Testing lambda on-off ratio
 

Which function does this correspond to on a multimeter please? Also, the manual states to connect the on-off ratio tester to the diagnostic socket and press the 100% button. Again, which button would this correspond to on my digital multimeter. My DMM has a duty cycle function.

TIA!

~Paul

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'91 300E, 215K miles

Since your DMM has a duty cycle function, you're all set. The duty cycle will read in %. That is what the lambda signal is.

There is a good article by Steve Brotherton about this in the DYI section, I think.

Good luck,

Thanks Larry..

My MPG had dropped pretty low in recent weeks, down to about 16mpg and I figured it was my O2 sensor going bad even though check engine light didn't come on. I replaced the O2 sensor and mileage appears to be back to normal but I won't know for sure until the whole tank is used.

I checked other sensors (temp sensor, coolant temp sensor) and they checked out ok. Lambda is next, and I'll adjust it if it needs to be, then EHA. I figure I should be getting at least 20/21 mpg in city/hwy mixed driving.

I'm just now getting the hang of using this handy multimeter -- great tool to keep your fuel system optimized :D

Take care,

~Paul

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'91 300E, 215K miles

ok, being that your meter will read duty cycle its simple. Set your meter to duty, put the postive lead into the #3 pin of the round connector on the l/h fender well. Ground the other to the engine. Start it and let it warm up, set the mixture to 40 to50%. Unless there are other problems your duty should not vary much more than 5% either way of set center.

Joe

Well I put red probe into pin 3 on the left fender and black to engine ground and set to duty cycle %. I got a constant 69.9 with engine fully warmed up, at idle and at 2000 rpm's.

Does this point to a possible EHA problem? To test EHA, do I absolutely need the test cable to test it accurately or can I do some preliminary tests with just my digital multimeter?

TIA as always! *edit -- OVP is new

~Paul

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'91 300E, 215K miles

As Larry stated, I think you could find value in the article I wrote. One important thing I think it states: Check the duty cycle,key on engine off, first. You should get 70% if its a federal car and 85% if its a CA car. The point to this is that it confirms your hook up.

If you have a fixed duty-cycle then you are reading a realtime fault code. Don't have my book to tell you what 70% would be.