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Old 13-12-2018, 12:36   #1
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Volvo MD3B "throttle" unresponsive

The speed control lever on the injection pump has become unresponsive. Engine starts and runs at about 2k rpm but cannot slow it to idle. Also had to kill it by opening the valves using decomp lever ... whew that was close! Any and all thoughts will be appreciated. Thanks, Roger
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Old 13-12-2018, 21:18   #2
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Re: Volvo MD3B "throttle" unresponsive

Most often, ime, inability to idle at desired slowest rpm is from clogged fuel filters. If you got some contaminated fuel somewhere, that can sure do it fast.

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Old 13-12-2018, 23:01   #3
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Re: Volvo MD3B "throttle" unresponsive

If you can't control the engine speed with the injector pump lever, make sure it's not he linkage keeping it from moving. Disconnect the linkage/cable and try to move the lever. If the lever will not move then you have an internal problem in the injector pump. Probably from dirty/contaminated fuel. If you don't know what you're doing you could cause more damage than good by taking the pump apart.
The pump should have a label on it's side. Probably not made by Volvo. You might find a troubleshooting guide online. Contact a local injector pump rebuilder and get their advice. Also info on timing the pump when you reinstall.
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Old 14-12-2018, 09:35   #4
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Re: Volvo MD3B "throttle" unresponsive

Thanks for replies. I can see the lever moving all the way between both stops but no response from engine. The fuel appears to be clean and good. Is the injector pump a Bosch product? Anyone know?
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Old 14-12-2018, 10:04   #5
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Re: Volvo MD3B "throttle" unresponsive

The injection pump is built by Bosch....but I would suspect that there isn't anything wrong with the pump. More likely there is an issue with the governor linkage which transmits motion from the throttle cable to the pump rack.

First thing is to check that the throttle lever is clamped tight on the governor shaft that goes down into the timing case. If the lever is moving but the shaft isn't turning, there will be no speed control.

Next is to remove the cover on the rear of the timing case and check the governor linkage. The most common issue here is that the return spring on the governor linkage has broken, and the pump won't return to idle because of that.

The governor linkage is very simple and usually you can see if there is anything misplaced, etc. Check the parts book breakdown to see how things should be arranged.

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Old 14-12-2018, 13:59   #6
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Re: Volvo MD3B "throttle" unresponsive

Doug, thanks for the detailed suggestion. I will try it and keep you posted. Attached is a schematic which spring are you referring to?
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Old 14-12-2018, 14:20   #7
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Re: Volvo MD3B "throttle" unresponsive

Spring #11 is the one I'm referring to....

Springs #20 & 21 have to do with the cold start device and max. fuel setting, and I don't think they are involved with your issue. Also check to see that there doesn't appear to be any issue with the governor weights and its springs.

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