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B20 keeps running after turning off ignition and disconnecting battery

S

Shinchan

Member
Joined
Jun 28, 2018
Location
Lafayette, CO
Hi All,

Some background: I have a megasquirted B20 that is running fine but battery was losing charge, so I assumed that the alternator was on the outs. I obtained another alternator from another B20 and installed it. Now originally when I put this engine back together after the rebuild I had the 2 smaller red wires hooked up wrong. One was going to the 61/D+ terminal and I don't even know where I had the other wire hooked up, probably to one of the grounded structural bolts coming from the back of the alternator.

Anyway, I looked at the wiring diagram to sort out how to hook up the new alternator. Thick red wire from the distribution block goes to the B+ terminal, both small red wires to the 61/D+ terminal, and the green wire to the spade terminal. Car starts right up, I let it run for a bit and turn off the ignition. The engine keeps running. I'm not talking about dieseling, it's running as if the key is still on. I jump out of the car and disconnect both battery terminals, the engine keeps running. Finally I block the intake which kills the engine.

Thinking that I got a bum alternator, I put the original SEV alternator back in thinking that my charging issue was just me stupidly not connecting everything correctly. Same hookup, thick red to B+, green to spade, and both small reds to 61/D+

Start the car fine, shut off the ignition and the same thing happens, the engine keeps running even after disconnecting the battery until I kill it by starving it of air.

It's like the damn thing is haunted. Does anyone have any experience like this or have any ideas what might be causing it? The wiring is on an original harness and doesn't look like it's hacked up or anything, looks totally original with factory wiring bundling sleeves.
 
Followed the MS documentation for the relay connections. Engine stopped normally before I connected the other red wire to 61/D+

Unfortunately I don't know if it was the regulator wire or the amp lamp wire which was not in the correct place originally.

bobxyz said:
Let me guess, you've connected the power to the main MegaSquirt relay to something other than _direct_ from the ignition switch?

If so, can you sketch out how your MS main/fuel relays are wired versus the standard diagram from here:
http://www.msextra.com/doc/pdf/html/MS2V30_Hardware-3.4.pdf/MS2V30_Hardware-3.4-14.html
Click to expand...
 
If you connect the dashboard lamp to the wrong spade on the alternator, it can provide an alternate path for +12v when the key is off.
 
Right, but right now it's on the 61/D+ which is where the greenbook wiring diagram says it should go, and the lamp goes out after the car starts.

bobxyz said:
If you connect the dashboard lamp to the wrong spade on the alternator, it can provide an alternate path for +12v when the key is off.
Click to expand...
 
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Here's my hookup. Fuel Pump on 85 actually means fuel pump output to MS

<a href="https://ibb.co/gVh6Nqj"><img src="https://i.ibb.co/0tvQT4D/IMG-7906.jpg" alt="IMG-7906" border="0"></a>
 
OK, do you have anything else non-factory that's been connected to the "ign" wire during the MS install?

Most likely, something gets powered on by MS, which then back-powers the "ign" wire, and with the ign wire still powered, turning the key off doesn't shut off MS. I sure expect that if you disconnect the ign wire from those relays, the relays will open and it will shut off.

Edit: I don't have a B20 wiring diagram around, but there may be no load left on the ign switch wire after converting to MS, and the dashboard Alt light might pass enough current to keep the MS relays energized. When it's running without the key, try turning on the turn signals, or shifting into reverse, or turning on anything else that's not normally powered with the key out, and see if it stops. If this is the case, I think you could move the coil power back to the ign switch, instead of the MS relay.
 
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Nothing else on the ign wire other than the relays.

I'll take a closer look at that. For now I'm going to assume there's a short that has developed somewhere and start testing continuity.

bobxyz said:
OK, do you have anything else non-factory that's been connected to the "ign" wire during the MS install?

Most likely, something gets powered on by MS, which then back-powers the "ign" wire, and with the ign wire still powered, turning the key off doesn't shut off MS. I sure expect that if you disconnect the ign wire from those relays, the relays will open and it will shut off.

Edit: I don't have a B20 wiring diagram around, but there may be no load left on the ign switch wire after converting to MS, and the dashboard Alt light might pass enough current to keep the MS relays energized. When it's running without the key, try turning on the turn signals, or shifting into reverse, or turning on anything else that's not normally powered with the key out, and see if it stops. If this is the case, I think you could move the coil power back to the ign switch, instead of the MS relay.
Click to expand...
 
Being a B20 is not the problem. Its what is the B20 installed in and the details of your Megasquirt configuration. I have a 1971 142 E with a megasquirt retrofit and I had a similar problem. Once the main relay has been energized the hold in current for the main relay is very small. After turning off the ignition switch off, the charging light circuit may be able to provided enough current back through the filament of the charging light bulb to the + supply bus in the car to keep the main relay energized and the engine running.

If you have a fuel only MS installation and you are supplying the ignition coil directly from the ignition switch (normal 140 design), the ignition coil would normally draw too much current to be supplied from the charging light circuit. The resistance in the charging light bulb would drop the voltage once the current exceeded a few milliamps and the engine would stop. However, in my case I am doing ignition control through the MS and I am using coils with integrated drivers and those coils are powered up from a fuse which is supplied off of the main FI relay. If your ignition components are powered up through the main relay then as long as the sneak circuit has enough current to keep the main relay held in the engine continues to run even though the switch is off. If you have a main relay with a particularly low drop out voltage then that just makes the problem worse.

In a stock 140, the wire from the ignition switch goes to the fuse panel and then to the ignition coil + terminal and the main FI relay. Its the connection at the fuse panel that facilitates the sneak circuits that back feed the main FI relay. In my case I solved the problem by switching supply to the fuse panel to a separate relay. The coil of that relay is energized off of the 87 terminal of the main relay. The only connection from the ignition switch is to the main relay 86 terminal. If the ignition switch is turned off there is no possibility of a back feed that keeps the main relay energized and the engine running.

If you retain the original arrangement where the ignition coil is powered directly off of the ignition switch it is still possible for this sneak circuit to occur
- if you have a short circuit in the instrument cluster which is bridging the charge light filament and allowing the 61 circuit from the alternator to keep everything alive after the ignition switch is turned off.
- if you have screwed up the connection from the 61 terminal on the alternator and some how tied it directly to the + supply in the car by-passing the charge light filament which will keep things energized after the ignition switch is turned off.
- your ignition switch has partially failed and is keeping everything alive even though it is switched into the off position.

If you are having a continuous drain on the battery once you get the engine shut off, I would be inclined to suspect that the ignition switch is not turning off completely and keeping circuits energized - or that you mixed up the connections to the ignition switch
 
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Thanks for the info.

It's a fuel and spark MS installation. Ignition switch goes to the 86 terminal on both the main and fuel pump relay.

I kept everything pretty much stock as far as wiring. It's definitely feedback from the amp lamp circuit as the problem goes away when I disconnect that wire from the alternator.
I'm pretty sure there's not power sneaking through the stock fuse block and I'm pretty sure it's not getting through the ignition switch as my stereo will not power up (connected to a switched channel on the stock block) with the key off.

I also got advice to check out this article about the same issue on a different car. Suggestion was to put a diode on the amp light wire which will cut the power feeding back from that wire when the ignition is off and the amperage drops below 1 amp. For now, I'll just leave the amp light wire off.

https://www.jalopyjournal.com/forum/threads/new-alternator-wont-shut-off.349836


142 guy said:
Being a B20 is not the problem. Its what is the B20 installed in and the details of your Megasquirt configuration. I have a 1971 142 E with a megasquirt retrofit and I had a similar problem. Once the main relay has been energized the hold in current for the main relay is very small. After turning off the ignition switch off, the charging light circuit may be able to provided enough current back through the filament of the charging light bulb to the + supply bus in the car to keep the main relay energized and the engine running.

If you have a fuel only MS installation and you are supplying the ignition coil directly from the ignition switch (normal 140 design), the ignition coil would normally draw too much current to be supplied from the charging light circuit. The resistance in the charging light bulb would drop the voltage once the current exceeded a few milliamps and the engine would stop. However, in my case I am doing ignition control through the MS and I am using coils with integrated drivers and those coils are powered up from a fuse which is supplied off of the main FI relay. If your ignition components are powered up through the main relay then as long as the sneak circuit has enough current to keep the main relay held in the engine continues to run even though the switch is off. If you have a main relay with a particularly low drop out voltage then that just makes the problem worse.

In my case I solved the problem by switching the internal + supply bus for the car to a separate relay. The coil of that relay is energized off of the 87 terminal of the main relay. The only connection from the ignition switch is to the main relay 86 terminal. If the ignition switch is turned off there is no possibility of a back feed that keeps the main relay energized and the engine running.

If you retain the original arrangement where the ignition coil is powered directly off of the ignition switch it is still possible for this sneak circuit to occur
- if you have a short circuit in the instrument cluster which is bridging the charge light filament and allowing the 61 circuit from the alternator to keep everything alive after the ignition switch is turned off.
- if you have screwed up the connection from the 61 terminal on the alternator and some how tied it directly to the + supply in the car by-passing the charge light filament which will keep things energized after the ignition switch is turned off.
- your ignition switch has partially failed and is keeping everything alive even though it is switched into the off position.

If you are having a continuous drain on the battery once you get the engine shut off, I would be inclined to suspect that the ignition switch is not turning off completely and keeping circuits energized - or that you mixed up the connections to the ignition switch
Click to expand...
 
I was just going to write to add a diode to the charge light circuit. You want to go ahead and add the diode because without the charge light exciting the alternator. It won't charge unless you rev it high enough to self excite which takes revving up the engine to 4k rpm. You could use a standard diode like a 1N4001. There isn't a lot of current but you can use a 1N4004 if you want more current capacity.
 
Diode is on the way.

dl242gt said:
I was just going to write to add a diode to the charge light circuit. You want to go ahead and add the diode because without the charge light exciting the alternator. It won't charge unless you rev it high enough to self excite which takes revving up the engine to 4k rpm. You could use a standard diode like a 1N4001. There isn't a lot of current but you can use a 1N4004 if you want more current capacity.
Click to expand...
 
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