M103 Rough idle and vacuum leak - Page 4 - Mercedes-Benz Forum
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post #31 of 174 (permalink) Old 08-03-2017, 10:52 PM Thread Starter
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Yes, I should have believed you on the OVP H.D. But I figured it was work a shot..

I assume a VIN beginning in CA indicates the car was originally from California?

When performing the o2 sensor test the car may not have been at operating temperature. I'll have to double check the voltage the next time I drive. But I will go ahead with these tests the next time I can! Also, should I still be concerned with testing the fuel pressure?
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post #32 of 174 (permalink) Old 08-04-2017, 02:18 AM
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Cody have you changed the engine temperature sensor yet . A lot of information is sent to the electronics parts on your engine for it to operate right . If the sensor is stuck, then it could tell the computer its cold ,and in doing so the computer will then richen the mixture up . But can work the other way and make it weak when your engine needs rich mixture ..
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post #33 of 174 (permalink) Old 08-04-2017, 03:35 AM
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Yes, I should have believed you on the OVP H.D. ...
Be careful, believing people … I might be a loudmouth … (many of‘em out there today ) … LOL

I ‘believe‘ that it‘s much better to properly test things to find out what‘s causing a problem, instead of changing things to see if it goes away. …

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... When performing the o2 sensor test the car may not have been at operating temperature ...
o2 sensor voltage tests only make sense if done with the engine well at operating temperature !

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... should I still be concerned with testing the fuel pressure?
Not yet … let‘s get reliable o2 sensor voltage data first.

Btw, nothing you reported so far indicates a problem with your CTS (coolant temperature sensor) either. …

H.D.
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post #34 of 174 (permalink) Old 08-10-2017, 01:44 AM Thread Starter
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Check the o2 sensor voltage on the female part of the disconnected o2 sensor connector while the hot engine is running at idle, with the ECU connected and:
- EHA connected
- EHA connected and male part of the o2 sensor connected to ground (with a wire)
- EHA disconnected
- EHA disconnected and engine speed risen to 2000 - 3000 RPM
Upon attempting to complete these tests I realized I needed some clarification on how exactly to complete them.
Does this image show the correct configuration? This referring to the green wire in the passenger footwell.
Assuming I'm correct..
- EHA connected: .18-.21 Volt
- EHA connected and male part of the o2 sensor connected to ground (with a wire): Not yet tested due to confusion
- EHA disconnected: .52-.53 V
- EHA disconnected and engine speed risen to 2000 - 3000 RPM .27 V
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post #35 of 174 (permalink) Old 08-12-2017, 06:14 AM
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... Does this image show the correct configuration? ...
No … the attached sketch shows how the 2nd of these four o2 sensor voltage tests is done. … For the 1st, 3rd & 4th of these tests you leave out the wire between the female part of the connector and ground. For these four tests there must be no connection between both parts of the o2 sensor connector (open loop test)

Since the data you reported so far sounds a little implausible, I‘d also like to show you how the closed loop o2 sensor test that I suggested in post 17 and that you reported results of in post 29 is supposed to be done. … Both parts of the o2 sensor connector are connected in a way that allows you to measure the voltage between the o2 sensor wire and ground. In the attached photo you see an example of how that can be done. It shows a simple adapter that I made for this test. The black lead is attached to good ground somewhere.

For all o2 sensor voltage tests the engine must be well at operating temperature !

H.D.
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post #36 of 174 (permalink) Old 08-12-2017, 10:48 PM Thread Starter
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Open Loop: fluctuated between 750-800 mV
Closed Loop: Fluctuated between 0 -800 mV
Open loop without EHA: fluctuated between 400- 700 mV
Open loop, no EHA, 2500RPM: steady 815, minor fluctuation.

I used the bolt heads used to attach the seat as ground. While taking these measurements the electronics were very finicky, and I got some weird values. Let me know if any of these numbers still seem improbable as I may have made an incorrect measurement
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post #37 of 174 (permalink) Old 08-13-2017, 01:33 PM
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... I used the bolt heads used to attach the seat as ground ...
That's okay, but you can also use the battery minus pole.

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... While taking these measurements the electronics were very finicky, and I got some weird values ...
… which might also have to do with your meter ... plus, assuming that you‘re using a digital meter, an analog meter is much more comfortable for reading such fluctuating values.

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... Let me know if any of these numbers still seem improbable as I may have made an incorrect measurement
These numbers differ significantly form the implausible ones you reported in post 34. … Could it be that in post 34 you measured between both parts of the connector, and not between the o2 signal wire and ground ? …

The numbers you report now, look more plausible and more like what I expected. But you forgot one measurement. Anyway, since these tests are very easily done and you‘re not completely sure if you measured correctly, I suggest to repeat them, with the hot engine running at idle and the ECU connected, in the following order:

Closed loop test (EHA and o2 sensor connector connected):
1) Both parts of the o2 sensor connector ‘somehow‘ connected (diagram #1)

Open loop tests (o2 sensor connector not connected):
2) EHA connected (diagram #2 without ground wire)
3) EHA connected and male part of the o2 sensor connected to ground (diagram #2)
4) EHA disconnected (diagram #2 without ground wire)
5) EHA disconnected and engine speed risen to ~ 2500 RPM (diagram #2 without ground wire)

H.D.
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post #38 of 174 (permalink) Old 08-15-2017, 08:48 PM Thread Starter
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1) 150-850mV, seems like it wanted to settle around 650-750mV
2) Fluctuating around 770mV
3 fluctuating around 810mV
4) -10mV
5) 810mV
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post #39 of 174 (permalink) Old 08-16-2017, 03:35 AM
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Okay, based on these significantly more plausible o2 sensor voltages, there seems to be a problem
- with the FD‘s (fuel distributor) basic setting via Lambda adjustment screw
- or with the position of the CP‘s (control plunger) lock screw
- or with the AFM‘s (air flow meter) or CP‘s movability
- or with the cleanness of (at least the lower part of) the FD‘s metering slits
- or with the injectors


I suggest not to touch the Lambda adjustment screw, and to do the following test now:
  • First check the AFM plate‘s “zero position“ according to the attached PDF
  • Then let the engine reach operating temperature and switch it off
  • Push the AFM plate slowly & slightly down with your finger and attentively feel the mechanical resistance. On the first 1-2 mm of the plate‘s travel (starting from its correct “zero position“) you should feel almost resistanceless play. The only resistance you should feel along these first 1-2 mm is the one that‘s caused by the AFM‘s counterweight.
  • Then, latest after about 2 mm !, you should feel the other end of the AFM lever reach the CP. Up from that moment the AFM lever pushes the CP (in the center of the FD) upwards, causing you to feel some slight homogenous additional resistance. Additionally to that suddenly starting sensible resistance you should not have to apply any additional break-away force at that point.
  • Up from that moment there should also not be any noticeable resistance jumps along the rest of the AFM plate‘s travel.
  • After having pushed the AFM plate completely down, quickly and completely let go of it ... it must quickly and smoothly jump back into its “zero position“.
  • Then turn the key once or twice to ignition on for as long as you hear the fuel pumps prime.
  • Then push the AFM plate swiftly completely down with your finger again, but this time don‘t let it freely jump completely back. This time let it swiftly jump back in 5-10 mm steps. Hold it at these steps for a moment and feel if the CP is following the AFM lever (with a little delay) … you should feel it reach the AFM lever less than a second later at each step. This way feel if the CP follows the AFM on its incremental way back to its “zero position“ !

If you want to repeat one of these two test steps, first turn the key once or twice to ignition on for as long as you hear the fuel pumps prime.

Furthermore, I have a question: Has the FD ever been removed ?
If so, has the CP’s lock screw (in the center of the FD’s bottom side) ever been touched ?

H.D.
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post #40 of 174 (permalink) Old 08-22-2017, 01:05 PM Thread Starter
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I tried all these tests and they've all been passed, except for centering the plate. I attempted to measure the gap using a basic Napa feeler gauge at .483 mm. The guage is approximately 1 CM across, so I'm having trouble fitting it into the gap due to the curvature. Is there a trick to this test, or are circular feeler gauges (at .5 mm) an option? This was performed first thing in the morning before the car had been driven.

I'm unsure whether the FD has ever been dissassembled.

Additionally, since completing the o2 sensor tests my check engine light has come on. I pulled the code and got 5 blinks. If the chart I'm reading is correct this indicates a fault with the o2 sensor.
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