96 T100 3.4L Tach problems..

Hello,
anybody have a direction to point me to a area to look for a problem I am having with the Tach in my 96 3.4L Auto T100? When I start the truck, tach initially jumps up and reads correctly, then slowly settles back to zero @ idle. When I give it gas, needle responds correctly, also reads fine when driving around. When I come to a stop the tach goes to zero. Engine does not change tone or stall, or have any other negative symptoms other than the tach not reading @ idle. I do want to fix this because I am listing the truck for sale and think a interested buyer would not like the situation. The truck runs and drives fantastic apart from this, and has not given me any other trouble. This just started today too.....
thanks for any help.

There are 4 areas to check according to the FSM.

Combination Meter Wiring Circuit
Wire Harness
Igniter
Meter Circuit Plate

Check all yer grounds...even if you have to pull and clean each point. :D

Now, if only I had me a FSM....

I will figure something out and look into those leads you gave me. You are really a great resource on this board. Thanks again for your quick reply.

sent you a PM Bam....

PM sent... ;)

Clean the ground on your coil+igniter and the battery/body ground.

Common problem :)

Looking into this issue as well. I have a 96T extended cab 2wd, 3.4 L Automatic. I am having the same issue as described above. It is an intermittent problem. I was wondering if anybody had any pics or could describe the locations where to look for the problems. Any help would be appreciated. Its not a huge problem... but i am a perfectionist, and it drives me nuts:D:D

Still sounds like a ground problem...it's got too much resistance to ground somewhere. Again...check all yer ground points and clean them very well. :D

thanks fella's i will check out the coil / igniter ground, and the main ground soon. hopefully tonight!!! i will let ya know what i find... thanks

i had the same issue with my 96ext cab, its minor but yea drives me nuts cause i cant tell if it stalled or not when the music is cranked!!!! never has stalled but is a pain, i checked the coil grounds n cleaned em, hasn't happend again so far. i will keep an eye on it n let ya no.

took a look around the engine bay today, and im not 100% sure where to check for the coil grounds. is the ground where the coils sit on the valve cover?

does anybody have some pics or diagrams on exactly where to check?? it would be very very helpful.

took a look around the engine bay today, and im not 100% sure where to check for the coil grounds. is the ground where the coils sit on the valve cover?

does anybody have some pics or diagrams on exactly where to check?? it would be very very helpful.

The interior ground points should be behind the left and right kick panels.

The engine bay ground points start at the battery, driver side fender wall, the engine one looks to be near the air plenum close to the diagnosics port/throttle body.

Another thing to check is the harness on the back of the combination meter...yes...it means you have to tear things down to check it and the wires as well. It happens... :(

Not sure if you have any aftermarket radios/amps installed or not but the installer could've taken some shortcuts and screwed a screw into the wire harness that might make it tough to detect....but that's probably a long shot.

It would probably be a good thing to hunt down the factory wiring diagram fer yer year. It's come in pretty handy fer me... ;)

thanks bam... i will look at those places. i found the one that is in the engine bay. i will have to look at the others.

I also was thinking the same thing. I would love to get a service manual for my truck.

Thanks again!