Hey guys,

About a week ago, I noticed my tach at around 3.5k rpm while cruising in 5th gear going about 50mph. I thought that isn't right, it should be less. So I let off the gas, the tach stays, push in the clutch, the tach stays the same.

The tach isn't working properly most of the time. Sometimes when I just have the key in the ignition, the tach reads 500, without the engine running. When it is running, the tach starts out at around 500 rpm, but doesn't move with engine speed. But, the needle slowly moves up the tach scale the longer I drive. I drove for about 30min. the other day and it was around 5k rpm. I turn the car off, it drops back to 0 or 500.
Sometimes the tach jumps to the proper reading and works for a little while.

Actions I plan to take:
1. take out gauge, check connections, tighten screws
2. if 1 doesn't work, swap out tach

What other things can I do to check out this problem. I've searched and haven't seen anything quite like this before. I've only seen tachs staying at 0.

Advice?

 

I would rule out the tach being defective. If it is not going all the way back to zero when turning off and doesn't go to its correct idle position when turned on, it is going bad. Swap is a must.

 

Hey Dave -

Could be a couple of things really. Does your CC work ok? I'm thinking it might be the VSS - vehicle speed sensor (goes in the top of the trans and outputs a sig to the ECU). They can go bad from time to time, not a real common issue overall. Could be that, or it could be a defective tachometer. I'd guess the VSS first, and it's much easier to r+r if need be. Check the FSM - EL-70 - 78 (98' fsm). It goes through how to check the 'combination meter' (tach / speedo). It also gives mention to the VSS. Hope this helps. Hope you have a meter handy.

 

Check the battery terminals, too. I once drove, in my old Mercedes, a few hundred miles with one terminal disconnected. When I would do various things, the tach would respond in various way - e.g. I would put on the left blinker and it would jump between 500 and 3500, I would put on the cabin fan and it would go straight to 4000, etc. The tach was the only symptom (besides the car's not starting after I shut it off).

Obviously an '85 Mercedes and a '95 Maxima are two very different cars, but it's a good story and might help.

 

heheheheeeehhheeee

 

I think it's more likely that your gauge cluster is going to need changed. I don't think it's the VSS. The VSS is a little A/C generator. There is no way that it could be generating voltage with simple the key in the ignition and the engine off.

 

Good info guys. Thanks.

I'll be checking if the CC works today, hadn't thought of the VSS being the problem. It's like it's getting a signal, but a very weak one or something. I don't really know. Last night, I drove for 45 min. and the tach needle was at redline (obviously not the true engine speed).

 

Just checked if cruise control works and yes, it works fine. So, does that mean the VSS is good?

 

Dave -

The tach gets it's input signal form pin 5 on the ECU - to pin 3 of the tach. (it's the plug behind the spedo, above the fuel gauge - that pin set, refer to FSM for pinout if needed) According to the FSM, it says to run a diagnostic check on the gauge system. You have a 95'? I have a 98' with the digi odo display, it says to use (trip a or trip b) the display and set/reset button to run through the diagnosis mode for the intru cluster.

Lemme see if I can find and dl a FSM for the 95', otherwise someone else may have to help you. I do believe the pinout should be the same (at least from the ECU). You could, if you are handy with a meter, check the pin 5 of the ECU, just tap into the back of the plug if you can, or slip a small tab of wire in along with the plug (unplug, slip wire in, replug with wire in). See if you are getting any voltage (dc volts) out, the higher the RPM, the lower the voltage should be.

As far as I can tell here, the tach gets this signal from the crank sensor. A bad crank sensor should throw a CEL, like a bad VSS. So, to answer the ? about the VSS, it likely is good if you don't pull a P0500 (P0500 = 0104) code. On the other hand, it could also be the CKPS (EC-242/243).

Looking at this further, I'm gonna say it's the CKPS and here's a link incase it is, cheapest (most reliable) that I could find. http://www.rockauto.com/catalog/rafr...k931636-849902

The CKPS is what gives the ECU the signal for the tach, from what I can tell. Hope some of this will help. It's might help me in the future, who knows!

 

a new VSS cost 25 bucks on coutesy nissan. And its attached with one bolt on top of tranny. Ur gauge wiring could be gettin brittle, but its a lot easier to jus try the VSS first.

 

This is true. But faulty CKPS would also cause more issue than jus tach, i think.

OP may have to check wiring on ECU, pin (5) and ground. Hopefully the problem is evident.

VSS only influences speedometer.

Check FSM, EL-68

 

FYI - checked codes and nothing but the knock sensor code that has been a ghost code for a while now. Probably should change that as well.

I did find older posts about this same problem, and many just said it's the tach itself, nothing more. I don't think I'll change the VSS, doesn't really seem to be the symptoms of that. I may just swap gauges with my 96 to see if that's the problem, then go from there. Seems like the next free step.

 

+1... As I initially stated in my earlier posts just the tach itself...at least let this thread be an important tool in letting the newbies know how to search around first before reviving older threads..

 

Hope you gotta kid with tiny hands available! I used my neighbor kid last time I did one.

I think the only things that could cause this would be:

faulty tachometer /
faulty FCP (flexi connector on the back of the speedo cluster)
faulty ECU
or possibly a faulty CKPS.

I have to agree it's not the VSS though as I first might have thought. Another 'freebie' is to check the output of pin 5 on the ECU (dcv).

 

Yeah, when i was reading seems the tach has its own electronics and gets engine rpm from ECU. Prolly need to jus swap gauges and good.

 

The KS isn't that bad, I've done it myself, on my 96 Max, with only a couple scratches.

So, this afternoon the tach worked when I started out from work. So strange... Thanks for the suggestions. I'll keep you updated when I have time to work on it.

 

Switched gauges with my 96 GLE and the tach acts the same in that car (doesn't work). The 96 gauge I traded works fine in my 95.

Conclusion: I need a new tach for my cluster. Found a junkyard with a gauge cluster, but they wanted $50 and I'm cheap. Classified section here I come.

 

Swapped out the tach portion of the gauge and now the tach works great. A little harder than I thought, had to figure out the differences between 96 GLE black face gauges and 95 SE white face gauges. They are a little different. The hardest part was taking out the pin thing that keeps the needles from dropping.

In summary: Creeping tach = bad tach fixed by new tach

 

Good man. Did you find the instructions in removing the needle like I told you? It wasn't that bad compared to buying this part for ridiculous money from dealership.

 

Glad you got it figured out and it's working for you.