Bought the multimeter Larry Bible recommended. Now 2 Lambda questions
 

To test the lambda on my 1988 300SE I ran the car for about 6 miles and got it up to normal operating temp. Drove home, popped the hood and with the car idling in park took out my new Sears multimeter and set it for duty cycle and % and got the following readings: pin#3 constant 20.7; pin#4 84.3 to 86.6 with it constantly changing. I turned the car off, restarted and revved it a bit, and at idle got the same results.

Question 1. On my car is it pin 3 or 4 I should test? When I went back through prior posts I see reference to both pin 3 and 4. There's no way my car should be steady at 20.7 and I mean steady for 45 seconds, it never changes. It also does not appear to be a fault code.

Question 2. Isn't this a rather lean setting if pin 4 is correct?

I should mention I made certain of a good ground before testing duty cycle.

I think that the 20% steady is a fault code, unless you have a car originally delivered in California.

I have a few sheets of paper with these fault codes buried somewhere, but I'm not sure that I can find them. I will look.

I expect that the fault codes are on the CD, if you have one or can get someone to send them to you. 10% constant indicates one thing, 20% constant indicates another thing, etc.,

Good luck,

PS, that's an incredible meter for $30 isn't it? LB

it sure is a great meter. I'm a beginner at using it but now I'll have a lot to learn. I re-tested today after driving the 35 miles to work and got a steady 30.6 at pin 3 and a steady 0.00 on pin 4.

Sears Multimeter
 

Off-hand do you have the Sears Part Number or product name to look for? I think I want to pick one up. I'd like to check duty cycle on my 190e.

Thanks.

Do a search for "multimeter" in the Tech forum and look for my post of a week or so ago. Larry listed the item number.

Your Lambda reading indicates that the system is in fixed operating mode, and that there's definitely a fault somewhere -- most likely a sensor or short somewhere in the system.

If you have the CD set, it lists the % faults there, but you gotta dig deep. What 103 engine is in the SE? (103.xxx?) I will look it up for you if you have that information.

Thank you for your offer. If you have time, 103.981 is my engine number and 126.024 is the chassis ID.

Ron:

Are you still getting 2 different set lambda %'s? You stated you read 20% one time then 30% another.

According to 0.73-0121 "Testing electrical components of the KE injection system" p. 17 -- a 20% FOM fault indicates "Full load contact incorrectly connected or faulty. 20% readout only if throttle valve switch (S 29/2) operated."

30% would indicate a problem with your big coolant temperature sensor. It's 4 pin black, at rear of head and gives KE and EZL input into the control unit. 30% could also indicate a short or open circuit in your control unit.

I'm not up to speed on the problems you are having, but if you're experiencing poor fuel economy I would suspect the coolant sensor as the problem, but don't quote me on that since I don't know the circumstances surrounding your problem.

You want to be at pin 3 to check the on-off (lambda) ratio.

Also, if you have a pulse code reader, you can check for fault codes at the diagnostic code box on other side near battery.

Good luck :D

Thanks for the reply. It was 20.7 steady after driving the car up to temp and going home and checking while it idled. The following morning I drove to work 35 miles, pulle dinto the lot and popped the hood and check and it was 30.6 and steady. My fuel consumption is about 20mpg so it's not poor by any means.

As usual, I am left with no answers. It's a situation I have become used to. At least now I have a $30 piece of equipment to confirm that I have no answers.

I know the feeling!!:(

A quick question about lambda, I have a 85 190E 2.3 8vlv and I got a multimeter with duty cycle also, but when I hook it up to pin 3 in the diagnostic port, the reading does not change then when it is when the multimeter is not hooked up to anything al all, am I doing something wrong? Checking voltage shows a stable reading, not fluctuating as it's supposed to be, O2 was just changed and reports correct readings to the computer, what am I doing wrong? Does my car even have fault codes?

XP

xp190,

If all is well it will vary around 50% AFTER the engine is warmed up.

Good luck,

I will check it again as soon as I have a minute and the engine is warm, I hope all the electrical components work okay, I'm about to get my timing chain replaced along with both sprockets, rails, tenisoner, oil pump and main front seal. This should keep it going for a while as I save up money for a valve job.

XP