new member with some problems w/tach

[silverrex4]

Hello all, just bought a 85 f350 6.9 idi. I have been using your fourms to research and give me the answers to work on this old rig. The latest project on the truck is to get the tach to work. I just bought and installed a new sensor but no dice. I checked fuses under the dash and all work. I pulled the Guage cluster and unsure of which of those four wires that connect to the tach go to. I did a search through the fourms but still can't get this work. Any help would be greatly appreciated.
Thanks

 

[mblaney]

I would double check the sensor; you should be getting AC voltage out of it and that voltage will increase with RPM. Be a shame to tear the dash apart only to find out your sensor or connector was bad! I think dash cluster ground is a common problem.
Here is a nice thread that might help http://www.oilburners.net/forums/sh...g-a-tach-sensor-and-or-gage-amp-harness/page2

 

[silverrex4]

Thanks for the link, just put the new sensor on so I will have to check with a meter and trace everything back. I'll see what I get. Thanks again for the quick response keep you posted

 

[DaveBen]

New parts may NOT work. It still could be the tach sensor.

 

[silverrex4]

Now when you are saying the tach sensor your talking about the round 1 inch nut with the 2 wires going to the connector? It's a ford dealer part only. That is what is new and I put on. Is there another sensor?

 

[IDIoit]

thats the only sensor.
what dave is talking about is the best practical joke from the parts house.
"here you go here is your 80 dollar part, we know it dont work, and no warranty"

stupid question time,
did you check all fuses?
never had a bull nose i didnt cut up, so thats about all the info i can offer.

 

[silverrex4]

Oh man I would be mad if that's the case, yah I checked all the fuses and everything works. I have to pull the cluster and make sure everything on the tach are connected.

 

[icanfixall]

If the tach has not worked since you purchased the truck it might be an issue the other owner knew was not repairable too. I'm no expert with wiring or especially the tach. I did loose my tach in my 89 which takes out the trans. I did everything possible including replacing the tach. It then worked for 1 day but failed again. I finally found the problem by running a jumper hot wire to the teca relay hot side. Then searched for the fusible links. They are behind my passenger side battery. Found some fool long before me purchasing this truck in 1996 repaired a fusible link by installing 3 blue crimp wire couplers in about a 3 inch long piece of the harness. I removed the blown link and replaced it with an oem link found in a pic n pull. I bought about 15 of them. Funny how some of them made it into my hip pocket. I paid the 2 buck entry fee and bought several other "things". So I paid for them.....

 

[Waystro]

From what I've seen the tach in a bullnose is pretty simple I would check your sensor connections for corrosion even a little bit will(I take this line from space balls) jam the signal. Next I would take the tach out and clean the back of it(the circuit board)

 

[silverrex4]

This is my main concern of the tach, I don't want problems with tranny. There is no od on the this truck that I know of correct me if I'm wrong. I know some later models came with it but it appears this truck doesn't have it. So idk if by not having the tach hooked up correctly the transmission is waiting to explode since the previous owner never fixed the problem in the first place.

 

[Waystro]

Being a 85 you have a C6 transmission unless someone swapped in a E4OD.
The C6 doesn't give a flying flip if you have a tach or not.

 

[silverrex4]

Ok then that is good to know, now I know I won't have a problem with the tranny, I will work on it this weekend and see what I can come up with, you guys are the best, great feedback

 

[icanfixall]

Another really easy way to make sure you do not have an E4OD all electronic trans is look at the injection pump. If you see a black vacuum switch with 2 hoses on the drivers side of it then you have the C6. Nearly impossible to install an E4OD electronic trans in the 85 rig. The wire harness wont support it.

 

[gandalf]

I can't remember whether the '85 has an under-hood fuse box or not. If it does you might want to look there. Nobody has mentioned it, I thought I'd throw the idea out there. If there is, I also don't know whether it has anything which will affect the tach.

Do you have cruise control? Does the horn work?

 

[gandalf]

Another thought. Do you have, or have access to, a wiring diagram for your truck? When you're talking about a problem which likely has origins somewhere in the wiring, that would be real handy.

Another thing I think I'd do would be to check continuity of the wire between the tach sensor and the tach. I think you've said you have the dash panel out, so that shouldn't be too hard.