The following was supplied by Pastor Bob
GOVERNED SPEED/DEFUELING FUNCTION.
I don't mean to go on and on here but maybe this will help to understand it a bit better.
Ok....
Normally our pumps have a physical governed limit of roughly 2500-2550 RPM. That is the max upper limit that the engine will turn over under wide open throttle. This means that in "N" or "P" that with the throttle pedal on the floor, the engine will rev to 2500 or so and that's it, no matter how long you hold the pedal down, it won't climb any higher.
This limit is set using the "high idle" screw or governor screw. Under normal conditions the governed speed is preceeded by the defueling stage. By that I mean that around 2350-2400 RPM the injection pump starts to cut back the fuel volume or begins "defueling" as it's called.
This defueling happens due to one of two reason, or both reasons:They are > the engine RPM reaches a point were the governor conterweights open up and force the pump to start decreasing fuel amount.. and/or....The amount of Load on the engine decreases enough that the pump doesn't use/need as much throttle pedal to maintain speed.
One or both can kick in and cause the pump to defuel. Either way, the max speed is still set by the physical "high idle" screw setting, but the defuel point varies depending on the above factors. The high idle screw can be backed out to allow for a max RPM of as much as 3300-3500 RPM. Obviously that's a bit too high but it makes a point here....If you set your high idle or governed speed to, say....3000 RPM, the two defuel factors still exist. If the RPM climbs too high OR the load decreases OR both, the pump begins to defuel. In very general terms the defuel point usually starts roughly 200-300 RPM before max governed speed/RPM.
Now, the governor spring really does a couple of things, but primarily it does the following....
Lets use the 3000 RPM limit or governed speed again, as an example.
Under normal conditions you would start to see defueling at about 2700 RPM lets say.....With the governor spring in place that onset of defuel does not happen like normal. It holds the same amount of fueling you are demanding right up to the governed speed, then it finally looses the battle between the RPM and Load governor circuits and begins to defuel. With the governor spring in place and with that type of behaviour the pump can actually allow or permit an RPM "flare" above the 3000 RPM limit. This happens because instead of the fueling level starting to ease back prior to your governed limit (3000
RPM) the heavier fueling continues right up to or slightly beyond at physical governed limit of 3000 RPM. This can result in an RPM flare above 3000. I have seen a flare as high as 3700 RPM before the RPM/Load governor systems pull the fuel back drastically enough to stop the flare. It will finally settle back to the
3000 RPM level once this happens..... so.....In a nutshell you should do some RPM testing first. With the engine warmed up, and good oil pressure, slowly but firmly press the pedal to the floor. You would do this in Neutral or Park of course. This is the actual proper method of checking your governed speed as per the manual.
Make note of your top/max RPM. Ease out of it and let the idle come back down,... then repeat. You could have a consistent high idle of roughly 2500-2500 RPM. If that is the case the governor spring will allow heavy fueling (depending on the amount of gas pedal) right up to that RPM. If you back the governor scew out two to three turns and repeat you will see you governed speed (high idle) rise higher. Repeat until it's where you want it before installing the governor spring. I'd suggest 2900 RPM to start with and you can go from there depending on how the engine behaves after the install.
Hope this helps.
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Stan
93 D250, PDR Twins HX35&HT3B, 60+# boost,PDR stage 2 head w/o-rings, PDR Cam, modified VE Pump, piston style lift pump, modified 5" intake w/AFE, ATS ported manifold,DTT 89% converter, 4" RIP exhaust, modified tranny, EGT/boost/tranny/tach gauges, TPS removed, a little chrome under the hood. Mag-Hitec tranny and diff. covers. Rear sway bar. Line-x bed liner, after market seats. Front end rebuilt with new springs - 2 " taller now. Single stage Water/Meth system installed. Oversized intercooler w/3" IC lines.
05 Chevy 2500 HD, Duramax W/Allison, 17" Hummer wheels w/285-70-17 BFG's, modified air box, ported turbo mouthpiece. Predator programmer.
Last edited by Paccool : 01-03-2006 at 09:38 PM.