I've started looking into getting a Cummins, 1995 D2500 12v automatic to be exact. I've found one that is rather beat up but runs and drives for $3500, but I have a question about some odd **** located under the dash in the cab.

There seems to be a **** under the dash that I am assuming is a manual boost controller, however if it is turned too far it will set the check engine light and send the truck into what I assume is limp mode, as it seems to be down on power and will hardly get out of it's own way.

If I turn the **** counterclockwise (down) and restart the truck, the check engine light will go out and it seems to shift and accelerate with plenty of power. Does anyone have an idea what in the world the PO did to this truck?

I'm guessing some one tried to rice out this truck, but was wondering if anyone had some advice. Thanks!

You can see the **** just barely in this picture, it seems to be an aluminum rheostat type ****?



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It looks just like this, but I know the 12v cannot be controlled with a module:

 

Not real familiar with 12 valves but if it's a boost controller I don't see where that would have that effect on your truck. I have a USB bell turbo with a boost controller and I can crank it wide open or shut. The only difference is the amount of boost I can get. Can you follow the back side of that controller through the fire wall and see where it leads?

 

I am going to try that after I go back to look at the truck, I'm a bit weary of what the PO did to it. I'm mostly concerned with why it trips the check engine light, and confused considering that 12v Cummins are not electronic, certainly make me want to pull my hair out wondering what in God's name it does haha!

 

I would take a look at your turbo and see if the wastegate has been tinkered with
to take a blind stab at it i would say its a variable resistor that is jacked into a sensor
that is changing something but that makes no sense either because fuel control is mechanical
so that takes us to shifting
a common mod is to have a grounding switch for the tcc lockup
it will lock your torque convertor and force the trans to shift into OD
if you follow the harness and tell me wiring colors its spliced into it would help alot
also location of the splice

good luck
scott

 

it is a valet switch for a 12valve

 

I hadn't even thought of that, a rheostat that will cut off signal to the AFC correct? It seems like that would make sense with the check engine light being set on full cut.

 

somewhat this is the function

Override the power of your vehicle with the flick of a switch! By preventing full fuel flow to the injectors. This switch was designed for situations when you don’t want the vehicle operator to experience the full power of your engine.

It’s great for kids driving their parents truck, valet drivers, or just anyone who doesn’t feel comfortable will all that power.

 

Man, I hope you are right, it sounds spot on. You have saved me a giant headache if that's what it is. I'll let you know later this evening, I'm going to go look it over again and decide if I think it's worth spending some cash on

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Interesting development, so the little **** is to get voltage to the TPS. I tracked down the previous owner and spoke with him about the truck he traded into the dealer. Apparently the TPS was defective and he needed to rig a circuit to provide the voltage when he decided to trade in the truck. Pretty ghetto, but I'll buy a TPS and replace it after I pick the truck up tomorrow. He seems to have otherwise taken very good care of it and seemed sad to let it go but promised it would be a good truck for a long while.

I checked the front crank seal which seems to have a small leak, trans fluid and oil look and smell fine, no blow by through the crankcase or coolant system, truck fires up and runs perfectly without the check engine light coming on (unless you turn the **** up too far and block the TPS voltage).