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02-29-2024, 06:33 PM | #1 |
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Join Date: Dec 2002
Location: Northern Virginia
Posts: 1,267
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Truck won't start doesn't have 12V
Hello I have a 1971 chevy blazer. I had to redo the fuel system then mess with carb and a fuel pump putting out too many psi. So I have been cranking and starting it a lot lately and it has been fine.
The truck has a Mallory Unilite distributor that I didn't install, I have the same unit in 3 other trucks so I am familiar with the unit. I was looking at how to test the module According to Mallory with the key on I should have 12 volts on the negative side coil. The coil is brand new. I have 6 volts on the negative post. Any ideas on where to start. Thanks |
02-29-2024, 07:58 PM | #2 |
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Join Date: Jun 2022
Location: San Ramon,CA
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Re: Truck won't start doesn't have 12V
Bump the motor and test again?
Could be you caught it right at the point where it triggers a spark to the coil. Not sure how that type of optical trigger works, but with points, if it's sitting on the lobe, it'll show voltage like you describe.
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1970 C10 Custom longbed 350/350 |
02-29-2024, 08:49 PM | #3 |
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Location: Northern Virginia
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Re: Truck won't start doesn't have 12V
What they say is it should be 12 volts on the neg of the coil. Once you confirm that. Place a Credit card between the photo optics and the reader to essentially block it. When you do that the Volts should fall to 2 or less. If not the module is open and must be replaced. I didn't try that since I didn't get 12 at the coil.
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03-01-2024, 08:36 PM | #4 |
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Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,563
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Re: Truck won't start doesn't have 12V
Show a picture of your wiring to the coil. Perhaps you have the yellow wire that goes to the starter and through the white cloth-covered resistor wire to the firewall connector, as if it's wired for a points distributor.
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03-02-2024, 12:59 PM | #5 |
Post Whore
Join Date: Feb 2016
Location: Portland Oregon
Posts: 10,804
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Re: Truck won't start doesn't have 12V
First off was the truck running before?
Does it spark when you crank it over? Is it a nice hot blue spark? Since you've been cranking it over a lot I would check the grounds first. From the battery to the block and to the unit. Something may have gotten disturbed while you were working on the carburetor. I learned long ago to always go back and look at the last thing I messed with when these kind of failures occur. Good luck and keep us informed as your progress.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban the WMB,1991 S(stink)-10 Blazer,1969 GTO, 1970 Javelin, 1952 F2 Ford 4X4, 29 Model A, 72 Firebird. 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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