72 GMC Ignition problems

[Frijolito1988]

Hey guys, got me a 72 3/4 ton a few days ago and im trying to start it up. For the most parts it looks like most all the wires are a mess so trying to see if the engine is good (400 big block ) if so I will probably keep it instead of parting it out.

The truck cranks over for days ( giving the starter 12v direct ) has new starter, and has good fuel pressure but it has no spark. Took the spark plug wires out to see if i can arc them and nothing, got a 12v tester in one of the spark plug wires and nothing, I am giving the distributor straight 12v from the battery but it is not distributing anything to the coils. I had another distributor cap laying around put that one on and nothing. what can be causing the problem ? ignition module ? Should i just get a new distributor cap ? HEI ignition coil ?

Break down.

Giving the starter straight 12v

Giving the distributor straight 12v

Engines cranks fine and strong

No fire just crank.

Distributor not sending any spark to the spark plugs.

Much appreciate it guys.

[Frijolito1988]

Also like mentioned the wiring is a mess truck will not crank at all with key. Has killer switch and towing hitch / stereo wires all over. So I am starting the truck straight from a battery , trying to test it first if the engine is good before i go head in first to the complete truck wiring.

[TBONE1964]

Is the button under the coil good? These will burn off after some use and cause a no fire condition. Did you swap your existing coil to the different dist cap? What does the underside of the ign rotor look like? is it burnt?

You can also pull the ign module and have it tested at most parts stores.

The other thing maybe a break in the wires for the pick up coil. These wires move with the action of the vacuum advance and will break internally over time.

[geezer#99]

Could be a bad ground in the cap too.
Here's a link for troubleshooting.
http://www.crankshaftcoalition.com/w...EI_distributor

[TBONE1964]

Originally Posted by geezer#99

Could be a bad ground in the cap too.
Here's a link for troubleshooting.
http://www.crankshaftcoalition.com/w...EI_distributor

Excellent link with a lot of very good information.

[geezer#99]

THanks!
I do most of my searches with google images. Ask for what you want and a 1000 pics come up.

[motorcritter]

Test every component- get a local parts store to check the coil and ignition module, make sure the coil ground strap is intact and the wires and connectors in the distributor aren't cooked and nasty. I gather from your OP that you're running a stock HEI.
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[swamp rat]

Originally Posted by Frijolito1988

Giving the distributor straight 12v

.

Unless my Chevy is different i believe i have a ballast resistor so my distributor does not receive straight 12V.

[geezer#99]

Originally Posted by swamp rat

Unless my Chevy is different i believe i have a ballast resistor so my distributor does not receive straight 12V.

Yours is different only in you have points and he has an hei!

[Frijolito1988]

No luck,

I managed to fix some wires and now the truck cranks with the key , instead of me having to connect a wire to the + of the battery, but no spark yet.

I changed the module, cap , rotor , coil.

[am0254338]

Here is a link that has a HEI Diagnosis section that could be helpful http://www.chevelles.com/techref/ftecref5.html. Sounds like you have changed all the normal stuff. I would be tempted to try another new module. I work at a shop and we get bad new parts weekly.

[Dodge]

make sure youre not hooking the 12 volt feed to the tach connection on the HEI

[bigmac73]

i would check to make sure you are hooked up to a hot ignition source, so if they tied into the old resistor wire for the old points or ran a new wire to the fuse box, to a ignition circuit
sounds like you are not getting any juice to the dizzy

[Frijolito1988]

So it started!! now it wont again lol

It started for a good 4-5 seconds then i shut it off, turned it back on and now nothing same.

I tried 2-3 differnt caps / coils untill i used the one of my dads 67 and thats the one that cranked up, but now it looks like it burned the coil.



What can cause a burned coil condition when ever its started ? I am giving it 12v but after it turns on i think it burns the coil at the same time, could it be an internal distributor problem ? Should I just replace it ?

[Frijolito1988]

also, the way i was kinda testing the coils was I would connect the cap with coil with the bat+ and the 3 wires that come from the distributor , and I would test the center of the coil ( under the cap with a 12v tester) I would just get ground or continuous ground until i used the cap that gave me nothing, no ground nothing and i tried it and it cranked with that one.

I guess when the coil is bad, is just acts a ground ? Instead of killing the power ?

[Frijolito1988]

Also another thing. I realized that I have the tack wire that comes from the distributor un covered. If that makes contact with any metal sparks fly , Will that burn the coil ?
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[El Campo]

Make sure that you have a good solid 12 volts to HEI. Mine was notorious for not starting, misfiring and not running if it didn't have a dependable 12 volts to distributor. Even when I ran a wire straight to the distributor from battery it still wasnt enough because my battery was not fully charged. Eventually got tired of fooling around with it and threw it away and bought an entire MSD system. Best decision of my life!
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[Frijolito1988]

Ignition Condenser ?

So reading thru this, this condenser is that regulates the voltage ? If the condenser is no good then it can give too much juice to the coil it burns it ?

[Frijolito1988]

Originally Posted by El Campo

Make sure that you have a good solid 12 volts to HEI. Mine was notorious for not starting, misfiring and not running if it didn't have a dependable 12 volts to distributor. Even when I ran a wire straight to the distributor from battery it still wasnt enough because my battery was not fully charged. Eventually got tired of fooling around with it and threw it away and bought an entire MSD system. Best decision of my life!
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I think i might just have to do that, but trying to see if the if its the little stuff.

[Dodge]

Just run a wire right from your battery positive post straight to the dist. Then start it with the key. I have done this many times. Really not much chance all those coils were bad. Only thing that really ever goes bad to the point of not firing in hei is the module. If u have run a hot wire from somewhere that is dead while the starter is engaged then u will have no juice when you're starting it. i.e. the radio, wipers, fan ect.
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[Frijolito1988]

Well it was a burned coil and the carb is no good. It leaks likea mofo and wont stay on untill i spray it with ether down the throat , I see the carb has a crack and since it was sitting for years its probably all clogged up.

Thanks guys. Distributor is good, carb no good.

[motorcritter]

That old adage- '90% of ignition troubles are fuel related, and 90% of fuel problems are ignition related', or something like that! At least you know what to do next (hopefully).
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