1992, choking 300E

[Whiski]

I have a 1992 300E. When the car gets warm it starts to choke. I can only manage to drive it about 3 miles. If I give it only a little gas I can manage to get home, but if I drive it normally, it will stall. It will start again no problem but it just keeps choking. I put in a new O2 sensor and new fuel pump. That didn't make any difference. Can anyone give me some advise? Thanks

[Minnet]

When engine is cold, the injection system will operate on open loop mode:

• The airflow sensor plate will actuate the fuel distributor to provide a mixture proportional to the airflow

When oxygen sensor is warm, the injection system should operate in closed loop mode:

• The oxygen sensor will measure whether the mixture is correct and provide this information to the ECU
• The ECU will control the EHA (Electrohydraulic Actuator) to provide richer or leaner mixture according to the feedbadk from oxygen sensor and the input for engine temperature

Apparrently, the closed loop mode does not function correctly.

You already replaced the oxygen sensor, so remaining issues are coolant temperature sensor, ECU and EHA.

One thing you should check first though is the overvoltage protection (OVP) relay. If this fails (which it is known to do), the ECU will not get power and therefor never enter closed loop mode.

The OVP relay is behind a shield behind the battery, and it has a fuse on top of it. Check the fuse and try to replace the relay (not expensive).

[Whiski]

Thanks for the quick reply, Minnet. I will check this out and let you know what happens.

[Rusty Boltz]

As Minnet stated, the EHA controls the mixture. This is done through the fuel distributor which rapidly switches between high and low pressure chambers to get the proper flow.

It can malfunction in several ways. Mine was corroded in my 91 300TE and after replacement with a factory refurb the problem was solved. Our dealseship tried first replacing the oxygen sensor and ECU. They had recently replaced the OVP and several other related parts for problems with this component which were causing the engine to die or to run way too rich..

I have been told that the piston that allows the fuel to switch between high and low pressure in the distributor can get gummed up and stick.If nothing else works, try opening it up and cleaning it. The MB refurbs are a lot cheaper than the new part and probably just as good if you have to replace it. Possibly injector cleaner could help, but on mine it just made it worse. Hopefully it is not the fuel distributor.

[cc260E]

Originally Posted by Rusty Boltz

I have been told that the piston that allows the fuel to switch between high and low pressure in the distributor can get gummed up and stick.If nothing else works, try opening it up and cleaning it. The MB refurbs are a lot cheaper than the new part and probably just as good if you have to replace it. Possibly injector cleaner could help, but on mine it just made it worse. Hopefully it is not the fuel distributor.

Hello Rusty Boltz,

opening the fuel distrbutor needs to have new gaskets and membrane, do you where it is possible to buy them?
thanks

[cc260E]

Originally Posted by Minnet

When engine is cold, the injection system will operate on open loop mode:

• The airflow sensor plate will actuate the fuel distributor to provide a mixture proportional to the airflow

When oxygen sensor is warm, the injection system should operate in closed loop mode:

• The oxygen sensor will measure whether the mixture is correct and provide this information to the ECU
• The ECU will control the EHA (Electrohydraulic Actuator) to provide richer or leaner mixture according to the feedbadk from oxygen sensor and the input for engine temperature

Apparrently, the closed loop mode does not function correctly.

.

hello Minnet,

on my car there is no Oxygen sensor , because there is no catalysator (as far as I know)
could you tell me how it works in this case?
EHA, OVP, coil, and lot more have been replaced and car is still erratically stalling.

thanks

[Minnet]

Originally Posted by cc260E

hello Minnet,

on my car there is no Oxygen sensor , because there is no catalysator (as far as I know)
could you tell me how it works in this case?
EHA, OVP, coil, and lot more have been replaced and car is still erratically stalling.

thanks

It will still have Oxygen sensor without catalytic converter, so mixture is adjusted correctly.

Otherwise it would not be an "E" model, and it would not make sense with an ECU.

[Minnet]

[QUOTE=Rusty Boltz;1317266]As Minnet stated, the EHA controls the mixture. This is done through the fuel distributor which rapidly switches between high and low pressure chambers to get the proper flow.
QUOTE]

I may be wrong, but as well as I know, the EHA has a blade inside, which is spring loaded and will be rotated in one or the other diriction proportional to the current flow in it.

Functionally it is in parallel with the piston inside the fuel distributor, and in this way together they will determine the pressure in the lower chamber of the differential pressure valves, thereby determining the fuel pressure to the injectors. The fuel distributor piston is mechanically controlled by the air mass sensor plate will make the coarse adjustment proportional to the airflow, and the EHA will make the fine adjustment according to the feedback from the oxygen sensor.

In open loop mode, it will just work mechanically without electronic feedback. In fact, this was basically how it worked until it got the "E".

The reason why it will rapidly change for more or less pressure is because it is continuously correcting the mixture.

If someone knows for sure, please let us know.

[Whiski]

Hi Minnet:
This is an update on my car. After I brought my car home from the mechanic (by the way. he was supposed to do a tune-up) I decided to check the spark plugs. Well.....they were clean burned to a gap of .040. So, I replaced the spark plugs with a factory recommended gap of .023. I don't think they have been replace for 2 years. While in the carport it idled for 15 minutes at approx. 600 rpm and for 1 minute at approx 3500 rpm and pumped the gas peddle to make it go from 600 rpm to 1200 rmp for a dozen times. Everything felt smooth and normal. Then I took it for a test drive for approx 10 km including going up a long steep incline and numerous stop lights. All the symptions of stalling and hesitation and jerking disappeared. It appears that new spark plugs have solved the problems. I didn't realize that spark plugs would have such an effect. I will give you an update in a week and let you know how the car is running.

[pentoman]

Originally Posted by Minnet

It will still have Oxygen sensor without catalytic converter, so mixture is adjusted correctly.

Otherwise it would not be an "E" model, and it would not make sense with an ECU.

I don't think this is true - I have 2 190E's without catalyst. Neither have an O2 sensor.