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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,394 Posts
Discussion Starter #1
I know the stories about the m104 EGR valve and the video for roto-rooting the tube out (very entertaining to say the least). But my present question is how important is that simplistic EGR valve that just sits on the m103 exhaust manifold?

I put some vacuum on it and it loses it pretty quickly....I think that's how you're supposed to test it. I've got a pretty sweet idle scenario, so I'm wondering if the earlier EGR valves even effect idle?

Kevin
 

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Premium Member
About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
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5,466 Posts
*Any* EGR system leakage will affect idle; that's why there should be no EGR at that engine speed.
1) the valve vacuum chamber shouldn't leak down and if it does there's a problem
2) if you can manually operate the valve (by lifting the diaphragm from below or using a hand vacuum pump) and idle speed/quality doesn't change, the exhaust passage or the intake passage is plugged
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,394 Posts
Discussion Starter #3
Vacuum applied to the EGR with a hand pump does lift the diaphragm, but it will not stay that way when I stop pumping, nor will it hold vacuum. I was wondering if this is normal.

I'll check it out now by manual lifting the diaphragm while the car is idling and see if the idle changes. My bet is it's compromised and I'm pretty sure it's original. Maybe even the vacuum line is plugged somewhere....I'll trace that as well....thanks!

Kevin
 

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Premium Member
About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
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5,466 Posts
The vast majority of EGR valves I've encountered should have an airtight vacuum chamber so they should hold vacuum for minutes, at least. I see to remember some early GM valves that did leak down due to some sort of check valve but we're talking late 70s/early 80s.I think you can safely assume that your EGR valve is bad.

Do examine the EGR valve vacuum hoses and tubing. Back in the early days of pollution control devices a lot of people played tricks to disable them. One favorite was shoving a BB into the vacuum hose to the EGR. Everything looked good for an emissions test visual inspection but the EGR was inop. No sniffer tests back then so the inspector couldn't tell. Maybe some old pro had his fingers under your car's hood...
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,394 Posts
Discussion Starter #5
Yeah, I use to blank these things off with a sealing screw and put the vacuum line back on. And sometimes, I'd just fashion a metal plate/gasket and remover the EGR itself and plug the vacuum source...but those were the days with carbs.

This time, I'd just like to make the system operable, because with FI, it probably does serve a purpose and may help my idle....although my idle right now is good. The car when the ex had it was only serviced by the dealer....so I doubt if they plugged anything. Still....I'll trace the whole vacuum line. Or, I could put a vacuum gauge on the line and check for vacuum at idle and at higher RPM for a difference, correct?

Kevin
 

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1987 W126 420SEL, 2006 F350 Super Crew Lariat 4x4
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225 Posts
my 89 doesn't have any EGR system on it. the exhaust manifolds have a blank spot for it, but no hole. kind of weird.

I'm sure you could eliminate it, unless you have emissions testing in your area.

i've never really seen the point of them. they don't do much for the engine, intake or head, other then make it dirty.
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
Joined
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10,394 Posts
Discussion Starter #7
That is weird....I thought they would be standard on most cars by then. Maybe the FI bought MB some time and they put them on when the Feds said they had to? I'm just interested purely academically, in making mine work again....I can just as easily bypass the whole system if I choose.

Kevin
 

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1987 W126 420SEL, 2006 F350 Super Crew Lariat 4x4
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225 Posts
maybe mines not US spec?

who knows, i have Fahrenheit temp controls for the climate control.
 
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