LS swap fires then quits - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Haybag · 05-12-2021, 07:26 AM

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.

**mongocanfly** · 05-12-2021, 07:39 AM

Do you have the maf hooked up?
Any codes?

**A1971Blazer** · 05-12-2021, 07:42 AM

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?

Haybag · 05-12-2021, 07:53 AM

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.

Davidf · 05-12-2021, 10:16 AM

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.

ls1nova71 · 05-12-2021, 10:44 AM

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.

Haybag · 05-14-2021, 09:26 AM

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.

**A1971Blazer** · 05-14-2021, 09:37 AM

Quote:

Originally Posted by Haybag

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....

05-12-2021, 07:26 AM	#1
Haybag Registered User Join Date: Aug 2012 Location: New Boston, New Hampshire Posts: 34	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.

05-12-2021, 07:39 AM	#2
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,670	Re: LS swap fires then quits Do you have the maf hooked up? Any codes? __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

05-12-2021, 07:42 AM	#3
A1971Blazer Senior Member Join Date: Nov 2013 Location: East Tennessee Posts: 2,198	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? __________________ 1967 C10 Step side 1968 C10 Step side 1970 Chevrolet K/5 Blazer 1972 Chevrolet K/5 Blazer .............

05-12-2021, 07:53 AM	#4
Haybag Registered User Join Date: Aug 2012 Location: New Boston, New Hampshire Posts: 34	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.

05-12-2021, 10:16 AM	#5
Davidf Registered User Join Date: Nov 2014 Location: Austin Posts: 749	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.

05-12-2021, 10:44 AM	#6
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,118	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. __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html

05-14-2021, 09:26 AM	#7
Haybag Registered User Join Date: Aug 2012 Location: New Boston, New Hampshire Posts: 34	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.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.