560SL.. rough idle/shaking,then stalls...

[Frank Reiner]

Originally Posted by ioang26

The air screw is the idle air mixture screw on the top of the Fuel distributor which uses the Allen key to adjust.
Yes, I get a constant 20% Duty cycle and 70% when the engine is off but ignition on.
How do I check/test throttle position switch or air flow sensor?Do I unplug it to see if it will change the cycle value?

The "air screw" to which you refer is actually an adjustment of the initial position of the fuel metering plunger in the FD. With the EHA disabled (unplugged), it can be used to set the basic open loop mixture to be approximately stochiometric. This, unfortunately, also requires that the EHA has been adjusted to its basic position so that the lower chamber pressure is ~ .4 bar (5 psi) less than system pressure at an actuator current of 10ma.

The throttle switch can be checked for continuity in both the closed throttle and WOT positions. Unplug the switch connector, check between pins 1 & 2 on the switch for closed continuity, and between 2 & 3 for WOT.

The air flow sensor potentiometer can be checked by slightly loosening the plug so that the pins may be probed without disconnecting the plug. With engine running, pins 1-3, 4.5-5.5V; pins 1-2, .5-1.5V.

[ioang26]

Here are the test results:
The throttle switch showed 1,420 Kohms in closed position and in WOT 2,730Kohms. Is the throttle switch bad?
The air flow sensor pot(engine running) showed at pins 1-3 4.95 volts,and at pins 1-2 1.1volts.
With ignition OFF pins 1-3 showed 4.4 Kohms(plate at rest) and increases when defecting the plate .

[Frank Reiner]

The throttle switch contacts should have a resistance of ~ 0 ohms in both the closed and WOT positions (against the stops), and infinite resistance off of each stop. It is possible that the contacts are dirty, but cleaning them would require dis-assembly of the switch, which I think is riveted together.

The air flow pot is OK.

[ioang26]

OK.So do I need to remove and clean it or just purchase a new switch?
Also, I observed the following today- turning the air mix idle screw CW will keep the engine running and would not stall but it still has a rough idle and the Duty cycle would not change,it will be constantly 20%.If back up the screw (CCW) the engine will start and die .
What am I doing wrong?When I enrich the fuel then the fuel pressure leaks out of the FD plunger according to the fuel gauge .How do I balance about 50% duty cycle?
Thanks!

[Frank Reiner]

Unplug the cable from the throttle switch, and jumper the pins/sockets that correspond to switch pins #1 & 2. This will simulate a closed throttle switch of 0 ohms. Any difference in the idle, or in response to changes to the idle mixture?

The duty cycle will oscillate between 45% and 55% when:
1) the engine is at operating temperature
2) the O2 sensor is above 600 deg.F and supplying a valid signal
3) the EHA is properly calibrated to provide a lower chamber pressure that is .4 bar below system pressure at a current of 10mA
4) the mixture screw has been set to provide a stochiometric mixture
5) the ECU is working properly

[ioang26]

Frank Reiner,
I really don't know what is going on.
1.O2 sensor works and shows 487mV
2.The EHA measures around 10mA(when I adjust the air mixture screw) but the Duty Cycle stays constant either 20.3%(black on 2 and red on 3 ) or 79.7(when switch red on 2 and black on 3) .Whatever I do - either try to lean or rich the mixture there is no change at all.
With ignition ON Duty Cycle shows 69.8 %.
Engine would still run rough idle up and down and if I press on the gas bogs down but if EHA is disconnected it will improve and would acceleration very well.

Is this an electrical issue?Do I need a new EHA and FD ?I am confused.
Please,help!

[Frank Reiner]

[QUOTE=Frank Reiner;3244561]Unplug the cable from the throttle switch, and jumper the pins/sockets that correspond to switch pins #1 & 2. This will simulate a closed throttle switch of 0 ohms. Any difference in the idle, or in response to changes to the idle mixture?[QUOTE]

Did you make this test? What, if anything, happened?

I return to this because the duty cycle remains fixed at 20/80 (polarity sensitive), which indicates that there is a fault in the throttle switch or the wiring connecting the switch to the ECU and the Idle Speed Control Unit.

The improvement in idle characteristics that is experienced with the EHA disconnected indicates that the EHA is out of calibration. When both the EHA and the mixture screw are correctly adjusted, there will be almost no change in the idle when the EHA is unplugged.

[ioang26]

Yes. I did make the test- unplugged the throttle switch and the rpms went up to 950 then jumped pins #1&2 and rpms back to what it was and no change in DC (still 80%).So,that means it works?
Something else happened today - removed the EHA to readjusted about 1/8 CW and then I just blew it with compressed air to remove any gas left,installed it and...Duty cycle started to move from 37%-56% .Got to the point where it was exactly in the 45%-55% range .
I don't know how that happened.Turned off the car,removed fuel pressure test kit,and reinstalled that air filter housing.Started the car later again and the Duty Cycle back to 80% and would not change , giving it gas bogs down and wants to stall.
What is wrong with this car?

[ioang26]

Update:Today did pretty much the same thing- started cold with ranging DC from 34%-55% and then all of a sudden changed into 8-10% .After it went into normal working temp went back to 80%.
According to the manual - 80% constant mean problem with the Altitude Correction sensor?
Any suggestions?

[ioang26]

ANY IDEAS?
What is the cause of this 80% Fixed Duty cycle?

[ioang26]

Anyone??

[ioang26]

Another update:
I ordered another rebuilt fuel distributor. Installed on the car and jumped the
fuel pump.Then when I press down (gently about 5mm) the sensor/air plate, nothing will come from the
injector ports.The fuel will start coming right after almost 1/3 way pushed down and then further more
will start coming with more volume .
The car will do the same thing - start for 2 sec and then stalls- that's it, I can not keep it running.
I am very frustrated because this Fuel distributor has been sent twice to be rebuilt by the same person and
he claimed that he has tested it and it runs fine.

BTW the zero position and the basic positions are on specs .

What am I missing? Again a bad fuel distributor?

[nobby]

http://www.peachparts.com/shopforum/sl-forum/349895-bad-good-fuel-distributor.html

http://www.peachparts.com/shopforum/sl-forum/350175-duty-cycle-goes-50%25-1-4%25-constant-help.html


Keeping everything in ONE thread is the best advice I can give you.

[nobby]

Bosch KE-Jetronic Overview - Mercedes-Benz Forum

87 560SL KE Jetronic Fuel System Problems - Mercedes-Benz Forum


Some reading for you.

[ioang26]

Thanks nobbby for the links . I have read them all and still can not figure out the
mystery of this car.
Everything is on specs- pressure,vacuum (no leaks)injectors.
The only thing I am having doubts is either a stuck valve or spark/ignition issue somewhere.
It feels like it misses and some backfire.