injecter earth problem
Moderator: martauto
325i ,1987 high comp engine in 87 18i se ,swaped a while back ,now wont start its down to earth problem on injectors how can I improve this ,I have cleaned and added another earth ,but if I pull a plug on injectors and earth pin out she fires strait up,,,,,help,,,please
Do you have the Motronic 1.0 with 35 pins on the ECU?
Pin 35 is supposed to supply ground to the injectors.
Motronic 1.1 is a bit more complicated.
Edited! Pin 35 supplies +12 volts to the injectors...not ground!
Pin 35 is supposed to supply ground to the injectors.
Motronic 1.1 is a bit more complicated.
Edited! Pin 35 supplies +12 volts to the injectors...not ground!
Last edited by Billwill on Sun Aug 18, 2013 3:10 pm, edited 1 time in total.
35 pin motronic ,at the injecter plug red and white wire if I earth this she runs spot on ,so I think its an earth problem ,but what to do ,do I re earth at pin 35 as you say or can I earth on to plug with red and white wire,this as been an on going thing until its finally not starting its as if earth as been bracking down now nothing so,,,help needed big time
just been at it again if you take of one injecter plug any one it starts,its as if earth is not strong enough ,so is it safe without causing damage to anything ,to connect in to red and white before all injectors and put to earth
OK the Wiki for the ECU pinouts for the 35 pin Motronic 1 is incorrect where it states that pin 35 is the "injector ground"....pin 35 on the ECU is actually +12 volts which gets switched onto the Red/White wires on the injectors via relay 11 in the Haynes manual...actually called Relay 2. This relay should be activated when the CPS pulses are picked up as the engine rotates....this relay also in turn activates the fuel pump relay....you should see both these relays activating when the engine is turning over.
So you expect to see +12 volts on the Red/White wires at your injectors when ignition is ON and...I believe...when the engine is rotating.
What then happens is that the other side of the injectors, Brown/White and Brown/Yellow get switched down to ground by the ECU...using PWM for a variable duration pulse via pins 14 and 15 and this is what fires the injectors....at the correct time according to the CPS pulses.
So there should be no "grounding" at the injectors except the PWM ground pulses coming from pins 14 and 15.(Brown/White and Brown/Yellow) The ECU gets its ground from a few places and this may be where you are having a problem...pins17,16,10,19,5....all of which are Brown wires and should bolt onto the chassis somewhere.
So my advice is to not mess with the Red/White wires going to the injectors...they are supposed to have +12 Volts there.
One of your ground wires going to the ECU has probably gone missing....they are all supposed to be bolted onto the chassis at two different points.
Finally, you state that if you pull one of the injector plugs off then the engine starts to run. Effectively you are firing three injectors at once...Brown/White and then Brown/Yellow ....maybe the grounds are not firm enough to fire three injectors at once.
Try find where all these brown ground wires get bolted onto the chassis and clean up and tighten those chassis ground points and trace these brown wires back to the ECU pins I mentioned that should have ground.
So you expect to see +12 volts on the Red/White wires at your injectors when ignition is ON and...I believe...when the engine is rotating.
What then happens is that the other side of the injectors, Brown/White and Brown/Yellow get switched down to ground by the ECU...using PWM for a variable duration pulse via pins 14 and 15 and this is what fires the injectors....at the correct time according to the CPS pulses.
So there should be no "grounding" at the injectors except the PWM ground pulses coming from pins 14 and 15.(Brown/White and Brown/Yellow) The ECU gets its ground from a few places and this may be where you are having a problem...pins17,16,10,19,5....all of which are Brown wires and should bolt onto the chassis somewhere.
So my advice is to not mess with the Red/White wires going to the injectors...they are supposed to have +12 Volts there.
One of your ground wires going to the ECU has probably gone missing....they are all supposed to be bolted onto the chassis at two different points.
Finally, you state that if you pull one of the injector plugs off then the engine starts to run. Effectively you are firing three injectors at once...Brown/White and then Brown/Yellow ....maybe the grounds are not firm enough to fire three injectors at once.
Try find where all these brown ground wires get bolted onto the chassis and clean up and tighten those chassis ground points and trace these brown wires back to the ECU pins I mentioned that should have ground.
Stupid question but I assume you have the two sensors located on the bellhousing....one sensor is the position sensor at marked position B on the bellhousing (grey wire) while the other sensor is the speed sensor at position D on the bellhousing (black or white wire).
If the sensors are connected wrong then the engine will not start.
If the sensors are connected wrong then the engine will not start.