Author Topic: 280se- running down a vacuum leak  (Read 86 times)

dnaspazz

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280se- running down a vacuum leak
« on: 30 December 2019, 07:38 PM »
So, I’ve replaced all the vacuum lines and confirmed the lines hold vacuum with a mityvac. The car idle still jumps all all over the place from day to day,  and I have been pretty sure I have vac leak still.  In general the idle is high, and the vac line to the distributor retard will slow the idle ( with a mityvac) but the manifold isn’t pulling a vac on the line ( but not sure if it should at running temp at idle).

Today, I check if spraying gum out around the injectors would slow the idle. It didn’t, unless I spayed a lot and get the air intake manifold also wet.  When I sprayed at the air intake manifold gasket, the engine noticeably slowed. I am thinking that I have a leak in the air intake manifold gasket.  Does this make sense, and is there another explanation or diagnostic test I should do to confirm?

Seems like replacing that gasket is a bigger job....



Today, I

UTn_boy

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Re: 280se- running down a vacuum leak
« Reply #1 on: 30 December 2019, 09:03 PM »
From what I've read, you definitely have a vacuum leak.  Given the age of the car and the gaskets, I'd remove the intake and renew all of the rubber air hoses, injector seals, intake manifold gaskets, and the 8 rubber rings that go between the upper and lower intake manifold plenums.  All of the above are notorious for causing intake vacuum leaks. 

Out of curiosity, have you a 6 or 8 cylinder, and is it DJet or Kjet? 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

dnaspazz

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Re: 280se- running down a vacuum leak
« Reply #2 on: 30 December 2019, 11:38 PM »
Thanks, that is kinda where I thought I was going. The car is a 6 cylinder k-jet.

I just got done with a new fuel pump, fuel filter, fuel accumulator, rebuilt  fuel regulator, doc W9 dco plugs, and a  valve lash adjustment.

Any advice for the simplest approach to remove the intake?


UTn_boy

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Re: 280se- running down a vacuum leak
« Reply #3 on: 31 December 2019, 04:36 AM »
Well, since you have a U.S. M-110 with K-Jetronic there are two different intake manifolds used. It depends on the year model, engine number, etc.  For either one there is no simple approach to removal.  You have to start taking things off until you can access the nuts that hold it on to the head.  And you also will not have the round upper to lower plenum seal rings.  Those are on V-8 engines.  You'll only have to worry about the intake manifold to cylinder head gasket, injector seals, fuel distributor lower housing to throttle body boot, and all of the rubber hoses for the idle air valve, warm up regulator, and other ancillary vacuum connections.  Did you yet have your warm up regulator rebuilt? 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

dnaspazz

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  • Location: San Clemente, CA
Re: 280se- running down a vacuum leak
« Reply #4 on: 31 December 2019, 05:33 PM »
Still waiting on the wur. The wur on the car isn’t the right version, so I had to find the right model for a core.

Thurns out the wur line is causing the biggest headache for getting off the monifold. Almost there.