f550 rear in a 350,change ecm?

[94f450sd]

Ok so i took a 550 rear, springs and all and put it under a 99 350. also has the 550s motor in it. drivers says its a complete dog on hills.should i swap the pcm too? would the 550s pcm be programmed for those gears and 19.5 tires? Both trucks are 7.3 autos.

 

[79jasper]

550 pcm will be worse.
They're usually detuned from what the pickups are. I don't think gear difference would do that. If anything should be better on hills.
I would look elsewhere.

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[94f450sd]

Going to a higher gear will kill you on hills especially with a trailer hauling 3 cars.now add in the 19.5 tires.

 

[79jasper]

Start with the normal stuff. Clean the ebp tube, look for boost leaks, etc.
You can try the pcm. Don't have anything to lose really.

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[94f450sd]

I just put the motor in it.there is nothing wrong with the motor.its geared waaaay to high.the 550s pcm has to be programmed to compensate for the tall gear and tires.the little f350 is only supposed to have little 225/16 tire not 245/19.5 tires.

Im gonna try the pcm anyways.aint gonna hurt nothing.

 

[madpogue]

Width and rim size are meaningless without profile. What are the COMPLETE sizes (width, profile, rim size) of the tires on the two trucks? Only that will determine overall tire diameter, and whether there's enough difference for it to be a factor.

 

[94f450sd]

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[94f450sd]

It was fine before the rear swap so i know its a gearing problem.the 550 was a line painting truck with i think around a 19 foot stake body always loaded heavy dragging a heavy equiptment trailer.wasnt gutless on hills loaded.

Im also dealing with a 2002 motor running on 1999 programming.i know programming was changed threw the years.the 550s werent gutless