Tachometer Dead and Always on Zero

[prince402]

I've read all the posts on tachs in this forum. I found no posts on my tach situation: Tachometer Dead and Always on Zero. All other instruments are OK and the truck runs fine. I'm hoping to find something simpler than the circuit board requiring a tear out. (Saw the excellent post on the 3000 rpm problem). It is absolutely dead and the needle never moves from the stopping post.
I could use some troubleshooting advise here.

 

[prince402]

Solved
I put in a new speed sensor since the old one was slowly leaking transmission fluid and maybe not sending the tach signal. The tach still remained dead.

So following the very fine posts on this forum, I removed the cluster and soldered some questionable spots. The tach remained dead.

At this point suspecting that it may be the tach itself, I installed a salvaged one.

It worked. Maybe this feedback will be of some help to those with a dead tach.

Thanks to those who posted the cluster removal procedure I was able to make the repair.

 

[wantdeath]

im glad you got it fixed. it always makes me happy when people fix the non essential stuff like that. it seems some people (not the ones on EF) barely keep there car running long enough to drive it too the junk yard.

 

[prince402]

Thanks for the thumbs up and good humor.

Anyway now that I have a working tach I have a question about what I am seeing on engine rpm.

Say when I have cruise control on and I am traveling on level ground, the mph and the rpm are quite constant as I would expect. But when I would be going up a slight grade at constant mph, the rpm rises say from 1700 to 2100.

Is this normal or do I have too much transmission slippage causing the increase in rpm at constant speed?

 

[Yadkin]

Assuming that you have an automatic transmission, that is called "down shifting".

 

[prince402]

Thanks, I should have said that it's 2 wheel drive with 4 spd automatic.

I am aware of the downshifting from 4th to 3rd and can execute that manually by pulling the shift lever from D2 to D1 with cruise control on and see the rpm distinctly jump.

But what I am talking about is with no automatic downshift I get rpm increase at constant mph under a moderate enough grade that there is no downshifting. I can also get the tach to rise inordinately by depressing the accelerator just not enough to cause downshifting. There is no distinct jump as with a downshift but a gradual sweep up.

To me it would be slippage in the automatic trans and at this point I am just wandering if it is normal or not. This relates to my concern about getting a small travel trailer since slowly accelerating that load would also show the sweep up on the tach. If this is normal I can stop being concerned about it.

 

[wantdeath]

i would guess your torque convertor is unlocking to give it it a little help in power.

 

[Yadkin]

Your owner's manual should have info on that...