Mysterious engine dieing...help - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-06-2002, 09:28 PM
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Mysterious engine dieing...help

Sorry I haven't been on the board in quite a while. I'm in the Air Force and just moved to California, moved again and then the 11th came and finally I'm back home for a little while.

On to the problem...Been driving the 79 CJ7 w/304 and complete Team Rush upgrade with all MSD parts for about a year and a half with no problems at all. Friday it died on me 4 times just like someone cut the ignition off. The only thing different about my setup is I have the switched 12v source for the MSD box on a 30 amp switch under my dash for a little theft deterrent. This weekend I went through the entire fuel and ignition system. Nothing wrong with fuel (or air or vacuum), replaced the filters just in case. Went thru the ignition and could find no loose/frayed wires or bad grounds. Cranked it up and it ran for about 5 minutes and died. Pulled the coil wire on the distributer and checked the spark on a ground by jumpering the two pickup wires off the distributer...nothing. I had 12v going to the MSD box. Jeep sat for 2hrs while I went for parts. Came back, checked for spark and got one. Jeep cranked right up. Ran for 5 minutes, died, checked and no spark. Changed coil...checked for and got spark. Jeep cranked right up ran for 5 minutes and died...checked, no spark. Sat for 5 minutes, checked for spark again and got one.

Any clue as to what's going on? Is it a heat thing? Is my MSD box on the fritz. When the engine is running there is about 14.7 volts going into the MSD main power wire. Too much, maybe frying stuff? Any help is greatly appreciated. Like I said it's been running great for over a year and I'm very pleased with the setup.

Thanks,
Jeff

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post #2 of (permalink) Old 01-06-2002, 10:13 PM
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Re: Mysterious engine dieing...help

Just moving it backe up, I'm at a loss here.

post #3 of (permalink) Old 01-06-2002, 11:27 PM
 
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Re: Mysterious engine dieing...help

When you say, "Main Power Wire" to the 30 amp switch, do you mean the small red wire or the Large red wire?

If you added a bunch of wire and a 30 amp switch to the large red power wire you screwed up big time...
MSD modules LOVE current, and draw way more than 30 amps, (Hence the 8 Ga. input wire...).
Lets hope you didn't ruin the switching transistors...

Lucky for you, MSD has the best Tech department I've ever seen, and they will repair almost anything but gunshot wounds for free or cheap, (usually shipping and insurance, one way, they pay the return trip)
If they open the box, they will put ALL NEW INTERNALS IN every time...

Give them a call, Tech Line 915-855-7123, tell them what's going on,
(only I'd 'forget' to mention the 'switch' if I were you...)

In the future, if you want to disable the MSD unit, run the small white wire to your switch, and ground the other side of the switch. This will keep the box from firing, and effectively kill the ignition.

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post #4 of (permalink) Old 01-07-2002, 09:01 AM
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Re: Mysterious engine dieing...help

Not the main power wire. (it's running to the + side of the starter silenoid) I have the swithced 12v wire that turns the MSD on running to a 30 amp switch instead of the ignition. I sent MSD an email. I'll give them a call too, thanks.

Jeff

post #5 of (permalink) Old 01-07-2002, 11:14 AM
 
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Re: Mysterious engine dieing...help

If you used the small red wire to the switch....
(Still, use the white wire as your grounded kill switch)

And this problem started after you installed the switch... I'd take the switch out of the circuit and see if the problem still exists.
You may have a bad switch.
If even a very tiny amount of voltage leaks through that switch, your MSD module will stay 'ON' ...
Staying turned on continuously will take it's toll on the unit.

The switch may be leaking to ground internally. (Something loose inside)
Wish I had a dollar for everytime I ran onto a bad switch....
----------------

You might also want to check for even the smallest tear in the insulation, so your voltage isn't going to ground somewhere...
Running wires through the firewall has a tendency to chew them up sometimes...
Even the smallest ground on the wire going to your switch would cause the problem you describe.
<hr>

You may want to try some test procedures.

Connect a test light (any small light socket with two wires so you can put it anywhere...) to the red wire that originally went to the positive side of the coil.
One side to the ignition wire, the other to ground.
This will let you know if the problem is in the factory side of the wiring. Ignition switch, connectors, fuse box, ect...
If the light goes out when the ignition is 'ON', it's going to be a pain in the butt to track down!
----------------

If the Jeep dies, and the light stays on, then it's not the common ignition feed side of the circuit, and that rules out a lot of pain in the butt testing...
----------------

Next is the distributor input to the MSD module.

Check your connections! These operate at a few tenths of a volt, so anything in the connections will cause problems.
MSD doesn't have water tight connectors on anything but the Off-Road module, so that might be a worth while upgrade...

You also need to do a visual and Ohms test on the Hall Effect trigger. (replacement is $15)
But I suspect the wiring a lot more than the trigger.

ALSO...
While the ignition is throwing one of it's 'Fits', you can use the white wire to trigger the module.
Just 'spark' it against ground, and the module should fire the coil.
But with an intermittent problem, it's going to be hard to tell when the system starts working again....
-----------------





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post #6 of (permalink) Old 01-07-2002, 02:53 PM
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Re: Mysterious engine dieing...help

I tried it with the small red wire on the original switched 12v source (not using the switch) and it died in a couple of minutes that way too. I also let it run while I had a voltmeter on the swithced 12v wire. 14.7 volts when running then it dropped to 12.5 when it died. Is this essentially the same as putting a light on it? I'll check my wires thru the firewall to make sure nothing is frayed. Maybe the switch is leaking internally and has screwed up the MSD. I've checked immediatly after it dies and I still have 12v on the small red wire, 12v on the 8ga red wire, and good grounds everywhere. Then when I jumper the distibutor pickup I get no spark off the coil wire. After it sits for a little while it goes back to normal and I can produce a spark. It makes me think there is something switching/grounding/overheating internally in the MSD unit? Thanks for taking the time to help, cuz man I'm at a loss. Oh yeah I do have the offroad unit and all my wiring is either in tubing or is cold shrink wrapped.

Thanks,
Jeff

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