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Old 08-17-2000, 11:31 PM
Doug AZ
Posts: n/a
I have a 90 560 sel,If the o2 sensor is pluged in the car leans out,has low idle and will barely get out of its way.If I unplug the o2 sensor it runs great but with a check light.I replaced the o2 sensor and it has all new tune parts,I tryed to adjust the mixture at the fuel dist but it just seems to go back to the lean condtion.Any help would be great. Doug AZ
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Old 08-18-2000, 04:55 PM
H. O. Tyler
Posts: n/a
Hello Doug:

I would do a search for 560 CIS fule injection. I remember seeing several comments is the past.

I would also look at the EHA and if you see any signs of leaking. Change it. The O2 sensor through the computer tweeks the EHA for the right mixture.

How many miles do you have on the car. I had problems with brittle rubber vacuum lines and nozzle holders that were broken. This was my problem.

Good Luck,

H. O. Tyler
90 560 SEL 130K
85 300 SD 67K
83 240 D 260K
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Old 08-19-2000, 03:12 PM
Registered User
Join Date: Jul 2000
Location: Sunny Florida
Posts: 199
I own a 1989 560SEL, with the idle sitting at about 950 rpm, no accessories on. In english, what is the EHA? Also, any hints from anyone on the high idle speed? I have checked some things and no luck. Also, the CD Rom does not mention the EHA.The manual on CD Rom is great, by the way. More than you ever wanted to know!
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Old 08-19-2000, 04:04 PM
H. O. Tyler
Posts: n/a
The EHA is Electrohydraulic actuator. It is mounted on the left side of the fuel distributor.

The engine manual for the M116.96 & M117.96 (560) covers the CIS injection system fair. They don't tell you about nozzle holders and vacuum system on the fuel injection. I think the CD just covers the W126 chassis ?

H. O. Tyler
90 560 SEL
85 300 SD
83 240 D
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Old 08-24-2000, 10:01 AM
Registered User
Join Date: Jul 2000
Location: Sunny Florida
Posts: 199
Thanks for the info, H.O. I will sniff around for leaks. I have found the part on the CD-Rom, and you are right, no mention of the injector parts. Still sitting around 950 rpm. I found the cold air intake hose on the drivers side is brittle and has holes. Maybe the car thinks the air is hotter, (less dense air) and is trying to compensate? New hose will be replaced this week, as soon as I get time to run over to the dealer. I will let you know if this does anything. Thanks again.
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Old 08-27-2000, 03:42 PM
Registered User
Join Date: Jul 2000
Posts: 638
the 950 RPM is right on the money for a 'cold' engine. Probably the temperature switch has failed or has a bad connection. I have no helpful hints on why the computer is trying to lean out the engine--except when at idle, it is in the 'open loop' mode and the computer puts out a preprogrammed amount of fuel. The O2 sensor is not involved. If your is trying to use the O2 sensor at idle, the idle switch is not closing, telling the computer "I'm not at idle or wide open, so use the oxygen sensor output to adjust the fuel/air mixture to 14.7/1." Since at idle the O2 sensor is not hot enough to send out the proper signal, it can really screw things up.
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Old 08-27-2000, 10:39 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Oh boy what a bunch of wrong info. First of all closed loop is continuous once initiated except at full throttle. The O2 sensor is evaluated continously once hot.

950 is too high even cold, but what is more important than actual speed is whether the control is in control.

As to why the car won't run at the mixture the O2 sensor takes it, the answer will be costly unless you can properly test the system. I haven't heard one diagnostic word here except situational parts replacing. If you wish to find the answer you will have to test the duty cycle codes and integrator at the diagnostic port left fender. The long term memory should be checked on the diagnostic connector at right hood hinge area. The EHA current absolutely needs to be monitored. Most importantly you will need to know why any of that matters or it won't.

Do you understand closed loop?? Do you understand the O2 sensors part in it?? Can you recognise this activity which is administered by the EHA? I would be glad to explain it again (I've probably done it at least 5 times on this forum), if anyone is willing to follow. It can be done on these early cars with simple tools nothing more complicated than a good multimeter.

Don't mean to be harsh but without understanding, diagnostics are impossible. We are continuously dealing with problems on modern cars that just can't be fixed with just parts.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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Old 08-28-2000, 04:07 PM
Registered User
Join Date: Jul 2000
Location: Sunny Florida
Posts: 199
Well, results of the new air intake are as expected. No change in idle speed. I did poke around the EHA, and did not smell gas. Also checked continuity of the throttle switch, (down low on the manifold), 3 prong guy that tells the CIS the throttle should be idling. Looked good. In reviewing the CIS portion of the CD Rom, I will need to hook up the multimeter and take some data before proceeding further. Thanks for the advice to date, I will update my progress. Stevebfl...keep your eyes open for a 560 with seminole county tags pulling into the shop.....gainsville isn't too far from here...
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