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4x4 low range has hard, hi rpm shifts

M

millsroger

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Bonanza, Or.
1994 Silverado HD, 6.5THO, in low range the tranny, a 4L80EHD, shift points are very high and very hard. Have read that the ECM should re-program the tranny, also read Tech Bulitin 343 from '99 which says that this happens if the ECM loses the low range switched +12. I know the axle is locking in and the tally lite on the floor works too.

The Tech Bullitin gives the pin for the ODBII but I have an OBDI. I have also read that there is a tally switch in the axle actuator that turns on the lite on the floor. I am assuming it also is the source for the ECM.

Problem is; the wiring diagram shows that it goes to the "convenience center" and then to E2 on the ECM, but that pin has no wire in it. The other models have it going to B2 but the pinouts I have show that pin is not used.

Can anyone clarify what it should be for the '94???
 
Mine was the same way for the 1-2 shift, but the 2-3 and 3-4 weren't as bad. if it wasn't reading the 4X4 low switch it wouldn't shift into 2nd until it around 12-15 MPH like it does in high range. Also if it wasn't reading the low range switch, you would get a check engine light and a trans ratio error code.
 
According to the diesel truck ODBI code list for '94 there is no "ratio" error code. Transmission codes are 28 Range pressure switch error, 68 component slippage, 74 input speed fault.

All shifts are above 3000 RPM even at light throttle and hard enough to rooster tail from all four tires.
 
millsroger said:
According to the diesel truck ODBI code list for '94 there is no "ratio" error code. Transmission codes are 28 Range pressure switch error, 68 component slippage, 74 input speed fault.

All shifts are above 3000 RPM even at light throttle and hard enough to rooster tail from all four tires.
Click to expand...

The code 68 is your ratio error(slippage means it senses a problem wit the calculated gear ratio. Do you get these codes all the time, or just in 4 low?
 
Thanks for clarifying code 68 but I don't get any codes of any kind. I put 30 miles on it on the back roads in and out of low range and it acts like the ECM thinks everything is OK.
 
millsroger said:
Hey guy, I looked at your sig. So--what's a "pump rub kit"
Click to expand...

The newer style transfer cases used since about 99 used a magnesium case and were known to wear through in the rear where the pump sat in the housing. It wasn't a problem on the older style cases, but only from about 99 to 08 or so before GM went back to aluminum housings for the transfer case.
 
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