engine and drivetrain Engine Wont Stop(!)

[Rustpile]

I have this cool problem. When I start the engine, it wont stop. I´ve converted it to MJ, and all +12V runs from battery through a relay, and it seems to cut power as it should. If i turn the key to ignition, the MJ light turns on, and if i turn it back, it turns off. Now, the cool part. Even if I pull of the + from the battery, where everything should be getting power from, it keeps running!

 

I am slightly amazed by this, but I think it might be because something wünderschön is happening in or around the charging-circuit. All advise is very appriciated as to how I can solve this mystery. Tried to cut fuel to stop it, did not work either. Was thinking about leaving it as is, and sell it to BMW, the car that runs without fuel or eletricity. The future was here, in 1974.

[FunkyLaneO]

Disconnecting the battery won't kill your car, the alternator is still generating power, try unplugging the positive terminal on the coil and watch the engine die.  That is the wire that should be switched on and off to control whether the engine runs.

 

Get out your test light and get to work, something is wonky.

 

Edit, just realized that MJ stood for Megajolt, not Marijuana. so you are not stoned the power going into your Megajolt should be switched off some place close to the unit to shut the car off, if you grabbed your power directly from the battery then it is not switched power.

Edited May 21, 2014 by FunkyLaneO

[Dev02]

I have this issue also, but mine is because I installed an MSD box. My understanding is that I need to now install a diode (sp?) in line with it to fix this issue. I know nothing about MS, but maybe it has the same effect?

[FunkyLaneO]

I am not familiar with the MSD box  but I use the Crane box in my car, you should not need to use any kind of diode with the installation unless there is something plugged into it that would cause backfeeding.

 

What a diode does is it acts as a one way valve, only allowing electricity to travel in one direction, it can be used to prevent backfeeding of power if you have accessories that span multiple circuits, for example the parking light circuits on our cars are left and right, separate,  but if you want all the lights to flash at once like with an alarm installation then you would need a couple diodes to power those two circuits from the same source yet still keep them separate (you could do the same thing with relays but diodes are easier)

 

So what exactly needs a diode, I am curious, sometimes you need one for your tach signal if you are doing a wasted spark configuration to prevent both coils from firing at once but that doesn't sound like your scenario.

[Dev02]

Hm... it was last Fall that I did the research, and got the diode. I will try and find the info. I DID get a tach adapter cuz my tach also stopped.

[Dev02]

Here is some info I used last fall:

http://www.bmw2002faq.com/topic/112300-just-installed-msd-6al-engine-run-on/

 

http://www.msdignition.com/page.aspx?id=3296

 

http://www.msdignition.com/forum/showthread.php?t=19814

 

It might be that I install the diode and it doesn't fix it, but thought I'd try this first.

[FunkyLaneO]

OK, so it looks like it can backfeed through the exciter circuit, interesting. You learn something new every day, just make sure you orient the diode correctly (it will only work in one direction) or your battery may stop charging and your problem won't be solved.

[Dev02]

Good to know, thanks!

[stuff]

Had the same run on issue on my megasquirt build. Solution can be found here:

http://www.msextra.com/forums/viewtopic.php?f=131&t=40167#p280830

[Rustpile]

I don't get it. Where should this diode go? On the back of the alternator or on the 12v signal (green wire) on the ignition?

[stuff]

I run an upgraded alternator with a built in voltage regulator (removed the external voltage regulator), so ymmv, but it should be the same for stock alternators.

There's a blue wire hooked up to the D+ terminal on the back of the alternator. The diode needs to be placed on the wire. Snip the wire, place the diode in line, make it all good and tidy... And secure.

Assuming you buy the diode from radio shack or somewhere similar like it did (very cheap) the leads are pretty fragile and will likely break over time with continued movement being so close to a moving engine. Once I had wired the diode in, I enclosed the section of wire with the diode in a short piece of rigid tubing to act as a sheath limiting flexing. I might go back and hot glue it to further solidify things.

[Rustpile]

Put in a 1N4001 diode, and engine stops now, but I the charging lamp is constantly on, is it supposed to do that?

[AustrianVespaGuy]

I think you either have the diode in the wrong way or on the wrong wire.  I'm pretty sure it should be in the BLUE wire which runs to pin #12 on the back of the gauge cluster, and should only let current flow 'towards' the alternator (so that the light lights when alternator output is low), and inhibit current flowing 'from' the alternator, which is what will keep your ignition relay energized when you try to turn the car off.  I would recommend putting the diode inside under the dash instead of in the engine compartment too.

-Carl