The EHA is still available from Bosch, but it is not cheap.   Still, I can only imagine it will get more expensive in the future.   It is easy to tell if your car has a replacement unit as the screws holting it on will be torx.    The original ones are flat head.  If it is not pretty clear the EHA is leaking, it can be worth trying to change the o-rings first.

The EHA is accessible once the air cleaner assembly is removed.   It attaches to the side of the fuel distributor, near the fuel pressure regulator.    Its only a 10 minute job to change it out.  The most important thing is to make sure the o-rings are seated properly.   I like to put some paper towel underneath the EHA during this process.   Not only will it catch any fuel that leaks out, but it will also catch the o-rings if you drop them.

Obviously, as I was working with fuel I had disconnected the battery.   Since I was doing the battery tray at the same time, I had remove it completely.

The EHA makes minor adjustments, but it is possible to adjust for baseline settings.   I already covered the adjustment of the EHA in a previous article.   It is worth watching the two videos linked in that article.   I hooked up my gauge set to check the pressures.  My initial readings were 5.9/6.35.   The ideal pressure differential between control pressure and working pressure is 0.4.    I adjusted the EHA 1/4 turn, which changed my pressures to a tad above 5.8 and 6.35.    This mean the differential was very close to 0.4, just a tiny bit over.   This was exactly where I needed it to be.   These pressures are tested with the EHA unplugged as I was trying to set baseline pressure.

After re-checking the pressure then removing the gauge set I carefully checked for any leaks.   After the EHA replacement I took the car for a test drive it felt no problems.   At this point it is normally worth checking the idle mixture.   My injectors are about to be replaced, so that would be premature.

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As I own two KE Jetronic cars and one K Jetronic, It made sense to purchase some fuel pressure gauges.   They were about $100 USD.  The test gauges plug in to the fuel distributor in two places.   The first plug (without the valve) goes into the test port on the side of the fuel distributor.   The second plug goes into the outlet for the cold start valve.     The gauge set comes with the right fittings to rig it up.

Immediately I was able to rule out the fuel pumps and fuel pressure regulator as my starting fuel pressure was good.   The test calls for two readings.   the first one is from the test port and the valve closed.    The second is with the valve open to the cold start fitting.   The ideal readings are 6.0 bar with the valve closed and 6.4 bar with the valve open.   What is more important than the actual values is the 0.4 bar difference.

As can be seen from the picture above, I had an 0.3 bar difference.   This meant the car was too lean – which is what I had observed on the dyno.   Most KE Jetronic cars have an oxygen sensor that controls the operation of the electro-hydraulic actuator (EHA).  The 560 ECE does not have an oxygen sensor.  In this case, the EHA can be adjusted manually.   It is the small back control unit on the right hand side of engine.

Once removed, the slotted screw is removed to allow for adjustment.  A small allen key is then used to adjust the EHA.  In my case, I adjusted it in about one third of a turn.  The EHA is then replaced, carefully to avoid disturbing the o-rings.

With the EHA adjusted and re-fitted, I re-ran the test.  This time, I saw 5.9 bar on the test port with a bit over 6.3 valve open.  Success! I now have the pressures in specification.  I’m happy to leave that bit extra over 6.3 – I would rather be ever so slightly rich than too lean.

These test were all done at idle.  Next thing was to check the pressures at some higher RPM levels.   I asked a neighbor to hold the car at 1,000, then 2,000 RPM.  The fuel pressures stayed steady at these increased revs.

I also ran another test from a member of BenzWorld.   Holding the revs at 2,000, I pressed on the air flow meter plate.  This tricks the car into adding more fuel.  If the engine is lean, the revs will increase, but if it is not, the car will bog down from getting too much fuel.   In my case, the car bogged down.  This was another sign the pressures were at the right level.

The final test was to check the readings of the potentiometer for the air flow meter.  This is on the other side to the EHA.  Correct spec is 0.7 volts at idle between pins 2-3.   My car was at 0.9, so very close even if not perfect.  The voltage also increased as I pushed down on the air flow meter pressure plate.

After these tests, all evidence points to having fixed the lean running condition of my car.  I don’t have a dyno to test it on, but the car is now adjusted back to the correct specification.    I found the KE Jetronic EHA adjustment to be fairly straightfoward, with the pressure gauges.

Update, 26/11/19:  While the car was in for an A/C regas,  I asked to have it quickly tested on the exhaust gas machine.   Air/Fuel was 14.8, so this adjustment was perfect.  

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