No Spark Question??
 

I have a 502 with an "all-in-one" MSD distruibuter and MSD coil. The other day the engine was running fine and then just quit. Rolls over fine but when I pulled a plug, no spark. I canged the coil and still no spark. The rotor looks ok and there was quite a bit of carbon/build up on the cap. I cleaned the cap up a little and tried it again, still no spark? What else can i check? Would like to try and fix myself but the only thing I know what to do i have already done. Any comments would be appreciated. Thanks, MIKE

sounds like you MSD box went out

Friend had the same problem, bought a new MSD box still no spark. Found out the gear on the distributor got chewed up. Check to see if your rotor is turning with cap off before spending a few hundred on a new box.

Shift interupt? . neutral safety?

I dont have a seperate MSD box, it is a Pro-Billet Ready-to-Run #8360 distributer. I tried moving the shifter a little while i was turning the engine over to see if had something to do with not thinking it was in neutral but still nothing. I will have to check if the rotor is turning. Hopefully it isnt a bad gear, that has happened to me before, because of a walking cam which required a entire rebuilt. If the coil is good, what can i check in the distributer to see if anything is bad? MIKE

You need to check and see if you have 12v at the wire on the coil. Make sure you are getting power there first.

If not, then you may have a ign switch problem, broken wire, kill switch issue(lanyard loose?), etc.

If you do have 12V, possibly a bad module or pickup in the distributor.

Im bettin that you are not getting power to the coil. Get a voltmeter or test light.

It's very common to have a lot of moisture and corrosion inside the distributor cap on MSD ignitions. Pull the cap and check the pick-up/igntion module connections. Those little terminals tend to corrode and break.

Looked at it last night and found hardly no power at the coil. My OHM reader wasnt working but when i put the test light to it, it had a very faint glow. So i checked the ignition switch wires and found the consistant hot wire very loose. I tightened it up and still no power at the coil. Also, after having the key in the "on" position for a couple minutes, the hot wire at the ign switch was extreamly hot (hot to touch) at the switch. This must be a ground issue??? I checked the grounds off the battery and also the wires at the selonoid off the starter and everything looked ok and tight. A little lost on where to go from here. Should i use a jumper off the battery to the coil to make sure everything else is ok and i have spark from there on out? MIKE

At your ign switch , check for output on the ign circut. It will be the one that stays hot when cranking. If nothing comes through the switch you can "hot wire" it there and check that power will go to the coil. sounds like a bad ign/key switch.

So your talking about the hot wire that sends power to the coil when the key is in the ON position and not the one that sends power to the seloniod when in the CRANK postition right? And when the key is turned to CRANK the other hot to the coil will maybe loose power? Would a bad ignition switch still be able to turn the motor over and also send power to the gauges when ON? Because when i turn the key to ON the the gauges do still turn on which shows that power is coming off the switch itself. Sorry, i might be rambling but i want to be clear. MIKE

Your guages should be on the accessory circut I believe. They will be cut out when cranking. The starter circut will crank the starter regardless of the ign being on. You're not rambling , I think the switch may be bad since you referenced the it heating up. Check it with your test light or preferably digital multi meter and you can work back from there if the switch checks out. You said there was no power at the coil so I'm thinking the problem lies up the line as the feed from the ign switch.

OK, that makes sense. There is good power coming to the switch but the switch itself was very hot after staying in the ON position and might be shorted out internally. If that was the case, is there anywhere else to look after i replace the switch and still have the same problem? Thanks, MIKE.

As far as tracing the problem from the coil back, does the positive off the coil go directly to the ign switch or run though somewhere else first?

Not sure , You can see the wire color on the positive side of the coil so see of it is the same at the engine harness plug , both sides , engine side and harness side. See if it is the same color on the ign switch at the helm.

Well, found the problem, or atleast one. The power wire going to my fuel sending unit was what was shorting out the power to the coil. After removing the wire from the sending unit i had full power to the coil and everything seemed fine at the ignition switch. How can this be? I do not see the correlation between the two. I know shorted wires can do crazy things... I still need to get the fuel gauge working and looks like i need to get a new sending unit because it looks like the top of the sending unit got hot and might have fried. Thanks for the advice guys, really appreciate it. MIKE

Do you mean power to your electric fuel pump? The wire going to your fuel sending unit is not a 12 volt hot wire, its measures Resistance in ohms.

No, the wire off the sending unit that goes to the gauge. I have no idea why or what the problem was unless there was a shrot somehow in the sending unit itself, if that is possible. I unhooked the red wire from the unit (the cylinder style sending unit that can be calibrated) and everything want back to narmal, good power at ign switch and to coil and i have spark. WTF??

path of least resistance !!!!!

the coil wont do work when it can go straight to ground