1995 3/4 ton not shifting

[Bill Harper]

I have a 1995 Chevy 2500 with the 350 and 4-speed auto for a work truck and recently when startig it up, the tach will not register and the trans is stuck in second. This does not happen every time but on random it will. I have tried a replacment pcm, and that is not helping, in addition to checking the ground wires for the pcm on the engine block. Any suggestions are appreciated very much. Thank You.

[john8662]

This is a shot in the dark. But on the same truck equipped with a 6.5TD the tachometer is driven off the alternator, and could possibly cause the issue you're seeing. I don't know if this would apply to the 350 as it would probably see it's tach signal off the HEI.

Since it's a 2500, is this the 4L80E tranny, in a HD 2500 (8 lug wheels). There have been some times where a dirty speed sensor has caused intermittant issues with this tranny. Simply removing the sensor and cleaning the deposits off of it has resolved some problems.

Last, are there any codes?

[White Truck]

Next time this happens, check to see if you have 12 volts on the Trans fuse. (located in the end of the dash) Keep a voltmeter handy so you can do this with out turning the key off. Ignition switch failures were common in the '95 model year. One of the switch contacts powers the affected items you mentioned. Cycling the key will sometimes temporarily remedy this, that is why I suggest checking for power at the fuse before moving the switch.

DKB