2-3 Shift Issue: Is it the tune?

[The Black Sheep]

We're having issues with the 2-3 shift not happening on a friend/customer's truck. The 1-2 shift happens around 6700-6800 rpm, everything is scaled correctly: shift mph, shift rpm, gear, and tire size. We do a run and the truck shifts 1-2, then when coming up to the 2-3 shift, the check engine light flashes, truck free revs, we let it coast down, then it goes into 4th. I'm thinking the trans can't make the shift happen that high up, but I'd like some suggestions as to what could be wrong.

1GNEC13V25R260341 tuned.hpt
18-12-13 11-22-26.hpl
Video: https://youtu.be/sCl2NnAuRc4

[kevin87turbot]

Does the fluid look and smell ok? If it's not dark/burnt, then try the following.

Try adding some more pressure to the entire 2-3 shift curve from 260 lb ft - up.
Also top off the transmission with an extra quart of fluid.

[Shnraines]

Does it shift ok at light throttle?

[The Black Sheep]

Kevin - That worked for us, but only once. Got a solid pass, truck shifted firm, next pull it popped again but stayed running instead of turning off. I've seen this issue before with another friend's truck. I tested my theory on that truck by controlling the DC on the Force Motor Current. We got that one to shift solid, the only difference was that truck had a built transmission and the shop told him he needed to lower the line pressure in the tune before he hurt it. It seems there's a safety in the ECM that if the line pressure is too low or too high the ECM just cuts (or loses?) power for a moment. I have another truck now doing the same thing, tried your advice, and it shifts sometimes and others it will pop, cut out, then resume.

Shnraines - Yes it shifts fine at part throttle.

[Shnraines]

Put a gauge on the pressure test port of the transmission and see if you're maintaining line pressure at high rpm. I assume you log the solenoid shift signal. If solenoid is getting energized and you have pressure, it's a mechanical problem in the transmission. Need to consider the rev limiter as your cut out problem

[The Black Sheep]

Shnraines - I have the pressure test kit, that was also a thought I had. I do not log the shift solenoid signal, I will add that to the log. The truck can shift 2-3 at 6400 rpm just fine, so it’s looking like we are losing pressure with higher rpm.

[kevin87turbot]

It appears to be hitting the rev limiter.

You've only got 200 rpm from your commanded WOT shift rpm to the rev limiter rpm.
That's just not enough cushion. You need around 500 rpm difference. Raise your rev limiters by 300 rpm (including the ETC rev limiter.), or lower your 2-3 shift point by a couple hundred rpm. It will complete the shift then. Also lower the WOT 2-3 shift MPH by a couple MPH. With the 4.56 gears, it will accelerate pretty quickly, and that one could cause an issue as well.

[The Black Sheep]

The truck is now missing the 1-2 shift randomly. We lowered the shifts to 6500 rpm left the rev limiter at 7000, still cut out. SUPER interesting to note, we did a pull to the top of 3rd and as you know the 3-4 shift isn't set up from the factory to happen at WOT, so when the truck got up to 6500-6600 rpm, it cut out again. Crank signal is clean so I don't think it's an rpm issue, but now it cutout with no shift scheduled? Short in crank signal that happens with higher rpm/vibration maybe?

[Shnraines]

Valve float?

[The Black Sheep]

I don’t see how it could be valve float, it pulls solid. Do you notice the wave in the mass air flow hz? It’s a BTR stage 4 truck cam I know it’s making power up at 6500 rpm, it might be just starting to fall off around 6800. Springs are the beehive springs supplied in the kit.

[kevin87turbot]

The truck is now missing the 1-2 shift randomly. We lowered the shifts to 6500 rpm left the rev limiter at 7000, still cut out. SUPER interesting to note, we did a pull to the top of 3rd and as you know the 3-4 shift isn't set up from the factory to happen at WOT, so when the truck got up to 6500-6600 rpm, it cut out again. Crank signal is clean so I don't think it's an rpm issue, but now it cutout with no shift scheduled? Short in crank signal that happens with higher rpm/vibration maybe?

I just had one do this very thing on the dyno. It was at 6200 rpm...very consistent. At first I thought it was the crank sensor. Turned out, It was a spun crank reluctor. It had spun on the crank.

[Shnraines]

Just FYI, gen 3 rod bolts don't do well above 6500 rpm

[Shnraines]

Kevin, wouldn't a shifted reluctor just cause timing to be off by the amount of the shift?

[The Black Sheep]

A shifted reluctor would cause timing and injector timing to be off, but to an extreme absolutely could cause a problem at higher rpm. The “window” for the crank to see the signal gets tighter with rpm, at least that’s my understanding of it. If we are too far out of the window, it acts like it has a bad crank sensor and just shuts off. That makes sense on why it would do it even with the shift not scheduled. Sounds like we’re turning down the tune. As for the rods, 200 rpm difference does not change the piston speed much, and on a 4.8 6500 rpm is quite a bit different on accel and decel forces on the rod.

At 6500 rpm on a 4.8 we have a piston speed of 3,539.25 fpm versus 3,648.15 fpm at 6700 rpm.
At 6500 rpm on a 5.3 we have a piston speed of 3,923.83 fpm versus 4,044.57 fpm at 6700 rpm.

On a 5.3 we are getting real close to the edge (or at least where I’d prefer to stop on SBE), but on a 4.8 there’s still some ceiling left.

Tons of guys go higher than 6500 rpm on Gen 3 rods. Does it work? Yes. Will it hold? That’s debatable. “Give it what it wants and come up with a theory later.” -Shane T

Thank you Kevin for that thought, I’m almost certain that’s what we would find if, or when, we drop the pan. He needs to change his oil pan gasket anyway, what’s going a little further?

[Shnraines]

Still don't see the difference if the reluctor shifts except for timing and cam correlation (which I would expect a code). Rpm shouldn't factor. The PCM couldn't know it shifted except for correlation to cam (unless it is actively slipping). The only other possibility is it's no longer in good alignment because of the shift.