Run-away pump

[vic_vr6]

Back story: mk2 1.6td motor. Head seal was leaking. Completely disassembled pump and resealed it. Pretty much adjusted every setting (max fuel screw, LDA smoke screw, idle screw, throttle spline index, governor shaft)

Motor runs fine but when reving the motor past around 3k the rpms rise exponentially. Fuel shutoff will stop the motor obviously.

pump timing is at 1mm advance verified with dial gauge.

I have backed off the max fuel screw as far as i can without it falling out of the pump.

governor spring is stock and not modded.

Any ideas?

edit: pump picture for views.

[libbydiesel]

Lower the residual pressure screw.

[vic_vr6]

lower the residual screw then re-index throttle for correct idle?

[theman53]

not necessarily re index, just adjust with the idle screw stop. When you go the other way is usually when you have issues with not being able to adjust the idle.

[vic_vr6]

So can i use the max fuel/full load screw to bump the idle up after lowering the residual fuel screw?

[vanbcguy]

You have an idle adjustment screw plus a residual fuel screw - the idle adjust screw is the vertical rod on the back of the pump.  The residual fuel screw will affect idle if it is too far in - basically you want it out enough that the governor lever in the pump is only being controlled by the actual idle adjust, which has its own separate spring inside the pump. 

The residual fuel screw sort of controls how fast fueling drops off when you let go of the pedal, but it isn't meant to control actual idle speed on this style of pump.

[vic_vr6]

so the linkage rod connected to the timing advance is the actual idle control? I noticed it has a spring under the pump lid but didnt know that was primarily used for that.

As far as I can tell the residual fuel screw is at or near the stock setting. The rust marks on the screw line up accordingly with the pump body.

[libbydiesel]

The linkage rod is not the idle control but is connected to it.  The upper lever that the linkage rod connects to rotates a little shaft inside the pump and increases or decreases the idle by pulling more or less on a little spring that connects over to the control lever assembly.  The two settings of that teeter totter lever are slow idle and fast idle.  Slow idle is for when the cold start lever is pushed, fast idle is for when it is pulled.  The residual pressure screw determines how much pressure the governor spring assembly is applying to the control lever when the accelerator lever is at rest.  Adjust that back.  If you run out of adjustment then jump the accelerator lever to shaft alignment one spline until you stop the revs from hanging.  Max fuel is for adjusting max fuel, it is not for adjusting idle although it does affect the idle. 

[vic_vr6]

Just so im clear on the adjustments I labeled everything in this picture. Is this right?

[libbydiesel]

Yes.

[vanbcguy]

It is sometimes necessary to adjust the rod itself too - the 'see-saw' doesn't actually always rest on the 'slow' idle screw unless the rod is adjusted. 

[vic_vr6]

Ok, I back off the residual pressure screw as much as I felt comfortable doing.

Rev's were still hanging running away. Pulled throttle off and set shaft at rest right before it raised the idle being pulled.

Still hanging; backed off max fuel and it no longer hangs but it is pitifully slow.

It also occurred that by doing this the max RPM screw is probably too high as well...

Ugh... I would love a tdi right now.

[theman53]

I am no pump guy, but did you mess with the nut/bolt in between the pressure regulator and the fuel inlet? If so I think some have had troubles after messing with that.

[dieseljunkie69]

Reference for next time, mark, label and write down all the adjustments prior to dismantling.

It will make this part of the process much easier.

[vic_vr6]

Yes, I had the governor shaft out to replace the o-ring. I followed the write up I found here which said 3mm from the edge of the pump body to the shaft face.

It's funny. I took photos of the throttle shaft and max fuel for reference but neglected to snap one of the governor shaft and residual fuel screw pre disassembly.