rev counter

brianbrian

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As some of you know i have converted my Sl from Petrol to diesel. Have everything working on instrument panel,except the rev counter.
Am i right in thinking that the rev counter on the 1992 sl worked off of the coil. So does this mean that i cannot fit the rev counter to the diesel as i am using the sl instrument panel.

any ideas would be grateful.
 

wireman

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The diesels have a different tacho, as noted the petrol works off the ignition system.
Diesel units have a sensor (on my 602 its flywheel mounted) and a tacho head which interfaces with the sensor. Some diesels use the alternator output ripple as their tacho signal.
You probably need the sensor and the instrument of the diesel. With the petrol system there are 2/3 pulses per revolution, I think the diesel uses the starter ring as a speed measure and if so will give lots more pulses. It may be that some (keen) electronics guy may be able to build you an interface to use the original tacho with a flywheel probe but it would probably cost somewhat more than a second hand diesel tacho system.
 

Number_Cruncher

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If the diesel engine's idle speed & EGR computer has been correctly transplanted into the SL, that outputs a tacho signal which drives the rev counter on older diesel MBs.

The engine will run without the computer, and so, it's possible that it hasn't been correctly moved across.
 
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brianbrian

brianbrian

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Many thanks Wireman I am going to leave the revcounter dead, as you can not over rev the deisel ,got the idle right just that I like every thing to work.
 
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brianbrian

brianbrian

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number cruncher

i put the diesel engine in without the EGR

cheers Brian
 

turbopete

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some cars (not sure about MB's) take a feed from the alternator to power the rev counter. if the diesel engine has same no of cyls as petrol, it may work fine anyhow! if not, try swapping the rev counter units (if similar) from donor car to your car
 

Number_Cruncher

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>>i put the diesel engine in without the EGR

I meant the EGR and idle speed controller, not the EGR valve itself.

The idle speed controller on this engine reads the signals from the sensor on the flywheel, and sends a signal to the rev counter to indicate engine speed and sends a signal to the injector pump to smooth and control the tick over, and operate the EGR.

If you haven't connected this controller up, then, while the car will still idle, it won't be as smooth and as tolerant of load changes, i.e., it will run like an old fashioned diesel, with hunting from the governor and will be susceptible to load changes from the alternator, for example.

You'll find a large disc shaped object on the rear of the injector pump with two terminals at the top - this is the idle control actuator.

It is worth swapping this controller over - you'll get idle speed control, and a signal output to drive the rev counter.

On these engines, the rev counter is not driven from the alternator.
 
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brianbrian

brianbrian

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hi my fuel injection deisel is pneumatic not electromagnetic so no terminals have got the idle just right as there is no stress as I have not got a/c ,I no that I could pick up from the alternator but am going to leave it for now,many thanks for your time.
 

turbopete

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>>i put the diesel engine in without the EGR

I meant the EGR and idle speed controller, not the EGR valve itself.

The idle speed controller on this engine reads the signals from the sensor on the flywheel, and sends a signal to the rev counter to indicate engine speed and sends a signal to the injector pump to smooth and control the tick over, and operate the EGR.

If you haven't connected this controller up, then, while the car will still idle, it won't be as smooth and as tolerant of load changes, i.e., it will run like an old fashioned diesel, with hunting from the governor and will be susceptible to load changes from the alternator, for example.

You'll find a large disc shaped object on the rear of the injector pump with two terminals at the top - this is the idle control actuator.

It is worth swapping this controller over - you'll get idle speed control, and a signal output to drive the rev counter.

On these engines, the rev counter is not driven from the alternator.

i wasnt sure if they had flywheel sensors on engines of this era. thanks for the info!
 

Number_Cruncher

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>>hi my fuel injection deisel is pneumatic not electromagnetic

I very much doubt it. What car did the engine come out of?
 
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brianbrian

brianbrian

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My wifes 1990 250d 124 model my 1990 250d 124 has electromagnetic have never found out why two cars same month same year same model were fitted 1 electromagnetic 1 pneumatic even mercedes could not give me the answer does anybody no.
 

turbopete

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there has to be a cut off point at some stage. probably when supplies at the factory are used up or your cars were made at 2 different factories! either way 1 was at 1 side of the changeover and obviously the other wasnt!
 
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brianbrian

brianbrian

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Many thanks both cars came from same factory the only thing I can think of is the electromagnetic had extras,perhaps the electromagntic system was to adjust the idle when these extras put more load on the car does this make sense.
 

Number_Cruncher

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>>mercedes could not give me the answer does anybody no.

Can you show us a link to the Russian site? I've never seen or heard of a pneumatic controller on these engines - very interesting!
 
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brianbrian

brianbrian

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The haynes book is not that great as far as I am concerned , but it does show the two different pumps. Hope this helps
 

wireman

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Is this electromagnetic/pneumatic debate refering to the engine stop system? If so it is only engine stop that is being controlled, on some models there is an additional electromagnetic idle speed control actuator on the pumps (mechanical) govenor casing back cover.
 

Number_Cruncher

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>>Is this electromagnetic/pneumatic debate refering to the engine stop system?

No, I'm on about the electromagnetic idle actuator which is located on the rear of the governor housing. The engines will idle without it connected, but the quality of the mechanical idle speed regulation will be poorer.

As an example of the device I'm on about, see part number 445

http://www.detali.ru/cat/oem_mb2.as...GM=717.413&CT=M&cat=502&SID=07&SGR=045&SGN=01

I'm not sure exactly what device Brian is calling a pneumatic control though.

This is why I'm amazed to hear talk of pneumatic systems. On many makes of vehicle, pneumatic governors were fitted to some diesel injector pumps, in comination with a throttle valve in the inlet to provide the vacuum signal. You would have to be of a certain age to remember them though!, I haven't seen one for many years. These fitments were before the time when diesel engines were popular in cars, and the only ones I've ever seen were in commercial vehicles.
 
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brianbrian

brianbrian

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Yes Number Cruncher you can disconnect idle actuator on the rear of the electromagnetic and still ajust idle, but M.B. fitted some 250d and 300d 124models 1985 to 1992 with pneumatic both are in the haynes book page 4d.10 the pneumatic is what I have fitted so adjust idle manualy hope this has not confused every body as it did M.B. at taunton somerset when I took the car to them, the stop is operated by vaccum on both pumps, Both pumps have a flow of vaccum 1 pipe of break vaccum pipe 1 pipe of fuel injection both go to small valve fitted on the steering ignition sorry for the long story.
 

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