4L60 harsh 1->2 shift and P1870 (but 3 bar COS)

[Tapi]

Hi.

This is a Corvette 1997 with LPE twinturbo upgraded with bigger turbos and 1100 cc injectors etc. That's why the engine displacement is something else if you wonder...

The problem: I haven't driven this before the triple disc torque converter failed (splines let go) and the built transmission was checked by the modifying company. I put it together with single disc torque converter and modified the TCC speeds so that it shouldn't use the lockup at all on >30% pedal and <40 speeds.

The 1->2 shift is very hard. The 2->3 shift seems the same but the speed hides it better. I tried to increase the shifting time on mild pedal and reduce the line pressures on those two shifts but it didn't make any difference.

I read that it's possible that code P1870 (which has occurred now 3 times within 500 mile driving) and hard shift from 1->2 can be a symptom of MAF dtc. This however is 3 bar COS which needs the MAF dtc to be active.

Should I be looking at the tune or the transmission itself for the code and the hard shifting?

One log attached as well as the start point of the tune and the latest one.

[kevin87turbot]

You can open the window for TCC slippage to eliminate the P1870 code. Just go to Trans Diag Tab and increase the max slippage from 800 rpm, up to a more appropriate rpm for your particular stall speed. It's hard to give a proper number without knowing exactly what stall you have. I'd double the max slippage to start with.

[Tapi]

Thanks! That different stall didn?t come to my mind at all. I will make a logging setup so that I will see the actual rpm differences when the dtc sets.

However the harsh shift is still a mystery to me.

[cadillactech]

Thanks! That different stall didn?t come to my mind at all. I will make a logging setup so that I will see the actual rpm differences when the dtc sets.

However the harsh shift is still a mystery to me.

Can you log delivered torque? Your shift pressures are maxed out at 180lb-ft and up so I wonder if you are in that section of the table during the 1-2 shift.

[Tapi]

I see delivered torque as below 200 Nm (sorry for the units, its less than 150 ft/lb) in the log file during shifts. I was looking at that same thing first when I saw that engine displacement has been altered to control the big injectors. To my surprise the torque in the log wasnt far away from the expected value.

The overall shift pressure table was maxed from majority of the table area already and I thought the safest way to try changes would be to only decrease the pressure via the 1->2 table and 2->3 table to test the effects.

[cadillactech]

I see delivered torque as below 200 Nm (sorry for the units, its less than 150 ft/lb) in the log file during shifts. I was looking at that same thing first when I saw that engine displacement has been altered to control the big injectors. To my surprise the torque in the log wasnt far away from the expected value.

The overall shift pressure table was maxed from majority of the table area already and I thought the safest way to try changes would be to only decrease the pressure via the 1->2 table and 2->3 table to test the effects.

Oh I see it now. You might try dropping the base pressures anyway and seeing if your shifts change at all, you can always change it back. That may give you an idea of the tune is the cause of the harsh shifts.