Just bought a 2015 f150 3.5 eco boost with 38,000 miles it’s missing under light throttle going up incline. Doesn’t matter what gear or sport mode. I have changed the spark plugs with motorcrafts and gapped at .028, new air filter, cleaned the intake sensors. No check engine lights. Dealer can’t figure it out, they did a transmission relearn. Problem is between -1- 5 psi boost can watch the fuel mpgs move lower and engine rpm jump up about 150 rpm. What can I do? Have tried 93 and 87 octane and injector cleaner. What’s next?

 

I am sure there is a ecm update since 2015 to address this. Not sure why they would do a trans re-learn, has nothing to with engine timing. I would go to a different dealer.

 

There might have been a Tune on it from original owner. They may have put it back to stock with the original program. Have dealer check for updates as said above

 

Has it been inspected for buildup on the intake valves? Condensation in the intercooler? Did the dealer perform a signal check on the input to the coils? Coil output?

As vehicles get more complicated, mechanics appear to be gravitating towards being tech oriented, and forgetting there are some simple old-timey checks that can be done with tools that are gathering dust in the corner of the shop. Breakout boxes and diagnostic computers still can't see the ignition system end to end.

I take it no codes have been thrown?

 

 

Sounds like fuel pressure.

 

If I were to diagnose it I would be test driving the vehicle with a graphing cylinder balance test running. This would either show me that it's NOT "misfiring" or isolate which cylinder is. Ask your service writer if this test has been performed. It's called a "Cylinder Balance Test".

 

 

Only up an incline... sounds like something is shifting due to gravity. I'd start with making sure there is no condensation in the intake and intercooler, and ensuring there are no intake and vacuum components that can move (potentially kinking vaccum lines) then if still present, start logging states to see what changes under light throttle between flat ground and a slight incline.

It's odd that this only happens on an incline, though, as giving throttle does the same to shift gravity as being on an incline. You should be able to give slightly more throttle than when on an incline and get the same results.

Some have 'logged' wastegate activity with mountable video cameras.

 

Don't rule out the possibility that it could be the torque converter slipping since you say it is noticeable going up inclines. My 2015's torque converter started doing this at around 32000 miles after I reset the adaptive learning on the transmission. Don't ask me why but it only started after the adaptive learning was reset. I had to have a friction modifier added and a full trans flush and fill and have had no further problems. I will say that the torque converter slipping felt just like a misfire. Might not be your problem but something to think about.