Diesel tach swap - strange donor

[PossumTruck]

Bought a diesel cluster w/ tach from ebay, for the purpose of wiring a factory tach to my 86' 6.9L.

Well, it wasn't what I expected. The first clue was an electronic speedo, so a direct/full cluster swap wouldn't work. Then I see the connector for the cluster is different and the circuity is green vs my brown. I did a little more research and see that the tach itself, while 3500 RPM and clearly diesel, looks to be from an F600-800 truck with a Cat or Detroit according to the tachometer info available on this site. (If I had only known beforehand)

The question I have is, can I still wire this thing to work with an IDI tach sensor, or is this money down the drain?

[Rembrant]

The question I have is, can I still wire this thing to work with an IDI tach sensor, or is this money down the drain?

I can't answer your question, but figured I'd post the link below in case it's any help. This guy fixes/rebuilds/upgrades the tachs for these trucks.

https://www.rccinnovations.com/index.php?show=menu-trucks-all

 

[mat in tn]

The question I have is, can I still wire this thing to work with an IDI tach sensor, or is this money down the drain?

I can't answer your question, but figured I'd post the link below in case it's any help. This guy fixes/rebuilds/upgrades the tachs for these trucks.

https://www.rccinnovations.com/index.php?show=menu-trucks-all

well onthe gas model tachometers anyway. they are the same tach for 6/8 yet they are wired differently. there is a different ground for 6 vs 8 and that will give the appropriate range.

I wonder if they used the same type circuitry from the 6/8 on diesels too? i do not know but its a question worth asking

[PossumTruck]

well onthe gas model tachometers anyway. they are the same tach for 6/8 yet they are wired differently. there is a different ground for 6 vs 8 and that will give the appropriate range.

I wonder if they used the same type circuitry from the 6/8 on diesels too? i do not know but its a question worth asking

My understanding is that the diesel and gas tachs are not directly swappable, as they take different input signals.

Here is a picture of what I have - it even looks like it has some sort of adjustment instead of a 4th terminal/screw.

[mat in tn]

My understanding is that the diesel and gas tachs are not directly swappable, as they take different input signals.

Here is a picture of what I have - it even looks like it has some sort of adjustment instead of a 4th terminal/screw.

that is not what I was questioning. my comment is drawing a possible comparison.

could it be that ford made a tach to be compatible with 6/8 cyl diesels only requiring a different ground for each? that is how they do the tach for gas engines to be able to be wired for either 6/8

[Rembrant]

that is not what I was questioning. my comment is drawing a possible comparison.

could it be that ford made a tach to be compatible with 6/8 cyl diesels only requiring a different ground for each? that is how they do the tach for gas engines to be able to be wired for either 6/8

I doubt the number of cylinders in a diesel matter...at least not on the old ones with mechanical injection pumps. The tachs in older diesels usually relied on a pickup on the crank or flywheel somewhere since there was no ignition system to read from like with a gas engine. I know nothing about the old Ford IDI's however...I'm just speaking in general terms.

[mat in tn]

that is not what I was questioning. my comment is drawing a possible comparison.

could it be that ford made a tach to be compatible with 6/8 cyl diesels only requiring a different ground for each? that is how they do the tach for gas engines to be able to be wired for either 6/8

I doubt the number of cylinders in a diesel matter...at least not on the old ones with mechanical injection pumps. The tachs in older diesels usually relied on a pickup on the crank or flywheel somewhere since there was no ignition system to read from like with a gas engine. I know nothing about the old Ford IDI's however...I'm just speaking in general terms.

exactly. my knowledge on it is limited too. just trying to ask questions in different ways to get other understandings. if the signal is a simple crank signal that would be reading 360 degrees per rotation and if both types are four stroke, then what would the difference be?

[Rembrant]

if the signal is a simple crank signal that would be reading 360 degrees per rotation and if both types are four stroke, then what would the difference be?

This discussion has come up in the past, but it has been a while. If Jonathan was here he’d know the answer. If I recall correctly, the tach for the old IDI Bullnose relied on a simple pickup on the crank or flywheel, and the tach for the later F600/F800 diesel trucks was electronic and worked off a completely different signal. I’m just going by fuzzy memory or an old discussion on here a few years ago.

I found an F800 diesel at the junkyard with a good cluster/ tach in it, and I was going to go back and get it but somebody told me not too….but I was looking for a gas tach at the time, so that was a different issue.

 

[PossumTruck]

exactly. my knowledge on it is limited too. just trying to ask questions in different ways to get other understandings. if the signal is a simple crank signal that would be reading 360 degrees per rotation and if both types are four stroke, then what would the difference be?

So with an IDI, the tach sensor reads the teeth on the IP timing gear, something like 26 teeth/pulses equals one RPM.

For gassers, it reads 4 pulses per RPM.

It is theoretically possible to get a gas tach to work on an IDI by rigging up a crank sensor to read the 4 bolts on the crank pulley. I don't think i'm going to go down that road, though.

[PossumTruck]

If I recall correctly, the tach for the old IDI Bullnose relied on a simple pickup on the crank or flywheel

Correct concept

the tach for the later F600/F800 diesel trucks was electronic and worked off a completely different signal.

I think this is what I am looking at. Wish I knew beforehand.

The 3500 RPM tach I have does not look like the one from the technical section. It must be newer.