Tachometer

[MonkUSMC]

So I just bought this 86' MJ with a 2.5L I4 4spd..and it has no Tachometer. My friends jeep has a Tach on his 89-90' Cherokee, so is it possible to switch the dash boards and just use that? Or would I have to buy a Tach from AutoZone or something, cause I'm not sure how would I go about installing those.

 

Thank you,

PFC Monk

[BLHTAZ]

If you can find an instrument cluster from a comparable year with the full guages, it is a pretty easy swap. You will need to change the temp switch to a sender for the guage and the oil pressure switch to a sender for the guage. A cluster from a 4.0L engine truck can be made to work, but it get's a little more involved.

 

OH...BTW...Welcome to the Club :cheers:

 

A big SALUTE & thank you for your service :USAflag: :clapping:

[smithe1811]

Welcome, Lejune eh? ive been there a few times.Semper Fi

With a little bit of searching, there is a thread on swapping the cluster somewhere, as soon as i find it ill post it here, unless someone beats me to it.

[maddzz1]

here's the link:

 

http://www.naxja.org/forum/showthread.php?t=921205

 

I think anything up to a 90 will work, but I would go with 86 thru 89 to be safe. Then they switched to the electric speedo.

[Pete M]

91 was the switch to a whole new system (came with the HO and chrysler electronics).

84-86 would be a direct swap, 87-90 would take some minor alterations.

[MonkUSMC]

I've swapped clusters before and it's so annoying, so I just bought a tachometer and a few other gauges at a discount, lol. I have another question, this might just be my wiring, but my Tach only reads 3k rpm when it seems the engine is running at its max. I know the engine shouldn't have any problems since it was rebuilt and all the parts are good on it, even though it runs a bit slow but I don't expect much from a 4cyl 86' truck engine. So any idea's on why it's reading the RPM's not matching the sound if the engine?

 

Thanks for the reply's,

PFC Monk

[BLHTAZ]

I don't know anything about installing aftermarket guages or tachs. It really is much easier to just swap the cluster in from another similar truck than to do what you are trying to do. It is plug & play and only takes about 30 minutes total including swapping the needed senders.

 

All I can say is good luck if you continue on your current path... :thumbsup:

[streetjeep2.5]

I will soon be switching my 87 to a gauge cluster. Mine comes from an 88 or 89 4.0. I was told by those that have done it all MJ's and XJ's are wired to take gauges. You do have to, as said, replace the two sending units, but the wiring that plugs into the back of the instrument cluster is already prepared to be either gauge or light, tach or no tach. I assume the difference is simply the way the back of the cluster is wired. I was told by those experienced with it the tach has a switch of some sort to go from a 2.5 to 4.0 reading. I have my cluster but have not torn into it yet. It is all on a thread I started in the tech section called "changing tachometer".

[streetjeep2.5]

oppps! sorry! Not "changing tachometer" but "changing odometer". :oops:

[Car RamRod]

an aftermarket tach install is not hard at all. It doesn't look nearly as nice as a stock cluster, but it's a cheaper and less time consuming option.

[BLHTAZ]

but it's a cheaper and less time consuming option.

:hmm: Cheaper & less time consuming that what?? A factory cluster should be maybe $20 - $30 and about 30 minutes or less to install... :dunno:

 

Seems to me that he already has more than that in to this and still has issues ;)

[smithe1811]

30 minutes if your taking your time, mine cost $30 and took maybe 10 minutes between changing the odometer to the installation.

 

Erik :beerhead:

[Eagle]

II have another question, this might just be my wiring, but my Tach only reads 3k rpm when it seems the engine is running at its max. I know the engine shouldn't have any problems since it was rebuilt and all the parts are good on it, even though it runs a bit slow but I don't expect much from a 4cyl 86' truck engine. So any idea's on why it's reading the RPM's not matching the sound if the engine?

You have a 4-cylinder, right? Did the tach come from a vehicle with a 4-cylinder? If not, that's the problem. Aftermarket tachs have a switch to set them for 4, 6 or 8 cylinders.

 

A tachometer just counts ignition pulses, and spins a needle on a dial that's calibrated in RPMs. Our engines are 4-cycle, so each revolution only fire half the cylinders. If the tach is calibrated for a 6-cylinder, 3 pulses indicate one revolution. But a 4-cylinder engine only produces 2 pulses per revolution, so it has to spin 1-1/2 times to have the tach show 1 revolution.

 

If you have a 6-cylinder tach in a 4-cylinder vehicle, when the tach reads 3000 RPM the engine is actually turning at 4500 RPM.

[streetjeep2.5]

A tachometer just counts ignition pulses, and spins a needle on a dial that's calibrated in RPMs. Our engines are 4-cycle, so each revolution only fire half the cylinders. If the tach is calibrated for a 6-cylinder, 3 pulses indicate one revolution. But a 4-cylinder engine only produces 2 pulses per revolution, so it has to spin 1-1/2 times to have the tach show 1 revolution.

If you have a 6-cylinder tach in a 4-cylinder vehicle, when the tach reads 3000 RPM the engine is actually turning at 4500 RPM.

This is what I was told by "Comanche Addict":

"Yes, this is true. However, I ASSume by your user name you have a 2.5L engine in your rig? If the donor vehicle of new cluster also had a 2.5L engine, you will be fine and the tach RPM readings should be correct. However, if the donor had a 4.0L, you'll probably have to calibrate the tach to read the correct RPMs. There is an adjustable potentiometer in the tach used to calibrate it."

 

I REALLY do hope this is true and it's easy to do!

[Eagle]

The '84 through '86 tachometers did not have the adjustable potentiometer. The '88 through ?? did. I am not sure if '87 went with the old style or new style, or if they may have used some of each in the '87 model year.

[streetjeep2.5]

The '84 through '86 tachometers did not have the adjustable potentiometer. The '88 through ?? did. I am not sure if '87 went with the old style or new style, or if they may have used some of each in the '87 model year.

 

Oh, great! I have a weird jeep! :ack:

Anywho, I guess I will find out on startup. And, my engine bay is the one that is sized for the 4.0, so I think I have the "later" wiring. I really hope so! Maybe I shudda gone back to making for me a street chevy from the mid to late 50's so later stuff was no problem? :bowdown:

[junior88mj]

howdy guys i just swaped a full guage cluster from 90 4.0 xj into 90 2.5 mj it was easy swap the light switches to guage senders and adjusting the tach . pull the tach out of the cluster there is a white rotory switch to adjust it make some jumper wires to reconnect it to the cluster screws that connect the printed circuit and connect a external tach ( i used a timming light that has tach ) and fire it up and let it stalize idle and adjust the rotory switch till it matches the external tach the rev it up to 2000rpm and check that it still is a match to the external tach then reasemble the tach to the cluster junior