Duty Cycle Issues - PeachParts Mercedes-Benz Forum

Rahulio1989300E · #1 06-22-2010, 09:49 PM

Hello,

I started an earlier thread regarding my emissions results. It was determined from the result that the car was running rich. High CO and HC levels with a low Nox level.

I connected my multimeter to the X11 ports 2 and 3. I put the negative (black) lead into pin 2 and positive (red) lead into pin 3.

When the ignition is turned to position 2, I get a reading of 30.7%. I have no idea what this means???

The pins are really confusing me since if I swap the red and black probes between pins 2 and 3, the duty cycle is now 70% which would indicate a federal car.

The way it is now:
When I start the car from cold, the duty cycle is 49.3%. Then after some time with the engine running, the duty cycle starts to fluctuate between 45%ish and 60%ish.

To get to this point, I did some adjustments to the mixture screw, a fair amount (1 full turn) of CW movements from which I understand is actually supposed to enrichen the mixture...

So as you can tell, I have no idea why this is occurring...

Weird thing is that when I hold the engine at 2500RPM, then duty cycle slowly but surely works its way to 0.00%. Which means the car is leaning itself out?

JohnM. · #2 06-22-2010, 11:51 PM

Sounds like you were able to get your IDLE CO mixture dialed in fairly well. Closed loop 45% - % 60 fluctuating is a well adjusted reading.

I would suspect your EHA valve might be bad. Mine did the same thing. I got the idle mixture adjusted, then when I rev to 2500rpm the duty cycle slowly maxed out / went to zero. The EHA is primarily what affects mixture above 2500rpm. A good functioning EHA will ideally keep the mixture in the same 45% - 60% range that you have at idle. I just swapped a used EHA into my car and it fixed that problem immediately. You can adjust the EHA, but it is pretty pointless. The stock setting should not be messed with.

rayhennig · #3 06-23-2010, 02:14 AM

Have you checked the engine coolant temperature and the air intake (if you've got one) temperature sensors.

My air temp sensor was dead, cost €12 to replace and changed the duty cycle from 50% to 90+%. Re-adjusted and everything was great aside from minor hesitate immediately after hot start. New Beru plugs (€20) solved that.

And all this is on the original, 19 year old distributor cap - that's the next purchase.

Good luck.

RayH

Rahulio1989300E · #4 06-23-2010, 03:15 AM

Hello,

I went ahead and purchased a used EHA from eBay ($59 with shipping).

Thank You for clearing that up. I need to change my thinking in that I should consider the system as two parts. 1. IDLE 2. AT SPEED (Throttle actuating.)

I looked for the coolant temp sensor. I think it is supposed to be right near cylinder 6 and is the last one in the line of sensors. People who posted previously kept mentioning about a 4 prong sensor but my sensor only has 2 prongs with two individual connectors coming from the wiring harness.

I searched the forum for the expected ohm values for a good sensor, but I was unable to find any posts or threads. (I know they exist, but my search terms are not finding the threads.)

Does anyone know how I should test the water temp sensor and what ohm values I need to be getting?

I do not have an air intake temperature sensor fitting to this car.

rayhennig · #5 06-23-2010, 06:17 AM

Quote:

Originally Posted by Rahulio1989300E

I looked for the coolant temp sensor. I think it is supposed to be right near cylinder 6 and is the last one in the line of sensors. People who posted previously kept mentioning about a 4 prong sensor but my sensor only has 2 prongs with two individual connectors coming from the wiring harness.

I searched the forum for the expected ohm values for a good sensor, but I was unable to find any posts or threads. (I know they exist, but my search terms are not finding the threads.)

Does anyone know how I should test the water temp sensor and what ohm values I need to be getting?

I do not have an air intake temperature sensor fitting to this car.

This is what I based my actions on:

1. 4-pin main engine temperature sensor (by water pump) - (measured across diagonals).
HOT: 250 Ohms
WARM: 1200 Ohms
STONE COLD 2600 Ohms

2. 2-pin aux fan sensor (by water pump)
HOT: 459/468 ohms (measured each pin to earth) - didn't measure across the pins.
WARM: Open circuit (measured each pin to earth) 2600 Ohms (measured across the pins)
STONE COLD: Open circuit (measured each pin to earth) 6470 Ohms (measured across the pins)

3. Single pole (temp gauge?) sensor (by water pump) - (measured to earth)
HOT: 55 ohms
WARM: 290 Ohms
STONE COLD: 720 Ohms.

4. Air intake sensor (on air filter housing) - (measured across the 2 pins)
HOT: open circuit.
WARM: Open circuit
STONE COLD: Open circuit
Assume it's failed. The specified values are:
20C: 2500 ohms, 80C: 300 ohms.
So, my ECU thinks it's always about minus 50C outside!!!!

Hope it helps.

RayH

Rahulio1989300E · #6 06-29-2010, 12:06 PM

Hello Everyone,

Thought I would update the thread...

I purchased a used EHA off of eBay. When it arrived I was a bit depressed as it looked like the brass cap screw that people remove to get access to the 2nd screw which actually adjusts the EHA was tampered with.

I swapped it out with my current EHA and installed 2 new green colored o-rings while I was at it. (I will post a write up on how to replace the EHA when I get the chance.)

After I changed the EHA with the 'new' one. I started the car with my multimeter set to duty cycle and the positive (red) probe in port 2 and the negative (black) probe in port 3.

Key in, ignition position 2, engine is off:
69.2%

Engine started, cold engine, idling:
49.2 to 49.8%

Engine warming, engine entering closed loop cycle:
Initially fluctuating between 49% and 65%, then eventually got 'lost' so to speak and by 2-3% increments per second worked its way to 92.3 - 92.7% and stayed there. (Note I was not touching the throttle at any point.)

I turned the engine off, removed the air cleaner, used a 3mm hex key to turn the tower mixture screw, replaced air cleaner... etc. (Repeated this procedure 4 times)

After a total mixture screw adjustment of slightly less than 5/8 CW...

My new numbers with the new EHA installed:
Cold engine idling: 49.2%
Hot engine idling: 44.3% to 55.4%
Hot engine revving (2500 to 4000RPMs) : jumpy as hell, but between 45 and 55%!

No longer does the mixture work its way to 0% or 100% anymore when revved. With the old EHA, I was able to stabilize the hot idle mixture between 45 and 60%, but when revved the mixture would work itself to 100%.

Replacing the EHA appears to have fixed my problem with the mixture when revving with a hot engine. (Please read above posts.)

Now I am going on a highway run for an hour and will take the car for an emissions retest. Today is my last day for a free retest at my emissions place. If I dont pass, it might be the cats or something else. My plugs are only 10K old, my cap and rotor are 25K old, my wires are 30K old. Engine seems to run great. I am going for a test drive to see how this new EHA makes the engine behave.

Wish me luck! Also, thank you for your assistance!

Rahulio1989300E · #7 06-29-2010, 02:31 PM

Hello, I just got back from the emissions test place for my free test...
(Test 2 of 2.)
I drove the car for 40 minutes before hand, which I thought would be enough to get the cat nice and toasty.

Here are the results from test number 1:

High Speed Results (25mph)
RPM: 1438
HC (ppm): 293 (Standard is 148) FAIL!
CO (%): 7.28 (Standard is 0.94) FAIL!
Nox (ppm): 102 (Standard is 1047) PASS!
Dilution: 17.38 (Standard is >6.0) PASS!

Low Speed Results (15mph)
RPM: 1705
HC (ppm): 284 (Standard is 152) FAIL!
CO (%): 7.35 (Standard is 0.86) FAIL!
Nox (ppm): 98 (Standard is 1146) PASS!
Dilution: 17.55 (Standard is >6.0) PASS!

Overall: FAIL!

Here are the results from test number 2:

High Speed Results (25mph)
RPM: 1433
HC (ppm): 306 (Standard is 148) FAIL!
CO (%): 5.28 (Standard is 0.94) FAIL!
Nox (ppm): 300 (Standard is 1047) PASS!
Dilution: 16.28 (Standard is >6.0) PASS!

Low Speed Results (15mph)
RPM: 1695
HC (ppm): 292 (Standard is 152) FAIL!
CO (%): 5.17 (Standard is 0.86) FAIL!
Nox (ppm): 229 (Standard is 1146) PASS!
Dilution: 16.37 (Standard is >6.0) PASS!

Overall: FAIL!

So my CO improved by 2 full points, HC went up a bit, Nox went up 200ish but is still well within bounds, dilution dropped about 1 pt but again, still within limits...

I am going to double check the duty cycle percentages to make sure the car is still running between 45 and 55% at all times.

My suspects: ignition coil, cap n' rotor, fouled spark plugs due to rich conditions...

S-Class Guru · #8 06-29-2010, 06:24 PM

Hmmm, based on the std Co/HC/Nox curves, it appears you were running too rich on the first test, and leaned it a bit on the 2nd test, but not enough to bring the CO and HC down to spec. NOX will peak up the nearer the mixture gets to perfect, and go down when either rich or lean. HC/CO go up when rich. CO goes down the leaner it gets, but HC goes back up if the mix is excessively lean.

I've forgotten most of this stuff, but I got this from a chart somewhere in the archives, that one of the guys published. You might do a search to see if you can find it.

Sounds like your Lambda control is now working better, but did you check the EGR valve? May not be that, though, because it really doesn't come in at idle, and your low-high speed numbers are behaving similar.
definitely check all the temp sensors.

DG

Rahulio1989300E · #9 06-29-2010, 09:38 PM

Quote:

Originally Posted by S-Class Guru

Hmmm, based on the std Co/HC/Nox curves, it appears you were running too rich on the first test, and leaned it a bit on the 2nd test, but not enough to bring the CO and HC down to spec. NOX will peak up the nearer the mixture gets to perfect, and go down when either rich or lean. HC/CO go up when rich. CO goes down the leaner it gets, but HC goes back up if the mix is excessively lean.

I've forgotten most of this stuff, but I got this from a chart somewhere in the archives, that one of the guys published. You might do a search to see if you can find it.

Sounds like your Lambda control is now working better, but did you check the EGR valve? May not be that, though, because it really doesn't come in at idle, and your low-high speed numbers are behaving similar.
definitely check all the temp sensors.

DG

Hello,

Thanks for the HC, CO, and NOX explanations, that is helpful!

I do not believe that my car is equipped with an EGR system, but I could be very wrong.

Here are what my row of three sensors for my M103 looks like.

Starting from left to right...
1. Two prong, blue base, used to trigger the aux fans at 105C.
2. Single prong, sends engine temp to instrument cluster gauge in car.
3. Older style temp sensor, has two prongs. I think this is why I am so confused with regards to this sensor. Everyone is telling me to look for a 4 prong sensor but I have not been able to find it. I think my car happens to have this older sensor which is significantly more expensive than the four prong everyone else seems to have.

PeachParts Store Link:
www.allpartsexpress.com/item.wws?sku=BSH006937&itempk=57106&mfr=Bosch&weight=0.09

Now I can test the left and center sensors with the information posted by an above forum member. Does anyone have the ohm values I should be getting for the older style water temp sensor on the right most side of the photo?

THANK YOU!

Rahulio1989300E · #10 06-29-2010, 11:13 PM

I went ahead and tested the ohm values across the two prongs for the last sensor (right most side in photo) and I get a ohm reading of 2.780kOhms.

Temperature in right now in TX is 79F. Car was run until about 2PM and then keep outside in driveway for the rest of the day.

Does this make sense?

rayhennig · #11 06-30-2010, 01:28 AM

Test it's resistance when the engine is cold and then when hot. Record the values.

My 4-pin main engine temperature sensor (by water pump) - (measured across diagonals).
HOT: 250 Ohms
WARM: 1200 Ohms
STONE COLD 2600 Ohms

I have no evidence that your sensor should give similar values.

Awaiting your figures.

RayH

400Eric · #12 06-30-2010, 07:03 AM

There were a lot of changes for the M103 that occurred starting in the 1990 model year. They didn't get the intake air temperature sensor or the EGR valve or the smog pump until that time. That's why your 89 doesn't have them. There were a lot of other changes at that time as well. For example, the ECU is very different and won't interchange. I'll bet that's when the change from 2 prong to four prong CTS occurred as well.

As JohnM and I can attest to, swapping a seemingly good ECU out for another one or two or three (in other words, try a few) can often cure these phantoms in the machine.

Sorry I can't be more help.
Regards, Eric

ctaylor738 · #13 06-30-2010, 12:02 PM

How old is your oxygen sensor? It's driving the mixture adjustment.

Rahulio1989300E · #14 06-30-2010, 06:26 PM

Hello, just got back from testing the right most sensor again.
I put the red probe in one of the sensor's holes and touched the black probe to the block near cylinder 1. Took a reading then moved the red probe to the other hole.

Prong 1: 1.680 kOhms
Prong 2: 1.665 kOhms

Car has not been started today so far. Current temperature in Arlington, TX is 75F.

So the values are very similar which is good. It would have been obvious the sensor was bad if one of the values was very different.

Oxygen sensor is less than 5K old, but if the car was running so rich then perhaps it has been fouled?

ctaylor738 · #15 06-30-2010, 09:27 PM

Well, then it sounds like you have a lambda system that's doing it's job and the primary suspect is the catalytic converter.

But it might be interesting to measure the voltage from the o2 sensor at hot idle. You can do this by sticking a pin through the insulation into the wire and connecting your meter between the pin and ground. You should see around .45 volts.