Engine/Transmission (1994 - 1998) no tach, speedo, a/c, and alternator charge

[Cumminsman]

pulling a gooseneck with my 95 the other day. had to slam on the brakes to avoid a crash and looked down and no tach or speedo. then noticed that the a/c wasn't working and the alternator wasn't charging. stopped, shut down the truck and restarted. all was good. took off down the road again and tach and speedo went to 0. no a/c or alternator. checked pcm grounds, visually inspected Enigine speed sensor. all looks good. before i start changing parts, any other ideas of things that i could or should check? thanks, nick

 

[DSiemens]

Check the electrical connection at the crank sensor. If that connection is intermittent, the pcm doesn't get a signal to turn on. So, no tach, speedo and so on.

 

[Cumminsman]

connection appears good. i can crank it up in the driveway and it will work until you put it in a forward gear. may go 10' or 300' before it stops working. it will work fine as long as it is ideling and not moving.

 

[DSiemens]

That is very similar to what happened on my 95. A little bit of engine vibration and nothing worked. The connection looked good but it was not. Used electrical cleaner and a zip tie to secure connector and no more problems. If you have a frequency counter you could check to see it the pcm was receiving a signal from the crank sensor.

 

[Cumminsman]

what is a good electrical cleaner?

 

[DSiemens]

Denatured alcohol works good. But for cleaning weather pak connectors I use a spray cleaner that is found in the brake cleaner section of most part stores (NAPA). I would use brake cleaner if it said that it would not harm the plastic.

 

[DavidGardner]

LPS contact cleaner. . I think you can buy it at auto parts stores or maybe radio shack. If all else fails good ol WD-40 will work o. k.

 

[Cumminsman]

ok, i tried cleaning it. no change. you can crank it sitting still and rev it up to 4500 rpms. works great. back down the driveway. works great. put it in a forward gear. let out on the clutch. before you get to the end of the driveway it stops working. may go 5' may go 300'. really weird. can you ohm the ess out? guess i'll carry it to the dealer tomorrow evening. i am not having any luck. maybe the computer will tell me something. thanks, nick

 

[DSiemens]

The PCM is located on the passenger side firewall. It is possible that there is some corrosion/tarnish on the pins. I would clean there next before going to the dealer. The only other thing I can think of is a pinched or broken wire. Good luck.

 

[Cumminsman]

oh god, i can't imagine trying to find a pinched or broken wire. that would suck. dealer is free, just 40 miles from the house. my 01 is up there now. so i have to go tomorrow nite. we'll see what their computer syas i guess. pcm connections are ok. checked them several times already. thanks for your help, nick

 

[Howard Durand]

Do you have a good ground connection between engine and frame?

The batteries are grounded to the engine and so are most of the sensors but I think the PCM is grounded to the body.

Your sudden stop may have broken a connection between the two.



I recently read in another thread on this forum where a reader solved a problem similar to yours by connecting a ground wire between the firewall, where the PCM is mounted, and the engine.



Might be worth a try.

 

[Missouri Mule]

Check wires/connections at steering wheel column. The symptoms seem related to the engine speed sensor (12v's)/engine crank sensor (24 v's) but one. The speedometer not working is not related to the ESS.

Home approvement stores carry eletrical contact cleaner/dryer, I b

bought some at The home depot a few weeks ago.



I believe that the sensor ground for pcm are located on the gound bolt in front of the grid heater.

 

[Howard Durand]

One peculiarity is that the vehicle speed sensor and engine speed sensors both use the same 8 volt supply from the PCM.

If the vehicle speed sensor or it's wiring is shorted to ground, it would disable both of them.

Try disconnecting the vehicle speed sensor at the transfer case and see if that makes any difference. If not, check the wiring.



It would appear that the sudden stop you made has something to do with the problem if it wasn't doing this before.