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1989 300SE 232k miles
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Discussion Starter #1
Hello All,

This regards my 1989 300SE with 234k miles. Today I smoke-tested my engine vacuum system. However, I was using a home-made unit and had some difficulty. I had smoke escaping at the smoldering can. I did use a clear hose from the smoldering can to the engine. I did see smoke in the hose, all the way to where I put it into the vacuum system (labelled B and circled in red in the attached picture). Additionally, if I move the hose off that point, smoke came out the end.

I did not see any leaks anywhere on the engine. I did place a clear ziplock bag over the air meter assembly (labelled A and circled in green in the attached picture), and I'm almost positive I saw smoke in there. So I'm checking that if I attached a smoke hose at point B, I should expect to see smoke at point A. If so, I'll feel very confident I don't have any leaks. And I'll start looking elsewhere for my problem with the fuel economy gauge dropping when I idle.

Thanks,
Bill
2611414
 

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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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4,017 Posts
Did your ziplock bag inflate during the smoke test? Mine did and I did have smoke. This on my '89 SEC.
 

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Registered
1989 300SE 232k miles
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1,049 Posts
Discussion Starter #3
Did your ziplock bag inflate during the smoke test? Mine did and I did have smoke. This on my '89 SEC.
It did not inflate. I didn't want all my smoke in that area, so I made the bag super-taut. And with the leaking at the smoldering jar, I never broke 2psi. So I'm not surprised. But the smoke went up into the areas of the bag that were the bent over corners and such.

Thanks. Knowing that the smoke does appear there gives me confidence. I feel pretty solid on my vacuum system being sealed.

The flap for my air meter assembly was grimy. And the inside, under the flap, is black and looks wet. While I have this apart, I'll hit it with some carb cleaner and see how much that's a factor as to my economy gauge not reaching reading left when I'm idling in gear.
 

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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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2,297 Posts
If I were you, and was confident there are no vacuum leaks under the hood, I would plug the vacuum hose that splits off and goes to the HVAC actuators in the cabin. Usually there is a Y splitter.
If you have leaks at the actuators the econ gauge will give a false reading.

Is the vacuum gauge not pegged at idle? If not, what is the idle rpm when it is not pegged?
 

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Registered
1989 300SE 232k miles
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1,049 Posts
Discussion Starter #5
If I were you, and was confident there are no vacuum leaks under the hood, I would plug the vacuum hose that splits off and goes to the HVAC actuators in the cabin. Usually there is a Y splitter.
If you have leaks at the actuators the econ gauge will give a false reading.

Is the vacuum gauge not pegged at idle? If not, what is the idle rpm when it is not pegged?
Interesting you mention the HVAC vacuum hoses. I've been dealing with AC where it consistently blows 18 degrees F cooler than my outside temperature. I pulled the glove box and it does not seem my recirculation flap activates. I plan to pull the interior and vacuum test the interior HVAC system in the next week or so (when I also upgrade my stereo and reinforce the springs in the seats). That could definitely be the issue. I'll let you know how that goes.

The vacuum (fuel economy) gauge is pegged to the left when I'm at idle and in Park. If I'm at idle and in gear, like stopped at a red light, the needle is about 2/3 to the left.

The car also idles rough. I have replaced the fuel filter, all the fuses, the spark plugs, spark plug wires, distributer cap, rotor, S-belt, and S-belt tensioner. I have 2 OVP's. The car totally dies with one, so I'm using the other. I also replaced the fuses in that OVP. I changed the oil and oil filter, and I've changed the transmission filter and fluid 2 x's.

I applied another layer of JB weld to my DIY smoke machine. I'm going do another smoke test of the engine vacuum system; hopefully with no leaks at the smolder jar this time.
 
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