O2 sensor electronics testing - Page 2 - PeachParts Mercedes-Benz Forum

emerydc8 · #16 10-16-2007, 08:45 PM

Understood. I was thinking of doing the same with my MAF and IAT sensors, but I wanted to see what the lambda reading was beforehand. Forgive my ignorance, but do they have meters at Radio Shack that measure "duty cycles"?

JimF · #17 10-16-2007, 10:25 PM

Quote:

Originally Posted by emerydc8

Understood. I was thinking of doing the same with my MAF and IAT sensors, but I wanted to see what the lambda reading was beforehand. Forgive my ignorance, but do they have meters at Radio Shack that measure "duty cycles"?

Yes, I think so . . . spent 20mins on their site and all I can say . . .

You can't find summary specs for their VOMs except in the "PDF" files which you'll have to wade through. Personally, I don't like RS for anything like this.

A better choice is "Fluke". . . be prepared to do some 'googling' and if you find something that looks interesting, I'd be glad to check it out.

Victor300E · #18 10-17-2007, 09:42 AM

Thanks for replies, guys.
I have checked everything again and here are the results. I had couple of shorts in my self made engine wiring harness going to ECT sensor. O2 sensor plug was broken apart and wires were swapped. Purge valve is leaking. I have fixed everything except purge valve. Just blocked vacuum tube to it for now and have new one on order. Erased all codes with home made reader.

No new codes are stored

Car gained more power and revs quicker but there are 2 problems. 1st is that when the engine is started and its warm duty cycle stays at 50% for 30seconds and then starts to drop down to 10% and stays there +/- 5%. At 2500rpms duty cycle is jumping around 27-35% and when I let go off the gas pedal it jumps to 50% and stays there and then 1st scenario repeats. 2nd problem is that when the car idles and duty cycle is at 50% the idle is very smooth. When cycle drops to 7-10% idle gets rough, engine shakes to the point that one can feel it inside the car.

emerydc8: I have used Craftsman multimeter I bought at Sears 2 years ago for $40 and it works great. I used black lead on ground and red on pin3 in connector x11 on driver side wheel well. Did I do it right?

JimF: Thanks for lots of info you have collected on your website. I went to menu 4a and followed instruction on cleaning MAF sensor. It's drying as I type. I will check it in few minutes and update this thread.

Thanks

Victor300E · #19 10-17-2007, 10:22 AM

I have MAF and IAT sensors cleaned as per Jim's instructions. Duty cycle on idle is 2-9% and at 2500rpms 23-35%. Cycle jumps to 49% if you give a little gas and let go. After it jumps to 49% it slowly drops to 2-9%. Engine starts to run a little rough. Exhaust smell bad. Does it mean that I have mixture too lean? No codes are stored.
Any ideas what can cause lean mixture?
Please help

JimF · #20 10-17-2007, 10:42 AM

Have you tried this . . . .

Disconnect the MAF sensor connector by turning it a quarter turn. This should force the car to run on the precoded fuel management mode and go to the 50% area. Supposedly, airflow info is generated by using rpm and throttle position instead of reading the MAF sensor.

If the lean drivability symptoms go away, the MAF sensor is probably bad. If they don't, the MAF sensor is probably OK and it might be time to replace the O2 sensor esp since it's been misconnected and sitting in the exhaust stream with no heater.

Victor300E · #21 10-17-2007, 02:12 PM

I disconnected maf sensor and duty cycle went to steady 59.7%. When maf is connected cycle goes to 50% and going down to 3-12%. I have O2 sensor on order. It will not hurt the car to have new O2 sensor since it's old anyway.
I did have a stalling problem before and I bought a used maf from good running car with 125k. I know the guy and it was his personal car he parted out. After maf replacement my car never stalled once. Maybe his maf was not good?

Victor300E · #22 10-17-2007, 02:24 PM

Jim, by the way, does duty cycle has to go to 40% when maf is disconnected? Do I measure cycle correctly? Red positive lead from multimeter to pin3 and black ground lead to ground? If I reverse leads then I get 40% maf code.

JimF · #23 10-17-2007, 03:19 PM

Quote:

Originally Posted by Victor300E

I disconnected maf sensor and duty cycle went to steady 59.7%. When maf is connected cycle goes to 50% and going down to 3-12%. I have O2 sensor on order. It will not hurt the car to have new O2 sensor since it's old anyway.
I did have a stalling problem before and I bought a used maf from good running car with 125k. I know the guy and it was his personal car he parted out. After maf replacement my car never stalled once. Maybe his maf was not good?

I think the 'test' showed that the MAF is bad since it goes to the 10% area unless it's contaminated and that contamination can't be removed.

Is it a "hot-film" type vs "hot-wire"?? In trying to clean them, the H/W MAF clean up better than the H/F MAF. My tech has tried a number of them with no success.

Quote:

Originally Posted by Victor300E

Do I measure cycle correctly? Red positive lead from multimeter to pin3 and black ground lead to ground? If I reverse leads then I get 40% maf code.

Red on pin 3; Black on Pin 2.

emerydc8 · #24 10-17-2007, 05:24 PM

Thanks, Jim. This is a good string of information. Any way to tell by looking if my 1993 400E is a "hot film" vs. a "hot wire" type MAF? Thank you too, Victor, and good luck.

JimF · #25 10-17-2007, 05:39 PM

Quote:

Originally Posted by emerydc8

Thanks, Jim. This is a good string of information. Any way to tell by looking if my 1993 400E is a "hot film" vs. a "hot wire" type MAF? Thank you too, Victor, and good luck.

. . . . look down the 'spout' . . . . it's somewhat obvious; L/H has a thin wire, H/F has black plastic assy that sticks into the venturi.

Victor300E · #26 10-17-2007, 09:24 PM

I was looking on electrical diagrams and it seems that maf sends signal from pin5 to ECU pin17. What kind of signal is it? I have read how maf works but it seems to have a solid state device inside that converts current needed to heat hot wire to some other signal that is sent ECU pin17. What kind of signal can it possibly send to ecu? It has to be some voltage that varies with amount of air passing through maf. I want to get to basics of my lean conditions. Also I have new universal O2 sensor from Bosch. Hopefully it will improve something.

Another question is can one adapt MAF from m104 engine to work with m119 engine? m104 mafs are way cheaper than m119 engines. I have no problem with resoldering the plug to fit m119 plug, but I have doubts about m104 maf ability to calculate extra air that m119 use. Also does m104 maf has same dimensions as m119 maf?

JimF · #27 10-17-2007, 09:51 PM

Menu#4a has a link to general info for a MAF (MAF Troubleshooting and Testing) along with typical voltage output levels. As you surmised, the amount of air flow is turned into a voltage; the more voltage = more air.

As far as interchanging MAFs from 119 and 104, it is "theoretically" possible if you could design a ckt to translate the output of one (119) to be equal to the other. Practically, it's not possible.

Well when you amass all that info you can teach us . . . .

PS: the other day, I checked my Lambda to see what's what; oscillating between 48 to 56 at idle and the same at 2K. Seems like the 'cleaning' is still 'effective'. I sold the K&N filters and now using paper!

myarmar · #28 10-17-2007, 10:20 PM

Inside LH MAF

emerydc8 · #29 10-17-2007, 10:23 PM

I just bought an autoranging multimeter at Sears (a step above Radio Shack) for $49.95 that measures "duty cycles." The Flukes were right next to them, but they were all well over $100. Jim, I know you have to plug the purge valve (Y58/1) line to check Lambda. Is that the valve that's mounted to the left fender well and makes a clicking noise most of the time?

Thanks, Myarmar. Is that a picture of a hot-film type MAF or hot-wire?.

myarmar · #30 10-17-2007, 10:56 PM

Quote:

Originally Posted by emerydc8

Is that a picture of a hot-film type MAF or hot-wire?.

Hot wire