Mercedes 280 se 1976 d jetronic extreme rich at idle

Hello Volker,

Thanks, i know there could be more faults but you would be surprised what stupid problems i allready found ...

(for example, : the explanation was we start the engine and when we put it in gear and want to leave then engine stops, that was all i know. But when the car came it didn't start at all. to make a long story short, the reason for this was that the fuel pump relay was rewired but in the wrong way, if you put on ignition the fuel pump was running and when you start and the ecu detects starting the relay switched and there was no fuel pump running anymore. But because the injectors sprayed that much the engine kept running a while without fuel pump and when you want to start in 1st or so it doesnt have enough and stops...
Because of this i think they allready changed the fuel pump and several things, i can write a book allready about it.
All cables are also hanging loose.

But we have to start somewhere now, as i am not sure if the map sensor is ok, you can't really do anything, only turning the adjusting nut doesn't help if the complete tuning of it is out of range or not working as it should be. This changes not only the values in your 3d map of rpm vs load, but also the load axe isn't right anyore...

I could try running on the road with the 450sl map sensor but that's also a car standing still for ages allready.

Hi Nick,

it lloks like you have a real challenge! Economically questionable but your passion will make you happy when you succeed.

So Volker helped me in getting this car back up running again.

Finaly with another ecu and a tuned and sealed map sensor, the engine was happy with the injection pulses it gets now

Co went from 9.0 and above to now 2.0 and HC (unburnt gasses) from 3000 and more to 80-100 now so it's a good engine.
And now it's possible to regulate the CO at idle as you want, every turn of the knob is something around 0.3-0.5 in CO percentage

Thanks for the great work

Hi Nick,

one of the few cases where an ECU is broken and abviously creates strange results. Good that you have it solved.

The car runs good now, customer did some 300 km with it allready.

But cold start seems to be not good according to him, (here it was good but low idle) , and now stalls when starting at -1C cold.

I taught about this before but, there seem to be no cold start air valve, most cars have a cold high idle until warming up.
Here you only have a cold start injector and offcoarse the enrichement with the air and water temperature sensor.

How should the cold start idle be? (also with 2-5 degree after igntion advance, that's not so good for cold offcoarse you want more when cold normaly).

Merry christmass to everyone

Hi Nick,

oh yes, this car also has an auxiliary air valve. But it is below intake manifold on engine block. And some people tend to break it apart as has a strange mounting socket on the block. So please look in the depth of your engine and you should find it. And when yoe mount it, first screw on both screws manually until your AAV sits straight on that socket. If it a bit askew, you can break the hosuing apart when you tighten the screws. And yes AAVs tend to hang after so many years.