After-Start Enrichment, 1987 560SL K-E Jetronic: Cold Idle Surges and Dives

Auto:
R107 560SL
Production Date 3/87
US VIN: WDB8AH809HA070170

Issue: Unstable Idle after engine start, Cold.

Description: Engine starts but after initial cranking enrichment times out idle becomes unstable, begins to surge and dive (see-saw), as high as 800 RPM, sometimes low enough idle to stall. After 2-3 minutes idle begins to normalize and finally stabilizes at 650 +/- 50 RPM. Idle becomes nominally acceptable yet with subtle but noticeable roughness. At normal operating temperature (N.O.T.) idle is consistent, engine has appropriate power and decent idle. With transmission in drive gear with auto at stand still (foot on the brake) idle is stable at 500 +/- 50 RPM. Moderate to heavy acceleration produces fuel smoke out of tailpipe.

Diagnostic data:

Fuel pressures: System Pressure 6.5 bar Lower chamber 6.1 bar Full Load Enrichment 6.0 bar
* note - after engine stops fuel pressure drops below 2.8 bar then slowly decreases to approx 0 after 45 sec to 1.5 min

Manifold Vacuum (reading taken from vacuum port at rear of manifold, banjo fitting of vacuum to transmission modulator): vacuum varies. peaks at 15hg/cm dives to 7gh./cm. Fluctuations in vacuum reading correspond to idle surge and dive.

Research to date:

Voltages, Resistances, Currents:
All resistances of sensors and related wiring to EZL and ECU are within spec as per Factory Service Manual (07.3 121 Testing electrical components of CIS-E injection system)
New spark plugs installed Bosch WR9DC (non-resistor plugs are near-impossible to obtain in my area)
Resistances of ignition high tension cables and rotor are within spec
Vacuum leak test was performed via LP gas exposed to all vacuum and air distribution connections. No leaks detected but air distribution hoses and connections are hardened and visibly questionable.

Current is correct through Airflow Sensor Position Indicator
Current fluctuates and will not stabilize through Idle Air Control Valve (IACV)
Current is out of parameter at Electrohydraulic actuator (EHA)

Question:
What is the cause of fluctuations in currents at IACV and EHA?
What is the source of instability in cold idle?
Are these issues related to subtle yet noticeable roughness in idle @ N.O.T.?
Are either issues related to the condition causing drop of fuel pressure after engine stops?
Are these issues related to fuel smoke during acceleration?
* note - diaphragmatic fuel pressure regulator, fuel reservoir and fuel pumps check valves need to be tested. It is assumed one or more of these components are at fault

Moin,
if you want answers to your questions, maybe you should add some "Hello" , Thanks and your first Name in your Thread, cos ´this is not the bad behavior Forum .

Greets
Christian

The English part of the forum would have been the proper place to ask your question.

Regards, Lutz

Hi Christian and other fellow forum members,
I understand and I apologize for bad behavior. I try not to be the typical american but I have shown here unfortunately I am not as aware as I should be.
I appreciate your advice and in the future I will bring my good manners with me.
Thank you for bringing this to light.
Kind Regards,
Austin James

Hello Lutz,
Thank you for your recommendation I appreciate you and I will do as you say.
Kind Regards,
Austin James

Good evening Austin,
have fun in the forum-107.
Rudiger

Hi Austin,

welcome to the forum.

Based on your description it is not clear, if you ever monitored the KE-Signal on the X11 socket?
(X11 socket: round black socket at the left side in the engine compartment).

The duty-cycle of this KE-signal has to be at 70% when you switch on inginition but not starting the engine.
The duty-cycle of this 12V square wave KE-signal is calculated by switch-off vs total time.

When you start the cold engine, the KE-signal's duty-cycle has to drop to 50%.

After the engine reached its operating temperature (above 80°C) the duty-cycle of the KE signal should start to sweep in the range of approx. 30-40%.

I made of short video monitoring the the behaviour of this KE signal and wrapped some descriptive text around at my website .

If the duty-cycle of this KE-signal is not as expected, the Factory Service Manual (07.3 121 Testing electrical components of CIS-E injection system) - as you mentioned already - should guide you in the right direction.

Greetings from Rosenheim

Uwe

Hi James Austin and welcome to our Startime-107 forum !

I have moved this thread to our English speaking part of the forum. I am surprised of your Username as it seems that you do not know German.

I am struggling with some of your terms and pressure units. 15hg/cm means 150 mmhg, equivalent to 0,2 Bar ? Then your vacuum is at a low level when idling. Should be in the size of roughly -0,5 Bar. This looks like your engine has vacuum leaks.

I also read that you use Bosch spark plugs. Free market Bosch spark plugs are know to cause trouble. I would recommend NGK BP5ES (without R). They are available on the Internet in the US. And NGK wrongly recommends NGK BPR5ES. You should have those without R as radio interference suppression is done via spark connectors and distributor rotor.

And yyes on off ratio would be interesting to know. Can you measure it?

Thank You Dr Djet,
I can read On-Off Ratio and I will include these readings and also review all data by repeating tests then post results.

I needed first to make progress on another project and when I returned to the 560SL its battery charge had depleted. I am charging this battery while I make progress in other work and I will continue this project today then post my findings.

Thank you for your guidance this far. In ignorance I assumed by clicking the UK icon I was in the english portion of the forum. This was lazy thinking on my part.

I have known resistor plugs are detrimental to engine performance.

I now know because of your sharing of experience Bosch plugs are troublesome. I have ordered the NGK non-resistor plugs as per your recommendation.

I will update the thread with ON-Off Ratio data and verification of vacuum readings.

Many thanks again already for conversing with me. I am eager to learn more from you and other experienced forum members in order to become proficient in CIS-E for myself.
Kind Regards,
Austin James

DR,

I have read the on-off ratio with these results:

Key on, engine stopped: 70%

Engine running: 40-60%

Current at EHA out of spec

I followed guidelines of testing CIS-E components as per this thread:

www.benzworld.org/forums/r-c107-sl-slc-c...tronic-overview.html

I discovered reference resistor R17/1 for CIS-E is 0Ω where the FSM manual states the value must be 750Ω

I am waiting for the arrival of a 750Ω resistor

I will update the thread with new test results.

Am I heading in the right direction to solve the issues of surging idle when cold and mild rough idle when at normal operating temperature?

Thank you for supporting me through a diagnosis.

-James

Dr D-Jet and Fellow Sternzeit107 forum members,

I placed a 750Ω resistor in the R17/1 place.

The condition of Cold Idles Surges and Dives has not recurred. Cold start has

been functioning normally

Thank you to all forum members who contributed.

Kind Regards,
Austin James

Hi AJ,

are we talking same coding resistor for KE ECU? On 560 SL this should be 0...10 Ohm. On other engines like M103 we have varying resistors from 50 to 12000 Ohm. Or do you mean EZL (ignition control module) resistor?