putting RPM in my truck

[wannabeMJ]

True, but I'm not sure the 90 and 86 tach pickups are the same. Are you? :D If it reads correctly, that's good. Stick it in there and try it.

Ill try that there both 6 banger ill post more on that when I swap the engine

probably next week

 

thanks all

[Eagle]

Correct. You will just have to change the way the 2.8L tach sees the signal from the harness.

WHY?

 

The 2.8L is a 6-cylinder. The 4.0L is a 6-cylinder. They make the same number of ignition pulses per revolution. Recalibration is only needed when using a 4-cyl tach with a 6-cyl engine, or a 6-cyl tach with a 4-cyl engine.

 

You guys are making this FAR more difficult than it is. All he needs is to use the old cluster with the old speedo cable into the "new" transfer case and he's done.

 

Now ... How do I know this works? Because my friend in Greece had a 1984 XJ 4-banger that originally came from the U.S. He liked the style of the newer (1988-1990) gauges better and he found a cluster out of a 1989 Comanche 4.0L (in Greece, mind you -- abandoned). He dropped the '89 cluster into the '84 XJ and all the electrics worked. He used the potentiometer to calibrate the tach against a hand-held idle tach, and the job was done. He Jerry-rigged a clip to hold the old speedo cable into the newer style speedo head, and that was that.

 

Don't over-think things.

[wannabeMJ]

ok so after this is all done Ill tell you who was right and who wasn't

[Automan2164]

Sounds good. Lets stop the madness.

 

Rob L.

[knever3]

:popcorn:

 

This is hilarious!!

[JeepcoMJ]

this post will end the debate.

 

 

the pinout to the foil on the back of the '86 cluster is DIFFERENT than the pinout on the '90 cluster. they route differently, though they go to the same respective locations.

 

the tachometer on the '86 runs off of a different range input than the tach on the '90 does, so it WON'T work.

 

the gauge cluster housing is different on the '86, so the '90 speedo WON'T go in the '86 cluster.

 

 

 

you WILL NEED a gauge cluster from mid 87 to 1990. early '87 gauge clusters are rumoured to run off of a different range input for the tachometer as well, even though they are 4.0's from '87+

[JeepcoMJ]

and before some retard debates what I'm saying, yes, the gauge cluster will "bolt-in". but the tach won't work, and the speedometer gauge won't even bolt into that cluster. as has been stated, there is NO POTENTIOMETER on the '86 tachometer. thus it is not adjustable.

 

 

eagle, hornbrod, I don't know why the signals are not the same, but they are NOT. I have tried putting an '86 cluster in an '88 4.0, no dice. can't do it, and it can't be adjusted. everything but the tach worked properly....end of story, this cluster will not accurately reflect the revolutions per minute of your 4.0. it can't be fixed, you will need a new gauge cluster. I had to use the '86 speedo cable to attempt this, end result was that the tach didn't work and I went back and bought a different cluster..

[Eagle]

eagle, hornbrod, I don't know why the signals are not the same, but they are NOT. I have tried putting an '86 cluster in an '88 4.0, no dice. can't do it, and it can't be adjusted. everything but the tach worked properly....end of story, this cluster will not accurately reflect the revolutions per minute of your 4.0. it can't be fixed, you will need a new gauge cluster. I had to use the '86 speedo cable to attempt this, end result was that the tach didn't work and I went back and bought a different cluster..

So how do you account for the fact that my friend in Greece was able to use a tach from a 1989 4.0L MJ in his 1984 2.5L XJ? Yes, he used the potentiometer to adjust for the 4-banger, but the reading when he first fired it up was consistent with what it should have been if his engine had been a 6-cylinder.

 

A tachometer only reads pulses, and counts them. If it did anything else, we would not be able to walk into Auto Zone, buy a Sun Super Tach, and just flip to switch to 4 or 6 cylinders and hook up the wires.

[JeepcoMJ]

eagle, hornbrod, I don't know why the signals are not the same, but they are NOT. I have tried putting an '86 cluster in an '88 4.0, no dice. can't do it, and it can't be adjusted. everything but the tach worked properly....end of story, this cluster will not accurately reflect the revolutions per minute of your 4.0. it can't be fixed, you will need a new gauge cluster. I had to use the '86 speedo cable to attempt this, end result was that the tach didn't work and I went back and bought a different cluster..

So how do you account for the fact that my friend in Greece was able to use a tach from a 1989 4.0L MJ in his 1984 2.5L XJ? Yes, he used the potentiometer to adjust for the 4-banger, but the reading when he first fired it up was consistent with what it should have been if his engine had been a 6-cylinder.

 

A tachometer only reads pulses, and counts them. If it did anything else, we would not be able to walk into Auto Zone, buy a Sun Super Tach, and just flip to switch to 4 or 6 cylinders and hook up the wires.

 

I told you that I don't know why they're not the same. and I also said that an '86 2.8 has NO potentiometer...at the very least I'm zero for five on that aspect...of five gauge clusters, zero had potentiometers on the tach.

 

there ARE different pulse signals between different brands of motors. case and point, I had to have a pulse signal adapter made in order to run the buick 3800 with the '86 2.8 tach. I thought that was wierd, as it was at least a gm motor.

 

 

I haven't researched into the "why's" of things. I HAVE figured out the "how's"....and it simply isn't something that can be made to work very easily.

[wannabeMJ]

:hateputers:

damn it I will have to buy a new cluster ..........

[Automan2164]

Does that mean you tried it and it didn't work?

 

Rob L.

[87Chief]

Get one like this... I can't remember what year you have but get it from a 87-90 Cherokee if it's like an 88 or something...I picked mine up for my 87 Comanche, got it from a 89 Cherokee at a junkyard for $20...

 

Here are the pics...

 

 

Hope that helps...

[wannabeMJ]

heeeeeeeeee :hmm: I just looked at mine and its the same as the pics you just putted up

[wannabeMJ]

like this one .......

Image Not Found

same pins same everything

[Automan2164]

Stop confusing yourself and just go get a new cluster already.

 

Rob L.

[87Chief]

Wait, what are you trying to do again? Use the 86 MJ cluster or the 90 XJ cluster for the XJ wiring harness?

[Automan2164]

Yes, thats what he was trying to do.

 

Rob L.

[87Chief]

Which one?...

[Automan2164]

Trying to use an '86 cluster in a '90.

 

I should stay out of this thread. Its going to drive me batty. :nuts:

 

Get a new cluster!!!!!!

Rob L.

[87Chief]

EXACTLY NOT what I said, "Use the 86 MJ cluster OR the 90 XJ cluster, for the XJ wiring harness?"

 

Now pull back behind you and pull your panties out of a wad :D

[HOrnbrod]

and before some retard debates what I'm saying, yes, the gauge cluster will "bolt-in". but the tach won't work, and the speedometer gauge won't even bolt into that cluster. as has been stated, there is NO POTENTIOMETER on the '86 tachometer. thus it is not adjustable.

 

eagle, hornbrod, I don't know why the signals are not the same, but they are NOT. I have tried putting an '86 cluster in an '88 4.0, no dice. can't do it, and it can't be adjusted. everything but the tach worked properly....end of story, this cluster will not accurately reflect the revolutions per minute of your 4.0. it can't be fixed, you will need a new gauge cluster. I had to use the '86 speedo cable to attempt this, end result was that the tach didn't work and I went back and bought a different cluster..

 

I'll be the retard to respond to this. :D Yes, potentiometers are not present on all the tachometers. If not there is a fixed calibration resistor on all tachs. These resistors can be changed w. another of greater/less ohms, which alters the meter deflection based on input and calibrated to accurately measure RPM. It's usually done by soldering in a temporary potentiometer. Don't say it can't be done just because you don't know how to do it. If the tach is indicating linearly with engine RPM, it can be calibrated with a function generator, an o'scope, a known good standard external tach, and a test potentiometer.

 

And to the original posted who started this mess, stick the 86 cluster in and try the damn thing.

[wannabeMJ]

wow 4 pages just to confuse me more lollllll

[JeepcoMJ]

and before some retard debates what I'm saying, yes, the gauge cluster will "bolt-in". but the tach won't work, and the speedometer gauge won't even bolt into that cluster. as has been stated, there is NO POTENTIOMETER on the '86 tachometer. thus it is not adjustable.

 

eagle, hornbrod, I don't know why the signals are not the same, but they are NOT. I have tried putting an '86 cluster in an '88 4.0, no dice. can't do it, and it can't be adjusted. everything but the tach worked properly....end of story, this cluster will not accurately reflect the revolutions per minute of your 4.0. it can't be fixed, you will need a new gauge cluster. I had to use the '86 speedo cable to attempt this, end result was that the tach didn't work and I went back and bought a different cluster..

 

I'll be the retard to respond to this. :D Yes, potentiometers are not present on all the tachometers. If not there is a fixed calibration resistor on all tachs. These resistors can be changed w. another of greater/less ohms, which alters the meter deflection based on input and calibrated to accurately measure RPM. It's usually done by soldering in a temporary potentiometer. Don't say it can't be done just because you don't know how to do it. If the tach is indicating linearly with engine RPM, it can be calibrated with a function generator, an o'scope, a known good standard external tach, and a test potentiometer.

 

And to the original posted who started this mess, stick the 86 cluster in and try the damn thing.

 

Don,

 

simply put if he can't comprehend what's been said so far, he can't do what you're saying can be done.

 

me, for the $30 that a cluster costs (AT MOST) from a junkyard....I'll just swap it. they're factory gauges, which are not entirely accurate anyways. I want it to be close, and I don't want to waste a bunch of time making it work.

[Automan2164]

I am with Pat here. Clusters are not that expensive, and easy to change as a unit.

 

Get a new cluster!

Rob L.

[jimoshel]

If it was me, I'd just put a dab of white paint on the tip of each fan blade, Check the crank and fan pulley, make sure they're the same size, cut a hole in the hood and then count the white dabs for one minute and divide by 4. For a 4 blade fan, :rotf: Or go to Auto Zone and buy a after market.