adding a tach??
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Junior User
Joined: Jan 2008
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From: portsmouth n.h.
adding a tach??
i have a 85 f250 c-6trans 6.9 non modified, 2wd, wanted to add a tach to the new cluster of guages ive installed, the only one that ive found, is electronic as far as the hook ups go, i see several (3-4) wires coming out of the assembly housing on the tach, and was wondering how this hooks up and to what, i know its probally unnessarry, but i want to know what kind of rpm i can push and watch on highway speeds, needless to say i want it more than need it, and how can i install it to make it work???
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
You will need to find an insturment cluster with a tach in it at a salvage yard.
If you can find one, you just remove the entire cluster and replace it with the one from the salvage yard.
First you need to find out if you have a tach wire and connector near the IP on the engine, this wire should exit out of the alternator harness.
You can see the connector in this picture.
If you have that connector, then all the wiring is already there, you just need the cluster with a tach.
And you will also have to buy a tach sensor at Ford, they cost about 50 dollars.
Standard gasoline motor tachs will not work.
Redline is 3800 RPM
Usually about 3300 RPM is normal for max RPM, and the IP is starting to defuel above that.
Max economy is around 2000 RPM, max torque is slightly under that.
As for cruise RPM, that will depend on what axle ratio you have.
If your max speed is around 85 MPH you probably have a 3.55 axle.
If max speed is around 75 MPH you probably have a 4.10 axle.
If you can find one, you just remove the entire cluster and replace it with the one from the salvage yard.
First you need to find out if you have a tach wire and connector near the IP on the engine, this wire should exit out of the alternator harness.
You can see the connector in this picture.
If you have that connector, then all the wiring is already there, you just need the cluster with a tach.
And you will also have to buy a tach sensor at Ford, they cost about 50 dollars.
Standard gasoline motor tachs will not work.
Redline is 3800 RPM
Usually about 3300 RPM is normal for max RPM, and the IP is starting to defuel above that.
Max economy is around 2000 RPM, max torque is slightly under that.
As for cruise RPM, that will depend on what axle ratio you have.
If your max speed is around 85 MPH you probably have a 3.55 axle.
If max speed is around 75 MPH you probably have a 4.10 axle.
Laughing Gas
Joined: Mar 2006
Posts: 1,083
Likes: 1
From: Fitzpatrick Alabama
My 88 3 spd w/ GearVendor and 4.11 gears would turn the speedo(which went to 85mph) all the way around to the P for PARK, but I only did it once, I trusted the engine way more than the suspension holding it together.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
Not saying it won't go that fast if the IP is in decent shape, but at those RPM's it sure will be sucking fuel.
A decent IP will usually turn 35 or 36 hundred RPM with the throttle on the floor.
As they get weaker, that number comes down to 31, 32 or 33 hundered.
A decent IP will usually turn 35 or 36 hundred RPM with the throttle on the floor.
As they get weaker, that number comes down to 31, 32 or 33 hundered.
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
Took mine as far as to jamb the needle against the trip meter reset button (guessing around 100 MPH). Had to try out the new tires after all. Quite erie how smooth the truck was at that speed, turning about 2100-2200 RPM and 850F EGTs if I remember right. Basically just let it gradually gain speed, and gain speed it did.......still lots of room to the floor.
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