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#1
05-14-2002, 11:03 PM
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Do These Engines Have Rev Limiters?
I was checking my tach circuit the other night by injecting a signal into the amplifier and bypassing the tach pickup to get the tach to read somethingeek: . As I increased the signal (Hertz), of course the tach did not work
 , but I heard the shutdown solenoid kicking in and out. Do these engines have rev limiters? I also obtained a schematic of the circuit from M.B and it shows a wire going to the overload protection control unit. Is this a rev limiter? If it is my circuit appears to be working, but my tach is not. FYI If you want to check the tach pickup, I measured it with an ohmmeter and found the outsdie, or yellow and black wires should read about 70 ohms. The center pin appears to be a shield. PeterG 79 300SD 75K miles 
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#2
05-14-2002, 11:52 PM
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It seems to me there is a safety switch on one this old, it's a switch located on top of the air distribution housing, near where the air is sucked into the engine by the fuel distributor. I've never studied how it operates, I believe it cuts out the fuel pump relay or something if the air flow sensor plate deflects down too far, just a guess though. It seems to me it was phased out in favor of the fuel pump relay with RPM limiter in the very early 80's.
Gilly
__________________
Click here to see a photo album of my '62 Sprite Project Moneypit (Now Sold)
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#3
05-15-2002, 12:39 AM
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Gillybenztech,
Sounds like you are describing a CIS injection system on a gasoline engine  PeterG, Perhaps this is some sort of supplemental protection system. I'm under the impression that all Benz diesels (excl the newer ones) use a vacuum operated fuel shutoff and that there is no fuel shutoff solenoid. Perhaps you heard the overboost solenoid clicking... perhaps this cancels fuel enrichment if the engine exceeds a certain speed. There is a mechanical centrifugal "rev-limiter" in the injection pump. It is possible that this electronic circuit is a backup system in case the mechanical system fails. Does anyone know for sure? -Joe
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#4
05-15-2002, 06:46 AM
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Oh crap, I sure was!
On the Diesel engine, the rev limiter is a device inside the fuel injection pump called the governor, simple. Gilly
__________________
Click here to see a photo album of my '62 Sprite Project Moneypit (Now Sold)
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#5
05-16-2002, 05:29 PM
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It was the shutdown solenoid that was clicking as I increased the frequency. so what is a overload protection control unit for and where is it located?.
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