* DPC MODULE & INJECTION PUMP CONTROLLER *

[asavage]

Since the IPC motor is non-reversing, you might put a spike damping diode across the contacts circuit. Shunts reverse field current to ground via the diode, rather than arcing the contacts. Same problem we discussed about the A/C pressure cycling switch.

Or just replace the relay every few years

[philip]

Or ... how about a power transistor (if that's the right gizmo) instead of the mechanical relay at all?

[asavage]

Yeah, but I'm not enough educated to size it or spec it And a transistor would need a clamping diode even more than the relay's contacts!

While adding a cheap (under $2) diode doesn't require an EE degree.



The connector diagram is 1982 FSM pg EL-53.

[philip]

TWO reasons for keeping the DPC system

This post has been updated for accuracy.

-Philip

[asavage]

2) Should the engine die for any reason, the DPC automatically moves the Fuel Control Lever to the OFF position. This prevents the engine from actually firing off and running in reverse rotation (ie, rolling backward in gear/clutch engaged).

Aha!

Those just joining us may wonder, "well, when would that ever happen?", but it has happened. Philip & I recall about three years ago when someone with an SD22 in a converted 4x4 (?), or maybe just booney-hopping, got on a hill and stalled the rig, rolled it backward, and it ran. The lift pump will work, as will the IP, if turned opposite direction from normal.

Another fellow rolled his rig and couldn't turn it off! It seems the crankcase oil somehow got vented to the air filter, and the engine was running on the lube oil. I don't know if the IP in the OFF position would have affected that one.

[philip]

Another fellow rolled his rig and couldn't turn it off! It seems the crankcase oil somehow got vented to the air filter, and the engine was running on the lube oil.

Wasn't that some Australian fella? He rolled the truck on its roof (didn't kill the engine) and the closed crankcase breather system fed enough oil into the intake manifold to keep the engine running fast ... even after he cut OFF the ignition switch? Running just on the lube oil.

Heh Heh

Makes a good case for the earlier road draft tube ventilation!

Crankcase Venting on SD22 vs. SD23 & 25

[asavage]

In this image:



There's something funny about those angles. In both pics, the angles are drawn as being roughly equal, but the numbers indicate drastically different angles of rotation.

[asavage]

Could the electric motor that opterates the pump be setup to run manually with switches?

Yeeeesssss . . . but then you may as well go to a cable, which is the simplest control system. The beauty of the DPC system, with all its complexity, is the various modes and situations it handles. Such as engine shutdown if oil pressure drops.

Zoltan, if your engine has EGR and the valve opens at idle, Philip says that the idle will increase.

Also, remember that venturi vacuum is what is pulling the IP's diaphragm to the idle position. If you have a leak on that line anywhere between the throttle body and the IP's diaphragm housing, it'll overfuel.

The definitive test of whether the IPC motor is your idle problem is to disconnect the rod from the Fuel Control Lever and run the engine. The Fuel Control Lever is spring loaded to the RUN position, and it will Start there too. You'll also have to manually move the Fuel Control Lever to STOP position to shut off the engine (or do as I do and let in the clutch whilst pressing the brake pedal; works nearly as well). If you continue to have a fast idle with the IP's rod disconnected from the Fuel Control Lever, it's not a DPC system problem.

[Zoltan]

Zoltan, if your engine has EGR and the valve opens at idle, Philip says that the idle will increase.

Also, remember that venturi vacuum is what is pulling the IP's diaphragm to the idle position. If you have a leak on that line anywhere between the throttle body and the IP's diaphragm housing, it'll overfuel.

Yup.... I just remembered that I put a loose vacum tube back onto the vacuum amplifier (attached to the firewall and looks like a land mine) just before we started to work on the transmission. It seems that this was detached on purpose by the previous owner. This tube goes into the EGR valve system. If I put this vacuum tube back, the idle goes up and it overfuels the engine. I'll continue my trouble shooting on the EGR thread. Thanks for all the help.

[dieselscout80]

Could the electric motor that opterates the pump be setup to run manually with switches?

Yeeeesssss . . . but then you may as well go to a cable, which is the simplest control system. The beauty of the DPC system, with all its complexity, is the various modes and situations it handles. Such as engine shutdown if oil pressure drops.

I was kinda wondering if it could be done. When I got my Tug SD33 that has the MZ govnenor to install in my Scout I got the electric motor that controls the pump, but not the DPC. I've been controlling it with a cable, but I have wondered about how to use the motor.

Carey

[asavage]

When I got my Tug SD33 that has the MZ govnenor to install in my Scout I got the electric motor that controls the pump, but not the DPC. I've been controlling it with a cable, but I have wondered about how to use the motor.

Are you handy with electrics? Can you read a wiring diagram? It can be done, but you'll need to be patient.

The IPC test procedure in the 1982 FSM gives you the clue you need to do without the DPC module. I've chopped this page from the FSM to make this a bit clearer (click on image for larger):



A nice rotary (multiposition) switch on the dash, a suitable fuse (do NOT omit the fuse!), and an afternoon of safely & correctly routing and bundling wires, and you'd have basic automation, without the DPC module.

(Note: although the FSM says what the expected result of those tests are, the one IPC I tested in that manner wouldn't stop at those places, it would coast on by and get powered by the next contact, resulting in the IPC running all the time. I mention this only for completeness, because I think that particular IPC is faulty in some way that I haven't resolved yet.)

Well, there's another hour shot to hell.

[dieselscout80]

I've chopped this page from the FSM to make this a bit clearer (click on image for larger)

THANK YOU!!!!!!!!!

[asavage]

If you do this, do let me know how well it works, and if there is any downside.

[philip]

If you do this, do let me know how well it works, and if there is any downside.

I've been having an infrequent problem with starting the engine. I rechecked the DPC and IPC electrical plugs. Key ignition stuff too. All the fuses. Even the blow-off fuses.

The occasion goes like this:

1). Cold engine. Start key ON to warm the Glow Plugs ... say 20 seconds. Also, the Oil Pressure Idiot glow is ON. The IPC/DPC leaves the injection pump's Fuel Lever OFF. (this is normal).

2). After 20 seconds, crank the engine. Starter cranks fine but there's NO engine run. QUICK ... turn the key all the way to OFF then ... reSTART the key. This time the engine starts and runs quickly.

Notes: The engine oil lamp sometimes goes out immediately when the key is let off START to ON ... regardless of engine running. USUALLY, an oil pressure lamp goes out when oil pressure passes above 8 psi. That would take a couple seconds engine running for oil pressure. Hmmmm.

I tried for two weeks with the oil pressure switch wire -removed-. In this situation ....

1). Anytime begin engine. Start to ON ... the IPC/IPC moves to START, then to ON ... and stays at ON. Of course, the oil pressure lamp is OFF. START the engine, the engine runs every time. There is a slight longer engine turning when the engine is COLD.

The problem turned out to be .... the wire plug to the oil pressure switch terminal was LOOSE. A little plier squeeze ... all done.

LOL I gotta love that one!

[asavage]

Just got my truck a few weeks ago and the previous owner bypassed the start key with a glow-plug/ignition-on switch and a push-start button . Ergo the IP lever NEVER goes to the START position 1.

The Mercedes Benz used a substantially similar inline IP (the same basic design that was licensed to Kiki-Diesel for use in Nissans) and the MB does not, TTBOMK, have an overfuel/Start mechanism.