Tach works intermittently

[BHerring]

Greetings all,
So my '93 Tach works intermittently and I can seem to find the problem. My symptoms are, (when the Tach is NOT working) 1. No Tach 2. No AC Compressor 2. low voltage on the voltage dash gauge. This will only last about 3 minutes or so, after driving all of the sudden the Tach and everything starts working. Sometimes the Tach will work for weeks then it just quits, but never quits once its working.

Everything else seems to be working. I have done some searching and can't find what could be the common cause to make the Tach, AC Comp and Voltage gauge not to work.

Any and all information on what to check when not working will be greatly appreciated.

 

[GrantP]

First, I have NO experience with first gens. However, I had very similar problems on my 2nd gen 12v and it was just the crankshaft position sensor. I would lose overdrive, AC would shut down, no tach, and no charging. Always intermittent. Maybe that helps...

 

[BHerring]

GrantP,
Thanks for the info, I did check the OD when the tach was NOT working, and she would drop down a gear and when I turned the OD on, it would shift up. I also read about the CS Sensor could be bad, but I will check it out.

 

[GrantP]

I'm pretty sure your trans is not electronically controlled like my '97 47RE was so you likely won't have the same problem with the overdrive.

 

[PToombs]

It's probably the CPS or the wires to it. It tells the PCM that the truck is running and it's ok to start charging, ACing, and yes, it does control the OD on the 518 trans.

 

[GrantP]

It's probably the CPS or the wires to it. It tells the PCM that the truck is running and it's ok to start charging, ACing, and yes, it does control the OD on the 518 trans.

Thanks for the correction, I assumed it was all hydraulic.

 

[BHerring]

Ok, I will check the charging system, when the TACH is not working, I will check the battery voltage to see if the she is charging or not....now I must just wait for the problem to happen again. Thanks y'all for the information!

 

[B.G. Smith]

The crank sensor is mounted at the harmonic balance on your truck, it turns the alternator and tach on when engine starts. Looking at front of engine it should located about 10 Oclock position.

 

[BHerring]

BG Smith,
You must be a mind reader, because that was next question, I looked thru the Service Manual for the location but it does not show it and does not have a install and removal procedure. Does anybody know if the procedure is in the Novel (Service Manual). I read somewhere that there I need to air gap the sensor, but cant find anything in the service manual. Any all information will be greatly appreciated.

 

[B.G. Smith]

I would set @ .010 To .015 In. A business card or index card is about .010 in. thick.

 

[PToombs]

.050 is the correct air gap for it. I stopped typing and went thru my FSM and couldn't find it, but I know that's correct. One of those strange tidbits of info you never seem to forget.

 

[BHerring]

Thanks again to everybody, I took the connection apart and everything looked ok to me. I have also read it is .050. FSM Should have had in there, but I concur its not in mine, unless I am looking in all the wrong places..... Now I put it the connector back together, and now I just must wait to see if it happens again and do more testing....I know what I can do now, I just for it to stop working so I can take some readings... Thanks again for the help out there!!!! I really appreciate it.