engine dies like a switch was thrown

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68 Wagon
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Location: Bozeman, MT area

engine dies like a switch was thrown

Post by 68 Wagon » 18 Jul 2018 10:28

I have a 78 L20b with matchbox EI in my 68 Wagon and the other day it just quit me (luckily close to home). Cranking did no good. Friend towed me home. I put on another known to be good matchbox control module and tried cranking again....nothing. I pulled #4 plug and set it up on the valve cover so I could look for spark....no luck seeing anything.....so turned ignition on, undid the black/yellow wire from the starter solenoid and jumped with screwdriver.....Be damned if it started instantly pumping air out of #4!!! Turned her off, put #4 plug back in, reattached black/yellow wire to solenoid, vroom, started right up again....and again....and again.....hmmmmmmmmmmmm. Figured I had rid myself of whatever "gremlin" was in there so the next day jumped in started out and made it about 1/4 before the same thing happened again....just shut itself off.

Anybody have this same bugaboo? I'm thinking a hidden broken wife somewhere but before I go replacing "everything" I thought I'd ask.

Thanks, Scott
I've been driving 70's Datsun sedans, wagons, and roadsters almost every day since 1983!

datzenmike
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Re: engine dies like a switch was thrown

Post by datzenmike » 19 Jul 2018 17:55

Not running but headlights work. Not the fusible link...

Crank the engine over and check for spark by holding coil wire near ground or use an old spark plug. Got spark?

Yes.... pull a plug wire off and check for spark. Confirmed no spark. Problem is between the coil wire and plug wire. Distributor cap or rotor carbon tracked or cracked and spark leaking away. Possibly a bad plug wire but not all 4.

No spark ... Check for power on the coil positive terminal with test lamp. Got power???


No power at coil positive terminal when ignition turned or during cranking would indicate a faulty ignition switch or loose plug to the ignition.

Yes there's power to coil. Make a jumper wire and briefly ground the coil negative terminal and release. Got spark???


No spark coil is faulty, probably heats up and quits.

Yes, spark See my next post below
Last edited by datzenmike on 20 Jul 2018 19:44, edited 1 time in total.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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Byron510
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Re: engine dies like a switch was thrown

Post by Byron510 » 20 Jul 2018 06:24

Intermittent electrical issues are tuff to locate.
Did you have power and signal from the EI module itself back to the coil? And was there power at the coil itself? That’s a good place to start.
There is a very good chance you just moved a conection or a connector somewhere in the process. There is always a chance of a broken wire, but unless the harness has been physically damaged it’s notnlokely hidden. Most often it’s a component that fails, or a conection at a plug.

Keep us posted.

Byron
Love people and use things,
because the opposite never works.

datzenmike
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Re: engine dies like a switch was thrown

Post by datzenmike » 20 Jul 2018 19:43

Ah... EI.

If power to the coil on the positive terminal, and a jumper to ground on the negative side produces a spark, then the problem is somewhere in the distributor.

Image

1/ Check for power right at the B terminal on the module.
2/ Check that the wire from the C terminal on the module is solidly connected to the negative side of the coil.
3/ Make damn sure the distributor is solidly GROUNDED to the engine, Even run a ground wire to it to be sure. No amount of parts replacement will fix an intermittent ground.

If everything checks out... Next time it quits pour cold water over the matchbox module to cool it down. If it restarts the module is affected by heat.



Image

Here's a great replacement for the matchbox module using the $10 HEI unit from an early 80's GM mullet mobile.

Image

Some people build elaborate heat sinks but this thing works inside the distributor cap just fine. Outside like the picture will be 5X better.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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toylet
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Re: engine dies like a switch was thrown

Post by toylet » 21 Jul 2018 17:59

I had a ignition switch that was causing my die in flight issues.

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