trying to understand the right eha reading - Page 2 - PeachParts Mercedes-Benz Forum

josev · #16 02-13-2003, 05:19 PM

when i re-touch mine ended with 45% then 50% then 53%then the cycles starts again 48%-50%-51% i'll shoot for 36% when the weather gets better here in ct

pesuazo · #17 02-14-2003, 07:07 PM

In my quest to solve my irregular idle problem, I plug my new duty cycle meter quite often into the diagnostic terminal X11 (pin #3).
Interestingly enough, when the crappy-oscillating (500-900 RPM) idle is at work I get the dancing duty cycle (27-33%). Which means the elements in the closed loop are working (right?)
Now the funny part, when it finally settles at normal steady idle
(about 600-650 RPM) the duty cycle stops at a fixed number (60.4%). This means there is a fault.
In the website I mentioned before, 60% fixed at idle means there is something wrong with the CMP sensor (L5/1). Lets not forget the disclaimer, these are codes for 1993 or newer. (I am assuming they are the same for mine since they are taken from the same diagnostic pin)
Questions:
What is the CMP sensor (L5/1), what does it do?
Where is it located?
How come it actually shows a fault when the idle is steady, while no faults while idle oscillating?
If I have a vacuum leak, and it is causing the problems described previously in the thread, how come is not permanent?.
Is there such a think as an intermittent vacuum leak that comes for a week, creates havoc with the idle, leaves for 3 weeks and reappears, and so on and on?

PS. Unfortunately they are predicting rain or freezing rain for the area. Which dims my hopes of playing with the idle control mixture screw. I'll still test the O2 sensor from inside the car.

stevebfl · #18 02-15-2003, 09:01 AM

It's steady when steady because its steady. When in control things are changing. The point is your car is having trouble handling control.

You can't use fault codes for other systems, not even other years. you must be specific. Being at home I don't have a code sheet, but there are links in these archives that should give a proper code list. It think CMP is camshaft position sensor and your car doesn't even have one. The 93 models all have electronic fuel injection (HFM on sixes LH on v8s) so they would have no codes the same as KE.

pesuazo · #19 02-15-2003, 01:59 PM

Thanks Steve.
Here is the update.
No rain here yet, so I removed the ICV. Sprayed (thru hose connections) the crap out of it with Brake-Carburetor cleaner.
Let it sit for a while, shaked it and removed whatever carbon deposits (not much) came out with the cleaner. Repeated procedure until the solvent was coming out the same color it went in. Put it back in, idles marginally better. Spray some of the stuff all around hoses. No change of idle (no vacuum leaks???). Idles fine. (600-650 RPM normal operating temp). Duty cyles 28-39%.
Rev. the engine to 2000 RPM steady, duty cycle 45-50.6%.
Go for a drive, find nice strech, gas it to 5000 RPM several times good response.
Stop, park. No dancing idle yet (500 to 900 RPM).
Remove 02 sensor, duty cycle rock steady at 50.2%. Plug it back in. Duty cycle 29-39%. (O2 sensor obviously working)
Start playing with idle control mixture screw. Turn, turn.. duty cycle at idle 39-49%, at 2000 RPM 50-60%.
For the life of me I can not get it to be 50% +/- 5% at both idle and 2000 RPM. Still idle appears fine.
Are the values I am getting good enough?

stevebfl · #20 02-15-2003, 02:05 PM

They say ten percent difference is acceptable. Without other symptoms your deviation from idle to 2000 is acceptable to me. It means that the system is mechanically richer at idle by a small amount. The results would be the opposite if you had airleaks.

pesuazo · #21 02-15-2003, 03:10 PM

Steve, about how much and how long would be a complete head job?,
Or would it be better to purchase one of those rebuilt heads?
I have been considering this for a while now. Rather than just changing the valve seals and guides. I have also thought of chain tensioner. Everyone says the bottom end and the chain last almost forever.