L jet info - running rich

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L jet info - running rich

Post by garyinwestoz » Wed Feb 06, 2019 5:45 am

found this today


" Document number: T0067
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Make: BMW

Model: 5 & 7 series, early to mid 80’s Subject: Running rich

Some early to mid 1980 BMW 6 cylinder engines used the Bosch L Jetronic system. This was the earliest of the air flap type engine management systems and used a 35 pin ECM.
The ECM pin 4 monitors crank signal from the starter motor and uses this signal to give start up enrichment. There should be zero volts at this pin when the engine is running or the key is just in the on position. When cranking there should be a crank voltage of approx 10 volts depending on the voltage drop.

Injectronics has had many customers call to say they have a running rich BMW and upon questioning we have learnt that starter motor work has been performed. In some cases a relay has been wired into the starter circuit, which causes a voltage to be present on pin 4 when the engine is running. This of course will make the engine run rich. To confirm this is your fault check the voltage at pin 4 with the engine running and it should be zero volts. If there is a voltage present, disconnect the relay or temporarily cut the wire going to pin 4.


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Mike W.
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Re: L jet info - running rich

Post by Mike W. » Wed Feb 06, 2019 1:59 pm

I did that by accident when I put L jet off an E12 onto a Bavaria. It wasn't rich, it was pig rich, black smoke rich. It ran, but not well. Didn't take too long to figure it out going over the schematic.
Mike W.

1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter

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