m117 CIS Diagnostics - PeachParts Mercedes-Benz Forum

JamesDean · #1 10-30-2010, 04:15 AM

Hello everyone,

I've got a MY90 560SEL here that I'm working on and its having some engine issues.

When I pull duty cycle from the x11 port, I get ~10v or so. Even if I adjust the lambda tower, it makes very little change to the voltage at the port.

I always thought that when first started these cars would run at 50% duty cycle then go into closed loop and let the engine electronics take over. Thats what my m103 does at least.

Another issue its having is a lovely high idle, however the IACV, Idle Control Box and vacuum leaks have all been taken care of....

My one friend, John, said it might be the ignition coil...

Not sure if it matters, the SRS light is on as the airbags delpoyed when the PO lost a flex disc...

Anyone have any thoughts/comments?

JamesDean · #2 10-31-2010, 02:18 AM

Just swapped OVPs with my 420SEL, no change in 560SEL's operation. Also, put 560's OVP in 420..420 operated normally.

Another symptom:
When started cold, engine will not start on first attempt usually. When engine does start, economy gauge is at 50% and engine will stall if not given pedal. After engine is warmed up 60+, engine will not exhibit these problems.

To me, that sounds like OVP, however, OVP has been tested and cleared, my 190E used to run like that when my OVP was damaged, it would do it all the time, at all temps.

Also,

Can someone tell me where exactly or post a picture of this guy:

JamesDean · #3 10-31-2010, 12:14 PM

I'm going to keep updating this thread in case someone replies or it proves helpful to the next guy with high-idle problems....

Found location of TVS, checked functionality, verified to be OK by FSM specs.

Still chasing down high idle.

Replaced
All temperature senders/switches related to CIS/EZL/Dash.

At 1500 RPM @ 80C
-IACV is receiving 4.5 or so volts
-IACV resistance meets FSM specifications
-Vacuum measures 22 inHg @ supply line to fender (dash gauge/hvac)
-Linkage disconnected to check for binds, none found, no change in idle

JamesDean · #4 10-31-2010, 02:37 PM

I'm running through electronics right now, just making sure everything in that dept is OK.

I was running down the IACV tests and it passed so I continued on to the "Idle Speed Stabilization Test"

I was unable to pass the "Input signal to idle speed control unit" test...

"Battery voltage in position P or N....when in D voltage drops."

I placed the + probe to in 12 and - to battery ground, and no voltage was present in either case of P/N/D

Then I placed the + probe to pin 12 and - to battery voltage and in P/N I got batter voltage..and in D I got battery voltage...no drops.

According to the guide, I should repair the open circuit according to the wiring diagram...

What I dont seem to understand is, based on the wiring diagrams from the ETM, That pin 12, should only be given voltage when the key hits the start position...

Any thoughts on this?

Hit Man X · #5 11-01-2010, 01:01 PM

I hate CIS.