Loss of Outputs

[Driftwood Ram]

I did not know what to title this because there are a bunch of problems, probably with a common cause. I have been searching the shop manual, but am looking for some help. The following are not working, speedometer, tach, OD button, wait to start light, The alternator appears to not be charging, the transmission is starting in second gear and does not shift. Any suggestions would be appreciated. There is probably more but maybe this is enough of a clue.
Thanks,
Tracy

 

[BigPapa]

Start by checking the I.O.D. fuse in the end of the dash. Next, check your Engine Speed Sensor, ESS. If both those are good, next thing I'd suspect would be the PCM. Best bet on it would be to find a friend that has the same truck and swap his in. The PCM will have the part number on it, just make sure it matches. I'm not sure, but '96 to '98 auto MAY work.

 

[Driftwood Ram]

Start by checking the I.O.D. fuse in the end of the dash. Next, check your Engine Speed Sensor, ESS. If both those are good, next thing I'd suspect would be the PCM. Best bet on it would be to find a friend that has the same truck and swap his in. The PCM will have the part number on it, just make sure it matches. I'm not sure, but '96 to '98 auto MAY work.

Big Papa, Thanks for your response. I give up. What is the I.O.D fuse? I ruled out the ESS because the wait to start light does not come on with the ignition switch as well as the water in fuel light.

 

[GAmes]

A PCM from a '97 (automatic trans) will work but not a '98 PCM. Since both the speedo and the tach are inop you can rule out the ESS. The IOD is ignition off draw, probably not the culprit. I'd be tracing the circuits in the FSM looking for a place where the vehicle speed sensor and the engine speed sensor merge. My guess is a ground point.

 

[BigPapa]

Gary’s the man. I’d take his advice. I’ll search some wiring diagrams and see what I can find.

 

[Driftwood Ram]

I have done more searching on this. First, it is not the PCM. Got one at a wrecker with the same results. I think it has to do with the 5 volt supply. On circuit K7, PCM connector B pin 31 I only have 2.0 volts with connectors B and C unplugged. On circuit K6, connector A pin 17 I only have .47 volts with B and C unplugged and 6 ohms to ground with connector A unplugged. As near as I can figure K6 only feeds the TPS and the ESS. I unplugged the TPS with no change in readings. So I guess my question would be, "could the ESS be faulty shunting the 5 volt supply"? This is a non EGR engine.

 

[Missouri Mule]

The engine speed sensor located on front of block by the harmonic/vibration damper when it went bad or moved some how caused a lot of those symptoms.

 

[Driftwood Ram]

And the answer is-------------------Engine Speed Sensor---------- also known as Speed/Crank Position Sensor. As soon as I unplugged it the 5 volt supply came back from the PCM. Now I just need to wait for the brass feeler gauge and ESS to show up at my door step.

 

[BigPapa]

Brass feeler gauge is unnecessary. Just use an old credit card.

 

[GAmes]

And the answer is-------------------Engine Speed Sensor---------- also known as Speed/Crank Position Sensor.

I'm sitting on pins and needles wondering if the ESS replacement fixed the tach problem. If it did I've been putting out false info for a long time.

 

[Driftwood Ram]

Gary, Sit no longer. ESS replacement fixed all. I think it was because of the 5 VDC being shunted to ground coming from the ESS.

 

[GAmes]

Thanks. Something new to add to my mental card file.

 

[PBJ2500CTD]

I tried following the circuitry in my 98 manual (a little challenging with all the different pages that had to be referenced) and agree the ESS could cause the symptoms experienced. If the ESS 5vdc shorts to ground it will affect a number of other components through their sensors and instrument readings.
I was a little concerned with a 6 ohm reading on a ground circuit but since the schematics do not show what happens in the magic boxes I had to dust off my electronic memory cells and visualize the intended circuit function then assume the ground is a common potential within the magic boxes and not earth ground referenced to the main charging system. Anyway, good fix and thanks for sharing!