Engine/Transmission (1994 - 1998) Tach went to zero and truck still running

[AZTURBO]

I was driving to the store the other day and all of a sudden My dash started beeping and I looked down to see I had NO tach, fuel gauge, or air conditioning but the fan motor was still blowing. Can anyone tell me what happened?

I had pulled into a parking lot after the fact ready to call AAA. I shut off the engine thinking I was going home on the back of a tow truck. But I restarted the engine and everything was back to normal. I still have not had it do it again as of yet.

 

[hsmith]

Crank sensor. Check the connector.

 

[Missouri Mule]

I've heard of the Engine Speed Sensor (crank sensor) taking out the Tach,voltmeter,overdrive,AC (when engine speed sensor looses its ground) and speedometer but not the fuel gauge. This could be a first!



Looking at the factory service manual the fuel sensor and a/c clutch have the same ground G119. Have not confirmed that the PCM has G119 as ground (since the PCM supplyies the ground to the engine speed sensor and operates the tach) .



Confirmed that PCM is grounded by G119 ( Front driver's side of engine, probably grounded to intake manifold. )

 

[WilsonF]

What year truck? 12V or 24V?

Floyd

 

[AZTURBO]

Sorry, it seems I left an import part of the info. My truck is a 1998 12v with an auto trans. and is 2 wheel drive. I have checked a couple of the suggested things that I was told, but have not found anything unussual. This is really got me stumped. I did have the transmission rebuilt about 4-5 monthes ago and it has not been shifting right. So whatever it is that is my problem it is affecting the shifting of the transmission.

 

[Allumsr]

i am having the same sort of issue. i have a 1995 12v but the enngin has been changed out to what i think is from a 97 model, looking for an engin number the label has been removed so i dont exactly what i got. the emission part of the label that pop riveted on the oil fill case is still there and say 1997 emission codes and what not. anyway my problem is the same but differant, the ac clutch keeps poping on and of every second or so, i know thats not right. and the tach sometimes it works and sometimes it doesnt. when it does the transmission shifts fine all the to overdrive lock in and stays for awhile. then the tach starts jumpin around like a short circut and the transmission then shifts in and out of overdrive lock. its got to be a bad ground or wire somewhere but im not sure where to start, there are wires everywhere due to the engin change out. what im wondering is where the crank senser is located and start from there chasing wires

 

[surfbeetle]

I believe the ECU controls both the AC and the auto trans. Both of you could be in need of an ECU.

 

[Missouri Mule]

Allumsr, the Engine Speed Sensor (crank speed sensor, crank sensor,crank position sensor) is located above the harmonic balancer. The engine speed sensor connector is located top front of engine, follow the wires down.

Try cleaning the connector with contact cleaner, but it sounds like the engine speed sensor is on its way out. You can check if it has power/ground to it also if it is sending a signal out. Do a search a lot of info on the engine speed sensor.

 

[Missouri Mule]

AZTURBO, it could be you TPS (Throttle Position Sensor) acting up.

You can do the key trick to see if you have any codes stored (key on,keyoff,key on, key off. key on. On a 98 should have codes appear in odometer,if you can do it onb 98s you mite need a scanner. )

 

[Allumsr]

thanks Mule, for the info on the crank sensor. but crazy enough i kept reading on some other posts and someone said that the main ground wire for the ac overdrive and power windows is on top connected to the intake air temp sensor. so i went and checked because i resently pulled number 2 and 3 injectors to replace the copper washers due to fuel leak. that was fun considering iv never worked on a deisel. anyway i must not have tightened those 2 wires tight enough, because i put a backup wrench and got the extra tight and the problem seased to excist. anyway i love this forum, ive been a member for several years and never even had post anything, just read whats there and find a fix. awsom thanks everyone

 

[DUtt]

tach sender

just a tip , gap at harmonic balancer and css is . 050 , a used piece of cd music disc is just that and non magnetic (12v) bad gap causes alot crazy tach

 

[PhillipFleming]

This same thing happend to me in my 95 it would intermittly show no tach and wouldnt charge then would be fine. What i found was the positive wire off the battery going to the fuse box was really crroded (sorry for the spelling)on the battery & not making contact once in a while. my truck also had no power to the cab one time when iwent to start it then the next time i went to start it it was fine. Thats when i new it was a major power sorce. Turned out to be the battery was leaking acid and the connection was toast.