Is a smoke machine a good aid in finding vacuum leaks? Are there an precautions in the use of one?

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Rebe

A hand vacuum pump is your best friend for finding vacuum leaks. A smoke machine won't show much unless it's a MASSIVE leak.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Buy or borrow a Mityvac.

I have a question on that black box on the valve cover. Does it just crunch down to fasten it in place? It's been a while since I removed one. It seems kind of tight & I didn't want to brake it.

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Rebe

I don’t what car you have - but on 82 300D there is one screw that holds it down the plastic cover. There is also a little nub that kinda clips over where the plastic multi connector piece mates with the rubber connector.

It's a '83 240 model. On the black plastic box in the center there is kind of a round button like, but it has no notch in it. I don't take it off to adjust the valves on this one, so I never have confronted it until the vacuum problem. I don't know hardly anything on the vacuum troubleshooting. So, far in the hood area testing. The vacuum lines are ok through the green check valve and the yellow 3 way valve. Beyond the 3 way I haven't did anything, as yet. What I don't know about is the valve on the injection pump that the little green check valve goes to I am not able to get vacuum on it. I am not sure if I should or not? Is it good to have a vacuum gauge in troubleshooting? I need some vacuum test hose and connections.

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Rebe

Go buy a Mity Vac tool, you cannot check for vacuum leaks without it .

The Harbor Freight vacuum tool is crappy, doesn't hold vacuum at rest making it worthless for this important job .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I am not sure why one vacuum tester would hold vacuum at rest and another one wouldn't? I am also unsure what your vacuum at rest signifies? I would like to know if the vacuum control modulator on the end of the injection pump should hold vacuum or not? I am not for sure if that is the correct name for it or not. It is a clear vinyl or plastic looking mechanism. If you tee in a vacuum tester in line with the engine running, will it measure the vacuum height? I was not of the thinking it would. That is why I was of the thinking a vacuum gauge would maybe be necessary. I know little to very little about going about isolating the leak by vacuum testing.

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Rebe

O.K. the deal is this :

A vacuum gauge only helps you to discern actual vacuum level when the engine is running .

The hand held vacuum pump is used to apply vacuum to easy part of the various vacuum circuits then you stop pumping and watch the gauge on the hand pump to see if it hols vacuum and if so, for how long .

A gauge cannot do this and so is useless to finding vacuum leaks .

It's not terribly difficult to do, mostly it takes patience and lots of fiddling plus the ability to understand cause and effect .

I don't understand why the Harbor Freight tool won't hold vacuum, it's very frustrating .

I hope this helps ~ once you understand how to test for leaks, _YOU_ will do a far better job because you'll care and won't be clock watching .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I hate to ask this - but the Harbor Fright tool - could it be that you have a switch or lever turned the wrong way? Mityvac has one to change it from vac to pressure.

Hazard Frought Tools sells two versions. One is a piece of junk. The other is the actual MityVac branded tool that works.

https://imgur.com/gallery/JcG3B

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

HF sells 2 types of tools. Some work, others don't. Those that don't fit 2 categories. Some are easily fixed, others need to be returned. Of those that work, some break soon, others take a little longer.

Never use them for something critical ie removing a spring (if they make the proper tool). They are mostly good for cheap infrequent use - but sometimes cheap infrequent is better than expensive and infrequent.

OP, track down the vacuum diagram for your engine. Work on 1 vac branch at a time. You can temporarily block those you aren't working on with a screw or golf tee.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Not sure why anyone would be hesitant to ask if I have any idea what I'm doing (I don't but it doesn't phase me) .

Yes, I know how to operate the tool, it holds vacuum for a *very* short time .

It's not like those who feel their Mercedes slushbox shift three times and so decide it must be a three speed box..... .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Like anything you can do without engine running supplying vacuum. Should you be able like to lock and unlock the doors a multitude of times? Then maybe leave for a week or two, and be able to unlock the car doors, trunk, & fuel door etc.? So, I was wanting to check, that actually operating the actuators should not lose vacuum with a healthy system?

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Rebe

Yes, the doors, trunk and fuel filler flap all should lock and unlock several times after the car sits unused for three weeks .

Just buy the darn tool, you'll see .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better