tach not working, strang findings...

[joshpntbl07]

i have a 95 240sx with a ka24de in it. the tach hasnt worked since i got it. at pin 3 of the ecm i am getting around 6 volts and it rises with rpms. my fsm says i should be getting around .9 volts at idle. i need to know where the ecm is getting its signal.

[Eikon]

I suck with electrical stuff, so I can't help you there... but, just out of curiousity.. Have you checked the rev sensor on the transmission? They are somewhat exposed, and once in a while a rock can kick up and hit the sensor or the connection or even dislodge the wire entirely. It could be that you aren't getting the tach signal????

Just an idea... something to cross off the list.

[joshpntbl07]

thanks for the reply man. i didnt know there was a sensor on the transmission. i figured the signal came from the dizzy. ill check for it when i get home from work. if you see this first, what exactly does it look like? thanks.

josh

[Eikon]

This is an S13 transmission, but it will be nearly identical to the S14 that you have.

Jack up the car a little bit on the passenger side and crawl under the passenger side door. Look toward the back of the transmission... note the picture above...

Here's a picture of a speed sensor... again not an S14.. but it will look the same.

Again, it may be something electrical like you guessed... but the speed sensor is easy to find and check, so you might as well do it.

actually the more I think about it... I'm wondering if your speedometer is working... if it is working.. chances are the problem is not the speed sensor. I would then bet that the issue is your tachometer itself. You may need to pull the cluster out and check the connections.

[joshpntbl07]

well my speedo works fine, i dont think the speed sensor affects the tach. I did some more looking today and found a few things that might help. i found that pin 2 at the ecm has almost 14volts to it. in the pinout i was looking at it says pin 2 is power transistor voltage? i have no idea what that is.i traced the wire and i found between the wire going to the ecm and the distributor a black fuse looking thing. on it it says 2.2k ohms. i ohmed it out and it was 2.2k. is this the correct fuse? its weird that there is the same voltage going into the fuse as there is coming out. i figured if there is 2.2k ohms of resistance then that would cut the voltage down some. or maybe pin 2 on the ecm has nothing to do with the tach signal, lol. im running out of ideas.....

[joshpntbl07]

well, another pinout shows pin 2 being distributor check resistor. still not clear if this has anything to do with the tach.

[r0llinlacs]

94 altima, ka24de 5 speed

tach is on crack. sometimes it works, most the time it doesn't. when it "switches" from not working to working, it goes crazy going back and forth from 0rpm to 8K+ really fast, then will work or not, whatever it feels like doing.

Took the gauge cluster apart, checked for loose connections and what-not. could not get the tach to read anything by "tapping" or "hitting" it while the car was running, it only goes crazy when driving, which makes me think it's not in the gauge cluster.

any ideas?