Duster Ignition problems when hot

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Dusterfreak

Dusterfreak

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Hi guys,

I have -71 Duster, its got 340 engine, Mopar distributor, MSD 6AL, MSD Blaster coil. Also got ministarter and electronic fan. No original resistors in the ignition.
Problem is when I drive around and the engine gets to 200 and I stop to MC or grocery store,it wont fire up immediatly. It starts but it wont fire, my rev meter dimms when normally the needle jumps a bit and the lights are on. I think hot engine cranking needs so much power that the MSD dies, could it be??
Problem only occurs when its over 180, that is so strange. last summer I bought a new battery and I had no issues, but now the problem is back. Has anyone ever experienced something like this??
 
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Very first thing to do is "catch it" when it's hot, and rig a multimeter to the battery, then crank it by jumpering the starter relay. That will leave the ignition "off." You want to see at least 10V at the battery when cranking.

If that is OK, try to access the MSD "big red" which is the main power, and should be connected "hot" all the time. See what that is when cranking

Another thing is to "rig" a spark tester and see what you have for spark........

This also could be fuel problem..............
 
Check the pickup coil in the distributor also pretty common to fail when hot.
 
does it crank at the normal speed or slower?
 
try backing down the eng timing a few degs and see if it cranks faster or just pull coil wire off and ground it to the engine and see if it turns over faster, if it does your timing may need to be set back a few degs
 
What happens if you just wait 20 to 30 minutes?
If it fires right up now, then your fuel system is probably just fine.

If you cannot trace it to ignition, I would normally recommend an engine LeakDown test, but in this case, with the lights dimming thing going on, I would suspect the starting system. But since this is an ongoing problem, I would suspect the pistons are swelling up in the bores. This happened to me, with KB 107s. The spec is .0015 to .0020. I was already baggy at .0020/.0025. I gave her another .001 and that was the end of it; But I run a minimum water temp of 205*F. Your results may vary.
 
If I wait 10-15minutes it`ll fire up like a charm. Also when the problem is on, it starts when I release the key. So its like the MSD dies while the key is in start position and when I release the key it gets a spark and boom, its running. What if the starter gets in short when its hot and sucks all the power?? Should I try with a new one...
 
Dusterfreak said:
If I wait 10-15minutes it`ll fire up like a charm. Also when the problem is on, it starts when I release the key. So its like the MSD dies while the key is in start position and when I release the key it gets a spark and boom, its running. What if the starter gets in short when its hot and sucks all the power?? Should I try with a new one...
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If it lights off when you release the key that means your problem is in the 12v switched ignition feed to the MSD box. You have 2 wires on the the ignition switch circuit going thru the firewall that provide 12v to the small red wire (switched ignition input) to the MSD box. When you are cranking the brown wire has 12v, when you release the key to run the blue wire has 12v. Start at the MSD switch ignition wire and work your way back to the ignition switch. Don't forget to check the firewall connector.
 
But why its only when the engine over 180?? Never, ever, ever during cold starts.
 
Dusterfreak said:
But why its only when the engine over 180?? Never, ever, ever during cold starts.
Click to expand...
That's why I said to check the firewall connection. Heat expands things (thermal or electrical load ie high resistance in a connector, and you could be losing contact. If you've ever disconnected a firewall connector and seen the crap inside you would understand. Work your way from the MSD box to the ignition switch.
 
Click to expand
67Dart273 said:
Very first thing to do is "catch it" when it's hot, and rig a multimeter to the battery, then crank it by jumpering the starter relay. That will leave the ignition "off." You want to see at least 10V at the battery when cranking.

If that is OK, try to access the MSD "big red" which is the main power, and should be connected "hot" all the time. See what that is when cranking

Another thing is to "rig" a spark tester and see what you have for spark........

This also could be fuel problem..............
Click to expand...
 
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