* DPC MODULE & INJECTION PUMP CONTROLLER *

[philip]

.... and the MB does not, TTBOMK, have an overfuel/Start mechanism.

Ok ... "TTBOMK" please?

[asavage]

"Google is your friend."

To
The
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Of
My
Knowledge

[jim derra]

I have been having a problem with my truck dying on me right after start up. It cranks great, starts and then dies. I noticed the actuator will make a complete revolution and sometimes goes around twice. Of course when I hold the acuator in the run position, it is just fine but when I release it....off it goes again. "?" DPC, Oil pressure sending unit, batt voltage. Sometimes when I hook up the battery charger it will stutter a bit but will run fine after a few seconds. But when I fully charge the battery, it will act up again

[philip]

I have been having a problem with my truck dying on me right after start up. It cranks great, starts and then dies. I noticed the actuator will make a complete revolution and sometimes goes around twice.

Isn't this "fun"? At least at the moment, your DPI module and controller/motor Okay. But there's more.

Of course when I hold the acuator in the run position, it is just fine but when I release it....off it goes again.

What do you mean by "actuator"? Your ignition key? Injection pump Fuel Lever? (??)

"?" DPC, Oil pressure sending unit, batt voltage. Sometimes when I hook up the battery charger it will stutter a bit but will run fine after a few seconds. But when I fully charge the battery, it will act up again

I don't know what to make end on these last 2 sentences.

1)pull / replug the two DPC plugs.
2)pull / " the controller motor.
3)pull / " the transmission harnass (includes wire to oil pressure switch)
4)pull the oil pressure wire from the pressure switch. This single female bullet (call Al for the word) needs a little "crimp" for tightness when you push it back onto the connecting pole on the oil pressure switch.

See how the controller motor behaves start/run normal.

As another "check" ... pull the oil pressure wire and leave it loose. Turn key switch from OFF to ON. You should immediate hear the controller motor / DPC rotate from OFF to START/RUN and hold. Then when you move the key ignition back to OFF, the controller motor/DPC should rotate to OFF also.

[jim derra]

Phillip,

Just a word of thanks. I crimped the oil pressure wire and cleaned the contact and it work fine now. I was pulling my hair out trying to figure it out.

[asavage]

I guess I'm not getting this . . .

The way I understand the relationship of the oil pressure switch and the DPC is that the only effect that the oil pressure switch has on DPC operation is:

* Key in ON position, switch shorted (low or no oil pressure): DPC turns off fuel.

Disconnecting the oil pressure switch wire "tells" the DPC that the oil pressure is OK -- always. Disconnecting it altogether means the DPC will never shut off the engine due to low oil pressure, but has no effect otherwise -- correct?

A loose oil pressure switch wire (bad crimp on terminal) should have a similar effect: DPC will continue to leave fuel lever in Run position.

I do not understand what negative effect a loose oil pressure switch would have on the DPC (other than flaky engine shutdown due to low oil pressure, which should not be a common situation anyway).

[philip]

I guess I'm not getting this . . . -SNIP-

Disconnecting the oil pressure switch wire "tells" the DPC that the oil pressure is OK -- always. Disconnecting it altogether means the DPC will never shut off the engine due to low oil pressure, but has no effect otherwise -- correct?

(pressure switch disconnected and engine not idling). Key to ON=DPC/controller motor from OFF to RUN (byway moment of START). Key back to OFF=DPC/controller motor to OFF (again). There is never "oil idiot" bulb ON.

A loose oil pressure switch wire (bad crimp on terminal) should have a similar effect: DPC will continue to leave fuel lever in Run position.

I do not understand what negative effect a loose oil pressure switch would have on the DPC (other than flaky engine shutdown due to low oil pressure, which should not be a common situation anyway).

Vibration.

A loose terminal during engine SHAKING means ... on-off-off-on-off .... etc circuit. When it happens, the DPC/controller motor message is to STAY the Fuel Lever OFF during key START or ... to allow the controller motor to turn through OFF/START/RUN ... and back to OFF.

I got this clue when I noted how the Oil Pressure idiot bulb would flicker while engine being starting over. But only once in a while, more so during colder nights. When this terminal is tightly connected ... the oil pressure bulb stays ON after the engine starts and runs for a couple of seconds.

[asavage]

A loose terminal during while engine is SHAKING means ... on-off-off-on-off .... etc.

Isn't the oil pressure switch ignored while cranking? It seems it would have to be. There probably isn't much in the way of oil pressure at cranking speed, so the DPC will have to put fuel lever in Start position while cranking regardless of oil pressure. Therefore, the oil pressure switch is ignored during cranking.

When it happens, the DPC/controller motor message is to STAY OFF during key START . . .

Really? How can that be? I can't see how the DPC can use the OPS signal during cranking.

[philip]

Isn't the oil pressure switch ignored while cranking?

"When this terminal is tightly connected ... the oil pressure bulb stays ON after the engine starts and runs for a couple of seconds." Remember...(1) the oil pump runs 1/2 speed than the engine crank, (2) oil filter (open down) is practically dry from sitting off some hours. To compare, look at the TD27. The oil pump runs equal speed of the crankshaft and, the oil filter (open up) cannot go dry after sitting.

There probably isn't much in the way of oil pressure at cranking speed, so the DPC will have to put fuel lever in Start position while cranking regardless of oil pressure. Therefore, the oil pressure switch is ignored during cranking.

Only the key ignition to Start has to turn the engine RPM. The DPC/Controller Motor can do a couple of things. (1)If the oil switch (or wire) is always open then the key Start does not matter. "Key to ON=DPC/controller motor from OFF to RUN (byway moment of START). Key back to OFF=DPC/controller motor to OFF (again)."

When it happens, the DPC/controller motor message is to STAY OFF during key START . . .

Really? How can that be? I can't see how the DPC can use the Oil Pressure Switch signal during cranking.

(2)"A loose terminal during engine SHAKING means ... on-off-off-on-off .... etc circuit. When it happens, the DPC/controller motor message is to STAY the Fuel Lever OFF during key START or ... to allow the controller motor to cycle through OFF/START/RUN ... and back to OFF."

[asavage]

A loose terminal during engine SHAKING means ... on-off-off-on-off .... etc circuit. When it happens, the DPC/controller motor message is to STAY the Fuel Lever OFF during key START or ... to allow the controller motor to cycle through OFF/START/RUN ... and back to OFF.

So to summarize:
* If the OPS wire is disconnected, the system works OK.
* If the OPS wire is firmly connected, the system works OK.
* If the OPS wire is loose and jiggly, the DPC can keep the fuel lever OFF.

Have I got this right?

[philip]

So to summarize:
* If the OPS wire is disconnected, the system works OK.
* If the OPS wire is firmly connected, the system works OK.
* If the OPS wire is loose and jiggly, the DPC can keep the fuel lever OFF.

Have I got this right?

*.... assuming the rest of the DPC/Controller motor and plugs are good.
*.... assuming the connect INSIDE the Oil Pressure Switch is reliable.
*.... the DPC can go nuts. The Fuel Lever can be stay at OFF or ... it can be moved to START, back to RUN, back to OFF or ... it can move the Fuel Lever to OFF at the darnedest time while driving along.

I call it the Gremlin.

[asavage]

[If the OPS wire is loose and jiggly, the DPC can keep the fuel lever OFF.]
*.... the DPC can go nuts. ... it can move the Fuel Lever to OFF at the darnedest time while driving along.

Can't. The OPS is OPEN while driving. A loose connection to an open circuit does nothing.

I cannot understand how a loose wire to an open circuit -- the same thing as if the wire is disconnected -- could affect the DPC while driving.

[philip]

[If the OPS wire is loose and jiggly, the DPC can keep the fuel lever OFF.]
*.... the DPC can go nuts. ... it can move the Fuel Lever to OFF at the darnedest time while driving along.

Can't. The OPS is OPEN while driving. A loose connection to an open circuit does nothing.

Yes it can. It is unusual but ... when the OPS diaphragm leaks internally, the contact comes Closed again. The pressure idiot light will also light or flick the Idiot Bulb (but would those lousy dim dash lights be seen?) just one second which will tell the DPC to shut off the Fuel Lever. Safety engine Turnoff, remember. Things are not Black vs White permanent.

[asavage]

OK, if the OPS switch is bad, then the circuit is less than open.

But that doesn't relate to the loose OPS wire or loose terminal.

Connected, disconnected, loose, tight: the terminal's condition should have nothing to do with the DPC shutting off the engine (unless the OPS is also bad and shorting when it's not supposed to).

[philip]

(1)OK, if the OPS switch is bad, then the circuit is less than open.

(2)But that doesn't relate to the loose OPS wire or loose terminal.

Agreed. Such are two different matters. Help me tech here; what do you call the moment when vibrating fizz contact occurs that is not 100% open or 100% closed? I never said I was a engineger.

Connected, disconnected, loose, tight: the terminal's condition should have nothing to do with the DPC shutting off the engine

If the OPS contact is already in OPEN .... then I agree.

(unless the OPS is also bad and shorting when it's not supposed to).

Agreed.

Let's disconnect the OPS wire. Now turn key ignition to ON. DPC will see the Controller motor rotate to START, to RUN. Now ... connect the OPS wire to ground. The DPC will now make the Controller motor rotate to OFF. Now ... disconnect the OPS wire. The DPC will make the Controller motor rotate to START, to RUN.

The muck comes along when a OPS wire terminal becomes closed-open-closed-open ... while the key ignition moves from ON to Start. (engine is shakying the OPS's loose wire).