1973 MB 450SL 12 inches of STEADY vacuum...help

[1025MB]

More practically speaking, I have a 1973 Mercedes 450 SL that is currently operating with vacuum of 12 inches, extremely steady with no needle deviation...that is obviously extremely low.

Let me provide some additional metrics:

-when the engine is running, I can remove and replace each fuel injector connector one by one on the driver side, and the vacuum drops exactly 3 inches for all four cylinders. However, when performing the same exercise on the passenger side, the volume drops by exactly 1/2 an inch.

-compression test was performed on the passenger side with all eight spark plugs removed, however, the throttle plate was closed (forgot to open...all values may be skewed low) and the starter was cranked seven times. Compression was 140 PSI for all four cylinders one, two, three and four on the passenger side

-eight new spark plugs, eight new wires (verified resistance in each), cap and rotor in good shape. Also, repaired the green insulated wire between the distributor and ignition amplifier. Good solid spark to all eight cylinders

-verified the performance of the four triggerpoints as indicated above, however, keep in mind that the injectors are fired in pairs one and five, two and seven, three and six and four and eight. Candidly, I find it extremely unlikely that the triggerpoints are responsible as the injector impulses appear to be being delivered flawlessly on the driver side

-all 8 injectors had values of 2.9 ohms and were firing as verified by noid light with the exception of number three on the passenger side. This injector will not open and close i.e. click when connected to a 12v source. Currently trying to source a replacement injector.


My intuition would lead me to believe that it is a camshaft timing issue on the passenger side. However, when removing the valve covers and verifying the relationship between the two camshafts and the crank, everything is in PERFECT alignment at TDC i.e. The PO obviously replaced the timing chain with IWIS verified by the presence of a MasterLink. The camshaft vmark lines up with the mark on the camshaft bearing cover. I should mention that the timing chain tensioner is in dire need replacement, and yes I clearly understand the pitfalls of a suspect timing chain tensioner…that is on order. In the meantime, I prime the tensioner by turning over the engine several times with no fuel and spark. In fact, I installed a separate button to facilitate this practice as I plan on continuing the protocol after installing the new tensioner. I simply do not like the design and prefer the ratcheting style.

[carock]

What is your idle speed?

[carock]

If your idle speed is close to normal, then you "almost certainly" have a problem with the ignition timing. The timing is too retarded. This means the throttle or idle speed bypass has to be opened to get the engine to operate at a normal speed when idling and you get the low idle vacuum you are measuring. There could be several causes for retarded timing on your car.

Retarded timing could be a simple problem, like the distributor is twisted in the wrong position. It could be an intermediate problem, like the vacuum advance is not working. It could be a sophisticated problem, like the distributor advance mechanism is sticking. Any mechanic familiar with older distributors should be able to quickly isolate the cause of your problem.