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Looking for someone to school me on the mechanical Bosch MW inline pump. I have a 1991 Ford F800 with the 7.8 Ford/New Holland and as it sat when I bought it, it was adjusted very conservatively. I have ready through nevrenufhp's (Low Buck Diesel Power) writeup on these pumps and there was a ton of good information in there, but it really only covered approximate adjustments that fits well for most engines that run the MW pump. Here, I am hoping to gain a little bit more understanding of how each adjustment affects the pump. The engine is a peach with practically no blowby but it spooled pretty slow given how little fuel it was using at little/no boost. I have already backed up the adjustment nuts on the stud inside the AFC housing to the end of the stud like nevrenufhp recommends. It spools almost immediately now and it isn't obnoxiously smokey, and I haven't touched the star wheel at all. The bump stop for max throttle on the pump lever is also set as far in as it can go. One of the questions I still have is with the adjustment screw on the top of the pump. Nevrenufhp says that it's for idle/very low rpm fueling for starting, but I'd like to know more about how that adjustment works exactly. I know if you run too much fuel at idle, you can end up with gunk in the exhaust from unburnt diesel, so I wanted to understand that adjustment before messing with it. I'm also assuming that I need to tighten the governor a few clicks. While in neutral, the engine can hit ~2600 rpm but going down the road wide open throttle, the truck feels like it falls on its face around 2100-2200 rpm. It pulls really well down low after the AFC adjustment but if I can get it to where it'll hit 2600-2700 on the road, I'd be happy.

Any info and tips are appreciated!
 

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"One of the questions I still have is with the adjustment screw on the top of the pump. Nevrenufhp says that it's for idle/very low rpm fueling for starting, but I'd like to know more about how that adjustment works exactly. I know if you run too much fuel at idle, you can end up with gunk in the exhaust from unburnt diesel, so I wanted to understand that adjustment before messing with it."

I wouldn't recommend messing with this adjustment. Bosch refers to it as a starting fuel interlock device. Basically the idea is that at say 0 RPM to 300 RPM (Pump) The fulcrum lever in the governor isn't high enough to hit the screw, so the governor allows the rack position to go to full starting fuel position. Usually a full 21 mm of rack travel. As RPM increases and the flyweights start to move, the fulcrum lever moves up until it will contact the screw and can no longer go into starting fuel. It's a safety device to keep from going into full starting fuel with the engine running, which could result in a runaway. The screw basically just changes what RPM it engages at, usually well below idle RPM. As far as increasing idle fuel, that will just raise your idle RPM. Keep in mind diesels are governed by fuel, not air like gassers. If you increase idle fuel delivery, idle RPM increases.

"The bump stop for max throttle on the pump lever is also set as far in as it can go. I'm also assuming that I need to tighten the governor a few clicks. While in neutral, the engine can hit ~2600 rpm but going down the road wide open throttle, the truck feels like it falls on its face around 2100-2200 rpm. It pulls really well down low after the AFC adjustment but if I can get it to where it'll hit 2600-2700 on the road, I'd be happy"

Most diesel engines have two higher RPM ratings- rated speed (Full Load) and High idle (maximum RPM). What you are describing is likely due to the fact the governor starts to cut fuel shortly after the rated RPM of around 2200 RPM, and high idles at around 2600 RPM. With no load on the engine it takes about the same amount of fuel to maintain high idle as it does low idle, usually 20 cc give or take a little. To maintain full load requires the fuel be at its maximum setting, probably 150-200 cc for this application. So with load on the engine driving down the road, the governor will cut fuel and the engine can't maintain the load. Maximum RPM won't be reached with load on the engine.

If you have the pump part number or can get it I would be able to give you more exact information on governor adjustments and specs. The fact is with these MW pumps there isn't a ton of room to turn the fuel up. The plungers are small compared to P pumps, limiting the capacity. To get the RPM up you should be able to use a standard 3000 RPM spring kit for a Dodge/Cummins P pump.
 
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