from Auto Zone. It’s a Duralast. It’s probably junk. I’m going to order a OEM replacement and see what happens.

 

[integritymechanicsbydavid]

Found Ford OEM on eBay for $40. Won’t be here till next week. I’ll keep everyone posted.

 

[integritymechanicsbydavid]

Found Ford OEM on eBay for $40. Won’t be here till next week. I’ll keep everyone posted.

My problem is a bad engine harness. I opened it up and found all my injectors wires and my fuel rail pressure sensor wires have been soldered. Looks like previous owner had the injector pigtails replaced. With my engine running I could touch the harness and cause misfires. I ordered a new harness directly from Ford and will be replacing this coming up Sunday.

 

[Powerstroke Cowboy]

Good for you. Sounds like you found the problem.

 

[integritymechanicsbydavid]

So,

I bought a better compression tester and got 410psi per cylinder. The wiring harness didn’t fix issues. What did fix the cylinder 7 misfire was a trip to SC doing 70mph at roughly 2,000rpm with Hot Shots in it. My lifter wasn’t compressing periodically during cold engine temps which was causing cylinder 7 to blow air through the intake valves ever so slightly. The long highway run has stopped this. But!, I’m going to lift off the cab and pull the motor and rebuild the valve train with a stage 2 cam and lifter and high rev spring set. Got an oil leak anyways that can’t be fixed unless the engine is pulled.