If this thread is in the wrong place, I apologise. 1979 Bronco 351 engine, MSD 6AL box and MSD distributor. Started out with an intermittent no-start issue. I was troubleshooting that issue, checking voltages ETC. while the owner was spinning the engine over when I asked him to. I had the main plug unplugged checking voltages, and plugged it back in to check something, told the owner to spin it over, and it fired right up. Every time we tried it, it fired up with no problem. Long story short, he wanted to replace the fuse box to go to one with blade fuses so I did. Got most things rewired correctly, and it never failed to start until a few days ago. I re-checked all voltages and all were good, except the battery possibly seemed a little weak. Spoke with Holley Tech Support and they stated that a low battery could keep it from starting and I concur with that. I did manage to get it start, pulled it back in the carport and put a slow charge on the battery. Next morning, fires right up again and did just fine every time until it didn't. Next step, I charged the batt again, left the battery charger connected and ran a wire straight to the IGN wire going to the MSD box. wouldn't start. No pulse to the coil. I was sure the box was not telling the coil to fire. I contacted T/S again, explained the problem again and told him everything I had done to this point. OBTW, on occasion, it still would start, other times, it wouldn't. Sounds like the box took a dump. T/S guy said the box could not have an intermittent problem, it either works or it doesn't per him. I have been working in electronics pretty much my whole career, and I can say components can work sometimes and not others. Components can have heat related issues, cold solder joints, and a lot more reasons that will cause intermittent problems. He is determined it is a wiring issue. I am running the two main power wires straight to the box from a battery junction block for the POS, and the NEG is hooked straight to the battery. I also ran a wire from the B+ terminal to the wire that feeds the box from the ign switch with a voltmeter reading the voltage while cranking and I have good voltage going to the box. Lowest it ever got was 11.9 after I had been cranking it for a minute or so. I'm convinced the box is failing. Am I overlooking something? Not using the rev limiter at all BTW. Suggestions?
@drummertom55 This help , last few pics Tech / Test . If a better pic needed let me know the page. You can byp*** box @ coil & that will tell you Box or other issues out side of MSD , from what I can remember Ford had issuse with box on fenderwel Ignition module? I would By p*** MSD & test run for a few weeks to see if a No start happen again ,,, Intermittent problems are damn headache BUT MSD Usually good or bad as in No Start or Start . Also MSD pulls 1 amp per every 1,000 rpms . So @ 6,000 rpms 6 amp's. On 5 & 6 box's
I remember chasing an intermittent wouldn't run condition on an older Ford until I about pulled my hair out. The vehicle had a MSD and a new coil. The problem was eventually found to be the ignition switch. While you try to start it, have a volt meter on the coil positive. The ignition switch has a separate lead that provides voltage while cranking that is not reduced voltage. The run wire from the switch is separate and has the voltage reduced as to not burn up the coil. If you do like most, you test the coil lead with the ignition on, and it has voltage. Test it for voltage while cranking and if it doesn't have it, you'll now know why. It's one of Ford's better ideas.
The Jalopy Journal
