Author Topic: 79 Small Block 5.7l 350 Wont Start After Driving.  (Read 146 times)

Offline jloar

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79 Small Block 5.7l 350 Wont Start After Driving.
« on: October 11, 2019, 07:54:24 PM »
Odd problem I have yet to figure out. I have a 5.7l Chevy 350 that starts and runs no problem. Its a little slow to crank but starts every time. If I take it for a drive and turn it off, it wont restart without a jump.
The battery is two years old, 700cca. Truck off it reads 12.5v, truck running its 14+v.
When I start the truck cold the volts drop down to 9.5v (while cranking) and it starts.
After driving, I try to start and the volts drop down to 9.0v, the truck doesnt start.
If I let it still for an hour or more after driving it starts right up.

Any thoughts would be appreciated.
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Offline Rapid Roy

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Re: 79 Small Block 5.7l 350 Wont Start After Driving.
« Reply #1 on: October 11, 2019, 09:25:38 PM »
Welcome.

Sounds like heat soaked starter. May need starter heat shield, if it doesn't have one, or new starter.
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Offline jloar

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Re: 79 Small Block 5.7l 350 Wont Start After Driving.
« Reply #2 on: October 11, 2019, 10:21:27 PM »
No starter heat shield, I will look into getting one on there. Thank you!!
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Offline Irish_Alley

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Re: 79 Small Block 5.7l 350 Wont Start After Driving.
« Reply #3 on: October 12, 2019, 01:29:20 PM »
Get the battery tested. Things that can cause a slow starter is like stated heat soaked or a weak starter and timing or a poor battery cable connection.

I would test the battery and then check timin max most people run is 12btdc. If both those check out you can either replace the starter or get a heat shield that may not work since you have this issue when the engine is cold..
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Offline Shifty

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Re: 79 Small Block 5.7l 350 Wont Start After Driving.
« Reply #4 on: October 12, 2019, 02:52:15 PM »
Also make sure that you're actually getting 12v to the starter, not just the battery. 
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Offline jloar

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Re: 79 Small Block 5.7l 350 Wont Start After Driving.
« Reply #5 on: October 12, 2019, 03:33:01 PM »
most people run is 12btdc. If both those check out you can either replace the starter or get a heat shield that may not work since you have this issue when the engine is cold..

Im not sure what 12btdc is?
Im not sold that the timing is correct or that the carb is adjusted the best either.

Also, when you say because Im having the issue when the engine is cold, do you think 9.5v while cranking is too low?


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Offline Irish_Alley

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Re: 79 Small Block 5.7l 350 Wont Start After Driving.
« Reply #6 on: October 12, 2019, 10:36:03 PM »
where are you getting that reading for the volts at? 9.5 is low and even on the threshold of being bad. but if youre not getting those reading directly from the battery there could be a connection issue causing a low reading

about timing read
http://forum.73-87chevytrucks.com/smforum/index.php?topic=32085.0
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Offline JohnnyPopper

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Re: 79 Small Block 5.7l 350 Wont Start After Driving.
« Reply #7 on: October 13, 2019, 06:25:08 PM »
Heat creates resistance to the flow of electrons in any circuit. So if your starter is getting too hot to start, that's one thing. I would get the thing hot, and then when it won't start, I would carefully hose the starter into a cool state and try it.

However, your description of 'not starting' is somewhat muddy. Does it crank at the same speed? Since the voltage drops by 1/2 a volt, I can't envision it being really slow. Please comment.

And as to timing, it's possible that it's too far advanced. If that the case, when you turn it over the spark plugs are  lighting too soon and fighting the pistons as they triy to reach the the top of it's travel.

Under this condition it will chug, real slow, like it's got peanut butter schmeared all over it's internals. This will show up at normal operating temperature.

Finally, like Irish and the Shifty one said, it's where you check voltage that matters. Checking voltage drop at the battery may be very different than checking it at the starter 12v post. If there is considerable difference between those two point look for a bad cable or weak connections.