LS3 will not run
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Teching In
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LS3 will not run I have an LS3 engine that has been running perfectly until now. Suddenly, it dies 2–3 seconds after starting. Could it be that VATS has been activated? I’ve done some electrical work, but nothing involving programming. Could it be a grounding issue? (I can't find anything obviously wrong) Thanks for any help, Harold
Teching In
Joined: Oct 2024
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From: Seattle, WA
I have an LS3 engine that has been running perfectly until now. Suddenly, it dies 2–3 seconds after starting. Could it be that VATS has been activated? I’ve done some electrical work, but nothing involving programming. Could it be a grounding issue? (I can't find anything obviously wrong) Thanks for any help, Harold
On The Tree
Joined: Nov 2015
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Electric fuel pump? Power from a relay? Test the relay power when the engine dies. If you have a later model fuse box with a bunch of relays, swap the fuel pump relay with one of the others of the same type...
Nick
Nick
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Thread Starter
Teching In
Joined: May 2026
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I’ve checked the fuel pressure now, and it’s fine both before and after the engine stalls. The engine starts, runs for about two seconds, and then dies. I haven’t made any changes to the ECU, so I'm assuming it's not an VATS issue?(I have double-check grounds and ECU/ignition connectors)
Any ideas what the issue could be? Thanks in advance
Regards
Harold
Any ideas what the issue could be? Thanks in advance
Regards
Harold
Thread Starter
Teching In
Joined: May 2026
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I replaced the battery and tidied up the wiring under the dashboard. I've double-checked everything, and all the fuses are fine. I also measured the power from the ignition switch, and it stays on after starting.
TECH Fanatic
Joined: Oct 2022
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From: Louisiana
yikes, you sure you didnt pull anything loose under the dash board? Are you sure vats was deleted in the tune and not by a resistor under the dash and you maybe pulled it loose?
TECH Fanatic
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From: Louisiana
yeh id be checking those wires under the dash and make sure there isnt a resistor but connected in somewhere that you may have pulled out or cut loose when cleaning up the wiring.
Thread Starter
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How can I know for sure if VATS is activated? Can I measure the injectors or check a spark plug to see if it stops sparking?Can I use a standard diagnostic tool to check if VATS is enabled?
Last edited by LSharold; May 11, 2026 at 12:40 PM.
TECH Fanatic
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From: Louisiana