[Vwdiesel] Injection pump testing for beginners 2----( OLD Rabbits mostly )

[H.Hagar]

So your OLD Rabbit is lethargic and smokes a lot ?   -- and you did EVERYTHING
exactly to Bentley.

It is time to look at DYNAMIC  timing inside the pump.    If this thread helps you please
let us all know. ---Thanks.

Like a gasser ignition  (vacuum and flyballs) the Rabbit also has to adjust timing 
of injection.    That is accomplished by a system that uses internal pressure --designed
in such a way that as RPM increases injection will be taking place sooner.

In other words the vane-pump output is regulated in a precise way to accomplish this.

The pump has a REGULATOR valve and an ORIFICE that does this.  Be careful this
orifice is mounted in the outlet Banjo.  This is really a bad system , in that the viscosity
of the fuel affects things.

As the pump gets older the vanes wear and the timing piston develops leak-by and the
timing ring sticks.    ----- So are we sunk ?  ---NO not just yet.

The simplest of all tests ?  ---at idle pull the cold start ----if you get a big difference
in sound and or smoke ?  your pump is worn. On Bunny Bondo I never get any difference
the pump is good.   (75 miles to a gallon Imp ? bet she is good) On my first Rabbit 
the  1980 ?  it made a world of difference. So do not fail to try that.

There are a number of DIY tests --that I consider super simple --and here is the first one.
(Yes I dreamed it up )  NO not from smarts --simple LUCK.

Get some fuel line 1/4 inch  stuff ---- run to a container both lines now.

Fill container with a mixture of Diesel and Heavy lube oil mixture ? say  fuel 5 lube 1.

Then test drive it on that--- and I guarantee you that if you have a tired pump --this will
blow your sock of --as it did mine.   I used Aviation piston lube AD-100 (SAE 50) but
any lube will do. We are trying to increase the viscosity of test fuel.

If that makes a major difference --then you are either going to send pump in or go to
Hillbilly Tuning.   I went for tuning --and it works.

The timing return spring is a very strong coils-pring --so it takes a lot of pressure
to advance injection.    Fully advanced say at 4500 Rpm ?  more than a hundred PSI.

Some variation in pressure according to pump and Engine will be found. ---
I say a really good pump should move the timing piston at about 3 to 5 hundred RPM's.
It should clear the cold start cam completely by say 2000 RPM or you have a severely
tired pump.

Yes I will try to write a case history for the umptiest time as part of this testing procedure.
It has to do with a 1982 Rabbit 1.6L NA  (mine)  that smoked for years ---  look at her now.
I never drove a GOOD Rabbit so how the hell was I to know it was not normal ?

The tired pump thing is most noticeable at load  --not at high speed.

And please read about pumps --Roger Browns links --Jake's --and Jagarstrands.

Are parts available for Pumps ? yes indeed. -----do NOT take apart if you are a beginner.
Be careful --- Cold start stub shaft and seal comes as an assembly --dirt cheap-.

 If yours leak leave cold start knob out all the time.  That puts spring pressure on shaft
to make it seal. When you stop engine.

By the way from idle to max RPM the timing may change 20 degrees or so Crank angle.

Hagar.

PS it must be fun ? or I would not be here. Remember to put a small inline filter
in the fuel line --to protect you pump.While testing.