[fat50chevy]

I have read and read pervious post and already done a little trouble shooting but the bugs took over tonight.
I have a mild built 350 chevy in a 50 chevy truck. I had a stock HEI in it and it ran fine but had a firewall clearance problem so I changed to a small body HEI and ext. oil filled blaster 2 MSD coil. The problem is when the engine gets up to temp. it dies at idle, it will start right back up, run for 30-45 sec. then die again. Idle is set at about 750-800 (no tach). New wiring harness before changing dizzy and no ballast resistor in use. The dizzy was removed sent back to the manufacture, bench tested, placed in another vech. tested everything was fine. Got it back, dropped it in today, same problem. I had the coil checked before I sent the dizzy back and went today and bought a dig. volt meter and checked it again myself. 00.7 primary and 11.8 sec. I will check the charging system tomorrow for 14.2 to 14.6 volts as suggested by the manufacture of the dizzy. I will also get the engine up to temp. and check the coil while hot. A friend suggested I my have a vapor lock problem, I tend to rule that out because I never had one before. Sorry this is so long , But just looking for other thoughts, suggestions or perhapses a todo list from the Doc. Thanks for any input.

[docvette]

Doc here,

Pull the module and have it checked several times..be sure it's warm during test..

Sounds like the module is going thermal .. a very common problem..

If you need a new one, have it tested the same way before you leave..and installing either make sure you use the heat sink grease..of you'll be doing it again real soon!

Doc

[fat50chevy]

Thanks Doc, When I sent the dizzy back to the manufacture he tested the module and magnetic pickup under heat conditions found them to be good but changed them both out anyway and retested. The manufacture is very knowledgeable and helpful. It was his idea to send it back so he could insure proper testing was done. That said, I will check it as you suggest but I also need to check everything I or anybody else can think of. The only other thing changed was the coil. Thanks Doc I will keep you informed. Its my last day off for a while so I'll get to work. I don't think I am suppose to drive this thing just work on it, oh thats hot rodding is'nt it. Thanks Doc

[docvette]

Doc here,

Just out of curiosity, this wouldn't happen to be Dave's Small body HEI's would it?

Check the module yourself, It's the only thing that will go thermal on that system..It's not uncommon to get a bad run of them..

Other than that, make sure you didn't mis~wire the Coil + to something like a Fan Relay?? or something going on/off with a temp range..

Try running a direct wire from battery to Coil + and see if it happens again..that'll tell ya if it's thermal or wiring..

Doc

[fat50chevy]

Thanks Doc, I did'nt get to pull the dizzy today to check the module but will try tomorrow before work. I did check the coil primary and sec. while hot same results 00.7 and 11.5. also checked the charging system at around 2500 RPM a pretty steady 14.45 to 14.50 . That was taking the readings from the coil + to a known engine ground. I will also try the wire from batt to coil + , but I am sure it is wired correctly and no temp relays in the system. I do have a fan installed but its manual sw no relays. I thought of that today while checking the charging system and turned it on to see if it had any effect. When I first turned on the fan it dropped to about 14.10 then went back up to 14.45 and engine did not stall during that time. I will let you know on the module,, Thanks

[fat50chevy]

Well Doc, It's going for now. I just drove it around for about 15 min. after letting it get up to temp and no problem yet. I took the module out and took it to auto zone. checked it 9-10 times bad, got a new one ck 9-10 times good, KICKER, then they ck the one I took them again 9-10 time and it ck good, Got a little concerned so took it to another store again 9-10 time good. So I came back home took my old HEI apart and put that module on the new dizzy. Used that wells grease a fair amount ( more than was on it before but not too much ). Anyway, it's going for now and I have ran out of time today. I will get a new one, nice to have a spare. And there is nothing like original GM parts. THANKS so much for your help, but stand-by there may be more to come.

Street Rod Nationals in town next month and I want to be DRIVING not wrenching.

[docvette]

Doc here,

If the module was not damaged in thermal cycles, It should hang in there.. If not you have a new spare.

One thing those testers can't add, is the added temp of the oil and engine heat transferring up the Dizzy shaft..(as high as 250 degrees..or the heat of the oil pump) They can only add the heat of the electrical load.

Keeps updated!

Doc