M103 Rough idle and vacuum leak - Page 2 - Mercedes-Benz Forum
 
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Old 07-12-2017, 06:07 PM Thread Starter
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Originally Posted by dolucasi View Post
Can you put it up on youtube instead and post a link?
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Old 07-12-2017, 06:32 PM
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I don't know how much help this will be and I'm doing it from memory here, the car was sold over two years ago. The 91 300SE I had for 12 years slowly over time got to running not as well as when I bought it. Over a period of trial and error I replaced all the rubber vacuum and two hard lines, got a duty cycle meter and adjusted the lamda/fuel mix, EHA was leaking a little and was replaced. It was about this point that sometimes I'd have to ride the shoulder uphill due to absolutely no power, downhill was better and this was erratic as hell. New cap, rotor, wires, and plugs (believe it or not 100K miles on the plugs that were in it when I bought it I had read that aluminum heads sometimes had stripped plug holes, these didn't). She ran some better but still sometimes no power and when she did and I floored the gas it looked like diesel exhaust out the back. Around this point someone mentioned the cats may be plugged, I had a set of pipes made and dropped the cat, problem solved and she was still running quite well a year later when I sold her. The new owners are my neighbors in-laws and I still see the car from time to time

Some days it's just not worth chewing through the restraints
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My Stable:
'91 560SEC "Ursula"
'91 300SE (sold) "Sadie"
'11 Suzuki SX4 Sport Sedan
'02 S-10 Truck
'72 SeaBird boat, "Riff Raft", overhaul restarted

Dif-tor heh smusma
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I'm surprised that NOBODY has asked me what this is / means
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LOL
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Old 07-12-2017, 09:57 PM
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After seeing that video my money would be your OVP. It is similar to my '89 M103's behavior although not exact. You can try to measure the output of the OVP when the idle is cycling to see if it is cutting off at that exact time and coming back on.

But your OVP is so old it needs changing anyway, so you may as well just change it and see if your idle cycling issue goes away.

Your vacuum problem is separate in my opinion and should be tackled separately. I assume the AC was not running during the video.
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Old 07-16-2017, 07:37 AM Thread Starter
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Last night I checked my duty cycle by checking the voltage across pins 2 and 3 of the x11 using a multimeter. It read out a constant roughly 14.1 to 14.2 volts. So if my assumptions are correct this would indicate 0% duty cycle, meaning the system isn't attempting to adjust the mixture at all. Does that sound right?
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Old 07-16-2017, 10:01 AM
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... So if my assumptions are correct this would indicate 0% duty cycle, meaning the system isn't attempting to adjust the mixture at all. Does that sound right?
The voltage you read out does indicate 0% duty cycle … but that does not mean that the system isn't attempting to adjust the mixture at all … quite the contrary … it‘s trying its best to adjust the mixture … which seems to be rich beyond the system‘s capability to lean it out via EHA.

For details see: https://www.benzworld.org/forums/w126...uty-cycle.html

Btw … your entry under occupation in your profile takes me back (35 years) …

H.D.

P.S.: Since, unfortunately, I’m not receiving notifications on threads I’m subscribed to from Benzworld, I might not notice further questions in this or in the above-mentioned thread. … Sorry if that happens.
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Old 07-19-2017, 10:26 PM Thread Starter
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So should I adjust my Lambda control adjustment? I've previously been instructed by a mechanic to never adjust it as he has set it where it needs to be.. Does a 0% duty cycle indicate any potential issues other than running very rich?
Once I get paid I will purchase a new OVP and let you all know how that turns out!
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Old 07-20-2017, 04:27 AM
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... Does a 0% duty cycle indicate any potential issues other than running very rich? ...
If you checked the Lambda control adjustment (at X11 across pins 2 & 3) with a voltmeter and read out “a constant roughly 14.1 to 14.2 volts“ (instead of measuring a duty cycle of 0% with a duty cycle meter), then:
- either the engine is running very rich
- or there‘s a problem with the ECU
- or there‘s a short circuit on the wire to pin 3 of X11

Quote:
Originally Posted by codycool55 View Post
So should I adjust my Lambda control adjustment? I've previously been instructed by a mechanic to never adjust it as he has set it where it needs to be ...
Very good question … much better than rashly changing the Lambda control adjustment when the meter shows a too low/high duty cycle. … And I hope that the mechanic made sure that everything else was in order before he set it.

I suggest to check a few things that might cause the 14 volts (0% duty cycle) reading … starting with measuring voltage, with “igniton on“ (engine not running), between X11 pin 3 & ground … and between X11 pin 6 & ground. The quotient of the pin 3 voltage and the pin 6 voltage should be about 0.3. … If that's the case, the third of the above-mentioned possible causes can be excluded (and the second one is less probable).

The next thing I‘d suggest, is to measure the o2 sensor voltage at the (connected) o2 sensor connector under the passenger side‘s floor panel (green cable). ... 0.8 volts or higher indicate “rich mixture“.
If that‘s the case, I suggest to check the CSV (cold start valve) for tightness.
If the CSV is tight, I suggest to check the fuel pressure.
With your engine running at idle, SP (system pressure) should be about 5.3 - 5.5 bar (77 - 80 psi) and LCP (lower chamber pressure) should be about 0.4 bar (5.8 psi) below SP ! … SP higher than 5.5 bar (80 psi), or LCP more than 0.4 bar (5.8 psi) below SP are possible causes for too rich air/fuel mixture.

Let‘s see the results of these test prior to further suggestions.

H.D.
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Old 07-20-2017, 10:38 PM
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Originally Posted by dolucasi View Post
For some reason the links to your google photo album is not working for me.
But if your OVP is truly 19 years old, like you believe it is, it has to be changed. A KAE unit is about $45 I believe. Mercedes Benz brand might be slightly higher.
I would recommend KAE, that's what i used and was was in the car for 12 years.
I have tested 2 OVP's on my M103 in the last 2 months, one was 12 years old the other was 18 years old.
Both appear to be OK but both were having intermittent idle problems because the ECU kept switching on and off, most likely because of the internal relay circuitry being defective/worn in the OVP.

Whether the OVP is your main problem remains to be seen but it is quite likely. However I would like to see your idle first to see if it is similar to mine when I was having similar issues at a lesser extent.
Can you put it up on youtube instead and post a link?
When you say "OVP", do you refer to the over-voltage protection relay behind the engine on the firewall of the 126? If so, yes, I agree: I replaced mine, too, when I was having all sorts of fuel delivery issues—as part of a fuel pump, fuel pump relay and overflow relay solution.

If not, what does "OVP" refer to, as I have a 300SE and mine probably needs changing as well. I have rough idle at cold start and even when accelerating from a standstill when cold. Once the engine's fully warmed, the problem seems to disappear.
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Old 07-20-2017, 10:44 PM Thread Starter
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Yes, OVP is the overvoltage protection relay. What is an overflow relay?
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Old 07-20-2017, 11:10 PM
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Quote:
Originally Posted by Strassenkreuzer View Post
When you say "OVP", do you refer to the over-voltage protection relay behind the engine on the firewall of the 126? If so, yes, I agree: I replaced mine, too, when I was having all sorts of fuel delivery issues—as part of a fuel pump, fuel pump relay and overflow relay solution.

If not, what does "OVP" refer to, as I have a 300SE and mine probably needs changing as well. I have rough idle at cold start and even when accelerating from a standstill when cold. Once the engine's fully warmed, the problem seems to disappear.
Yes OVP stands for Over Voltage Protection relay. I now recommend replacing OVP's now older than 10 years old (newly converted believer) no matter what to avoid future headaches.

I am skeptical that your cold issues are OVP related. AS the OVP matters the least during cold as the lambda control is actually in open loop mode so some of the sensors are ignored during cold (like O2 sensor, etc). OVP problems are amplified during Hot (not cold).

I would first look into things that effect operation during cold (like fuel mixture screw, EHA, coolant temp sensor, etc)
It sounds like your fuel/air mixture is not rich enough during the warm up period and once the engine warms up the ECU and actuators compensate for the problem.
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