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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. I'm currently making my way through the DJet checklist and using the online wiring diagrams with the index that you provided… the index is EXTREMELY helpful as the online interface is "very muddy". However, the wiring diagrams are not year and model specific. For instance, when verifying the resistance value for coolant sensor T2 at pin 11 and 23, the diagram does not address the fact the blue and white wire at 23 travels through a hot start relay, the changes to a green and white wire before connecting to the sensor at the passenger side rear cylinder head. I am obviously savvy, not sure that a newbie would be. It any rate, back to the low-vacuum issue, which I suspect maybe well beyond a simple leak. 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.
 

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Discussion Starter #3
Static with dizzy vacuum advance and retard connected. I will give you a precise data point when I resolder the connections on my timing gun this afternoon.
 

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1973 450 SL
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For instance, when verifying the resistance value for coolant sensor T2 at pin 11 and 23, the diagram does not address the fact the blue and white wire at 23 travels through a hot start relay, the changes to a green and white wire before connecting to the sensor at the passenger side rear cylinder head.
The sensor at the rear of the right cylinder bank is for the instrument cluster temperature gauge. The T2 sensor is at the front of the engine, next to the thermo-time switch. The hot start relay was introduced in 1974, does your '73 have one? (right passenger footwell, immediately inboard of the tail harness connector). 1974 ETM depicts operation of the hot start relay very well; '73 wiring diagram does not include it. PM me if you have a hot start valve and need the '74 ETM. (huge file - can't post it here)

My car does not have one but I have dealt with them rebuilding engine harnesses for '74 and '75 107s.

As for vacuum issues . . . I had to rebuild the entire system with new rubber hoses, new seals at the vacuum reservoirs, new check valves, and a few new "Y" connectors. The main check valve above the rear intake before all the splits to heater controls and manifold splits is vulnerable due to heat in my opinion. My vacuum improved once I cleaned up all the false air leaks. Many complain about the passenger door lock vacuum element; my weak spot has been the trunk lock actuator for some reason.

I did add a provisional vacuum pump with an internal switch that cuts off at 15 in Hg. I mounted it on the inside forward right fender next to my cruise control actuator. I'm doing some work on another project that has me considering a more substantial axial vane pump (Hella UP28/30/32 or Hella UP5X).
 

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Discussion Starter #5
Thank you for the prompt response; did you just compose that entire message in less than a minute?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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If manifold vacuum is 12", start with idle timing at TDC with vacuum and then advance until you get maximum vacuum. Should be at least 15" HG, but probably higher. At that point, you should be at something like 27BTDC which is good on these cars. If you can't get there, check that centrifugal advance is not stuck. If this doesn't improve vacuum, start looking for leaks - As Cush said, connector to locking system/transmission at back of engine is a good place to start.
If you really have a hot start relay, that must be a 74? Maybe post the VIN - someone may be able to conform.
 
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