1970 ls_c10

iTrader: (1)

I have a 99 4.8 heads cam intake headers. With the original 4l60e and the computer and harness from a 99 silverado. Anyways I was working with a friend that has done a lot of tuning but never with a chevy. He started tuning my truck and we have it running fairly decent. So we were going for a drive and the transmission (which was checked by a friend who has rebuilt about 1000 chevy transmissions including one for me. He said it looks great) shifts from first to second by about 5mph. And to 3rd by 10 and 4th by probably 20mph. Then it will search between 4th and overdrive a lot. I have driven several time it always acts that way. If I shift manually it acts fine besides the overdrive searching. My tuner never got to modifyING anything with the Trans. But we did switch to speed density and have a 2 bar map sensor. Would simply making those changes and of course the injectors to keep good afr make the Trans shift like this or do I have a Trans or computer problem. The setup is in a 70 chevy c10 so I'm not mixing wiring or anything with abother harness. Any guidance would be appreciated. My assumption is that we just need more tuning with the Trans but my tuner is somewhat inexperienced with automatics so just looking for some help thanks in advance

mrvedit

The PCM fully controls the shifting, so if the shifts are too early it is a tune problem.
Perhaps the rear end ratio (including tire size) was not adjusted properly for your vehicle.
Connect a scanner that read MPH from the OBDII plug and compare it to the actual speed.

1970 ls_c10

iTrader: (1)

Using the obd scanner and a GPS they are pretty close.

rpturbo

iTrader: (47)

Once you get a handle on the trans settings, it's pretty easy to adjust them where you want them.

RonSSNova

iTrader: (3)

The trans will switch to full line pressure when you go SD.
It sees the error codes P0101,2 or 3.
So that might be affecting things.

dw456post

Isn't there a tab to disable max line pressure for SD?

Nicelysedate

iTrader: (3)

I would convert the car over to a 1bar SD OS if you are using hptuners. Keeps you from going into limp mode.

joecar

There's a max line pressure table of DTC's... you disable the MAF DTC's in this table.

joecar

I'm not sure about HPT COS, but you *may* still have to do what I said above.

Russ K

iTrader: (1)

Sounds like your setting the P0121 code. Raise the P0121 Error Max Map to be higher than your idle Map KPA.

And Hp Tuners has the Max Line Pressure DTC's in the trans diag tab.

Russ Kemp