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Discussion Starter #21
(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!
So, it is very much of an intermittent sort of problem, sometime it is like this(on the video), sometimes it is alright, and what i have noticed yesterday, the light in the car(dashboard and the other bulbs flicker, and turning on or off the any electrical stuff in the car causes rpms go down significantly and than fluctuates. Also i noticed it drains the battery(battery is new, 8 months old), i'm still able to start the car in the morning, but i can feel that battery doesn't have much of juice, then i drive during the day, battery again is juicy for starting. During the holidays, i haven't started the car for 2 days, it drained the battery completely, had to jump start it. Also, i bought a new Voltage regulator(KAE) original, and on the third day after i installed it, i noticed that, when i turn off the engine and pull the key out, the check engine light stays on as if in the 1st key position and i can hear the idle control valve clicking and some other electronic works under the hood. I switched the voltage regulator back to old one and that problem was fixed, but i think, that there is some short or something, that killed it, I don't think it died itself in 3 days for no reason(both fuses were not burnt on regulator, what's weird).
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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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Well this changes things......
A picture (video) is certainly worth more than a 1000 words in this case.

You seem to have some electrical issues on top of a vacuum leak.

(1) Your Econ gauge needs to be pegged all the way to the left, particularly at 1000 rpm.
Mine is pegged even at 700 rpm. Leak could be benign at the vacuum actuators for HVAC so do not panic about that just yet. Are there any hissing sounds coming from the flaps/actuators under the dash? If there are leaks there it is just your meter that is wrong because the the loss would be between the intake and the meter. Not a big deal.

You also have some electrical problems, so your RPM stability should be the least of your worries at this point.

(2) I would recommend buying a $12 cigarette lighter USB charger online that has the voltmeter display built in it.
Stick it in the lighter and observe your system voltage for a while. I've been riding around with mine for 2 years now. It is pretty valuable to have with the M103 cars in my opinion.

Without bottoming out on items 1 and 2 above I would not start chasing your idle issues.

- Cheers!
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Run your car at idle....put all your accessories on including headlights. Read your battery voltage across its terminals....should be around 14.3 volts. This proves your alt is doing its job. These cars are wholly dependent on a well charged battery and voltages being at a minimum to spec. Consider you may have a bad chassis ground, bad ignition switch and/or a parasitic drain going on. To check for a voltage parasitic drain, there are a number of good YouTube vids. One of my favorites is from a guy called Eric the Car Guy. He goes straight to it without the usual YouTube craziness.

You definitively have a electric problem....I don't know the history of the car, but some PO might have inadvertently sabotaged your electric system....who knows. A vacuum leak is minor to your problems right now.

Kevin
 

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1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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with everything on at idle, I'd expect 13.8 V or better to be adequate voltage. if its much below 13.6, you definitely have a problem. 14.x V is 'absorption phase' which the regulators on the original w124's didn't do.
 

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00' ML55 AMG, 98' E430, 95' S320
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Where is the vehicle from originally? Any chance it's from California? Also if you haven't yet, replace the 4-pin Coolant Temp Sensor. You should also go through the FSM and do all the Ecu-to-sensor wiring tests. Another necessity is a parasitic draw test.

One other thing... KAE (Kaehler) brand is junk, garbage. I see those relays fail all the time. I would replace anything branded KAE with a genuine MB part. You won't regret it.
 

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1993 300CE Cabriolet (mine) ; 1994 E320 Wagon (wife's) ; 1990 Benz 300E 2.6 (son's)
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6,847 Posts
air leaks caused my 1990 300E 2.6 to stumble and stall occasionally comign off ldle. it was very erratic, it could drive great for a week, then you're hitting the gas when its your turn to go from a full stop, and it would just choke, stumble and stall.

after spending better than a year trying to determine the cause it turned out to be air leaks around the CIS injectors, the seals were not consistently keeping air out.

I'm not saying those seals are your problem, jsut that /any/ pinhole air leaks between the air flap and intake manifold will throw things off and cause it to starve for fuel at rpms.
 

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00' ML55 AMG, 98' E430, 95' S320
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air leaks caused my 1990 300E 2.6 to stumble and stall occasionally comign off ldle. it was very erratic, it could drive great for a week, then you're hitting the gas when its your turn to go from a full stop, and it would just choke, stumble and stall.

after spending better than a year trying to determine the cause it turned out to be air leaks around the CIS injectors, the seals were not consistently keeping air out.

I'm not saying those seals are your problem, jsut that /any/ pinhole air leaks between the air flap and intake manifold will throw things off and cause it to starve for fuel at rpms.

This is perfect advice for the M103 engine. The injectors and their seals are basically maintenance items. I don't see them last much beyond 60k miles. I think the original parts were of a better quality than the replacements you can get today. You also must replace the white nylon injector holders (and their o-rings), and make SURE you install the correct spark plugs as these engines are very sensitive to that. I have had nothing but success with Bosch H9DCO (non-resistor). FCP Euro sells them as "Genuine Mercedes" for a very reasonable price.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Low vacuum is the least of his issues....flickering dash trouble lights, a draining battery and other electrical oddities are the immediate problem here. As I suggested, the parasitic draw test is an absolute necessity.....so is testing his ignition switch and checking charging voltage at his battery.

Kevin
 

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00' ML55 AMG, 98' E430, 95' S320
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Sure, but all points are certainly relevant here! I'll leave his order of operations to his discretion lol.
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,185 Posts
Indeed, but let's get him through his electrical issues first. These are the issues that will leave him stranded somewhere. A rough or low idle you can live with until tomorrow....flickering trouble lights and a draining battery you cannot.

Kevin
 
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