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E28 (1982 - 1988)

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Old 08-12-2011, 05:42 PM
Tecmec Tecmec is offline
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Location: Connecticut
Join Date: Mar 2010
Posts: 21
Mein Auto: 1987 531is
535is no voltage pin 18 on motronics

Have a 1987 535is that has the basic motronics engine management control system. Vehicle after injector change and other work will not start. Have checked voltages at main relay and diagnostic connector, both checked out OK. Checked voltages at injectors, voltage was correct. Checked fuel relay, Checked speed and reference sensors, ETC. All seems well. When checking voltages and resistance at motronics connector I found that I have battery voltage at pin 35 of the motronics connector when checked as described in Bentley manual. However do not have battery voltage at pin 18. Both of these pins are fed from the red/blue wire coming from pin 87 of the main relay, through the main harness running along the fuel manifold, and on through the passenger side firewall terminating in the motronics connector. I did jockey the harness around a bit when I was replaced the injectors and at the same time I removed the intake plenum to facilitate replacement of the starter. I did check out the main relay and it was ok. I have not tried to check continuity between the main relay connector and pin 18 of the motronics connector yet. Plan to do that shortly. I would appreciate any advice and ideas to further trouble shoot this problem and determine how I get power to pin 18. I.E. do I try to pull a new wire through the harness, do I tap into the wire feeding pin 35 inside the car, do I run a new wire and marry it to the outside of the harness. Again, any comments, advice, or help is appreciated.
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Old 08-13-2011, 05:30 PM
catso's Avatar
catso catso is offline
Location: Chicago
Join Date: Dec 2009
Posts: 3,112
Mein Auto: 2000 323i, 1988 528e
You should double and triple check whatever connections you disturbed when you replaced the injectors and starter. Maybe you inadvertantly disconnected or switched some wiring. Check if you have spark. If you do, try starting the car with starting fluid to confirm whether it's a fuel delivery or ignition problem. Sometime the electrical connection break or are corroded under the insulation, especially on or near the starter. Corrosion is a continuing problem with these older cars.
Don't be gormless; get some gorm!
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