6nz driving me nuts!

unload it before it breaks you i had the same problem with a 6nz had over 50 grand in it never realy fixed it if its out of time it will give you a cel

 

I chased this similar problem for around 4 months . I had it on a cat dyno, had all injector o rings changed, fuel lines fuel pressure checks, cut out checks , etc etc etc. I finally had an injector wire changed and it made some difference but the problem was finally solved after I had a diesel spec tune and turned this old cat up to 620 hp. Wow all my troubles were gone and no more trips to Cat,trying to plug it in and hope the ET software will help the tech. It would seem my troubles were all in the ECM for as soon as the modified file went in, the truck started giving fuel miles and power with no stumble or rough running. The truck runs smoother and more responsive and gives me 6.5mpg all day long.

Good luck,


Supernova.

 

55 is the all clear code. Who did the ECM tune to 600hp . I know that a cat re-rate to 550hp on the dyno just compounded the stumble and rough running on my c15 plus also made fuel mileage crap. It wasn't until the ecm was totally redone by Diesel Spec that it ran better. It would stumble and hesitate around 1100-1250 then start to smooth out , but after the tune will lug down to 1100 and not stumble or run rough at all. At lot of guys complain of air getting into the lines and use a sight glass to find. Does it smoke or do anything else when it runs rough?

 

The cut out test would find a bad injector usually and the fact you tried a good injector through all 6 can put that to bed. I think but no guarantee that your issue is in the ECM . I might be wrong but it seems likely , especially as you have had issues with it previously. I know my thinking when my engine missed and stumbled was always leant towards mechanical things. I didn't want to spend $1800 on a ecm flash for nothing, but I tried as the tuner offered a no quibble 30 day guarantee. It's also worth checking that you have no bad earth on the truck that could cause electrical problems. The wires seem to swell with oil a lot and maybe worth a look in case one has broken. I bet you checked all that first though.
Hope you get it figured out as I know how frustrating it is first hand.

Supernova.

 

Timing should have been recalibrated with new ecm, probably not your problem but usually standard with an ecm swap. Since you replaced wiring harnesses, I would start with the injector codes. What injector codes did they use when they put new ones in? 5232 runs great and smooth on 6nz for across the board setting. You could have bad fls/fts codes loaded in your ecm. Boost sensor atmospheric and intake sensor all can go bad with no check engine light and affect timing but doesn't fit your situation.