M117 Intake Vacuum
 

Can anyone give me a reference point as to how much intake vacuum a 117.985 should produce at idle? Im trying to diagnose a vacuum related problem and I am only reading 15.5 inHG (or -52 KPA), I feel this is low as the levels I am used to in other vehicles are more around 20 inHG (-66 to -68 KPA). The FSM isnt being all that helpful in this regard.

Thanks fellas. . .

Hrm, I can't recall where I saw in the FSM. Look around the stuff for instruments/gauges. This is how I found what's "okay" for the M103...

15" is low, my 560's guage is pegged left at idle. 300SEL is just a hair off it and pulls around 17"

Honestly, if you suspect it... you probably do. Most of the rubber is pretty simple to replace.

thanks hitman. . thats what I thought, low.

Im sure it is engine related, all my rubber is supple and my intake line appears to be without crack (after thorough visual inspection, I really have to hook my mityvac up to the intake directly though ( thats tomorrow's project).

Just an idea I was pondering, how significant would valves out of alignment play in this loss of vacuum pressure? I figure they would play some role, however I cant determine to what extent.

Im attempting to alleviate a smoking (oil) situation that I long wrote off to leaky valve guides, but the more I think about it I want to attempt other remedies to more accurately address all that might be in disarray with a 30 yr old motor. . .

I want to stave off the enevitable top end job for as long as I can,

Tomorrow Im planning to adjust the valves, and check my chain for stretch, among other things. .

How about that air flow meter boot? Upper to lower intake manifold seals? Y and X connectors under the hood?

Can't comment on the valve issue too well, my 300sel needs valve guides bad but still pulls vacuum within factory spec. Some of those vac line connectors that appeared okay, were the issue.

I guess I'll have to give all that a better look, the airflow boot looked good, I didnt pull it off, but I didnt notice and deterioration to the outside. . .

you see, Im thinking this. . .the valves havent been adjusted in some time and the car is smoking, intermittently, sometimes off the line from a red light, most often not though. It'll always smoke at startup after sitting for a night or two as it is a garaged car and not driven daily. Im thinking that oil may be getting past the valve guide seals and into the engine, on top of the feeling that the valves are out of alignment and allowing air to enter the intake vacuum. This combined is where I feel my inefficiency and oil burning is lying. . .

any one else have any ideas?

M117 rebuild to get vacuum
 

I had the same symptoms in the 300SEL 4.5 156k miles. smoking and generally un-performing well compared to another 280SE 4.5. (this comparison car is just fast and tight)
I wrongly assumed valve guides.
This car was a short runner to the grocery store up and down the hills of La Jolla, not enough oil changes, never had sufficient warm up.

My solution,
disassemble entire motor,
do valve job, check everything.

Here is the problem & solution (i think)
The ring grooves were caked with solid carbonaceous crud between the inside diameter of the ring and the inside of the groove. I had to break a ring and scrape the grooves clean. Note that the groove tolerance (up/down) was very tight (not worn) but the ring could not "work" meaning the expanding combustion gas could not move the ring out to seal correctly.
Commonly known as stuck rings.
There was not enough cylinder ridge to bore and a hone cleaned it up fine(thank goodness). The crankshaft mains were .003" so the same bearings are back in. Pistons and full floating pins are perfect. The rod bearings and bolts are being replaced and a set of Deves rings installed. New cam gears and guides etc. all seals, all rubber replaced

Bottom line about $1200 parts (my labor free)
Good for another 30 years.

rebuilding the block is a matter of when. . .eventually I plan on boring out the engine and installing larger pistons... I want the car to look euro stock, however I want it to lay it down (as a sleeper). . for the time now I want it to run solid and fufill the role of 'weekend car'. . .when the Lexus in my sig dies its gonna be replaced with a CDI. .