M1008 throttle issue

[jmenende]

Howdy. Just installed by freshly rebuilt pump but the she is running a bit high on rpm. I can manually put the finger on the throttle lever and she will go down to the correct idle speed. I ruled out the pump weights since she spring back into position. I oiled my throttle cable and the situation improved. Its just a tad fast and shifts hard from park. Next thing to try is a shorter spring with more weight. What say the experts?

 

[Keith_J]

Idle speed is part of calibration, most 6.2 are set at 650 RPM and injection 12.5 to 16.5 mm^3 per firing stroke on each cylinder. The volume of diesel injected dictate engine speed.

When cold, the throttle is held open a bit by the external high idle solenoid. The power to this solenoid also opens housing pressure cold advance solenoid inside the pump. This increases injected volume and advances timing 1.25°.

The circuit powering these solenoids comes from a thermal switch on passenger bank of the engine. It should shut off when engine reaches 150°F. Cold engine speed is adjusted at the external solenoid.

 

[jmenende]

Idle speed is part of calibration, most 6.2 are set at 650 RPM and injection 12.5 to 16.5 mm^3 per firing stroke on each cylinder. The volume of diesel injected dictate engine speed.

When cold, the throttle is held open a bit by the external high idle solenoid. The power to this solenoid also opens housing pressure cold advance solenoid inside the pump. This increases injected volume and advances timing 1.25°.

The circuit powering these solenoids comes from a thermal switch on passenger bank of the engine. It should shut off when engine reaches 150°F. Cold engine speed is adjusted at the external solenoid.

Im in the heat all year so i disconnected the high idle solenoid and pulled back the shaft. I adjusted the throttle screw but no change. Its just an ⅛ of a pull to get her into the correct idle. Im gonna try another spring if not search for another throttle cable.

 

[Keith_J]

Idle speed is governed internally, who rebuilt the pump? Have you modified the maximum fuel delivery limit? Removed the guide rod?

 

[jmenende]

Idle speed is governed internally, who rebuilt the pump? Have you modified the maximum fuel delivery limit? Removed the guide rod?

A local shop rebuilt the pump. I have not modified the fuel delivery limit or guide rod.

 

[Keith_J]

It could be the throttle cable, you mentioned the 1/8th turn..is this on the throttle shaft?

When the pump is calibrated for idle, it is spun at 650 RPM engine speed (pump spins half this, 325 RPM ) with throttle at idle speed. Injected quantity is then adjusted by varying the internal low speed governor spring. More force is more fuel. If the engine speed drops, more fuel is injected because the force generated by the governor fly weights decreases. If engine speed increases without throttle movement, governor fly weight force increases and overcomes idle spring force, closing the metering valve which reduces engine speed.
If you adjust the throttle angle externally, stable idle speed by governor action cannot be assured.

 

[jmenende]

It could be the throttle cable, you mentioned the 1/8th turn..is this on the throttle shaft?

When the pump is calibrated for idle, it is spun at 650 RPM engine speed (pump spins half this, 325 RPM ) with throttle at idle speed. Injected quantity is then adjusted by varying the internal low speed governor spring. More force is more fuel. If the engine speed drops, more fuel is injected because the force generated by the governor fly weights decreases. If engine speed increases without throttle movement, governor fly weight force increases and overcomes idle spring force, closing the metering valve which reduces engine speed.
If you adjust the throttle angle externally, stable idle speed by governor action cannot be assured.

I removed both high idle spades and the rpm went down a bit. Then i discovered the top vacuum hose had a tear. Tommorow im going to replace all the hoses and see. Btw, i replaced the throttle spring with another thats tighter and it did solve the high idle issue but the pedal is hard and will fatigue my foot on long trips. Will report back tommorow after i replace the hoses. Thanks

 

[Keith_J]

The spade from the injection pump connected to the green wire does two things to the pump when energized, first is case pressure is reduced to less than 1 PSI (normally 10 to 12). This case pressure reduction increases plunger filling rate which can increase power over all speeds. The reduced case pressure also advances timing since transfer pressure no longer has 10 PSI of case pressure.
Governor regulation is 10% so the increased timing and fuel rate causes a bit of high idle. Cold advance is more of an emissions control than cold running ease.

If you don't have a sensitive tachometer but have a digital multimeter with frequency measurement, the tach output of the 27SI should indicate 220Hz when engine is at 650 RPM. 254 Hz when cold is 750 RPM.

Good luck tuning.

 

[jmenende]

The spade from the injection pump connected to the green wire does two things to the pump when energized, first is case pressure is reduced to less than 1 PSI (normally 10 to 12). This case pressure reduction increases plunger filling rate which can increase power over all speeds. The reduced case pressure also advances timing since transfer pressure no longer has 10 PSI of case pressure.
Governor regulation is 10% so the increased timing and fuel rate causes a bit of high idle. Cold advance is more of an emissions control than cold running ease.

If you don't have a sensitive tachometer but have a digital multimeter with frequency measurement, the tach output of the 27SI should indicate 220Hz when engine is at 650 RPM. 254 Hz when cold is 750 RPM.

Good luck tuning.

I have a digital multimeter and know how to use it. Will check the generators for the correct hz. Thanks alot for the specs.