LS1 fuel pump prime intermittent - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lux · 12-20-2016, 10:16 AM

My 72' has a LS1 swap with a fuel pump priming problem.
On occasion after driving for a while and switching the engine off for a while it will not start. It turns over fine but I don't hear the usual fuel pump priming that I get when switching the key on.
This has happened on thee occasions. After towing the truck home and letting it sit for a while it starts just fine.
I thought it might be wiring to the fuel pump and I checked it all. I found one questionable connection and fixed it, but I guess that wasn't the real problem because it happened again.

67 chevelle · 12-20-2016, 10:27 AM

It could be many things , most use a relay to their fuel pump , that would be 1 suspect , the pump itself another , the trigger wire from the pcm another [ but realize the computer shuts the pump off when adequate pressure is in the fuel rail or the key is on for awhile and the engine is not running . ls1tech.com and the ls section on the board may hold more guesses to your issue , post your results

Details on your pump and tank choices , and return - pressure regulator details will help in a diagnosis

lux · 12-20-2016, 10:36 AM

Thanks for the reply, I'm new to the LS game. The fuel pump seems to run fine once the engine is running, so I don't really suspect that. I believe you are correct in the #1 suspect being the relay. I have no idea where that is but I'll find it. Whats the best way to test it?

**Hart_Rod** · 12-20-2016, 10:52 AM

Quote:

Originally Posted by lux

Thanks for the reply, I'm new to the LS game. The fuel pump seems to run fine once the engine is running, so I don't really suspect that. I believe you are correct in the #1 suspect being the relay. I have no idea where that is but I'll find it. Whats the best way to test it?

Whose LS wiring harness do you have? Once you find the relay, I would just install a new one.

lux · 12-20-2016, 10:55 AM

Painless wiring harness.

**Hart_Rod** · 12-20-2016, 11:18 AM

Quote:

Originally Posted by lux

Painless wiring harness.

Their instructions should point you to the relay. I would go with a new 50 Amp relay when you replace it, just for added protection. What fuel pump are you running?

**Hart_Rod** · 12-20-2016, 12:27 PM

Also, you should repost your question here:

http://67-72chevytrucks.com/vboard/f...play.php?f=206

lux · 12-20-2016, 01:10 PM

Thanks for all the help guys. I'll try the relay and if I continue to have problems I'll repost in the correct place.

12-20-2016, 10:27 AM	#2
67 chevelle Registered User Join Date: May 2013 Location: WEST PALM FLORIDA Posts: 1,174	Re: LS1 fuel pump prime intermittent It could be many things , most use a relay to their fuel pump , that would be 1 suspect , the pump itself another , the trigger wire from the pcm another [ but realize the computer shuts the pump off when adequate pressure is in the fuel rail or the key is on for awhile and the engine is not running . ls1tech.com and the ls section on the board may hold more guesses to your issue , post your results Details on your pump and tank choices , and return - pressure regulator details will help in a diagnosis __________________ 68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive Last edited by 67 chevelle; 12-20-2016 at 10:32 AM.

12-20-2016, 10:36 AM	#3
lux Registered User Join Date: Oct 2016 Location: Austin, Texas Posts: 306	Re: LS1 fuel pump prime intermittent Thanks for the reply, I'm new to the LS game. The fuel pump seems to run fine once the engine is running, so I don't really suspect that. I believe you are correct in the #1 suspect being the relay. I have no idea where that is but I'll find it. Whats the best way to test it?

12-20-2016, 10:55 AM	#5
lux Registered User Join Date: Oct 2016 Location: Austin, Texas Posts: 306	Re: LS1 fuel pump prime intermittent Painless wiring harness.

12-20-2016, 12:27 PM	#7
Hart_Rod ************* Join Date: Apr 2005 Location: Pensacola, FL Posts: 17,835	Re: LS1 fuel pump prime intermittent Also, you should repost your question here: http://67-72chevytrucks.com/vboard/f...play.php?f=206 __________________ Rob - https://www.instagram.com/hart_rod_c10 As Iron Sharpens Iron, So One Man Sharpens Another. Proverbs 27:17 FOR SALE: DBW pedal bracket - http://67-72chevytrucks.com/vboard/s...d.php?t=651123 FOR SALE: Hood Brackets http://67-72chevytrucks.com/vboard/s...d.php?t=679945 1987 Silverado SWB - 34.5K original miles http://67-72chevytrucks.com/vboard/s...d.php?t=801834 1969 SuperBurb - http://67-72chevytrucks.com/vboard/s...d.php?t=200387 1968 Farm truck - http://67-72chevytrucks.com/vboard/s...d.php?t=358692 1968 SWB - http://67-72chevytrucks.com/vboard/s...d.php?t=551258 1948 Chevy - http://67-72chevytrucks.com/vboard/s...=122164&page=3

12-20-2016, 01:10 PM	#8
lux Registered User Join Date: Oct 2016 Location: Austin, Texas Posts: 306	Re: LS1 fuel pump prime intermittent Thanks for all the help guys. I'll try the relay and if I continue to have problems I'll repost in the correct place.

12-20-2016, 10:16 AM	#1
lux Registered User Join Date: Oct 2016 Location: Austin, Texas Posts: 306	LS1 fuel pump prime intermittent My 72' has a LS1 swap with a fuel pump priming problem. On occasion after driving for a while and switching the engine off for a while it will not start. It turns over fine but I don't hear the usual fuel pump priming that I get when switching the key on. This has happened on thee occasions. After towing the truck home and letting it sit for a while it starts just fine. I thought it might be wiring to the fuel pump and I checked it all. I found one questionable connection and fixed it, but I guess that wasn't the real problem because it happened again.



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