Let me start out by saying that I am an Electrical Contractor. I do not even change my own oil, but I do know that there is nothing more dependable than my Ford F 250 Super Duty, and would'nt trade it for nothing.
Here's the back story. A couple of years ago, with about 177 K, it started running a bit rough so I had it in to get it checked. Long story short, I decided to replace the stock engine with a remfg. 5.4 Jasper engine. Total cost was just north of 5 grand.
A few months ago it started "missing" at about 40-45 mph running 1500 rpms. I took it back to get it looked at, and the computer shows no codes, and they say it has not "Missed" since the engine change.
They did tighten a spark plug, and tried changing out the coil packs one at a time. Still didn't smooth it out.
It got a bit worse, so I took it back, and this time they replaced a "mass air flow sensor " it did seem a bit better for a couple of days, but it is getting worse again.
Sitting still, at idle, it ( what I call a Miss) shimmys every few seconds, at excelleration it is sluggish but improves as speed comes up. Then at about 45 MPH & 1500 rpms, it runs " rough as a night in jail " almost jumping. It is not as noticible at interstate speeds, and punching the pedal still has that Ford get up & go.
If anyone can shed some light on this subject I would greatly appreciate it. I don't mind paying to have it repaired, but 2 different shops have failed to locate the trouble.

Thanks in advance. Chuck

 

Come On Guys, 47 views and not a single idea ? I'm desperate !

 

Per my experience lot of mechanics are still learning the automotive computers.
Don't know it that applies to your car, but the cars of last decade, while hooked up to expensive computers can show each cylinder performance, fuel to air mixture, spark advance and several things we can only dream to understand.
Find qualified mechanic

 

I agree, if you go to someone else I bet they can read for any codes/pending codes. They can also do a diagnostics on the above items.

years ago they had the technology oscilascopes that would should firing patterns ect.

I am thinking cam sensor issues.

 

Scott, great idea about the CMP sensor!

I would first think about why the PCM can't see a misfire, may have a bad crankshaft position sensor.

What year is your truck?

 

I don't have any experience with that engine, but in general, with something like that, I'd look at the O2 sensors and make sure they are reading correctly and check the EGR valve. Could also be a fuel injector that is getting a little plugged or even spark plugs that are wearing out.

Is the engine at a high load or low load when it's missing? Are you trying to accelerate from 40 while in OD, or are you just cruising a long real easy?

I'd ask to get a tech to ride in the truck with you, and have a scan tool hooked up that will show him what the O2 sensors are reading, the EGR valve is doing, injector duty cycle, fuel pressure, ETC. If the shop is confused by that request, you might be better at a different shop.

I'd stop letting them swap parts till they are sure it fixes it.

Engineers put a ton of effort into ECM diagnostic capabilities, it's a shame they get ignored by parts swappers.

 

I had the same problem with mine and replaced the coils and boots. Problem solved. What if you have 2 or 3 coils getting bad at the time. Changing coils one at a time proves nothing. I never had a CELs ever just a miss or stumble.

 

Have you changed the fuel filter? I've used Chemtool fuel system cleaner; it is supposed to remove/reduce crud and also clean the injectors. On the 4.6l I had, the stumble was caused by plug wires and corrosion on the coil packs but you may have COPs so that doesn't apply. There are boots, from what I'm told, that will replace the COPs boots; you might check if the boots are cracked or otherwise compromising the ignition system. One screw holds the COP in place, careful with the connector when taking it off; pull out the COP and check the condition of the boot and spring.

I recently changed plugs due to what I call stumbling; missed when accelerating at highway speed in OD. I found 3 plugs that had eroded (burnt electrode means greater gap). No more stumble.

I've also found vacuum leaks will cause similar symptoms; check vacuum line condition.

I hope this helps.