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Discussion Starter #1 (Edited)
So, here is the problem with my 1989 300e:
(I am not mechanic, and never had any experience fixing any cars, before bought this one in Feb. this year)
When I am trying to adjust the duty cycle, and connect my multimeter( tried 3 dif. meters) to x11 port with the key in the ignition(on position) to 2 and 3 accordingly and in DC mode i get the correct readings, around 3.7v (70%), but if change to duty cycle on meter, i constantly get 100%, after starting the car and after warming up always stays 100%. Although in DC mode I can see the right numbers, around 3.7v engine off, solid 6.8v before reaching the operating temp. and fluctuating around 6.8 once operating temp is reached. So I tried testing the ground(#2) for continuity and resistance to the ground on the battery and to couple other ground connectors (always brown wire) under the hood, everything seems to be normal. I also popped the the cover of x11 connector to see the wires not touching each other or messed up, everything looked fine, #2 is brown as supposed to be. For some reason I tried to connect to #1(should be engine rpm, i believe) instead of #2, and get the correct duty cycle readings(70% - idle, 50% - open loop, around 50% close loop) but when trying to read DC voltage connected to #1 and #3 get nonsense readings, don't remember for sure can check later again. The reason why I still want to figure this one out, because the engine doesn't run perfectly when warm, the rpm goes up and down all the time( by not much though, maybe by 50rpm), and there is small hesitation when trying to rev it up, and once release the gas, once it tries to go back to idle rpms the engine hicks up a little for a sec and runs ok again. I also measured the duty cycle on 2500rpm(while connected to #1 and #3 in duty cycle mode on meter and connected to #2 and #3 while reading DC, the readings I get are in range +-10% from idle readings.
the new parts i've thrown on it so far:
Battery
OEM distributor cap (Bosch)
OEM ignition rotor (Bosch)
Spark plugs( 9657 double iridium) (Bosch)
Spark plug wires
OEM oxygen sensor (Bosch, MB)
Throttle potentiometer(set to right value 0.7-0.9v dc) (Chinese crap)
Fuel injectors (Bosch)
Injector seals and holders
OEM (KAE) Over voltage relay, was no change so returned it, put old one back.
ECU (used) tried before changing the oxygen sensor, was no difference, so didn't go for that.
will add if remember more.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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There is a lot to distill in your post but I'm not sure why you are measuring anything referenced to pin#1. Duty cycle is between #2 (ground) and #3 (signal). I believe you are getting correct results when you measure DC voltage (approximately). Most people in this forum have trouble with duty cycle measurements, you are not alone, half of them don't realize the meter is still in the frequency (Hz) mode so they always read 100 (Hz not percent) the rest have meters that may not be working properly at 100Hz. But if your DC measurements are correct you are good. Also check the frequency and make sure it is 100Hz when you are making the DC measurements.

From your readings adjusting the duty cycle should be the last thing to do. If when the engine is warm it is fluctuating and it is somewhere between 30% to 50%, you should not be able to even tell the difference though if at 30% the engine may feel a little more "lively".

My understanding is that you have 2 issues that are bothering you:

(1) Idle a little rough, fluctuates by 50rpm or so. Does this happen when the engine is colder, and between 40c - 75c ?

(2) Hesitation on take-off. Could be a lot of things most likely unrelated to your idle issue. Have you tested your AFM pot by disconnecting it and sweeping the AFM plate and measuring the resistance. Rule out a worn out or bad pot first. It should gradually increase from ~1.5Kohm to ~10Kohm and role back to about 6Kohm or so when it is completely deflected. It should have no discontinuities in the resistance.. An analog ohm meter works better.

Also you should measure the duty cycle during taking off and report on that. Does it change wildly?

- Cheers!
 

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Discussion Starter #3 (Edited)
There is a lot to distill in your post but I'm not sure why you are measuring anything referenced to pin#1. Duty cycle is between #2 (ground) and #3 (signal). I believe you are getting correct results when you measure DC voltage (approximately). Most people in this forum have trouble with duty cycle measurements, you are not alone, half of them don't realize the meter is still in the frequency (Hz) mode so they always read 100 (Hz not percent) the rest have meters that may not be working properly at 100Hz. But if your DC measurements are correct you are good. Also check the frequency and make sure it is 100Hz when you are making the DC measurements.

From your readings adjusting the duty cycle should be the last thing to do. If when the engine is warm it is fluctuating and it is somewhere between 30% to 50%, you should not be able to even tell the difference though if at 30% the engine may feel a little more "lively".

My understanding is that you have 2 issues that are bothering you:

(1) Idle a little rough, fluctuates by 50rpm or so. Does this happen when the engine is colder, and between 40c - 75c ?

(2) Hesitation on take-off. Could be a lot of things most likely unrelated to your idle issue. Have you tested your AFM pot by disconnecting it and sweeping the AFM plate and measuring the resistance. Rule out a worn out or bad pot first. It should gradually increase from ~1.5Kohm to ~10Kohm and role back to about 6Kohm or so when it is completely deflected. It should have no discontinuities in the resistance.. An analog ohm meter works better.

Also you should measure the duty cycle during taking off and report on that. Does it change wildly?

- Cheers!
I forgot to mention, if measuring HZ, between port 2 and 3 i get way over 100hz, didn't really measure that a lot, but usually get somewhere 130-150hz(no clue what that means).
I tried to measure between 1 and 3 after couple weeks of trying everything to figure out why im not getting the readings between 2 and 3.
Rpm starts to fluctuate on hot, but i can hear how it goes up and down by little while still in warming up and rpm are held higher, but becomes more distinctive once fully warmed up.
I'll probably shoot a video and post it in here.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Not sure what a "gz" means on your meter, but it sounds like garbage. Turn your meter to Hz mode and see if it shows 100Hz.
Also on some models you have to turn that signal on "3" by pressing a button near the battery. If yours need that make sure you are doing that.
CA model '89's certainly require it.
Pin one goes to the ignition control unit so it is your engine rpm's referenced to pin 2 (ground).
Pin 1 to pin 3 is nothing, could be garbage.
And I assume you know than pin 6 is your system voltage at the ECU (output of OVP) so your duty cycle calculation based on DC voltage should be divided by the voltage on 6.

Unplug your EHA at idle and see if the idle rpm's stabilize when warm. It may not though, since you are saying it is also not stable when cold. Try it as an experiment.
When you unplug your EHA, you are breaking the lambda control loop so if there is any issue in the emissions system, it may stabilize. This is assuming your duty cycle is close to 50%. If not, it may cause your RPM's to rise a bit.

You did not address the POT. If I were you, I would look at that tomorrow to rule it out.
 

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Discussion Starter #5
Not sure what a "gz" means on your meter, but it sounds like garbage. Turn your meter to Hz mode and see if it shows 100Hz.
Also on some models you have to turn that signal on "3" by pressing a button near the battery. If yours need that make sure you are doing that.
CA model '89's certainly require it.
Pin one goes to the ignition control unit so it is your engine rpm's referenced to pin 2 (ground).
Pin 1 to pin 3 is nothing, could be garbage.
And I assume you know than pin 6 is your system voltage at the ECU (output of OVP) so your duty cycle calculation based on DC voltage should be divided by the voltage on 6.

Unplug your EHA at idle and see if the idle rpm's stabilize when warm. It may not though, since you are saying it is also not stable when cold. Try it as an experiment.
When you unplug your EHA, you are breaking the lambda control loop so if there is any issue in the emissions system, it may stabilize. This is assuming your duty cycle is close to 50%. If not, it may cause your RPM's to rise a bit.

You did not address the POT. If I were you, I would look at that tomorrow to rule it out.
I recorded 2 videos to better explain everything.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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That is very strange indeed. Almost seems like your x11 port is mis-wired. An oscilloscope would be useful to diagnose this but without one I would suggest taking an "AC" measurement between 2-3. Make 2 your ground in the meter. Because the DC voltage is near correct I wonder if there is an AC signal there at all. the AC value should be larger than the DC value or comparable in magnitude.

You should also measure the resistance (with the igniton key not inserted) between 2 and chassis and 3 and chassis. Be curious to know what those values are.

AS far as the idle hunt, hard to tell how bad it is in the video(s). You may want to re-take that and display the rpm's on your meter, better if you have an analog engine analyzer.
With EHA plugged in and without.

You should also display your IACV voltage during idle. Let's see if that is all over the place when idling.

- Cheers!
 

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89 300E; 00 E320
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wrong plugs:
2612526


you need fuel pressure gauges to test top and bottom pressure of fuel distributor. EHA controls it and may have to be adjusted. And you could put one of your ammeters on the ECU as well for testing - see notes from H.D. below

The fuel distributors have diaphragm that breaks, best component I have ever replaced but expensive for a rebuilt. I need a fuel pressure regulator replaced on mine I think too.

Accelerator cable could be sticky, maybe replace if necessary. Clean and lube throttle linkage with transmission fluid.

ECU is working and making adjustments and O2 sensor must be sending a signal as well. It is going into closed loop as you pointed out so that is good.

Advice from friends:
2612532
 

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95 E300, 91 300TE, 84 190D
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Since you said you're not a mechanic or experienced fixing cars, I'll add to cbc comment about wrong spark plugs. Your car and the M103 engine require a non-resistor plug; cbc listed the two available above.

Yes, the website you ordered from likely said the bosch iridium fit, but that plug is a resistor plug, as are most plugs. The MB engines were unique back in the day requiring non resistor plugs. Been there, done that.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Since you said you're not a mechanic or experienced fixing cars, I'll add to cbc comment about wrong spark plugs. Your car and the M103 engine require a non-resistor plug; cbc listed the two available above.

Yes, the website you ordered from likely said the bosch iridium fit, but that plug is a resistor plug, as are most plugs. The MB engines were unique back in the day requiring non resistor plugs. Been there, done that.
Yeah, generally not a good idea using resistor plugs and add an additonal 6Kohm of resistance to the existing 3K ohm in the system.
However, I have never seen an ill effect of using a resistor plug (I only did this once). Meaning I can not tell the difference the way the car runs.

Should the OP switch back to the non-resistor Denso ?(I use those as well) Absolutely. It is a 20 minute $15 improvement. Chances of this fixing this problem he is having is near zero.....

Now, the reason why I wanted to not get into the FD right off the bat without further diagnosis is that is a big job. Better make sure that is the issue before going in that direction.

So taking pressure measurements as was suggested will be necessary at some point. once the low hanging fruit is picked.

This is why I wanted to see the actual results of disconnecting the EHA and breaking the closed loop to see if any component in the loop is faulty. The result was not deterministic. It would be good to measure the RPM's with and without and the fluctuation. So this is a critical observation in my opinion.

Also, since the actuator for idle is the IACV, it is good to take a measurement there as well for completeness.

- Cheers!
 

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1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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I stuck the NGK plugs in my 300E about 8-9 years ago and its still running strong. the odometer broke shortly after we got it, but its gone to college with two kids (including one going to grad school), I'm sure they've put 100K miles on it...

its probably due for a 'tuneup'...
 

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Discussion Starter #11 (Edited)
Yeah, generally not a good idea using resistor plugs and add an additonal 6Kohm of resistance to the existing 3K ohm in the system.
However, I have never seen an ill effect of using a resistor plug (I only did this once). Meaning I can not tell the difference the way the car runs.

Should the OP switch back to the non-resistor Denso ?(I use those as well) Absolutely. It is a 20 minute $15 improvement. Chances of this fixing this problem he is having is near zero.....

Now, the reason why I wanted to not get into the FD right off the bat without further diagnosis is that is a big job. Better make sure that is the issue before going in that direction.

So taking pressure measurements as was suggested will be necessary at some point. once the low hanging fruit is picked.

This is why I wanted to see the actual results of disconnecting the EHA and breaking the closed loop to see if any component in the loop is faulty. The result was not deterministic. It would be good to measure the RPM's with and without and the fluctuation. So this is a critical observation in my opinion.

Also, since the actuator for idle is the IACV, it is good to take a measurement there as well for completeness.

- Cheers!
How do determine if they have resistor in it? i tried to find any information on that and didn't. I just measured the resistance of my spark plugs - 4.6 Kohms, is that what non-resistor once should have?
The AC voltage between 2 and 3(key is in on position) - 5.374v.
The resistance between #2 and battery neg or body - 0ohm.
I cracked x11 open to see it is miswired, everything looked ok.
If i disconnect eha, the dc voltage(2 and 3) goes up to around 11v.(can shoot another video later)
The IACV is idle control valve (if i understand that correctly)has dc voltage of around 4.5 to it while idling(if disconnect it rpm is going up).

2612584
 

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Discussion Starter #12
wrong plugs: View attachment 2612526

you need fuel pressure gauges to test top and bottom pressure of fuel distributor. EHA controls it and may have to be adjusted. And you could put one of your ammeters on the ECU as well for testing - see notes from H.D. below

The fuel distributors have diaphragm that breaks, best component I have ever replaced but expensive for a rebuilt. I need a fuel pressure regulator replaced on mine I think too.

Accelerator cable could be sticky, maybe replace if necessary. Clean and lube throttle linkage with transmission fluid.

ECU is working and making adjustments and O2 sensor must be sending a signal as well. It is going into closed loop as you pointed out so that is good.

Advice from friends:
View attachment 2612532
The fuel was rebuilt recently, by me, and the diaphragm is in perfect condition.
The accelerator cable is new(febi)
Never measured the fuel pressure, don't have any pressure gauges.
 

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Discussion Starter #13
I stuck the NGK plugs in my 300E about 8-9 years ago and its still running strong. the odometer broke shortly after we got it, but its gone to college with two kids (including one going to grad school), I'm sure they've put 100K miles on it...

its probably due for a 'tuneup'...
are these the ones?
NGK V-Power Nickel Plug Number 2238 Spark Plug
 

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1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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IIRC, its a NGK non-resistor copper plug. I'll have to dig for the P/N.

ok., I dug. it was BP6EFS (3812), the F for tapered seat, apparently discontinued. so it looks like Denso T20EPU is it, unless you can find NOS Bosch H9DC0 or H8DC0. Someone on here, sbaert perhaps? stocked up on a big batch of the genuine Mercedes branded/selected Bosch plugs, I dunno if they have any left.
 

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1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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How do determine if they have resistor in it? i tried to find any information on that and didn't. I just measured the resistance of my spark plugs - 4.6 Kohms, is that what non-resistor once should have?
a non-resistor copper plug will be as close to zero ohms as what you can't measure.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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The AC voltage between 2 and 3(key is in on position) - 5.374v.
The resistance between #2 and battery neg or body - 0ohm.
I cracked x11 open to see it is miswired, everything looked ok.
If i disconnect eha, the dc voltage(2 and 3) goes up to around 11v.(can shoot another video later)
The IACV is idle control valve (if i understand that correctly)has dc voltage of around 4.5 to it while idling(if disconnect it rpm is going up).

View attachment 2612584
OK, so your AC voltage (and your picture) suggests everything is in order however it looks like your #1 pin is not connected to anything.
Is it possible what you are calling pin1 is actually pin2?

This aside I'm not sure then why your meter can not take AC (Hz/duty cycle) measurement on 2 and 3.
(1) You forgot to measure the resistance between pin#1 and ground. That would still be interesting.

When you disconnect the eha the ECU must be trying to correct the lambda so it is railing to lower duty cycle because it sees an open circuit and can not correct the mixture. Probably normal assuming your duty cycle was a little in the other direction in closed loop.

Your IACV DC voltage is normal. I wanted to see how it is fluctuating (or is it fluctuating) during idle when you get those little hick-ups that cause the idle to drop 50rpms.

(2) It is also valuable if you can take a video of the engine RPM's during idle with and without the EHA plugged in so we can witness it.

(3) Also, one more observation please.
- Does the idle seem more unstable when it is hot outside and the engine is hot?
- Does the idle hick-ups take perhaps 3-4 seconds to return from higher rpms? So basically when you come to a stop it is OK for 3-4 seconds and then it starts fluctuating?
 

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Discussion Starter #18 (Edited)
OK, so your AC voltage (and your picture) suggests everything is in order however it looks like your #1 pin is not connected to anything.
Is it possible what you are calling pin1 is actually pin2?

This aside I'm not sure then why your meter can not take AC (Hz/duty cycle) measurement on 2 and 3.
(1) You forgot to measure the resistance between pin#1 and ground. That would still be interesting.

When you disconnect the eha the ECU must be trying to correct the lambda so it is railing to lower duty cycle because it sees an open circuit and can not correct the mixture. Probably normal assuming your duty cycle was a little in the other direction in closed loop.

Your IACV DC voltage is normal. I wanted to see how it is fluctuating (or is it fluctuating) during idle when you get those little hick-ups that cause the idle to drop 50rpms.

(2) It is also valuable if you can take a video of the engine RPM's during idle with and without the EHA plugged in so we can witness it.

(3) Also, one more observation please.
- Does the idle seem more unstable when it is hot outside and the engine is hot?
- Does the idle hick-ups take perhaps 3-4 seconds to return from higher rpms? So basically when you come to a stop it is OK for 3-4 seconds and then it starts fluctuating?
1) #1 is connected, it has the wire, just not seen on the pic, it is the same wire as marked on the pic, according to my previous testings with the meter.
I have played with it today a little, enriched fuel pressure on eha(by 1/4 of a turn clockwise) and lowered the readings on potentiometer, to somewhere 0.725 - 0.750vdc (by the way, I have no clue why no one, i mean literally no one ever mentioned about the adjustment screw on the potentiometer, with which you can change the resistance between bottom and top pins, so change the output (top pin) to the ground by around +-0.150vdc without unscrewing all those 4 screws to move the potentiometer physically.) After that adjusted the duty cycle. the problem stayed, rpm still fluctuates.
The IACV is behaving normally, actually tested that this week, on cold 6-8vdc, on hot 4-5vdc(which i believe means closed(no air going through))
2) I will shoot that as soon as have free time, but I'm a student, and right now have final exams going on this week, so...
3) It starts once it goes into the close loop, before rpms are stable(on cold). Yes, there is that most irritating hick up when the engine goes to idle rpms, and when trying to rev up, there is like a tiny delay, i used to think it is because of the wrong mixture, too much or too little air, but tested IACV and don't actually know now.
And I tried to measure the AC duty on 2 and 3 - same, crazy readings on HZ, and 100% cycle. As far as I understand, the duty cycle, for example 70%(on MB the opposite way), is when you get the voltage 30% of time and nothing 70% of time. In my case, between 2 and 3 i get constant voltage, no matter DC or AC, it is constant, i mean it never suddenly goes to 0. Although between 1 and 3 if I read it in DC I can see it going up and down to 0 all the time.
So far I have 2 options:
1) It is either the messed up wiring somewhere, although my year(1989) is not the case with degradable wires, and I've taken a close look before at the harness everywhere, no degrading symptoms ever noticed. so might be something else, as far as I know, what was done to the car post factory electric-wise: the stereo and alarm(not sure, the owner removed it before selling to me).
2) Bad ecu, last time i tested it before changing the oxygen sensor, because again, I couldn't figure out the readings(the old one was bad for sure, because before I couldn't even get any reasonable vdc on 2 and 3).
2612615
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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(1) So it looks like pin 1 is connected to the ignition coil low voltage side from your picture. Perhaps it is providing a virtual ground (or battery voltage) when you take measurements. Maybe that's why it sort of works.

(2) Some meters will give you garbage if you reverse connect the leads. Mine does. Even though it is a very good meter. Though yours seem to work that way I would not trust it 100%, always go ground to signal and do the math. Safer that way.

I also have an '89 M103. I can take some measurements and collaborate your results and connections. Not for a few days though, it is raining heavily here, and will do so for a week or so.

Seems you need to hit the books anyway. Good luck with the finals.....

- Cheers!
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Just use the voltage measurement between #2 and #3....should be somewhere in the neighborhood of seven. Best check your voltage first so that's black on Pin #2 (ground) and red on Pin #6. Say you got 13.77 volts...,..now put red on Pin #3 and black on Pin #2. Look for an average over a couple of minutes.....best to do this with an analog meter if you have one. Say your average was 7 volts (usually fluctuates a half volt @idle in closed loop), take 7 and divide by 13.77 = .50. Take 1 and subtract .50 = 50%

This takes your fabulous duty cycle meter out of the equation and does it old school. If you have an analog dwell meter, you could use that instead. Because that's all this is; dwell.

Kevin
 
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