Fuel Injection Fault Finding for bosh motronic, bmw K11 by Frank Warner.
My fuel consumption rapidly increased, leading to overly rich running.
Adjusting the CO2 pot did reduce the rich running at idle but had not effect on the overall consumption.
The motronic unit does store errors, but it will only store gross errors not subtle errors.
Gross errors are shorts or open circuits, a sensor that changes its characteristic will not be detected as that
would be simply assumed to be a change in the sensed quality.
These notes are for my 1993 K11LT and may have some relevance to other motronic equipped vehicles, but you need to do the thinking to check for the differences. The date of manufacture looks to be indicated within engine serial number mine says xxxxx 2293 xxxx. I think this is the same structure as the tyre dates, 22 is the 22nd week of the year (about end of May?), 93 is 1993.
The following is firstly a description of the motronic brains memory and its readout. Then a description on the test setup. Then on each component used, their characteristics and methods to test them.
The motronic brain stores faults within it self, these stored faults should be retrieved and investigated as this could save a lot of work.
There is a blue 3 way connector on the left side of the bike near the battery, you'll need to remove the side cover to gain access. Turn on the ignition and then shorting the number 1 pin on this connector to earth for 5 seconds, then the temperature light near the tachometer will flash. The light will light for about 2.5 seconds, then a give a number of short flashes, count these short flashes. This count is for the first number, if this is a 1 then you have a fault. Another 2.5 seconds of light follows the first count, then follows the second count and this is repeated for the third and fourth count. This repeats until you turn off the ignition, or reshort the pin 1 to earth for 5 seconds to get the next fault.
|1133||Hall effect - no signal No 1 motronic plug connections 8 (signal)|
|1122||Hall effect - no signal No 2 motronic plug connections 26 (signal)|
|1223||Water Temperature motronic plug connections 21 to 32|
|1224||Air Temperature motronic plug connections 22 to 32|
|1215||Throttle Position Sensor motronic plug connections 25 to 31; 13 to 31 and 10 to 31|
|1111||CO2 pot motronic plug connections 25 to 31; 25 to 28 and 28 to 31|
|3333||Not a fault - a fan test and memory erasure.|
You will need a ohm meter (resistance meter, most Digital Voltmeter [DVMs] have them included these days) to
do these tests. You will need to remove the electrical plug from the motronic brain located on top of the Battery.
You need to do this as part of battery maintenance anyway. Once the brain is disconnected it will lose all stored faults,
so this should be tested before disconnection.
All the connector numbers refer to the motronic connector above, unless specified other wise. This is done so that there is a common test connector, includes following wires and connectors. This makes the test simple. If a test fails then you should test the interconnecting wires and connectors. It may be worth noting that the procedure here does not check for shorts to the chassis, you should do these while flexing any and all wires from this connector to the item being tested.
Located on the left side of the fuse/relay box is this Pot, it has a slotted screw driver adjustment.
This is a ten turn Pot
meaning that the adjustment range takes about 10 turns (complete revolutions) to go (travel) from one extreme to the other.
Measure the resistance from 31 to 25, this should be 1k ohms +/- 10% and is the value of the pots resistance.
Measure the resistance from 28 to 25 and is the slider to bottom resistance. Measure the resistance from 28 to 31 and is the slider to top resistance. The sum of the slider resistance should approximately add up to the value of the pots resistance. If either or both of the slider resistance is well above the pots resistance then it is faults - get a new one.
If you record the slider resistances then you can always return to this setting. If the bike is running rich at idle then you may like to turn the adjustment say 2 turns clockwise to try to lean the mixture off. But as you as testing the fuel injection system now then I would continue with the tests.
Located somewhere in the inlet tract, this is a fragile component!
This is a Negative Temperature Coefficient resistor.
That means as the temperature rises the resistors resistance falls.
Measure the resistance from 22 to 32. BMW say it measures 2k5 ohms at 20 degrees C. As your air temperature will not be 20 degrees your measured value will be different, but should not be less than 10 ohms or more then 200k ohms.
The real test comes with the next sensor measurement, provided your water temperature is at ambient temperature (eg if you bike has not been operated for some hours).
Located on the left side of the water inlet riser in a most difficult to get at location!
This is a Negative Temperature Coefficient resistor. That means as the temperature rises the resistors resistance falls.
Measure the resistance from 32 to 21. BMW say it measures 2k5 ohms at 20 degrees C. As your water temperature will not be 20 degrees your measured value will be different, but should not be less than 10 ohms or more then 200k ohms.
Compare the measured valve of the Air sensor and the water sensor, they should be within 10% of each other provided the engine is 'cold'. If not then one of them is faulty. To determine which one it is probably easiest to start the engine and get it a little warm then remeasure the water sensor s resistance, if that has not significantly reduced then the water temperature sensor is at fault.
I measured 2k66 for the air and 2k52 for the water, a difference of 6%. A mild warming of the engine decreased the water sensor reading to 1k69.
Located on the left side at the end of the throttle body.
This is two inter connected potentiometers.
Measure the resistance from 31 to 25. BMW say it measures between 500 and 1000 ohms, I get about 700ohms.
Measure the resistance from 31 to 13. BMW say it measures between 600 and 2400 ohms. Measure the resistance from 31 to 10. BMW say it measures between 600 and 2400 ohms.
|Position||From 31 to 13||From 31 to 10|
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