1984 325e, 2.7 I6. I have a cobbed together assortment of fittings & reinforced hose that I am going to use to test the delivered oil pressure on my car. Should the lashup start to leak while testing, and I am under the hood watching the gage and working the throttle by hand, I would like to kill the engine quickly...without running around to the driver side and getting in to operate the key. Is it possible to simply jerk the central coil wire out (certainly killing the engine) without causing problems for the Motronic ecu? (I've heard that doing the convenitonal "power balance" by pulling one plug lead at a time and noting rpm drop is very apt to cause damage to the Motronic, so I wonder if hyankign the coil HT lead woudl do similar...or if it is OK. Or is there a wires and push button lashup I could make that would slip into the diagnostic connector to kill the engine cleanly?
You can pull the main relay located on the side of the fuse box. You could put a "dead man's switch" on the coil positive wire to interrupt power to the coil (much less likely to shock you that way.) I pull single wires all the time to find misfires. I won't guarantee it won't hurt anything, but I have not had any problems for many years.
<<ou could put a "dead man's switch" on the coil positive wire to interrupt power to the coil (much less likely to shock you that wa>> OK. I can use a stinger switch I made for the MGB that will work that way just fine. (hold button, pwere, release, no power)_ Now...what oil p should I see in a healthy engine?
It would not necessarily die instantly. Pulling the ECU fuse would be better, but killing spark would kill it instantly.
I think that will work OK if you don't mind waking up on the ground a few minutes after getting your butt zapped. I'd go with breaking the coil's power circuit. I know there's a starter jump in the diagnostic connector, but I don't recall whether there's an engine kill circuit you could short out.
A better way (for my purpose) on the 84, at least, I'm told that I can use the diagnostic connector and attach a momentary push button switch (like a remote starter or stinger) between pins 11 and 14. This allows you to easily step/crank the engine without starting...enough to generate oil pressure. Or for setting valve lash, etc. only part of my post ended up here...the rest is below.
You can also just connect pin 11 to battery positive through a start switch. I wasn't sure if you could make enough oil pressure just cranking it because that only spins the motor around 3-500 RPM. I do use that to bump the motor to adjust valves.
A better way (for my purpose) on the 84, at least, I'm told that I can use the diagnostic connector and attach a momentary push button switch (like a remote starter or stinger) between pins 11 and 14. This allows you to easily step/crank the engine without starting...enough to generate oil pressure. Or for setting valve lash, etc. (the pin numbers might vary for different engines./years) this is supposed to crank over the engine w/o enabling ignition or injection. such a switch it easily made up. visit radio shack. get a pushbutton that is ON when the button is down and turns OFF when you release the button. $5 should buy a package of 2 of em. I then used an old prescription pill bottle (the old standby, 35mm film canisters, being hard to come by these days<G>) and drilled a hole in the bottom. Then I soldered two leads to the switch, inserted it into the hole (in my case it screwed into the slightly too small hole...since there was no way to use the retaining nut with the wires and small diameter canister). at the other end of the wires I folded the copper up into a bunch that would fit snuggly into one of the connector ports (I disconnected the battery and let it sit for a day before I tested the fit -- not wanting to cause the Motronic unit to have a stroke or something). and voila. Haven't tried the BMW version I made yet (I made one for my MGB as a remote starter switch for similar purposes)
BTW, it is pin 11 for all BMW engines up to 12/94. You can also purchase a remote start switch at most auto part stores for about $10. If you are extremely cheap, you can just use a long wire from pin 11 and touch it to the battery positive post when you want the motor to crank.
