AAZ ESP Repair: Questions & Answers

I have a 1998 Volkswagen Golf 3 TD Variant (estate/wagon). It was originally a car kept in a garage by an elderly person, so it's in very good condition with almost no rust, which makes it worthwhile to keep the engine.

Unfortunately, it had been sitting at the dealer for three years, and some parts had deteriorated. For example, a few weeks ago, the ESP (VE4 with electric cold start control and electronic load-dependent fuel injection start control) started leaking.
Okay, so, replacing the seals with Viton right away because of rapeseed oil might not be worth it at the moment, but who knows.

Unfortunately, there were some issues, and the injection pump piston broke during the assembly of the high-pressure part. So, I took out the old ESP (Electronic Solenoid Pump) from the previous vehicle (also a Golf 3 TD Variant, with the part number VE4/9F2300R433-2) and transplanted the high-pressure part. During this process, I encountered the following problem:
The new pump (the model number is unfortunately no longer legible) has a high-pressure section that is 2mm longer (probably due to the magnetic regulator for the start of delivery). The pump head is identical to the tenth of a millimeter, but I don't know if the control channels are drilled differently in the newer pump. The piston is virtually identical; only the plunger disc has a slightly thicker drive pin, so I had to replace the plunger disc as well. Otherwise, all dimensions are identical to the tenth of a millimeter.
The only difference is the internal dimension from the top edge of the pump body to the pressure point of the rotor (with the spring underneath removed so that the piston is at its uppermost position). In the new pump, this dimension is 1.80mm greater.

Does this need to be compensated for with a thicker pressure plate on the piston rod? Or do the cylinder head-piston combinations fit well enough because the valve timing is dynamically adjusted, and the operating range is large enough to accommodate such tolerances?

Hi,

I'm not entirely clear which measurement you are comparing with which.
Generally, one thing must not happen: The plunger in the pump's top dead center (TDC) position must not protrude too far, otherwise it will rupture the high-pressure component.

I would have measured the remaining space in the cylinder of the booster piston until the end of the high-pressure section and adjusted the other pump accordingly. Of course, I also made sure that the control valve was in the correct position.

Best regards, Rainer.

I've measured everything (except for the critical K-mass, the central screw is still in place). All the comparison values were very similar (within a tenth of a difference, including the impeller diameters). The only measurement that differs significantly between the two pumps is...
a) The height from the support point of the balancing disc in the impeller to the top edge of the pump housing (without the manifold) is approximately 1.8 mm higher for the new pump than for the old one.
and b) the depth from the surface of the central screw when it is installed.
"From the distributor head to the top edge of the plunger in the UT, the measurement is also approximately 1.8mm larger than when compared to the old, original pump housing, from which the plunger, control slide, and distributor head originate."
I now understand that the K-Mass must be correct, and to achieve this, the central screw needs to be removed. For the older AAZ pump without an electronic injection timing adjuster, the K-Mass would likely be around 3.6-3.8 mm. The compensating shim for the corresponding distributor head would then need to be approximately 4 mm thick to achieve the correct K-Mass. Whether the control slide bore and regulator position would still be compatible in this case is questionable.
I suspect that the original distributor head for the pump with electronic fuel injection start control has control bores that are 1.8 mm deeper, because the corresponding plunger is almost identical to the replacement part.

I found and installed a high-pressure component for the ESP (Exhaust Gas Recirculation) with electronic boost control, and it's working again.