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L jet info - running rich

Posted: Wed Feb 06, 2019 5:45 am
by garyinwestoz
found this today

http://www.injectronics.com.au/assets/Uploads/T0067.pdf

" Document number: T0067
TECHNICAL BULLETIN
For further technical information regarding testing, repairs or to search for New or Remanufactured Automotive electronic products, please visit www.injectronics.com.au, call our office on (+613) 8792 6999, or email sales@injectronics.com.au

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.

T0067.doc

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Re: L jet info - running rich

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