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  #1  
Old 03-06-2017, 12:28 AM
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Is my intake cam advance mechanism working in the M104

So I recently did the head gasket replacement in my 95 E320 wagon. And this car, the 95 wagon, has never seemed as powerful or gotten as good MPG as my previous Merz, which was a 94 E320 sedan with similar mileage, both around 200K and neither one smoking or burning oil and passing DEQ beautifully..The 94 would spin the tires with full accel and the wagon seems far less powerful but will AT TIMES seem to get much better mileage..on trips very near 30 but not always..

Anyway its hard to say how accurately the computers are set up on the wagon since it was a rebuilt wreck. It has lots of new parts from Starmark program rebuild, had a quickie head gasket replacement by them IMO, as shown by a loose head bolt and pitting on the cylinder head which was not repaired, and only the intake valves were ground, not the exhaust. Although it ran beautifully. I did the gasket because of both oil and water leaks on one side, although there was never mixing of oil and water.

I had a top quality cylinder head rebuild done and installed with new OEM head gasket and when put together it had absolutely no leaks and ran great but still the same lower power output..And mileage is 17 to 24 rather than the 24 to 30 I got in the other sedan.

So is itpossible intake the cam advance is not working properly and if there is a way to check? Perhaps pull the activation wire and see if there is a difference?? Other ideas??

Thanks in advance for the awesome knowledge shared on these forums!
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Old 03-06-2017, 12:40 AM
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OkayI found this interesting discussion of just this question..

Variable valve timing
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  #3  
Old 03-11-2017, 01:20 AM
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a conversation of one here, but I just pulled the pin plug to the cam advance solenoid and find full battery voltage across the leads with the key on, not running or running, same. There is no click or activation sound or magnetic field I can detect when the plug is touched to the pins. And there is no click or activation at any RPM up to about 3000. And there is continuity across the electromagnet (solenoid) pins..Not sure the resistance exactly. So yeah, pretty certain the cam advance solenoid needs repair, possibly pull it off and bench test it and then shop for a replacement. I also noticed the mechanism on the cam is slightly bent as if it's been dropped. It seems to work perfectly but if its been bent maybe this is also an issue.

Looking forward to getting the performance I had with my 94 sedan with this thing corrected!
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Old 03-11-2017, 08:35 AM
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Did you use an incandescent test light on the cam wires? Using a digital meter can lead to picking up stray voltage leading to a miss diagnosis. If you only have a digital meter, leave the plug installed and probe the wires from the back. On some plugs you can pull it back a bit to gain access to pins bit I don't know what type of connector you have.

The cam magnet has 3 bolts holding it on then a stem comes from the cam sprocket., this stem opens / closes an oil passage to actuate the advance.

With the cam magnet wire unplugged, I'd apply 12 V and see if the idle speed changes, if so this end of things is working. You might trip a trouble code when doing this.

Past that I'd need to see a wiring diagram.
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Old 03-11-2017, 12:01 PM
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Thanks 97SL320, good idea. Yes I can pull the plug back and test with it plugged in and I plan to use a 12V probe and apply known power..Actually would be cool to wire a light across the leads and rev to 2000+ rpm and see if the light comes on as it should. And I do see a trouble code for an open or shorted magnet coil in the list of codes. I have a lot of error codes, bad wheel speed signal and many other transient random codes.. I have no check engine light but on a longer trip it usually comes on and then resets after a restart. I found a good video on you tube by Victor at "restore your mercedes.c..". Hes a self taught guy with a wide range of knowledge and was dealing with just this issue on a v8 merz with the same mechanism having failed on one bank causing low power and mpg..
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  #6  
Old 03-11-2017, 04:29 PM
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Okay the light tester was interesting, it showed 12V supplied to all leads when the key is on or engine running but one can see that the bottom pin supplies 12 V and then the top pin is energized by the continuity through the coil. The function is obtained by the ground being closed to the top pin..When I ground the top pin the magnet energizes and at low RPM the engine dies, no click or rough idle, just dies. At higher idle it does not die or click but runs..no change in engine sound or speed. I can feel a magnetic effect at the very center of the coil with a screwdriver on connecting the top pin to ground..a VERY weak pull and there is no spark when the top pin is grounded. About like a speaker wire, very low amps. Anyway its normal to have 12V showing here continuously and the coil is activated by grounding through the ECU at the specified RPM. Pretty sure this unit is not functional, and yes doing this triggered an error lite, The ASR light came on and then it reset after one restart.

An added note is that Ive got upgraded wiring and ASR throttle unit, but the lower wiring harness has not been replaced. Its got flakey insulation..And this harness seems to include the cam position sensor and or perhaps an oxygen sensor lead..Ive got the harness but not yet installed it because of bad weather and all the under-car work needed..
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  #7  
Old 03-11-2017, 06:02 PM
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The electro magnet operates a valve that controls oil pressure to the adjuster, you won't feel much pull or hear a click. Oil pressure is what operated the cam adjuster.
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  #8  
Old 03-11-2017, 08:54 PM
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Okay thanks 97SL320, I was finally able to see a low speed RPM drop at about 1200..slight shift in sound as I manually grounded the negative side. And thank god for fuse seven which saves the works when you hit the wrong pins and ground the feed. So I should be able to observe continuity to ground when the rpm hits the 2000 range and the ECU closes the ground path..The advance mechanism could be fine but Im still thinking about its appearance of being bent a little, bent attachment bolt perhaps. The actuation was free and the advance system seemed to work fine. And now it also occurs that the reason for lower performance feel and MPG could be the result of having ASR on this car which my other did not..And that wagon suspension and added weight.
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  #9  
Old 03-12-2017, 09:07 AM
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A data point on ASR. No matter the brand, wheel speed sensors can age, become covered in metal dust changing their output, this can cause an ABS system to actuate when it does not need to . I'd expect this would have some effect on ASR as well.

Somewhere in the MB service manual there is a way to completely disable ASR for dyno testing, might be a good idea to try that. The snow chain button supposedly only mutes ASR not completely shutting it off. In the day someone was selling a high dollar magic box to shut off ASR but it just turned out to be a few relays that put ASR into dyno mode. Have a look on this site and others for info.
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  #10  
Old 03-14-2017, 05:47 PM
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Thanks again for the info, I need to add cleaning the wheel speed sensors to my summer tasks..and I will look into this issue as well.
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