ignition problem

[Kennymonster]

Bear with me guys, just got a s30 after owning a z32 for several years. I got very familiar with the VG platform, but have never worked on a carburetor vehicle before.

Quick summary:

- Ran fine as of 2 weeks ago, just had carbs tuned by a mechanic.

- It sat for a week, few days ago I drove it around the block a few times to get used to the 6 puck clutch. I noticed a major stumbling/hesitation under load.

- Yesterday, I had planned to get the timing checked and carbs retuned to address the stumbling hesitation, couldn't get the motor to start. Realized the battery had gone dead. Flooded it in the process of trying to get it going so I can limp to the shop, didn't happen.

- Put in a new battery(25-DL), it cranks fine, now it won't spark. Another look see and saw that the ignition coil has been leaking oil.... must've been for few days. It was overly hot to touch. The vehicle is a 240z with L28 and MSD ignition system.

Ok.. so I replaced the coil (with a non MSD brand if that matters), cleaned the plugs. Nothing.

Distributor spins, rotor is clean, just not getting any spark from the coil. + and - cables on the coil has power, the main cable from coil to distributor has none.

I honestly don't understand what could've gone wrong between swapping batteries, but the coil's been leaking for a while maybe that killed the module? I'm not sure where to go at this point since I think I covered the basics, anything more extensive is foreign territory to me.

edit: The new ign coil also gets overly hot to touch, can't rest your hand on it for more than a sec. I cleaned all the grounding wires.

Edited December 11, 2010 by Kennymonster

[Unkle]

Are the cables / wires put back the way they were before a new battery was put in ? Did you have the new battery tested ? Did you test the module etc. ? Is the vehicle properly grounded ?

Edited December 11, 2010 by Unkle

[Kennymonster]

No wiring changes were made... just a simple battery replacement. I'll have to look over the grounding wires again, hot coils and no spark is making me look that way but apparently it came undone by itself somehow since I didn't change anything else.

[FastWoman]

Doesn't your 1972 240 have points ignition?

Check that the (+) post of your coil gets 12V when you turn on the ignition. Disconnect the wires from the (-) side of the coil, and measure the resistance between those wires and ground, while you crank the engine. You should see the resistance alternating between zero and infinity (pretty sure about this). If not, there's probably a problem with your points, condenser, or wiring from the distributor to the coil. With the wires still off the (-) post, measure the resistance between the (-) and (+) posts of the coil. Resistance shouldn't be infinite, and it shouldn't be zero-ish. (I don't know what a normal resistance would be.) Points ignitions aren't really my thing, but that might get you started.

[Kennymonster]

It currently has a MSD hook up, http://www.msdpowersports.com/pdf/frm22049_pn8920.pdf

All the wiring seems connected, nothing's been changed since last operation except for the coil itself.

On ignition, I'm only getting ~9.8 at (+) coil post though.... not 12. Hard to think it's battery related even though I haven't tested the new battery.

Edited December 12, 2010 by Kennymonster

[Zed Head]

You might have a short on the negative side of the coil. Current runs through the primary windings of the coil to charge up the secondary windings. The MSD breaks the circuit to the primary to fire the secondary, creating spark. Not technically rigorous but essentially what happens. If your coil is getting hot it's because there is too much current flowing through the primary windings, all the time. It could be shorting through the MSD unit or a crusty wire or a dirty terminal or through anything else you have connected to the negative terminal (aftermarket tach? or whatever). This would make your coil hot but not give spark since the MSD can't break the circuit.

Forgot to say if you're measuring 10 volts this could also be signs of a short.

Full disclosure - This not an area of expertise for me...

Edited December 12, 2010 by Zed Head

[Kennymonster]

^Thanks for the feedback, expertise or not it makes lot more sense than what the diagrams told me

That seems to be exactly what's happening, the replaced coil has also started leaking after I left the battery hooked up for couple of hours, unintentionally while I was out, started dripping oil.

Something definitely is shorted or not making contact, probably during my first attempt when I was trying to force start it with a weak/almost dead battery. The problem is now finding exactly where the cause of the shortage is...

[Kennymonster]

Update: I left the negative terminal unhooked overnight on my new battery (mainly because the coil gets superheated), after failing to find the culprit yesterday. Today I hook it back up, the battery is almost near dead.

I've ran out of time officially since the week's started, I'm now looking into getting it towed to my knowledgeable z mechanic. I will update when the situation is resolved, thanks for all the feedback guys.

[SteveJ]

Can you clarify something here?

First, was the coil getting hot even when the ignition was off? The coil should only be energized when the ignition is on.

Of course, the battery dying and the coil getting hot are related. You have a big time short. I don't know enough about MSDs to say one way or the other that it could be the cause.

[Kennymonster]

^That's correct, it would get overly hot without the ignition engaged.

That is the reason why I left the neg battery terminal unhooked overnight, but to my surprised the battery was completely drained in the morning.

If not the MSD, which worked perfect for 2 years according to the previous owner, would there be any obvious place for the short? I might've tried to crank it little too long while the first dying battery was going out, but have not made any wiring changes (that I know of.)

[Unkle]

Maybe the cables are shot - underneath the plastic / rubber coating there could be massive corrosion . Tough to know unless you take it to a reliable shop at this point maybe...

[SteveJ]

Thank you. That helps a lot. Look at the wiring in your steering column, in particular, around the ignition switch. Look for damaged/melted wires or connectors. Also check where the dash harness goes to the engine harness. I have a strong suspicion that the short is in the wiring the steering column.

Focus on these three wires: White with red stripe, Black with white stripe, and Green with white stripe. I really suspect that the short is between the White/Red and Black/White wires since you saw 9.8 volts at the coil. The Black/White wire goes to the ballast resistor before going back to the Green/White wire. On the other hand, the low voltage could have been from the battery draining.

When you turn the key to Start, the contacts close between the White/Red and Black/White. When the key is in Run, the contacts close between the White/Red and Green/White wires. If you don't see any physical damage to the wires, there is still some testing to do.

Disconnect the plug from the back of the ignition switch. With the key in the Off position, look for continuity between the contacts for the White/Red wire and Black/White wire. Also check for continuity between the contacts for the White/Red wire and Green/White wire. If you see continuity in either case, replace the ignition switch.

Whether or not you saw continuity on the ignition switch, you should also test the wiring for continuity. You can push spade lugs into the connector to give yourself a place to measure continuity. With the battery disconnected (positive and negative), look for continuity between the White/Red wire and Black/White wire. Also check between the White/Red wire and Green/White wire.

If you don't find physical damage and you don't have continuity between the circuits, that pretty much clears the stock wiring from being at fault.