LLY 5-spd "hangs" at the top of 3rd WOT

[bluthndr]

Like the title says.

Trans is not commanding upshift - only under WOT acceleration. OSS reaches and passes upshift point, and power falls off a bit. Has new OSS for ABS problem. No codes. Fluid is good. When it does shift (after you lift some, or just stay in it for a few seconds at the top of third), shift is nice and firm.

Truck has EFI Live, stock fuel system. Replaced fuel filter and vac went from 18" WOT to 10" WOT. Actual FRP was below des FRP by maybe 20 mpa. FPRV replaced with shimmed one and Des vs Act is the same on almost all data points on the curve. Looking through TCM instead, des vs act torque output is the same as well while the problem occurs.

Any idea why it is not commanding the upshift?

How big a discrepancy should I be looking for in act vs des torque or FRP?

 

[juddski88]

How hot of a tune is it? What kind of pressure and pulse is it commanding when the shift is supposed yo happen

 

[bluthndr]

Don't know "how hot" but it doesn't really smoke much. It's not my truck. FWIW the seat of the pants meter says the truck is making really good power - probably 80ish% of some of the (dynoed) 500+hp Fords and Dodges I have driven/worked on.

Commanded FRP is about 160 mpa steady when it is happening. Des flatlines at 160, act goes to about there, but the line is more jagged. If you go data-point by data-point it is 160/160 80-90% of the time, with a few blips where act drops to maybe 155 mpa while 160 is being commanded.

I did not think to look at the pulse.

I guess my gut tells me he needs a pusher pump/air dog/fass, but I wanted to bounce it off everyone here, as I am only one guy, and my expertise/experience is more Ford and Dodge when you get out past more basic mods (tuner/exhaust programmers) on stuff.

By the book, the fuel supply vac, and the act vs des FRP and TQ numbers look pretty good (compared to a stock system), but I don't know how sensitive the Duramax/Allison management system is, or how adaptable it is to modding once you get out past the 99%ers.

How much power can they make before they need a supply system, and can that be done with just the basics, and a good EFI Live tune, or am I chasing a ghost since this truck has a stock turbo, no studs, and (I think) stock injectors?

Is the FRP or TQ, des vs act, the only thing that will cause one not to command a shift (as long as the OSS, etc is clean) with no codes stored?

 

[Devon]

My truck had that 3rd gear hang, I just replaced the motor on the airdog. I haven't driven the truck really sense. But it would climb up to just about 4000rpm just in that shift (3-4) all other shifts are around 3600. It didn't hang long but it is enough to be noticeable because you can see it jump before it shifts to 4th. All other shifts are on the money. I run a 01 tcm tune so the shift points are a little higher anyways. But it definatly hangs a bit from 3-4. No banging or slamming into 4th. Just feels like a dead spot at 3800-4000 before it shifts. We will see later how she goes, just got my ECM and autocal back and did the new airdog motor a few weeks back. Been in the hospital an recovering from a broken leg so the truck hasn't been being drove. I could actually post a video of how it hangs.


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[McRat]

Try programming the 3-4 WOT shift higher. Dunno why that works on some, but it does.

 

[whitetrash21]

My LLY did the same thing on the bigger tunes.... lift pump got rid of it. Never logged it, just the butt dyno, but it definitely quit hanging the 3-4 and 4-5 once the pump went on.

 

[Devon]

Hopefully in my case is was a bad airdog motor not pulling as much fuel as it should of been pulling,or dropping fuel pressure to 0psi on my bigger tunes #4 and #5 or any of them for that matter.


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[juddski88]

did you check feed pressure with a gauge?

 

[Devon]

A while ago I did Tim and it basically went right down to 0. My pumps no longer making crazy death noises. I will check again this week to assure that it's got positive pressure at wot


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[Devon]

No more hangin 3-4 gear. With the new tuning and the 01 Trans tune. It seems to shift/lockup alot better with the s472 setup. Love it! She locks up quick as hell.


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