Finally got my tach to work!

[AKimmel]

After a long battle I have finally gotten my tach to work today. I determined that my computer is screwed up in my truck for the tach output. I bought the isspro tach and hooked it up, and it didn't work below 1200RPM's. I posted a thread and ya'll said I needed the isspro harness. Well I bought it and hooked it up, and it didn't work at all. I sent everything back to isspro and they said the harness and tach were fine. I got them back and hooked it up sraight off the crank sensor, and it worked correctly up to 1500RPM's then would quit. My air gap was too big and it was loosing the signal, but my alt. , A/C, and cruise never had a problem, so who cares it finally read all the way up to 2500 at least. I didn't want to free rev it higher than that. I ended up unhooking the PCM plug and cutting the tach wire (43) and soldering it in with the crank sensor wire (24). Now my tach works off the under dash plug, and everything else seems to function correctly.



Note: If you want to run and Autometer tach in your truck, I'm pretty sure I have found a way. In my tach battle I bought a Dakota Digital SGI8 tach interface and got it to work staight off the crank sensor but it died at 1500RPM's like the isspro. I thought the SGI8 just couldn't read something in my truck so I sent it back. But I know now it was just the air gap that was too big. If you have a good tach signal it may work off that, if not just tie the wire in like I did along with the SGI8, and you should be in business to use any standard auto tach.

 

[Philip]

I might give that Dakota Digital box a try soon.

 

[dpuckett]

I'm having similar troubles with my tach- cant figure it out. My airgap is at . 049"as per the advice here. I looked in my 93FSM (1579CPL engine), and came to the conclusion to try that you apparently succeded with, but I am somewhat confused- which wires are you hooking up where? I found the signal wire under the dash, and get 350rpm displayed for about 5sec, then it goes dead. With this cut and splice, has it affected anything else- alternator, cruise, a/c, etc?



Daniel

 

[paccool]

I had the same problem when I tried to get my tach to work. Bought an ISSPRO setup and it would not work. Tried different things, no go. Finally gave up and bought a TinyTach.



Then I had the opportunity to by a new OEM tack the same as they used in the firstgens and bought it. Tried hooking it up, same problem. Finally decided the PCM was not putting out the trigger to the harness inside the cab. Got a new PCM and that took care of the problem. Only reason I bought the PCM was I got a killer deal on one, it was still sealed in the original Dodge package. Paid about half of the normal amount. It has been working real nice since then, no problems.

 

[AKimmel]

What I did to test it before I cut anything, was take a piece of mig welding wire and slide it inside the back of the connector beside the GY/BK wire. I did this on the grey plug thats on the back left side of the engine. I ran a jumper wire from the piece of mig wire to the tach input. My tach worked like that. Then to do this permanently just unbolt the PCM plug, take the plastic cap off that covers the wires, cut the tach signal wire that goes to the under dash plug (GY/LB,#43), and splice it in with the crank shaft sensor wire (GY/BK,#24). I sealed the end of the old tach signal wire just incase so it doesn't short out, or you can take the red retainer out of the plug and remove the pin and all. After I did all this, I cranked the truck up, the tach worked, Alt was charging, and A/C was cooling. I reved it up to 2500 and the Alt didn't fluctuate so I think everythings all right. I'm not sure but, I don't think the computer uses the crank signal after its running, because my air gap was way to big and the tach would loose the signal above 1500 and I never notice a problem with the Alt,A/C, or Cruise.