kumowoon1025

Hi everyone, newbie here,

I just got a 1993 convertible, it's a fixer upper.

First problem I'm tackling is the engine not stopping when I turn the ignition off. It looks like it's almost going to stop, the lights dim, and the tach needle drops a bit, but it goes right back on again.

I was trying to check if the alternator diode was shot (do car alternators have diodes in them??) by running the engine with the alternator disconnected, but it won't start? I was really confused by this. I should be able to start the engine without the alternator, right??

Is there any way to test the alternator diode theory? Should I add a diode to the positive connection outside the alternator? If so, what ratings do I need on the diode?

Thanks in advance,
Ted

SELLC

Sounds like you got some kind of back feed going on there. May be the result of a poor ground or relay of some sort. I'd check the lead from the alternator so see what else it's branched to, then check them circuits out for an issue as well.

And yes, you should be able to run your vehicle with the alternator disconnected providing the batter has enough charge. Might not run for long, but it should still run.

Ratboy

Ignition switch, unless its really low miles.

kumowoon1025

Brand new ignition switch (previous owner's suspicion as well), so it's not that, or really unlikely at least.

Any pointers as to which relay I should look for? The one I can think of off the top of my head is the starter relay but that really shouldn't come into play when you're turning OFF the car, right?

Also now that you confirm that the car should start without the alternator, it is driving me crazy although its a separate issue. Like what could possibly happen by me unplugging the alternator that won't let the car start??? It's not even turning when the car's off, it doesn't do anything to start the car!

Cliff Harris

When you start the car the alternator is not involved since it's not rotating (or at least rotating very slowly). Sounds like you are missing a connection somewhere that connecting the alternator replaces.

Alternators do have diodes inside them. 6 to be exact. They are called diode trios and there are two of them. The alternator generates 3 phase AC electricity, which is rectified and transformed into pulsating DC voltage by the diodes.

Ratboy

Is there an aftermarket alarm system? If so, remove it.

pcolt94

Check the connection linkage and the adjustment/position of the switch.

kumowoon1025

I think its stock... I haven't removed the dash yet. Can you explain how the alarm system might be causing this? I don't really understand.

kumowoon1025

I can't really think of a way the alternator completes another separate circuit... Really need a service manual.
I did a quick'n'dirty check by checking for AC output at the alternator with the engine running. It's sub-10mV, so I think the rectifier diodes are good.

Thanks for the suggestion. I checked, and the switch seems to have been installed correctly, unless the switch rod thingy was deformed.

While I was down there, I thought to check the wiring from the switch to the ignition, and the ignition control module connector (the two wire connector labeled A and D) is missing a wire. It only has a green wire going to A. It's supposed to have both, isn't it?

EDIT: I'm not actually sure if I was looking at the ignition module connector... It's located on the lower passenger side of the engine. Is this the ignition coil module connector?

Could someone help me find a wiring diagram? I subscribed to the repairsurge one but it does not work (diagrams won't load...) and is missing a lot of info. A pointer to a good service manual to get would also be appreciated. Thanks.

JimLentz

What happens if the car is running and you pull the connector off the alternator and then try to shut off the car?

kumowoon1025

I wanted to try that, but it didn't feel very safe. Sparks happened when I went to remove the pos terminal (chassis grounded, so no go on the neg). Is there a safe way to do this?

JimLentz

Not the positive terminal but the connector that plugs into the alternator.

kumowoon1025

there isn't one. The positive lead is bolted onto the positive terminal by a ring connector, and the alternator is bolted into the bracket ground.

EDIT: I just realized I said I tried to remove the positive terminal of the alternator, sorry that was an error haha. I did NOT take apart the alternator with the engine running. What I meant to say is that I tried to remove the positive lead, but sparks flew off so I got scared off.

kumowoon1025

I went ahead and disconnected the alternator while the engine was running, still wouldn't stop when I turned the ignition switch off.

Still looking for suggestions...

WVZR-1

I've sent you an email using the link in your user ID.

Is the car an A4 (auto) or a MT (6-speed).

VikingTrad3r

Fascinating!

I am an L98 guy and my ignition knowledge is limited but personally, id lean towards a short in the system downstream of your ignition switch. Id be looking for a place where either a wires rubbed together or some other previous install created a situation where 12v is being applied to te ignition wire between the ignition switch and the ignition switch is overridden as such.

or, id look for the tach indicator (again, im an L98 guy, not sure if its relevant for the LT1) which the ecm uses as a feedback to keep delivering injector pulses.

There was recently an L98 "dieseling" thread that was resolved in the end, cant recall how but reading it might give you some ideas.

Hooked on Vettes

Remove the 10amp coil fuse located in the passenger side end of dash fuse box position 25.

When the ignition is OFF there should be no 12 volts at the Coil fuse. The 12 volts comes from the Ignition Switch which may have defective contacts inside of the switch or is misadjusted.

The switch is held in position by a nut and bolt. It can be moved up and down the steering column.

kumowoon1025

It's a manual, thank god. At least I can stall it :s

I'm trying to check the wiring, but it's currently a cluster**** down there. If anyone has a wiring diagram for the ignition switch, I'd be much obliged.

Okay, I checked the voltage at the fuse box, and here's what I found:
When I turn the ignition to the "off" position, there's 0 volts at the coil fuse. As expected, right?

When I start the engine, and turn it off, then remove the fuse, the engine shuts off (also as expected). BUT, immediately after, there is 12V at the coil fuse, which drops down to 0 (over several seconds). Which made me think maybe it's the alternator back feeding into the circuit, but the engine keeps running when I turn the ignition off and disconnect the alternator. I'm just completely lost.



If I had an unlimited budget + time, I would rewire the whole car, it could really use it, but as of now, I'd like to pinpoint the problem and repair it.

antfarmer2

Have you tried to ajust the ignition switch?

kumowoon1025

I was going to, but when I dropped the steering column, the switch was in the furthest position (lock i think?). This was with no key in the lock, so I thought that was good and left it alone. Should I try taking it off and remounting it? At this point I'm starting to think calling an exorcist wouldn't be such a terrible idea so any suggestions are welcome.