PCM question

[Shadrach]

My friend want to convert a 92 D250 auto to 4X4 std. I know the PCM controls O/D but WITH a stick he wouldn't need that. Could he still use the auto PCM or does he have to change it ? What all does it control? voltage regulator, O/D cruise, grid heaters... ??? Thanks Shadrach

 

[mweiman]

I am pretty sure from what research I have done an auto pcm will work on a manual but not the other way around. I can't say I have tried it though.

Matt

 

[Bob Beauchaine]

That's the way I understand it also. ^^^



Bob

 

[Paul Herioux]

Yes, that is the way it will work. The pcm will just set fault codes for the OD and TC solenoids that are no longer there.

 

[Shadrach]

So I will have the check engine light on all the time? Shadrach

 

[Paul Herioux]

I don't believe it will be. My memory is a little fussy on emissions regs from the 92 model year. I believe at that point in time an OD failure on a diesel motor was not considered an emissions failure so no check engine light. Another way to get around this would be to install a 60 ohm resistor between the wires going to the OD solenoid so the computer will think there is one hooked to it.

 

[ihegdal]

My son converted a 92 from auto to manual and did not do anything to fool the PCM. It does not cause the engine check light to come on.

 

[Shadrach]

Thanks guys. Shadrach

 

[JDancoe]

Just for information- Last summer my brother & I converted/retrofitted a 92 CTD with Auto into a 1986-D-200. The PCU for the auto trans. turned out to be faulty (Alternator control circuit was inop. ) We replaced it with a PCU I had for a 5 speed. Engine wise, everything worked OK- no fault lights, etc. As for the transmission, we eliminated the TPS and used the switch on the dash to engage/disengage the O. D. at the driver's control. Starting from dead stop, if the O. D. switch is "On", the trans will shift up through all four gears, and the full throttle 3-4 kick-down works as normal, as it is controlled hydraulically inside the trans. Jack Dancoe

 

[DVolk]

Other than possibly controlling the overdrive all the ECM does is controll the alternator

you dont need the ecm in the truck to get it to run with a manual and there is a way to bi pass the overdrive with a kit from jet transmission

 

[Kirwin]

PCM inputs and outputs

The PCM on 91. 5-93 intercooled trucks has very little to do with engine operation. Its does control the intake manifold heaters (including the wait to start light), water in fuel light, regulates the charging circuit via controlling the alternator field, and operates the cruise control. The transmission outputs are only to engage/disengage 4th gear in the 91. 5-93 years. There was no provision for a lock up torque convertor during this time for diesel applications. If you get a copy of the 91. 5 diesel supplement it has a wiring diagram that was very handy when I converted my 85 Ramcharger to Cummins power. You don't really need the Vehicle Speed Sensor (VSS) if your not going to use the PCM outputs for cruise control. This wire inputs to the PCM and the instrument cluster . The pair of wires come form the transfer case speedometer drive. They are needed however in order for the speedometer to work. The speedometer uses the same VSS signal to determine speed. Since the 85 did not have this I used a vehicle speed sensor for a Dakota application which goes in the speedometer cable to obtain the VSS signal and then everything worked on my application. I used the VSS input to the PCM so my cruise would work but kept the speedometer cable drive to run my 85's mechanical speedometer. Hope this helps. I could fax you a copy of the pages from the 91. 5 service manual if that would help. Ken Irwin

 

[Paychk]

Here is a simple schematic



https://www.turbodieselregister.com/user_gallery/displayimage.php?&photoid=3751&width=4