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Any Jetronic experts out there?
plentywahalla - 6/4/15 at 04:14 PM

My faithfull old Merc is in a bit of a sad way. She is a SL300-24 from 1991. I have owned her for 21 years after one lady owner had taken the shine off her. I am, rather attached to the old roadster and only get her out in the summer when the sun shines.

Well its that time of year again so I went to get her out of the shed. The engine cranked but did not start. It then occurred to me that the fuel pump was not running. I pulled out the MAS (german for ECU) and jumped pins 1 & 2 and the pump whirred into life, so it is a switching/relay problem. After checking everything else out I isolated the problem to the MAS itself. The unit is completely sealed any only appears to run the injection system. The ignition is a dizzy.

Now I happened to have another MAS which I bought off ebay for the a SL500 I used to own. I never used the unit as it turned out not to be the problem. The serial number is 011 545 85 32 whereas the 300 one is 011 545 83 32. There is only one digit difference but clearly not the same unit. To help isolate the problem I popped in into the slot and the engine started instantly and appeared to run perfectly.

I have not ventured out in the car yet but have had it ticking over for some time and all seems fine. No apparent overfuelling etc. The 500 was a V8 whereas the 300 is a straight 6. In theory the MAS shouldn't work. The injection system is a KE Jetronic which is a continuous fuel injection system. It has individual injectors for each cylinder but they pump fuel continuously, there is no sequential fuelling of each cylinder. The metering system seems to work on air mass and flow and throttle position so could a system made for 5 litres 8 cylinders work on 3 litres 6 cylinders just by adjusting to demand?

A new MAS is £180, but is it a false economy to run the wrong unit? Can any injection experts give me the bottom line?

britishtrident - 6/4/15 at 04:57 PM

The Ke Jetronic is essentially a mechanical system the electronics are just for what Bosch termed "Auxiliary Systems" so in normal running conditions the electronics probably have little effect.

plentywahalla - 7/4/15 at 04:16 PM

quote:
Originally posted by britishtrident
The Ke Jetronic is essentially a mechanical system the electronics are just for what Bosch termed "Auxiliary Systems" so in normal running conditions the electronics probably have little effect.


Thanks for the info. It encouraged me to take it for a run to a friend who has his own MOT station and put it on his exhaust gas analyser. It all came up normal. I think you are right, and that the only electronics relate to recording and storing fault codes.

I put the same question to a Mercedes Benz SL forum about 2 weeks ago and no one had any idea. All they seem to talk about are what watch and sunglasses they wear while driving their 'Benz' .... posers all !

Trust LCB !!