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Old 05-12-2021, 07:26 AM   #1
Haybag
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LS swap fires then quits

Swapped a 99 4.8 into my 72 c10. Got everything hooked up and ready to run. Starts immediately and then quitsafter a few seconds.. Computer was sent to Lt1swap.com to remove vats and what was not needed. In searching my issue it sounds like vats, how do I test for that or what else could be the problem? Thanks in advance.
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Old 05-12-2021, 07:39 AM   #2
mongocanfly
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Re: LS swap fires then quits

Do you have the maf hooked up?
Any codes?
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Old 05-12-2021, 07:42 AM   #3
A1971Blazer
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Re: LS swap fires then quits

does the fuel pump prime for a few seconds when you turn the key to "on" if so make sure it's also running when you get it started.
If so the VATS may not be disabled?
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Old 05-12-2021, 07:53 AM   #4
Haybag
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Re: LS swap fires then quits

Maf is hooked up. Checked with a scanner and shows no codes. Pump has power with key on and cranking, can hear it when I turn key on.
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Old 05-12-2021, 10:16 AM   #5
Davidf
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Re: LS swap fires then quits

Maybe check fuel pressure. You have enough gas in tank, right!

Maybe crank sensor...but usually that is a no start situation, not a run and stop scenario.

Hope you get if figured out. Soon I will have my 2001 5.3L dropped in my '71...I am always nervous what is happening to you will happen to me. I too had LT1SWAP reprogram my ECM/PCM.

EDIT: Per other thread...check for massive vacuum leak...such as leaving a port on the manifold wide open.

Last edited by Davidf; 05-12-2021 at 10:38 AM.
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Old 05-12-2021, 10:44 AM   #6
ls1nova71
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Re: LS swap fires then quits

Can you keep it running by feathering the throttle? I have had swaps that when you first hook up the battery after it has sat a while with it unhooked, that it won't stay running. It has to recalibrate where the IAC is, and once it's done that runs fine there after.
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Old 05-14-2021, 09:26 AM   #7
Haybag
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Re: LS swap fires then quits

Found my problem, forgot to plug hole in intake for egr tube, huge vacuum leak! Starts and runs now, just need to put exhaust and 02 sensors on.
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Old 05-14-2021, 09:37 AM   #8
A1971Blazer
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Re: LS swap fires then quits

Quote:
Originally Posted by Haybag View Post
Found my problem, forgot to plug hole in intake for egr tube, huge vacuum leak! Starts and runs now, just need to put exhaust and 02 sensors on.
Good news!
that also shows how difficult it is to diagnose a problem without actually being there in person...an extra set of eyes is most always helpful....
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