Thread: 4BD1 Hard starting

Originally Posted by goanna_shire

I don't know which adjustment is the fuel screw, and which way to turn it??

The screw in question limits fuel at maximum load - when your foot is flat to floor.

The governor on the fuel injection pump has fuel enrichment for cold starts, which probably achieves what rovercare has found, but in a different way.

While the engine is stopped, push accelerator to floor - this allows the sensor lever (inside the governor) to travel under a notch in the torque cam. When the engine runs the governor will move the torque cam so the notch is away from the tip of the sensor lever.

Edit: The diagram showing control rack travel (fuel delivery control) on the vertical axis and pump rpm (half engine rpm) on horiz axis (this diagram is for a 4BD1T - stock calibration). The very left, where rack travel is greatest is the fuel enrichment when the tip of the sensor lever is under the notch of the torque cam. Point 'A' is max load calibration.

In the drawing, does this depict where everything is when the engine is stopped with the throttle off fully or does it depict eng stopped with throttle flat out? If it is demonstrating eng stopped throttle off (pre start), than I can see how half a turn out on the adjustment may help the situation. This would suggest that my 'sensor lever' hook is not being allowed to drop over the torque cam therefore not giving 'full enrichment' for the start. Adjusting the screw out half a turn would shorten the distance between the tension lever and the torque cam allowing the 'hook' to drop.

Would this adjustment change the fuel settings throughout the rev range?

Originally Posted by goanna_shire

In the drawing, does this depict where everything is when the engine is stopped with the throttle off fully or does it depict eng stopped with throttle flat out? If it is demonstrating eng stopped throttle off (pre start), than I can see how half a turn out on the adjustment may help the situation. This would suggest that my 'sensor lever' hook is not being allowed to drop over the torque cam therefore not giving 'full enrichment' for the start. Adjusting the screw out half a turn would shorten the distance between the tension lever and the torque cam allowing the 'hook' to drop.

Would this adjustment change the fuel settings throughout the rev range?

Engine stopped foot of accelerator. BTW the 4BD1 like most diesel engine doesn't have a throttle.

The parts in that diagram are inside the governor housing and you shouldn't adjust that particular screw unless you know what you are doing and have a test bench for the injection pump.

I included the diagram to show the torque cam and sensor lever.

The full load set screw, outside the governor on right side, adjusts the limit of rotation of the full load set lever shaft, and in turn the U shaped lever.

Edit: The full load set screw adjusts the fuel rate across the rev range, but not across the range of accelerator travel - only when the engine is at the full load for the particular rpm.

As speed increases the fly weights push on the tension lever, which rotates the torque cam. The control rack can only travel as far as the sensor lever allows (when its tip reaches the torque cam). The full load set screw adjust how far the accelerator can move the U shaped lever, which in turn, changes the pivot point of the sensor lever.

I apologise for using the blasphamous term 'throttle' in reference to our beloved diesel injector pumps. My mistake . Its taken a couple of hours of staring at the diagram you gave me but I think I am starting to understand.

By adjusting the full load set screw and therefore moving the 'u' shaped lever, how does moving the 'sensor' lever pivot point away or closer to the torque cam change the way it would start? I understand that doing so would simply move the control rack closer or furter away depending on which way you adjusted it........ maybe i'm totally lost

Have you tried turning the max fuel screw out a turn yet?

Originally Posted by goanna_shire

I apologise for using the blasphamous term 'throttle' in reference to our beloved diesel injector pumps. My mistake . Its taken a couple of hours of staring at the diagram you gave me but I think I am starting to understand.

By adjusting the full load set screw and therefore moving the 'u' shaped lever, how does moving the 'sensor' lever pivot point away or closer to the torque cam change the way it would start? I understand that doing so would simply move the control rack closer or furter away depending on which way you adjusted it........ maybe i'm totally lost

Neither the U shaped lever or sensor lever move the control rack. The fork at the top of the sensor lever is engaged with a pin on the control rack so that as the control rack moves in the fuel increase direction the lower tip of the sensor lever moves toward the torque cam. When the tip of the sensor lever contacts the torque cam, the U shaped lever will pivot until the full load set lever hits the full load screw, then the control rack is prevented from travelling in further.

The accelerator pulls the control lever on top of the governor to increase engine speed. This control lever changes the pivot point of the floating lever. The left end of the floating lever moves the control rack (to increase the fuel if the accelerator has moved in the increase speed direction, or vice versa).

As the speed increases, the flyweights move out and push the tension lever against the governor spring. This moves the other end of the floating lever to pull the control rack back to lessen the fuel rate.

Rovercare said that he found adjusting the full load screw made starting easier. I don't know if that is the case or not - I have no reason to doubt what he found and only described the fuel enrichment for starting procedure, which is not obvious.

Hi rovercare. I'm going to make sure I fully understand what I'm fiddling with here because these pumps are fairly complicated, and also for my piece of mind.

Bush 65. Thank you for clearing that up a bit. I was lost but it all makes a lot more sense now. I was wondering how the sensor lever was attached to the control rack so i was way off. Sometimes it takes me a while.... Now I know what that one adjustment does.

I've had a freind suggest that it may be the priming hand pump letting the fuel back to the tank and therefore taking a few turns to get the fuel in the morning. So I'm gonna change that tomorrow and see if that helps at all. Then i'll fiddle with the injector pump.

Once again thank you for the info it is much appreciated!!

Originally Posted by goanna_shire

Hi rovercare. I'm going to make sure I fully understand what I'm fiddling with here because these pumps are fairly complicated, and also for my piece of mind.

Bush 65. Thank you for clearing that up a bit. I was lost but it all makes a lot more sense now. I was wondering how the sensor lever was attached to the control rack so i was way off. Sometimes it takes me a while.... Now I know what that one adjustment does.

I've had a freind suggest that it may be the priming hand pump letting the fuel back to the tank and therefore taking a few turns to get the fuel in the morning. So I'm gonna change that tomorrow and see if that helps at all. Then i'll fiddle with the injector pump.

Once again thank you for the info it is much appreciated!!

There is no harm in fiddling with the screw (slightly). You can't do any harm unless you screw it out too much - but if you do you will know by the cloud of black smoke every time you put yor foot down.

I screwed mine out half a turn or so while my engine was still NA to get a bit more go. It is a free power upgrade!



If my hand priming pump is unscrewed (open) it will let air into the fuel system, but not if screwed down. My engine has done 370k km and still has the original injector pump and lift pump.