Hey guys , so my work truck is a 2015 f550 6.7 , I am a mobile mechanic for ag , this truck has been down for 5 weeks now , I took it to a couple places and now it’s back for me to try to figure it out , so first I had the seals leaking around injectors to valve covers , I wanted to put new seals in , (truck ran perfect ) I removed each injector and installed new seals , installed injectors and torqued in the same position they came out , after that I keep getting code 1291 after about 1 sec of starting it , so unplugged each injector on bank 1 till #1 if u unplug it and clear codes the truck runs better but has a miss from injector not being fired . As soon as you plug it in it will labour engine and throw the code , i since , replaced all 8 injectors , made no difference , tested harness and it all tedted hood , but I just replaced the harness anyways and it didn’t make a difference, then I replaced and programmed the pcm and it still made no diffence . The one shop I took it to has # 1 injector hooked up to a tube and let it spray out in a pail , (he just stuck another injector in hole , it sprayed hood and the code wasn’t up , but as soon as he unplugged it and plugged it into the new injector in the hole it threw code , I’ve swapped injectors from diffrent holes thinking maybe the new injectors was faulty but it doesn’t matter, compression is also good , I’m lost on what to do next!! Seems like it has to be in the hole for the code to come up but yet not an injector ??

 

So this is a short to ground code. It means it is a wiring issue, something is creating a short. I presume it is only happening on one cylinder since you said you replaced an injector and the problem didn't go away.

Since you say it does it ONLY when the injector is plugged in and in the hole, regardless of what injector, we can presume it has to do with the wiring harness pigtail. I would see about fixing or replacing that - it could be as simple as a chaffed wire, try forcing some space between the wires of the injector pigtail, clearing the code, and starting the truck. If the code goes away inspect the wires closely, if it looks like you can tape them up that would be the cheap fix, Ford probably sells just the pigtail you could replace, or you could probably buy a whole new injector harness but those are $$$.

 

I replaced all 8 injectors and the injector harness like I said in the post still nothing

 

With the truck off I would do a resistance check of each injector wire to ground with everything plugged in, I’m thinking #1 will have different reading than #3,5,7. I can’t say exactly what this means but may help isolate it a bit closer, maybe the pcm has a fault and when the injector is isolated from the truck that fault doesn’t show up? Just a guess.

 

Didn't see where you said you replaced the harness. Sorry.

Might want to post this in the 6.7 forum down below, someone there may have seen something similar.

If the harness is good, the injector is good, and no code is thrown when the injector is physically out of the bore, then there is something between the interaction of the injector and the bore causing the problem.

Maybe try putting some dielectric grease in the connector? It is possible that it is arching.

 

P1291 Ford Code - Injector High Side Short To Ground Or Battery Voltage Bank 1

Have you verified all of the injector wiring and associated grounds?