pressure modulating valve???

[Nitrous05]

So I just bought a 1993 dodge cummins. it has a 1990 motor and trans (5 speed). I notice a sensor unplugged that's hooked to the injection pump. ive researched and found its called the pressure modulating valve. I understand that it advances timing and all but what controls it? the truck runs a little rough, would it have any connection to this valve being unhooked? any help would be appretiated
thanks in advance

[PToombs]

That's the KSB, it's the cold start advance. If you have a pre 91.5 engine when you add power, it retards the timing. If it's post 91.5, power advances it. Yours is advanced when you start it, there is a wax pellet inside that expands when the power is applied when it warms up,(thru a switch on the intake plate) and that pushes on the timing piston and retards the timing. When the engine warms up the switch on the plate closes, turning the power on.
The later engines work the opposite, power goes to a solenoid and pushes the piston advanced when cold. When the engine warms up the switch opens and cuts power, and the timing goes back to normal.
If you add power to it when it's warm the engine should smooth out some. If there's no power to the wire you need to check the switch on the intake plate behind the air intake pipe. I think the power for that comes from the shut off solenoid, it should have 2 wires on it. I know the later ones do, not positive on the early ones.

[TRACTJDS0428]

are there any ill affects on the engine if you unhook the power to the KSB and keep the timing advanced? I dont know that im ready to tackle advancing my timing mechanically so thought it would be worth asking?? Also have a '93

[PToombs]

It depends on where it's set to begin with. IIRC, Nitrous' truck will run better (quieter and smoother) if he adds power and it retards the timing.
Yours is a '93, so you have to add power to advance the timing. It will add 7*, and may make it clatter. You can try it by running a jumper wire to it and see how it runs. It's not recommended to leave it on all the time, it increases case pressure and could blow out the front seal.
I have mine wired to my valet switch so my AFC and KSB both come on. I unplugged the KSB on the dyno, and lost 30hp. My truck is far from stock, so you won't notice that big of a difference.

Adjusting the timing isn't that hard, loosen the 3 bolts on the flange, the one under the pump at the rear bracket, and loosen the lines. Some people don't even loosen the lines. I do, because if you don't it puts a strain on them, and with the vibration they can crack. Twist the top of the pump towards the head about 1/8th of an inch and tighten the bolts down. Use the marks on the flange and timing case so you know where you are. You may need to whack the pump, or use a ratchet strap, 2x4, or something to twist it. They don't just, "twist" real easy.

[TRACTJDS0428]

ok. so what are the advantages to advancing the timing on these trucks? i know itll give alittle better burn and alittle power but what else?
and what if i put a diode in the power to the KSB and ran another on a switch so i can turn it on and off without hurting its normal function?
i just ordered the wrenches off the snap on truck today to make it easy to take the pump off and adjust the timing when i rebuild it. i know i dont have to have the "special" ones but i thought it would make it easier for me.

[Nitrous05]

I jumped power to it and it did smooth out a bit and get quieter but still runs rougher than it should. Do you thing it's too far advanced? And if so can I do the same thing by loosening the bolts and turning it towards the drivers side fender? I have no idea where it's at because I don't know what was all done to it besides a turbo and injectors. Thanks again, best site I've been on yet!

[PToombs]

Tractjdso0u812, it will also give a little cleaner burn and lower EGT's because more fuel is burned before the exhaust valve opens. You can just run a wire from a switch to it and piggyback it on. It won't hurt anything because the intake switch is open and it's easier than a diode. I bought cheap wrenches and heated them and bent them to fit. I had $15 in a set of Harbor Freight wrenches. I know you payed way more than that.

Nitrous, it may be, and yes you can. There should be marks, but not always. Look at the edge of the flange where it mounts to the timing case, on the ear towards the fender. The marks should be lined up, or can be 1/8 apart if it's been advanced.

[Nitrous05]

thanks again, I will be looking into this tomorrow. hopefully its to far advanced.