I just recently did a Harley blower swap off an 03 Harley F150 to my 02 King Ranch 4x4. Ever since I had it tuned, the transmission (4R70W) has been acting weird. The motor runs great and is building boost but here lies the problem...

Under normal acceleration (everyday regular in-town driving) the transmission shifts fine. Even under half throttle it gets up to speed like you would expect it to.

With 3/4 to wide open throttle, its not the same situation. It launches from a dead stop just fine, but once I hit between 2,500 and 3,000 rpm I can hear the power but its not making it through the transmission. Once it hits 4500 (which is my rev limit) it stays there for a second or two before it decides to shift to second gear. Once it hits second, the power is back and it takes off until 2,500 to 3,000 again, then it does the same thing from second to third gear. This all happens with the overdrive button off OR on. What could be going on? First thought is to check fluid level, but I doubt that's it. I need advice on where to go next if that's not the case.

If I have to replace the trans, will a 4R70W out of an 09 Econoline work? I found one for $200 on craigslist.

 

If it's from an 09 Econoline, it would be a 4R75W. They look the same on the outside, but the solenoids and EPC valve may need to be transferred from your old trans. Not 100% sure on that. It would be a stronger transmission though.

I'd be more curious about the tune. It's possible that something was screwed up in there. And I'm not absolutely certain, but shouldn't full throttle shifts be at 5,000-5,200 RPM on that motor?

 

I had them set the rev limiter a little lower since my block and head internals aren't as beefy as the lightning and harley's. Just a caution thing because I get paranoid. I am also running 5.13 gears on 38" tires (not the best combo for that tranny with a supercharger lol). I trust the Ford engineering tho So, you think it's a tuning issue? I think my friend has a diagnostic reader that will tell me whats wrong as it's shifting and driving....may resort to that.


thanks for the input and for any other suggestions I can get.

 

I'd definitely have the rev limiter set properly. That can and will screw with your transmission shift schedule. If it thinks that it's not allowed to shift until 5,200 rpm and you have a 4,500 rpm rev limiter, there's an obvious conflict.

And I'd change the gears to something more reasonable. Especially considering how much more torque you have now. But that's me.

 

The shift points need to be set at least 400 rpm less than the rev limiter.