4l80 jumping back and forth 3/4

[ncnichol]

So I have an 02 short box 1500 Chevy 2 wheel drive. It has a built 6 l in it with a fairly large blower cam. I recently upgraded to a 4L80E with a circle D 3200 stall converter. The plan was to put a Magnuson blower kit on it after the transmission upgrade which I did. Drove it for a month after the transmission swap but before the blower install. Transmission worked great everything worked great. Park the truck put it in the shop installed the blower now it jumps between 3rd and 4th continuously when you shift into drive back and forth back and forth it's crazy. It does it a little bit second to Third but not as bad but it still does it. Wasn't sure if it was the converter locking up and unlocking or actually upshifting and downshifting.. didn't seem like the converter because it starts to do this as soon as it shifts into fourth it hasn't got up to speed yet to shift into converter lockup. But still I needed to check so I plugged in my HP tuners and commanded the torque converter to lock up once it got into high gear, no change still did the same thing so then I unlocked the converter and commanded it to stay in 4th gear no change. I went into the tune file and commanded the converter not to lock up till 256 mph in every gear so essentially eliminating the lockup converter. Still does it. So then I put the tune back so the converter has it to normal settings and I took the truck out on the highway and commanded the converter and 4th and 3rd gear to either be locked or unlocked in all different combinations you can think of nothing changed the problem it just keeps jumping back and forth in and out in and out in and out between 4th and third. Before I parked the truck to put the blower on it was perfect never touched anything to do with the transmission. I'm having trouble finding information on whether the transmission has to be tuned for a blower? My thinking is originally the transmission depended on a vacuum signal.. done through the ECM now but still a vacuum signal. Now it has a blower there is no vacuum would that have anything to do with it? I've gone over everything outside of the transmission shifter cable speed sensor plugs and wiring it has a brand new harness so the plug on the side of the transmission is not leaking it's got brand new Shafer synthetic oil in it. Anyone got any ideas? Also transmission is a new built-in a reputable shop And has all brand new speed sensors ... It has Brand new everything actually ,Every seal and bushing And every other component.

 

[movietvet]

Maybe @NickTransmissions can help sort this out.

 

[Sean Buick 76]

in short yes I would have a pro tuner tune both the engine and trans as it’s a package deal.

 

[Jimmy D]

Try this little test. While driving when it does this lift up slightly on the shift lever. Not enough to change gears but just a little bit toward neutral.

 

[CumminsFever]

The 4l80e does not use vacuum to shift, although the tuning may reference vacuum to determine a shift point. It is more plausible that the throttle position sensor needs reset for the increased power/torque curve of the engine. Also, there is possibility that wherever the rpm reading comes from is not reading correctly, a sensor got bumped or broken while installing the blower.
It doesn't sound like an actual transmission problem, but rather a tuning or command issue.
You don't mention slippage, and indeed, that may be difficult to detect with a 3200 stall converter.

 

[RDF1]

Do you have a datalog of this happening?
Post datalog and tune.
Is it commanding the shift to do this?

 

[NickTransmissions]

The 4l80e does not use vacuum to shift, although the tuning may reference vacuum to determine a shift point. It is more plausible that the throttle position sensor needs reset for the increased power/torque curve of the engine. Also, there is possibility that wherever the rpm reading comes from is not reading correctly, a sensor got bumped or broken while installing the blower.
It doesn't sound like an actual transmission problem, but rather a tuning or command issue.
You don't mention slippage, and indeed, that may be difficult to detect with a 3200 stall converter.

This is the most likely explanation.

In short:

No blower - trans worked
Blower - trans doesnt work (at least not normally).

@ncnichol - Take it for a drive with a bi-directional scan tool with trans and engine data displayed and see what's up. Then go from there based on what you see/find.

 

[ncnichol]

Thanks very much next your help is well appreciated. 09 Your advice Is encouraging, I have a tuner that was telling me it's gotta be an internal leak or a Converter o-ring.... I really don't believe that's The case. As soon as the weather cooperates I'm gonna try what you suggesthanks very much for your time my name is Joe by the way . I will let you know how I make out

 

[Sean Buick 76]

Can you try it with the blower belt removed or is it a roots?

 

[ncnichol]

Yes it is a roots type