Engine/Transmission (1994 - 1998) stuck in 3rd no tach and no charge

[JonWilson]

I am trying to find a problem with a 96 12 valve with a 47 re trans the tach doesn't work,the alternator doesn't charge , the trans does 3rd gear starts unless shifted manually. Ive replaced engine speed sensor , tried different pcm checked and switched relays . governor sensor and transducer have been replaced . the reference voltage to the sensors is a little high 5. 13 to 5. 33 volts I have checked and re checked grounds following a factory service manual all to no avail. I have charged the batteries up just in case it was just lack of good charged batteries all still changes nothing . Ive searched under dash for loose wiring nothing found . unpluged and cleaned all connectors still no change any other suggestions or ideas would be greatly appreciated ThanksOn this vehicle Ive already isolated all wiring back to pcm and nothing found . I played with the crank sensor gap from . 046 to. 051 no change and yes I realize that the trans is in limp in mode . the other problem I have is that the Pcm will not communicate with my snapon solus scantool it powers up thru the dcl but kicks out a no communication reading Ive tried the setting on both chrysler testing and obd generic and same results. Im about ready to tell the man who owns the truck to drive it into the lake Ive also torn apart all things under the dash folliowng wires back to no avail . any other advice is definately appreciated Thanks guys for your quick replys so far this is the only site ive found on the internet worth its wieght in gold

 

[bmoeller]

The transmission is in limp mode.

 

[tp0d]

First, Welcome to the TDR!



Sounds like your new speed sensor either has a bad interconnector wire (rubbed thru) or is gapped improperly. It should be gapped at . 050 i believe, with a brass feeler. Try to isolate those wires back to the PCM and test the interconnector for continuity, and check to see if you can read the coil thru the pcm connector. Next would be verifying all grounds that the PCM uses, sounds like you may have a bad one somewhere. What are you cleaning the connectors with? Radio shak's tv tuner cleaner has always worked very well for me.



hmm... sounds like you got a good one there... (sarcasm intended of course)



good luck, keep us posted. .



-j

 

[JonWilson]

On this vehicle Ive already isolated all wiring back to pcm and nothing found . I played with the crank sensor gap from . 046 to. 051 no change and yes I realize that the trans is in limp in mode . I rebuild transmission s for a living the other problem I have is that the Pcm will not communicate with my snapon solus scantool it powers up thru the dcl but kicks out a no communication reading Ive tried the setting on both chrysler testing and obd generic and same results. Im about ready to tell the man who owns the truck to drive it into the lake Ive also torn apart all things under the dash folliowng wires back to no avail . any other advice is definately appreciated Thanks guys for your quick replys so far this is the only site ive found on the internet worth its wieght in gold

 

[Lightfoot]

Stuck in third

My '96 got stuck in third. Lost the tach and speedo. Dash warning lights, advisory lights stayed on after starting the truck. Turned out to be the altrnator. The on board computer power draws directly from alternator output, not the battery. When alternator power begins to fade, the computer begins to dump controll systems. This may be what is happpening to your truck.



'96,4x4 quad cab,AT,4"exhaust,high flow muffler,Power Lock rear diff. , 12. 000 lb. Warn winch,PacBrake,354 gears

 

[JonWilson]

Well Ive still not been able to pin down the problem with this vehicle I did try another known good alternator and pcm still no charge and no read out of the diagnostic link. If I can get the diagnostic link to read I will probably have found my problem any more Ideas guys Thanks Jon Wilson

 

[HFreeman]

My '95 did the same think. Was caused by a major f***up by yours truly. After replacing the shutoff solinoid that I fried I still had the no tack no charge problem. Turned out to be a 15 amp fuse in the block at the end of the dash. It was about half way down toward the front of the truck. I'll try to find which one it was, I forgot.

 

[K5IP]

If you have access to a scope, you can verify the engine speed sensor output. It switches between zero and the reference voltage each time the notch in the damper passes the sensor. I think you can also observe the output with a vom while cranking the engine. It is crude but operational.

Rog

 

[K5IP]

One other thought,

The service manual for my 95 indicates that the reference voltage for the engine speed sensor is 8 volts. Not the 5 + you indicate. This comes from pin#7 PCM INPUT.

You might want to open the connector to the speed sensor and check the voltage, both loaded and unloaded. The 8 VDC reference is also used to provide power to the vehicle speed sensor. It is possible that either sensor is loading (pulling down) the reference causing other problems.

You are on the right track. That engine speed sensor function is the root cause.

 

[Reb.B]

Your PCM is shot. I'm sure your A/C doesn't blow cold either, a/c clutch won't engage. PCM controls trans, a/c, tach, voltage regulation.