88 560Sl fuel injection, service questions.

[dmorrison]

Learning as much as I can about the 88 560 SL fuel injection system and I have some questions for the experts. I have a annoying miss at idle, cold and hot. Runs fine at speed but once stopped at a light, the engine starts to miss after 5-6 seconds. Stumbles upon acceleration for about 1 second and then runs fine.
I will check the following. All vacuum lines. fuel filters ( car sat for a couple of months). Injectors for spray pattern and missing, and all wires. The physical stuff prior to getting into the CIS-E system.
But It's time to learn about the CIS-E system.

I have read the service manual for the M117.96 engine. As well as read quite a few links to articles on the X11 terminal and how to use it. Here are the following questions.

First, I have read Steve's article

http://www.peachparts.com/Wikka/EngineControls

and

http://www.landiss.com/mixture.htm

and

'86 300E rich mixture - Duty cycle help

By using the Sears MM ( which I must purchase) in the duty cycle mode I should get a reading of the lambda value.
The Service Manual for the V-8 engines M116.96, M117.96 Job 07.3.077-124 page 4 discusses
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"c) with fault diagnosis by measuring on/off ratio.

Effective 12/85, faulty input signals are detected by the CIS-E control unit (N3) and passed to the lambda test output. The faults detected can be output with the lambda control tester (012) at the diagnosis socket (x11)."
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Then on page 07.3.0711-121 pg 16 the manual shows the On/off ratio in % ranges for the "what I assume to be" ( it did not really specify since it had the tech connect the Bosch test unit) the X11 pin 3 readout on the Sears MM.

They show a reading of

0% no voltage or ground ----

10% air flow sensor potentiometer wrongly connected---

20% Full load contact wrongly connected or faulty---

30% short circuit or open circuit---

40% ---

50% O2 sensor not operating or faulty. Open circuit

etc
etc

I'm confused with this info in the manual and Steve's article on adjusting the lambda. and determining any faulty components
In his article he uses his equipment in the duty cycle mode on pin #3 at the X11 terminal.
If the manual specifies all those values how do you determine a faulty unit in the CIS-E system as per the manual.
If I connect the Sears MM and get a 10% reading Then by the manual I should have a Air flow sensor problem.

How does this work. Am I reading the manual correctly?
Is the manual page 16 not for the X11 #3 pin or am I looking at this incorrectly.
Can I determine faulty components of the system by using the X11 #3 pin and the Sears MM.
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Second.

To trouble shoot the entire system the manual goes into connecting a pin access board to the N3 connector under the floor board in the 560SL.
By measuring voltage or ohms or amps of various pins you can determine the condition of the various parts on the CIS-E system.
Is this normally how it is done? Can you access the pins under the floor board, without the service manual equipment, or should I test the components another way.
This is located the the same manual 07.-.0711-121 page 20

Thanks all

Dave

[emmydotnet]

I am going through the same learning experience as you are due to idle/hard start issues on my 91 560SEL. As I understand, the on/off ratio and possible problems (per the manual) you mentioned above are true with the following conditions; that the car is in operating temp when on/off ratio is measured; that the reading is constant, meaning a reading of 50% for example does not fluctuate, then it incdiates an O2 sensor problem. You can try and simulate a fault condition, and measure the on/off ratio, and compare it with the table you mentioned above. There is a concept called "closed loop" in the injection system which says that the on/off ratio under certain conditions will display a fluctuating reading ( ie 40% to 60% for example). This fluctuation in readings indicate that the O2 sensor is continously monitoring the exhaust gas and giving a feedback to the CIS control. The CIS control module in turn sends a signal to the EHA that then regulates the chamber pressures in the FD. The on/off ratio is a way to measure this normal behaviour as explained in the articles you mentioned above.

Others may have more informed inputs regarding this topic...

[dmorrison]

One additional question. I have seen "KOEO" posted in various questions on injection system.
What is KOEO???

Dave

[emmydotnet]

KeyOnEngineOff

[Roncallo]

You have done some good reading and worthwhile. But before you go overboard with this. Have you tried fuel injection cleaner, it does work. When I worked at the Mercedes Dealer 16 years ago we used a product by Cheveron. You might do a search on the latest fuel injection cleaners.

John Roncallo

[dmorrison]

I have done fuel injector cleaner, Chevron Techron
I will try some more before I can get to this. it may help.

Today I did some more reading and amazingly the light came on.

OK this is what I figure with the #3 pin in the X11 connector.

If you use the Sears MM meter and get a number that is a multiple of 10. ( 0,10,20,30,40,50,60,70,80 or 90) You have a fault in one of the components.
If the value is variing then your getting the lambda input produced by the CIS-E computer.

Here are the values in the manual for the various fault codes

0% No voltage or ground at the diagnostic socket. Open in wiring of the diagnostic socket contact 3. lambda tester faulty. mixture to rich.

10% Air flow sensor potentiometer wongly connected or faulty. Possibly, fast idle speed

20% Full load contact wongly connected or faulty. 20% readout only if microswitch connected

30% Short-circuit or open circuit between CIS-E control unit and coolant temperature sensor or coolant temperature sensor faulty.

40% Open circuit or short-sircuit to air flow sensor potentiometer or faulty. Possibly, fast idle speed.

50% O2 sensor not operating or faulty. Open circuit

60% Not assigned

70% No TD signal (open circuit) at CIS-E control unit.

80% Open cicuit or short to ground. Altitude correction sensor fauity.

90% Not Assigned

100% Lambda setting too lean. O2 sensor faulty (short to ground). No voltage or ground at CIS-E control unit or CIS-E control unit faulty. Lambda tester faulty.

Here are the other pin outputs on the X11 connector based on the pin #


Pin Function
1 RPM signal, 0 to 12 V, 4 pulses per revolution. A frequency of 43.3 pulses per second corresponds to the desired idle speed of 650 RPM. (To check your tachometer you could measure the frequency at this pin and multiply by 15 to get RPM.) This signal is derived from the ignition amplifier and is synchronized with the low side of the ignition coil.
2 GROUND
3 Lambda on/off ratio, 0 to 13.6 V, 100 Hz. This is not a replica of the output of the oxygen sensor. The "duty cycle" in Mercedes literature refers to the percentage of time this signal is low. Longer duty cycle (lower average voltage) = lean, shorter = rich.
4 Low (negative) side of the ignition coil. This is where to monitor the dwell angle of the electronic ignition amplifier, and is also a good place to view a reflected and attenuated image of the spark. This is about 50 VPP, safe for an ordinary oscilloscope.
5 Hot (battery voltage) in Run or Start, NOT FUSED! This is actually the positive side of the ignition coil.
6 Hot at all times, through fuse 2
7 Shielded cable from TDC sensor. This is not the same sensor which triggers the spark control unit, but it could be used in a clever circuit with pin 1 to measure spark advance.
8 Shielded cable from TDC sensor.
9 Shield for pins 7 and 8.

So I have that figured out so far.

I still have the second question that was not answered. The one about the N3 connection access.


"To trouble shoot the entire system the manual goes into connecting a pin access board to the N3 connector under the floor board in the 560SL.
By measuring voltage or ohms or amps of various pins you can determine the condition of the various parts on the CIS-E system.
Is this normally how it is done? Can you access the pins under the floor board, without the service manual equipment, or should I test the components another way.
This is located the the same manual 07.-.0711-121 page "

ANY BODY OUT THERE KNOW??

Thanks

Dave

[Steve Gutman]

I had similar problems and after R&R of the primary ignition and idle control systems and using some exotic German fuel injector cleaner I changed the fuel injectors. It made all the difference. My car has a K-Jetronic system with manual fuel injectors. If yours is the same, it only cost (only?) $230 to change them and all the plastic and rubber parts. Unless you want to learn the system for the future or are just curious, I would check the fuel injector spray pattern first. My car was at 120,000 miles at the time.

I alo had a negative experience with aftermarket wires. The ends were not stripped and crimped. This forces the current to jump a gap before making it to the plug. At low RPM it may fail to do so.

I have had more than one mechanic tell me that these engines never idle well, but I keep trying...

[dmorrison]

OK OK OK!!!!

One bottle of Chevron Techron in 4 gallons of fuel and a drive to the Chevron station in my best Italian tune up mode, without getting a ticket. The station is 5 miles away. By the time I got to the station, it was running better. By the time I got home, it was purring like a kitten.

BUT THE EDUCATION OF THE OWNER ON THE CIS-E SYSTEM WILL CONTINUE.

Besides I just bought the Sears MM Model 3482400 with a 500 degree temp probe included. So I want to try out the new toy and continue my education. besides I can fine tune the air/fuel mixture to the perfect 50%.

So the education will continue and I will continue to ask questions and post information that has registered in the brain so that it may help others.
Many of the posts are from engineers , As in Steve Brothertons case or other members that are highly educated. so the technical jargon is verbose (SP). I'm a Meteorologist by degree, Clouds, rain, lying, that my expertise.
Again I will continue this post on the education of the uninformed CIS-E owner.

Dave


Thank God for Techron

[dmorrison]

oopps
Spoke to fast. Still getting a slight miss now and then. So I'll check the fuel filter and pressure and see what I can find. At times the engien RPM soes search a little which will probably be reflected in the Lambda output.

Dave

[dmorrison]

Want to conclude this post on the rough running 560SL I have.

I did test the lambda and found 97.5% steady which I considered 100%. So It says,

100% Lambda setting too lean. O2 sensor faulty (short to ground). No voltage or ground at CIS-E control unit or CIS-E control unit faulty. Lambda tester faulty.

I also suspected a bad injector or plug problem.

I tested the O2 sensor output under the passenger floor board. Its output should be .2 volts at start up, then .1 to .9 volts after warm up ( 2-3 minutes) while in closed loop. I suspect that mine is bad. Duty cycle code 100% and the closed loop output is steady around .85. I'll install a new O2 sensor next weekend.
I also tested the heater circuit to the O2 sensor. It showed battery voltage.

Someone suggested pulling the spark plug wires at the distributor to determine the cylinder that was missing. He's a better man than I. It's very difficult to pull the wires off the cap and , sorry, but getting zapped is not fun. Even with thick rubber gloves. I just was not interested.
I did remove each spark plug and check appearance and gap. While doing that I measured resistance. I found one wire with no continuity. So that was my problem.
Check all the others and found another where the wire pulled away form the end piece inside the spark plug connector.
Park Place Mercedes gives the MBCA a great deal on parts the first 10 days of the month at the Dallas location and the last 10 days of the month at the Mid Cities location. The prices, I'm afraid to say, beat Fastlane and the other on line prices.
I got a Bosch OEM set of spark plug wires for $126.
That required a post about the angled spark plug connectors.

Adding angled spark plug connector to wires, how is this done?

I found that the angled connectors were not required for spacing problems. There may be another reason but I can't find one. I'll talk to the dealer guys this week.

The manual does suggest that for a rough idle, first ensure that the electrical spark system is operating normally prior to checking the CIS-E system. This problem proved to be true for my car.

So a new set of wires and the engine is purring nicely.
I also cleaned and gapped the plugs as well as cleaned the disruptor cap and rotor. While I had the air filter off I also cleaned the injector intake manifold area. You must do this carefully to prevent flooding all the electrical equipment or getting water in the intake. I used a degreaser and then carefully washed it off with running water. No heavy stream.

So the end result New wires and she's running great, so far.

Dave

[Steve Gutman]

THe angled plug caps are for the Euro models because with the battery under the hood the straight plug caps touch the battery box.