10%= new airflow meter? - PeachParts Mercedes-Benz Forum

fahrgewehr2 · #1 12-11-2003, 02:45 PM

I read another post ("duty cycle stuck at 10%) and the diagnosis was a bad airflow meter.

The reading I am seeing is around 10%. Reading is for the most part stuck on 10%, but sometimes there is fluctuation. I am unable to change the % by adjusting the mixture screw.

KOEO=69.9%
During warm up=10%

What thinks the forum?

mhingram · #2 12-11-2003, 05:20 PM

70 % koeo is normal the system will not read correctly untill warm wait till operating temp before adjusting.
m

fahrgewehr2 · #3 12-11-2003, 05:37 PM

Thanks for the reply

70% KOEO indicates that the system recognizes electronic control, correct?

The car is at 80 degrees celcius when I attempt to adjust mixture. There is some fluctuation happening around 10%, sometimes it sticks exactly at 10%.

Before, I would see 49% while warming up, and at around 60 degrees, when the 02 sensor became active, this reading would start to fluctuate around whatever it was set to (I was at about 50%).

According to the manual, only a FIXED reading indicates a fault. 10% can have the following "possible causes:"

-----------------------------

Sensor air volume meter wrong pole connection or defective. Speed Approx 2000rpm.

Wire routing of plug, idling speed and full load contact, wrong pole connection or short circuit.
(Full load contact closed at insufficient rate of air flow)

-----------------------------

That info is taken from the manual.

Any other ideas? Anyone seen this before?

Mike

mhingram · #4 12-11-2003, 05:50 PM

70% koeo means US non calif system and all is well at that point. However, the fixed reading at temp is wrong unless the car is overly rich. 10% is very rich but not fluctuating is wierd. I thought the reading was meant to be read at koeo. Steve any ideas?
Have you checked your EHA numbers?
m

fahrgewehr2 · #5 12-12-2003, 10:26 PM

Well I ordered the EHA test harness today, should be here next week.

I have not yet tested EHA current. Can I do anything without the harness? Anything obvious to check? Connections wires etc...

Mike

fahrgewehr2 · #6 12-15-2003, 05:28 PM

Well, I let the car sit for a couple of days. Started her up and everything was back normal. 49% while warming up, then fluctuation around 50% like in the past, indicating the o2 sensor was alive and kicking.

Today, began experiencing hesitation in the upper RPM ranges. Car still idles fine, and does not hesistate from a standstill.

Checked the reading at pin 3 when i got home- 10%- with a little fluctuation around 10, sometimes sticking exactly on 10 for a few seconds.

What gives? This is very frustrating.

(still waiting on harness)

Mike

mhingram · #7 12-15-2003, 07:07 PM

i just re read the manual and you where right the 10 % steady at 80 degrees is potentiometer. But that usuually effects idle more than lumpyness at speed. the check according to the manusl is the following :
:EDIT: Removed dead link..........
at the bottom of the page 25.

The good news is the potentiometer is replaceable without the replacing the entire airflow unit. But lets see the eha numbers before we make the leap cause i do not think that is your problem at least not convinced.
m

fahrgewehr2 · #8 12-15-2003, 07:20 PM

Yes, from what I have gathered on this site, the failure of the airflow meter should cause an idle problem. Strange that my driveability issues are only during hard acceleration.

Hopefully my EHA harness will arrive tomorrow and more "evidence" can be gathered.

I appreciate your help.

Mike

fahrgewehr2 · #9 12-16-2003, 11:20 PM

So I start the car up this morning, and wouldn't you know it, runs perfectly. Checked the duty cycle out of curiosity and its perfect.

Drive the car around during the afternoon. While on the road home, notice it wont accelerate and is hesitating in the higher RPM ranges (remember- 300SE will cruise at 3500- 3.46 rear end!).

I get home and once again, she is reading 10% (sometimes fixed) at pin 3. Starting her back up is a chore and she doesnt want to idle with out a little gas pedal persuassion.

Mail came, and with it, my test harness. Just got her plugged in and will report back with the results. By the way, your (Martin) pictures of the set up (from a previous thread regarding your 560) have been worth a thousand posts.

So problem only occurs after car has been driven for a bit. Hmmm. Ignition coil?...I'll get to the bottom of this.

Mike

EDIT- Oh yes, she sure is sucking down that premiuim petrol!

mhingram · #10 12-16-2003, 11:30 PM

Mike, I hate these problems they are so frustrating to figure out.
By the way my coil did caused stumbles on acceleration, not at rpm. It was great at speed not to say it is not the coil but I think it is the signal to the lambda that is fishy. If you disconnect the eha does she run better that takes the electronic control system out of the picture. Which other than starting should run the car on the default settings. It also masked my coil in that my stumble on acceleration was almost entirely gone but, not completely, hence chasing the fuel system instead of the darn coil. I have however found steve's advice invaluable, EHA readings are the first place to start then go from there. Keep us in the loop.
m

mhingram · #11 12-16-2003, 11:34 PM

should also mention rich gas setting also masked the stumble but by rich I mean black smoke on hard acceleration.

mhingram · #12 12-16-2003, 11:59 PM

Mike, I pulled my bosch book out and it points to the obvious: for engine misses and hesitations under load: fuel injector clogged, fuel pressure incorrect, fuel leak(s), lambda control faulty and coolant temp sensor or wiring faulty. Pretty generic but I figured I would let you know as at least we are not of the mark with lambda problems.

fahrgewehr2 · #13 12-17-2003, 12:55 AM

Well I attempted to test with the harness, but I believe I am doing something wrong. I hooked up the harness correctly and started the car. Very hard to start. Numbers read with the DMM were all over the place. Couldn't get 20mA KOEO either. Its late now, so I will try again tomorrow.

Yes, I agree, its probably not the coil, as I doubt it could lead to the car enrichening itself.

Tomorrow should produce more conclusive results with the EHA current.

Once again, I really appreciate your help.

Mike

pesuazo · #14 12-17-2003, 09:07 AM

I have been following this thread closely, and have not replied due to your good diagnostics.
You are correct about the EHA current with KOEO = 20ma.
When engine is idling at normal temp, it should fluctuate around 0ma if the duty cycle is set at 45-55%.
I agree with the potentiometer acting up when it sticks at 10%.
How is the idle when DC=10%?
Is it rough or just high?

fahrgewehr2 · #15 12-17-2003, 12:18 PM

Pesuazo,

When the DC hovers around 10%, idle is just about the same as when it is at around 50%. I can't tell a difference. No difference in rpm either.

I had a thought today- this car has always been a highway car, so perhaps the problem wouldn't show up at idle?

Thanks for the response, I'll work on getting those EHA numbers.

Mike