OK Tach Question

[Mudbug]

OK, I just bought this truck and already has tach, after market. Seemed to work when I first bought it. But now its off and on. Former owner has it linked into the factory plug. One of the wires has a small capacitor bridged into the circuit. Could this be the problem? How have you guys wired up your aftermarket Tachs? I would really like this thing to keep working consistantly. Thanks

[Richie O]

Sounds like an Isspro tach. Some of there models need the line with the diode ( thingy ) and others do not. The tach is run off the crank position sensor then through the ecm. There could be an issue with any number of things thats not related to the tach itself. If the crank sensor is frigged then it also will discharge when the ecm looses its signal. I lost a crank sensor in my 93 but it just totally quit.

[Mudbug]

How or where would a guy begin to check this crank sensor deal out? I figure if I can find out where the other end is maybe I can troubleshoot it better.

[Richie O]

When the tach stops working does the truck still charge? That would be first I guess.

[Mudbug]

When the tach stops working does the truck still charge? That would be first I guess.

Well the tach hasnt worked the last two times that I have driven it. So,, now that you ask the question, I went out and checked to see if it was charging, and no its not. I guess one of the reasons I didnt know was it has
2 brand new batteries in it. But they are showing below 12 volts. So is that the alternator? or something in the
ecm? And would low voltage keep my fuel shutoff solenoid from working properly? thats an added question. Heres a pic of my guage setup. The 2 on the left are RW products, ? Manifold pressure is isspro.

[Richie O]

Well then, 1 cause of your broblem could be the crank position sensor. Here is a link on how to test it. Philip wrote this and his light bulb is brighter then mine.

http://www.cumminsforum.com/forum/89-93 ... ensor.html



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[Mudbug]

Um, where exactly is this CPS? This is my first cummins.

[oldestof11]

Look directly below the fan, directly above the harmonic balancer.

[Mudbug]

Ah found it.
I checked it with a voltmeter like Philip showed and it shows hardly any voltage at all going back to the pcm.
Now I performed these tests while the engine was running. Anyone done this before?

[PToombs]

Did you pull the plug apart and check it for corrosion? It's at the front of the head, just follow the wires up. The other thing is the sensor clearance, needs to be .050 off the balancer.

[Mudbug]

Did you pull the plug apart and check it for corrosion? It's at the front of the head, just follow the wires up. The other thing is the sensor clearance, needs to be .050 off the balancer.

Ok, couple of questions on this. Its factory, how would or could it have moved? It has 197k miles on it.
2nd question,, how the heck do ya get a feeler guage up in thar?

[PToombs]

Maybe someone changed the front seal and didn't set it correctly, or it may have vibrated and moved a little.
To be honest, I can't remember how I set mine. I had the fan off because I was doing the KDP. I either used a feeler guage, or found something the right thickness and used that. You know, use a mic and measure a matchbook or something on that idea.

[Richie O]

Thats what I did Pete. I found some paper or matchbook and stuck it between the sensor and the balancer. I then pushed the sensor down and wound it tight. Take out the matchbook and good to go. PETE, did I spell everything right??

[PToombs]

Not my day to babysit ya buddy, ask Jon, it's his turn.

[Mudbug]

wow, I knew I did a good thing when I joined up here. Sounds good to me. Now to find my feeler gauge and commence to finding something the same thickness. Would love to have the tach working again.....