engine and drivetrain Megasquirters and Electrical Gurus: Here's a wierd one...

[JohnC]

I parked my megasquirted car the other night, and it wouldn't shut off. When I turned the key to the off position, all the dash lights and the tach died, but the L (alternator) light came on, and the engine kept running (it's not detonation, the sparkplugs are firing, and it's idling normally).

I pulled the ECU power relay, and as expected, the engine died. Put the relay back in the slot, and turned the key on and off, and the relay clicked appropriately. Started the car, had my son turn the key off, with my fingers on the relay, and no click - it's still powered.

The #6 fuse position is my my source for switched power to operate the relay. Important note: I tapped the same source for an auxiliary "painless" fuse panel. The painless panel has seven fuse positions, 3 hot and 4 switched. The power source for the painless panel is from the battery, and a relay is used to "switch" the four positions. I'm using the switched fuse positions for the EDIS, Radio and a couple of other incidental functions. I'm convinced that the keyed ignition switch is functioning properly because every thing shuts down except for the things powered from the megasquirt relay board and the painless fuse panel

I opened the original 2002 fuse box (early car with six fuses), so that I can test what's going on with the number six position. Using a Voltmeter and a test lamp, I determined that there was some current bleeding back from the painless fuse panel that was keeping the ECU relay (and thus the fuel pump relay) active. A voltmeter showed the voltage dropping from 13V while running to just over 5V with the key in the off position (but with the engine continuing to run). The 5V current wasn't even enough to keep a test lamp lit, but it was enough to keep the solenoid in the ECU relay active.

To fix the symptom (not the problem, I still have no idea what's causing the problem, but I suspect it has something to do with some inductance some way somehow from the EDIS or coilpack), I inserted a diode in the lead that activates the painless fuse panel relay, so that current cannot bleed back into the lead that operates the ECU relay. All is well for now!

I wired in the diode with removable connections, so that if the diode blows and the engine dies, I can easily bypass it without a lot of muss and fuss. I can always kill the engine the old fashioned way that many of us learned with our carb cars with carbon buildup on the pistons (dump the clutch while in gear with foot securely on the brake). The diode is rated for 1A and 400V, I figured that's more than enough to keep the relay activated without overheating the diode.

I doubt that anyone else has experienced this because it's unlikely that anyone else has haywired their car like mine, but I thought I'd throw it out there just in case.

I know, I know, I should spend the time to really fix the problem, but I'm lazy. I don't want to tear into all my wiring if I can get away from it.

So any thoughts as to what might be causing this? Anyone have thoughts on this use of a diode?

Thanks!

[Tommy]

Interesting but pretty hard to figure out without wiring diagram of the whole system. Sounds that you're good with electrics and you can probably solve it by yourself if you put some more effort in.

Was it so that until now it has been working fine and now it does the same every time? If so something must have changed/broken...

Tommy

[ar_kid]

I occasionally get the same symptoms with my car (air cooled). Oddly by putting the car into reverse gear the engine will shutdown, I suspect that any back emf drains via the reversing lamps.

BTW the original Bosch L-jet double FI relay does have a diode in there also.

[ClayW]

I had a similar problem in my car before I megasquirted it. Is your alternator upgraded?

Anyway, what is likely happening is that your alternator is feeding the "Ignition On" circuit through the alternator light. Basically, the alternator is still producing some low voltage power and that power is finding it's way to ground through the dash light. This is providing just enough voltage to trip the relays for your Megasquirt ECU, which is continuing to power the EFI. That's why everything is running and you're getting a dim alternator light.

The fix is to find a giant diode and put it inline from the line that goes to the dash light. It's the smaller line from the alternator (if yours is an internally regulated later unit upgrade). If I recall correctly, the diode should be pointed toward the alternator. Anyway, you can test it with alligator clips each way....nothing will get hurt.

I can't recall the size of the diode...I just used one that my dad had lying around. It was almost as big around as a pencil.

Let us know if that fixes it!

[JohnC]

Interesting theory. Yes, I have an E30 80 amp alternator. If I put the diode pointing toward the alternator, how would the lamp light if the alternator fails? The diode would block current flow to the lamp.

If this is the case, I would think that the fix I installed would have been effective. If the current was coming through the system to the ignition switch to the #6 fuse position and then flowing to the two relays, the engine should just continue to run despite the diode I installed.

I had a similar problem in my car before I megasquirted it. Is your alternator upgraded?

Anyway, what is likely happening is that your alternator is feeding the "Ignition On" circuit through the alternator light. Basically, the alternator is still producing some low voltage power and that power is finding it's way to ground through the dash light. This is providing just enough voltage to trip the relays for your Megasquirt ECU, which is continuing to power the EFI. That's why everything is running and you're getting a dim alternator light.

The fix is to find a giant diode and put it inline from the line that goes to the dash light. It's the smaller line from the alternator (if yours is an internally regulated later unit upgrade). If I recall correctly, the diode should be pointed toward the alternator. Anyway, you can test it with alligator clips each way....nothing will get hurt.

I can't recall the size of the diode...I just used one that my dad had lying around. It was almost as big around as a pencil.

Let us know if that fixes it!

[JohnC]

Yes, you got that right, it is hard to figure out without a wiring diagram. Note to self: Next time you do a project like this, DOCUMENT EVERYTHING. I threw everything together and documented very little. Yes it was working fine, but I suspect that there was always some current flow. Maybe it just got a little worse and now keeps the relays activated.

Interesting but pretty hard to figure out without wiring diagram of the whole system. Sounds that you're good with electrics and you can probably solve it by yourself if you put some more effort in.

Was it so that until now it has been working fine and now it does the same every time? If so something must have changed/broken...

Tommy

[ClayW]

Interesting theory. Yes, I have an E30 80 amp alternator. If I put the diode pointing toward the alternator, how would the lamp light if the alternator fails? The diode would block current flow to the lamp.

If this is the case, I would think that the fix I installed would have been effective. If the current was coming through the system to the ignition switch to the #6 fuse position and then flowing to the two relays, the engine should just continue to run despite the diode I installed.

I had a similar problem in my car before I megasquirted it. Is your alternator upgraded?

Anyway, what is likely happening is that your alternator is feeding the "Ignition On" circuit through the alternator light. Basically, the alternator is still producing some low voltage power and that power is finding it's way to ground through the dash light. This is providing just enough voltage to trip the relays for your Megasquirt ECU, which is continuing to power the EFI. That's why everything is running and you're getting a dim alternator light.

The fix is to find a giant diode and put it inline from the line that goes to the dash light. It's the smaller line from the alternator (if yours is an internally regulated later unit upgrade). If I recall correctly, the diode should be pointed toward the alternator. Anyway, you can test it with alligator clips each way....nothing will get hurt.

I can't recall the size of the diode...I just used one that my dad had lying around. It was almost as big around as a pencil.

Let us know if that fixes it!

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/topic_view,threads/p,514970/t,307437/

Yep, face the diode toward the alternator on the D+ line. I just checked on my car. It's not a normal circuit, but I promise you that the diode will fix it. I read somewhere that some voltage regulators have them built in and others don't. Anyway, what's the harm in trying? Just pick up a 1n4004 diode and connect it between the D+ line and the terminal on the alternator with alligator clips. I'd bet dollars to pesos that that will fix it.

[JohnC]

Very good. I'll give it a try and report back.

I'll be damned. I thought that this was something new. Just one more bit of testimony reaffirming the value of the FAQ!

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/topic_view,threads/p,514970/t,307437/

Yep, face the diode toward the alternator on the D+ line. I just checked on my car. It's not a normal circuit, but I promise you that the diode will fix it. I read somewhere that some voltage regulators have them built in and others don't. Anyway, what's the harm in trying? Just pick up a 1n4004 diode and connect it between the D+ line and the terminal on the alternator with alligator clips. I'd bet dollars to pesos that that will fix it.

[canadamatt]

I concur, I needed a diode on my megasquirted car as well.

[AustrianVespaGuy]

I had this problem in my car too after installing megasquirt (but not before megasquirt, even with the 80-amp alternator) and I have a slightly different theory on why this happens.

When we install megasquirt, we are all usually wise and use a relay to power MS and the ignition circuit (EDIS/etc). However in the original 2002 electrical system, the ignition coil was powered DIRECTLY via the ignition switch (key), and NOT via a relay! The coil is a big load, and in the factory setup when you cut out the battery by turning off the key, the little bit of juice from the alternator at idle isn't enough to power the coil.

There is enough juice at idle though (especially with the bigger alternator), to keep the RELAY energized! So while the relay stays energized from the little trickle from the alternator, your ignition circuit is still being fully fed from the battery.

My solution was to use a 15W light bulb as a load in series with the relay so that there is enough voltage drop that the relay will switch off when you turn the key off. You could also use a power resistor, but I like the added light in my engine bay from the light bulb! (Remember though, you need a load to dissipate the extra power from the alternator, so a regular low wattage resistor won't cut it. Load is the key here, not resistance.) All that being said, I'm sure a diode would work fine as well if it's in the right spot and doesn't get burned up. I didn't use a diode because I never figured out through what path the relay was staying supplied, but that dash light does sound the likely culprit. Hope this helps some people!

-Carl

[Todd21]

I've been stalking this thread for some time.... my car is suffering due to an inability to shut off. My car is a 75 2002 standard motor trim. I have a stock alternator but have converted to a 6200 MSD box with blaster II coil. The distributor is still running points but I'll convert to Petronix soon as I burnt up a set earlier before the MSD conversion and have yet to convert.

I've done Clay's conversion using the diode (same one as described in the thread) and this did cause my "L" light to not light during start up. I suspected this was part of using the diode but I am not fully sure.

Anyway the car still tries to run after switching off the key forcing me to use the clutch and second gear to shut her down. Is there something I can do to remedy this issue? I could use a relay for the power to the MSD box, that might get it shut down but I don't want to do anything silly here.

The car does run well and I can see no other issues beyond the fact that it won't shut off. Suggestions please....

Todd

[AustrianVespaGuy]

I suspect that you have a similar issue as with the Megasquirt EDIS I described above, however you'll need to look into how your ignition is wired to really tell, specifically how power is supplied to your ignition coil. When you turn the key off and the car runs on, trace the 12V backward from your coil to either the alternator or battery and determine where/why you still have voltage after the key is off.

Along other lines, do you have high compression pistons? Any chance that your run-on is due to the car dieseling (compression-ignition) instead of the plugs continuing to fire? Just want to make sure we're hunting the correct monsters.

-Carl

[Todd21]

Carl,

Thanks for the information. I don't have a dieseling issue. I my motor is very tired and very stock. I run the power back see what I find.

Todd

[AustrianVespaGuy]

Ok, good luck with your hunting then Todd. The 'L' light is just one potential pathway for power to find its way back to the coil and keep the coil alive. The diode 'blocks' this path but depending on how it's wired, there is the potential for other pathways too. If you can't seem to find where the trouble lies, my final suggestion would be to simply install an additional kill switch in the wire that supplies power to the ignition system. This will a) fix your problem, can function as an emergency cut-off (like in the event your throttle gets stuck open), and c) my favorite, is an anti-theft deterrent.

-Carl

[Todd21]

Thanks Carl,

I has thought of installing a relay to block power coming to the ciol. I could do this down stream of the MSD box so it would have no potential to mess up my box.

I need to scratch my head some more and get in there with a meter and run things down.

I think I'll remove the diode since it didn't solve my issue and keeps the L light from working. I find that changes should only come one at a time, otherwise I never kow what cleared up the problem.

Appreciate the advice,

Todd