Tach not working

[mattbuch96]

A few days ago I upgraded my "base model cluster" to the most upgraded one. I followed these directions http://www.naxja.org/forum/showthread.php?t=921205. And my tach isn't working. Any idea?

 

 

 

 

 

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[AMC86Kid]

with out any pics of how it looks hooked up in the vehicle i can't really determine what could have went wrong 

 

when you say your Tach isnt working 

do you mean that all of the gauges work 

but the RPM gauge does not work?

 

also tell us what year your MJ is 

the guy in your link did it in a 87 XJ

so he might have already had a RPM gauge even in his old dash

witch made the swap to the new one super easy for him 

[mattbuch96]

Its a 1990 2.5l ax4 rwd 

 

The cluster on the top is my old one with the "idiot lights" and I swaped in the more upgraded one

I switched my oil pressure sender and engine temp sender to sensors. 

 

After driving it around all other guages work except the tach.

[AMC86Kid]

ok that help me out so i believe 

since you have a in line 4 motor and your vehicle is 2 wheel drive

you have no sensor from your tranny telling the dash what your rpm is 

i think the only way to get it to work 

is to take the tranny to a tranny shop and have them put in a sensor 

so that you can hook it up to your rpm dash gauge 

 

now i may be wrong but I'm pretty sure that since the original dash did not have an rpm gauge 

then why would they install a tranny that has a rpm sensor in it ???

 

on the other hand you might be lucky

they might have the sensor in the tranny

and they just never ran the wire for it up to the dash

 

i would look at the tranny and see if there is any evidence of an electrical connection and go from there

[Minuit]

ok that help me out so i believe 

since you have a in line 4 motor and your vehicle is 2 wheel drive

you have no sensor from your tranny telling the dash what your rpm is 

i think the only way to get it to work 

is to take the tranny to a tranny shop and have them put in a sensor 

so that you can hook it up to your rpm dash gauge 

 

now i may be wrong but I'm pretty sure that since the original dash did not have an rpm gauge 

then why would they install a tranny that has a rpm sensor in it ???

 

on the other hand you might be lucky

they might have the sensor in the tranny

and they just never ran the wire for it up to the dash

 

i would look at the tranny and see if there is any evidence of an electrical connection and go from there

 

This is incorrect. The tach should work out of the box. The signal comes from the ignition system and every MJ is equipped for it, whether it originally had the tach or not. I've converted two trucks now and the tach has worked correctly both times. Check that the two plugs are snapped in all the way (on my '89, sometimes they won't go in completely and the gauges won't work) and check the ground under the dashboard. You mentioned everything else works fine, so neither of those are probably the issue but they're still worth checking. Other than that, I've never personally had a tach go bad but if everything else checks out I'd start suspecting the tachometer gauge itself may be bad. You might also want to look for any nicks or tears in the cluster's printed circuit board. Let me know what you determine.

 

I have quite a few parts for these Renix clusters (no complete ones, sadly) so if you need another tach or a printed circuit board I could probably help you out.

[AMC86Kid]

well there you go check and make sure it is connect and grounded well 

then if it still don't work take it back and try a different one

if it still does not work then let us know and i can look up some schematical specs for you 

[mattbuch96]

Thank you, I do not see any imperfections on the circuit board, where is the ground under the dash located? I will have to check that. 

[Minuit]

On the left side of the dash above the hood release cable. Should be a 5/16" bolt. You might have to take the knee panel off to see it.

 

http://cruiser54.com?p=110

[mattbuch96]

I will check that tomorrow morning and let you know, i really hope it works its self out. thanks again!

[Eagle]

If I remember correctly, there are two contacts where the tach head attaches to the printed circuit. Under the hood, there are two small, yellow "thingies" (highly technical term there) with flip caps on them. Inside, there are contacts for running some basic diagnostics. The smaller of the two has six terminals (receptacles). That's the one with the feed for testing the tach. You can check it by taking the cluster out of the dashboard and running jumpers from the test terminals to the tach head.

 

I'm not set up to scan the diagram of the diagnostic connector. As drawn, it shows two columns and three rows. The right side of the block has two notches cut out of it. Oriented that way, top right is #1, #2 below that, #3 bottom right ... then #4 top left, #5 below that, and #6 bottom left. #1 is the positive tach feed. #3 is the ECU ground -- you can use that for the tach ground, or just ground it to the engine block.

[buckwheat]

My assumption would be in using a tach from a 6 cylinder engine in a four cylinder engine doesnt work. Since it is based on the ignition system, wouldn't that change based on how many cylinders are firing? Sorry if this is incorrect information.

[DirtyComanche]

My assumption would be in using a tach from a 6 cylinder engine in a four cylinder engine doesnt work. Since it is based on the ignition system, wouldn't that change based on how many cylinders are firing? Sorry if this is incorrect information.

 

It will 'work' even if it's the wrong one.  It just reads incorrectly.

[Eagle]

 

My assumption would be in using a tach from a 6 cylinder engine in a four cylinder engine doesnt work. Since it is based on the ignition system, wouldn't that change based on how many cylinders are firing? Sorry if this is incorrect information.

 

It will 'work' even if it's the wrong one.  It just reads incorrectly.

 

 

^^^ What he said.

[AMC86Kid]

what exactly do you guys mean when you say it runs off of the ignition system

[Eagle]

what exactly do you guys mean when you say it runs off of the ignition system

 

The tachometer is electronic, not mechanical. It receives electrical pulses and "counts" them, converting that into an RPM reading. The electrical pulses for the tachometer come from the ignition. What it's doing is counting how many times the coil sends a spark to the spark plugs.

[mattbuch96]

Thank you guys for all the input, i ended up just taking it out and plugging it back in and everything works! I must have not had it all the way plugged in  :doh:

[AMC86Kid]

congrats bro at least you figured it out and got it to work

does it work correctly or is the reading off at all ?

[Eagle]

congrats bro at least you figured it out and got it to work

does it work correctly or is the reading off at all ?

 

Good news that he got it working.

 

If the "new" cluster came from a 6-cylinder, the tach probably doesn't read correcttly. The good news is that that style cluster is the newer style ("newer" as it relates to the Renix years, with the mechanical speedometer), and those have a potentiometer on the back of the tachometer that can be used to adjust it to read correctly for a 4-cylinder. If it came from a 4-cylinder, no adjustment should be required.

[Minuit]

Thank you guys for all the input, i ended up just taking it out and plugging it back in and everything works! I must have not had it all the way plugged in  :doh:

 

Always the simple stuff! :thumbsup: Sometimes those plugs don't want to go all the way in for whatever reason.