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Discussion Starter #1
I have a query concerning a very early R129 500SL 119960 engine.

It has the CIS injection system with the EHA valve on the side of the fuel distributor.

This is the black rectangular box on the side of the fuel distributor controlled electronically.

My car has no lambda sensors, it says on the Mercedes label under the bonnet no lambda and obviously no catalysts.

How does the minute mixture adjustment occur with this device?

Where does it get its signal from? The KE bosch book always shows a lambda sensor when this is fitted, I know it gets a signal from the ECU but it runs open loop so how does it know what the mixture is?

I have very high hydrocarbons. It runs ok but could be smoother. I cannot get the CO down below 3% without it becoming rough.

So far I have replaced the spark plugs, HT leads, distributor caps, rotor arms, rotor arm brackets, all vacuum pipes and rubber hoses to the injectors. Also replaced the injectors for new bosch ones.

Its done 106000 miles.

Next check, fuel pressure and I am going to change the ignition coils as they are 25 years old.

I think it may be the diaphragm in the fuel distributor but will check everything first.

Any other ideas from anyone please?

Thanks in advance.
 

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I would start from a visual.
I don't care about labels.

All have there parts, located in the same way, they don't have it sideways.
That means get under her, look for a cat, 02 sensor. Etc.

They all have an ECU/brain.

One octopus/fuel distributor.

Fuel pressure regulator.

EHA controls the upper/lower champers pressure.

Air sensor plate, feeds air in conjunction with the fuel distributor.

Other parameters that your car may use instead than the above....
Intake temperature from the left front air pipe.

Engine temperature four pin sensor.
Throttle switch.

And maybe add an oil sensor.
All these can adjust the ECU.

ECU to EHA.

EHA adjusts the continuous fuel injection pressure.

Different but doable.

These are my thoughts, to a system that I have never seen or heard.
In reality if you go primitive, they had a screw adjusting...
In your case just add the EHA.

I suspect that you do have, an oxy sensor. ;)


Regards,
aam.
 

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Sounds like basic KE-Jet. The brain controls the EHA, which makes mixture adjustments based on temperature, throttle position, etc. It's not a closed-loop system.
 

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You might go over to the R107 board. The K-E JET system was the last used in the SL's there. Also at the top, in a stickie, is the "Encyclopedia Germanica" That can lend a wealth of information on how the K-E JET works. I would be shocked if you didn't have an O2 sensor.
 

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Discussion Starter #5
Thanks for all replies. I decided to have a good look at the injection system, tried adjusting the EHA valve and then hooked up a pressure gauge to the upper and lower chambers. I now know exactly how this device works and there was nothing wrong with my injection system. I have 86 psi in the lower chamber, 94psi in the upper. If it leave it overnight I still have 55psi. Not bad for a 25 year old!
I am going to use an emissions tester in the coolant reservoir as I suspect a slight head gasket failure. I have a slight misfire at 2000 - 4000 rpm and lots of steam in the exhaust. I will monitor the coolant level.
To confirm because my car is a very early UK R129 it does not have any lambda sensors. I double checked and the voltage between 2 and 3 stays the same whatever you do so it's open loop.
Will let you know my findings. That's again
 

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my car definitely has no o2 sensor and no cat. the radiator data plate has the code "828 delete cat" plus I looked underneath. the o2 plug is in place on the transmission bulkhead but the cable is sheared off flush with the connector.

my understanding is that a variable resistor (potentiometer) takes the place of the o2 sensor but I don't know the location. according to mb the cat deletion is worth an extra 8 hp :smile ....... if u don't mind the fuel consumption.
 

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my car definitely has no o2 sensor and no cat. the radiator data plate has the code "828 delete cat" plus I looked underneath. the o2 plug is in place on the transmission bulkhead but the cable is sheared off flush with the connector.

my understanding is that a variable resistor (potentiometer) takes the place of the o2 sensor but I don't know the location. according to mb the cat deletion is worth an extra 8 hp :smile ....... if u don't mind the fuel consumption.
Hi feedingtherat :)

PM sent!
 

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Thanks for all replies. I decided to have a good look at the injection system, tried adjusting the EHA valve and then hooked up a pressure gauge to the upper and lower chambers. I now know exactly how this device works and there was nothing wrong with my injection system. I have 86 psi in the lower chamber, 94psi in the upper. If it leave it overnight I still have 55psi. Not bad for a 25 year old!
I am going to use an emissions tester in the coolant reservoir as I suspect a slight head gasket failure. I have a slight misfire at 2000 - 4000 rpm and lots of steam in the exhaust. I will monitor the coolant level.
To confirm because my car is a very early UK R129 it does not have any lambda sensors. I double checked and the voltage between 2 and 3 stays the same whatever you do so it's open loop.
Will let you know my findings. That's again

Chris,

My 1990 500SL (R129) is also an early UK car and I can confirm that it does NOT have any cats or a Lambda sensor as I looked today when it was on the ramp having its MOT.
Seems these early cars are a bit of a mystery.

Regards
Ned
 

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Discussion Starter #9
Hi Ned,

Im going to have a look at the wiring diagram for vehicles with the lambda and also the ecu number, see if it's the same computer. It seems strange no lambda is fitted as on most cars of that time they only had one before the cat (cat monitoring was later). So if it the computer is the same maybe it's possible to install a lambda signal. It would give slightly better fuel consumption I would of thought. Not that I'm worried but interesting subject. Thanks
 

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Plate adjustment;

1.Pressurize the system by removing the fuel pump relay and use a fused jumper wire with a 16 amp fuse between terminals 7 and 8.

2.There should be a gap of 0.002 inch all the way around the plate.Rest position should be 0.008 inch below the top edge of the narrowest part of the venturi.Free play should be 0.040 inch to 0.080 inch.If this does not occur,adjust until this measurement is achieved.

Potentiometer adjustment;

3200 to 4800 ohms of resistance between terminals 14 and 18 when the airflow sensor is at rest.

560 to 1060 ohms of resistance from terminals 14 and 17.

The reading should increase to 3760 to 5640 ohms when the plate is at its lowest point.Adjust until this is achieved.
 

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Plate adjustment;

1.Pressurize the system by removing the fuel pump relay and use a fused jumper wire with a 16 amp fuse between terminals 7 and 8.

2.There should be a gap of 0.002 inch all the way around the plate.Rest position should be 0.008 inch below the top edge of the narrowest part of the venturi.Free play should be 0.040 inch to 0.080 inch.If this does not occur,adjust until this measurement is achieved.

Potentiometer adjustment;

3200 to 4800 ohms of resistance between terminals 14 and 18 when the airflow sensor is at rest.

560 to 1060 ohms of resistance from terminals 14 and 17.

The reading should increase to 3760 to 5640 ohms when the plate is at its lowest point.Adjust until this is achieved.
Hello Nutz 4 Benz,

I would like to ask if you have pictures/diagrams of the procedures above?

Very informative :thumbsup:

regards,
 

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my car definitely has no o2 sensor and no cat. the radiator data plate has the code "828 delete cat" plus I looked underneath. the o2 plug is in place on the transmission bulkhead but the cable is sheared off flush with the connector.

my understanding is that a variable resistor (potentiometer) takes the place of the o2 sensor but I don't know the location. according to mb the cat deletion is worth an extra 8 hp :smile ....... if u don't mind the fuel consumption.
OFF-TOPIC POST & SORRY for the THREAD HIJACK :eek:

Hi feedingtherat,

Went to my parts guy yesterday, showed him the picture that you attached and your VIN. The part part number for the "RHD non-kat" down pipe system for the R129.066 is 129-490-17-19. I asked him to verify with MB Germany if it is still available...for use as pattern for a future project of mine :wink

Also, would check if there is a used part available from the link on this R129 sub-forum today, a thread about an England based company with a lot of used R129's :wink
 

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I've also got a non cat early 90 model and replaced all of the electrics as you have and it was still not that smooth and turned to the fuel side to have a look,but long story short there are seals behind the distribitor and one of them was cracked ,replaced it and wow it's now perfect so make sure to look at them before discounting the electrical side
 

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Hello,
Along these lines, my '91 300SL has never started nor run smoothly since I have owned it. I have tried fuel system cleaners and a new in line fuel filter. My mechanic adjusted the mixture he said it was running too rich and leaned it out a bit and it worked great for a day, now it is back to the same rough running, stalling out after restarting and having to rev the engine a bit to keep it running. Then it smooths out. My mechanic suggested that I may need to replace the fuel distributor. I just don't want to spend another $1500 on the car at this time. Can any of you suggesst something that may help the situation?
Thank you all in advance.
Phil
 

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Discussion Starter #18
If it's a fuel distributor issue you could measure each injector fuel volume, they should all be the same. Funny how it ran ok when it was adjusted before. Have you checked for air leaks, like the injector seals and vacuum pipes? Fuel filter changed?
 
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