...my on-off (lambda) ratio readings are fluctuating wildly -- 4-7% at idle, 40-45% at 2k rpms. According to the manual, this means I either have a bad EHA, or the wiring upstream between EHA and CIS-E control unit has an open circuit, no? (BTW, wonderful article on this topic Steve)

Off to test the EHA's mA readings but I don't have the "test cable" or harness that the manual refers to in gathering these readings.

My question is: can I get any meaningful values at all out of the EHA with just my DMM, or is it absolutely necessary to have this harness?

If the latter, I suppose I'll run by the dealership tommorrow to pick one up.

Thanks in advance for any insight in this area!


~Paul

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'91 300E, 216K miles

The readings should be fluctuating rapidly esp at 2500 rpm.
Having more than 10% differential at idle & 2500RPM can be due to several things: including a charcoal canister that has a lot of fuel vapors from the tank. Also the Governor (EHA) could have a slight misadjustment of the BASE differential pressure. Vacuum leaks can also cause this problem. Try adjusting the Lamda at idle to say 20% & then see what happens the higher reading. AS long as the duty cycle changes at idle & at 2500 you WON'T have any problem!!!

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Thanks DOC for the reply!

I fiddled with the lambda today and got 20% at idle and about 45% at 2500 rpm. I guess that's the best I can do for now until I check out the possible culprits you listed.

Hopefully my MPG will rise at least some!!

~Paul

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'91 300E, 215K miles

This is the first time I've heard that my 124 has a charcoal filter in the fuel system but looking at the KE injection function diagram I now see it! :p

Apparently it's located between the vent valve and the regeneration valve next to the fuel tank.

Does anyone know exactly where this filter is located and how to access it?

TIA!

~Paul

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'91 300E, 215K miles

Under the left front fender! You have to remove the inner fender liner to get to it.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

MBDOC or anyone else:

Is this canister a maintainence item or is a life-of-the-car type part? Also, would it be possible to simply disconnect the canister hose that leads to the throttle valve body to then check to see if my on-off ratio readings stabilize, or would this affect chamber pressure and make matters worse?

Also, if you have a p/n for this charcoal filter I would appreciate it!

Thanks again!

__________________
-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi

Should be for the life of the car unless the car was HIT in the left fender!! Never replaced one for any other reason!!
YES disconnect the line at the check valve & block off while checking the duty cycle.

AS long as you have a good duty cycle at idle & at 2500 the car will give you as good performance as it would if they were excatly the same reading.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator