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Discussion Starter #1
Hi,

I have a 2018 F350 6.7 getting P1266, P1268 code. The strange thing is that if I clear the code, running idle, the truck run smooth and no code for hours and hours as long as I don't rev up the engine.

But if I step the accelerator, rev up the engine, I can quickly get this code. after this code happen, the engine is no longer running smooth.

Do I have bad injectors or bad PCM? I can't think of how either can be good at idle and bad when running higher RPM?
 

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Here is what I found. Your build date is obviously after the date listed for the copy and pasted info below but Ford doesn’t correct problems in newer trucks. Lol. There might also be a newer revision with build dates modified. I am not a technician but I remember tripping over this a few days ago when I was looking for an old TSB. I won’t be able to answer any questions on this issue but I hope this helps.


Illuminated MIL – DTC’s P1261, P1262, P1263, P1264, P1265, P1266, P1267 and/or P1268 – 2017 Ford F-Super Duty


SSM 46453 – 2017 F-Super Duty – 6.7L – Illuminated MIL – DTC’s P1261, P1262, P1263, P1264, P1265, P1266, P1267 and/or P1268 – Built On Or Before 20-Feb-2017

Some 2017 F-Series Super Duty pickups equipped with a 6.7L engine and a rear auxiliary power point may exhibit a illuminated malfunction indicator lamp (MIL) with diagnostic trouble codes (DTCs) P1261, P1262, P1263, P1264, P1265, P1266, P1267 and/or P1268

If freeze frame indicates DTCs set below 600 RPM and there are no drivability symptoms, inspect the center consolerear auxiliary power point for aftermarket devices

Items such as a 12 volt refrigerator or cooler may induce feedback voltage into the vehicle that will cause the powertrain control module (PCM) to falsely set injector circuit fault DTCs.

If no aftermarket devices can be located or are being used by the customer in this power point location, refer to the Powertrain Control/Emissions Diagnosis (PC/ED) manual for normal diagnostics.
 

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Discussion Starter #3
Does not looks like it's aux power issue in the TSB. See screen shot. Looks like cylinder 6 triggered the code around 2200RPM and cylinder 8 triggered at 3400RPM. I will try to measure the resistance of the injector if I can find a plug on ebay. Does the computer put more power/voltage at higher RPM on the injector? Anything below 2000rpm, I can run the truck for hours without any code.
 

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I think you are on the right track with testing the resistance.

I gave up trying to fix these modern vehicles. You try to diagnose what’s wrong and suspect it’s a faulty part but it turns out to be a damn computer glitch or corroded wire harness. Lol
 

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hi, I measured the resistance of both #6 and #8 injector. One is low at 30k and the other one is around 120K. #5 injector is at 180k. So, looks like I have two bad injectors.

One thing which is a bit strange for me to understand is that for #6 injector, the resistance started at 30k but keep changing higher. If I keep the meter on for a few minutes, the resistance eventually going to 180k. what can cause injector resistance keep changing under meter? Should I try to clean this injector?
 
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