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  #1  
Old 07-18-2007, 07:51 PM
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Exhaust puzzler

I bought a 77 450SL DOA. After getting it started I discovered a 1/2" hole drilled in the right side front pipe half way between the manifold and the cross over pipe. What is this for?
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  #2  
Old 07-19-2007, 05:50 PM
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That would likely be for an oxygen sensor.
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  #3  
Old 07-20-2007, 10:06 AM
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Oxygen Sensor

I'm not sure but with mechanical fuel injection (CIS) I don't think there is an oxygen sensor. All I have for reference is a Haynes manual and it makes no reference to an oxygen sensor.
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Old 07-20-2007, 12:05 PM
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Your car may not have one, but mine does. My car is a 1980 and has the mechanical FI system. Could be that someone replaced the exhaust system with one from a later model.
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  #5  
Old 07-21-2007, 04:20 PM
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I while I'm in no way knowledgable, or an expert. A search of the manual for a 1977 450SL does not show an O2 Sensor. The section on emissions makes reference to an air pump, EGR, Charcoal cannister, pressure transducer, Thermovalve, and connection tank vent.
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  #6  
Old 07-22-2007, 10:25 PM
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I don't think the 450's got sensors until 1980. My project 1977 is very original, and does not have one. And there's no point to a sensor unless it's connected to some sort of mixture control. On the SL's this involves a valve on the left side of the intake manifold and a computer in the passenger footwell.

You may have an incorrect exhaust pipe installed. But, buying and installing a generic single wire Bosch sensor, and measuring the voltage is a good way to check the mixture. Several posts on this.
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Chuck Taylor
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #7  
Old 07-24-2007, 05:18 PM
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Thanks for all the feedback. Why I was puzzled by the hole in the pipe is that it is just a drilled hole, no means to attach an oxy sensor or any thing else. I do think that the cat converter is partially blocked. "Lazy" exhaust at the tail pipes when drilled hole is pluged, also the engine will not rev much above1200 RPM.
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  #8  
Old 07-24-2007, 06:29 PM
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If it was drilled, likely to test the pressure on each side of the cat. A hole in front and one in the back of the cat can tell the pressure difference and therefor tell if the cat is pluged.
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  #9  
Old 07-24-2007, 09:52 PM
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If the car sat for a long time, there are several reasons why it won't run right. You may have done this already, but I would chase fuel delivery (pressure and volume), mixture, and ignition tuning before I wrote off the cat.

Every car is different, but my 1977 would barely run when I got it, and the cat was pronounced dead. But the problems turned out to be insanely advanced timing, pig-rich mixture, two vacuum leaks, and two bad plug wires. Once those problems were dealt with, I was able to get the car to run well with the CO under 1%, which needs the cat to be working right.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #10  
Old 07-25-2007, 11:22 AM
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Thanks again for the input. I have replaced the broken vacuum lines that I have found with over the counter vacuum tubing (black) I could not find a source for the color coded tubing. The manual that I have (Haynes) has the vacuum diagrams spread throughout the manual, part in the emission control section, part in the fuel & exhaust section and nothing about the door & trunk lock feature. So far I have replaced the fuel pump and filter. This car sat untouched 6 years so I have a host of problems facing me.
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  #11  
Old 07-26-2007, 02:14 PM
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Reading through the tune up section of my Haynes manual I came across the following paragraph "If a CO meter is available connect it according to the manufacturers instructions. Starting with 1977 models there is an exhaust backpressure line coming out of the exhaust manifold which the CO meter should be connected to instead of the tailpipe". Could this be the reason for the hole in my exhaust although technically it is not in the manifold.
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