LS3 Engine doesnt start after sitting

[brgarris]

Need a little troubleshooting assistance. I have an LS3 in a '69 camaro and just recently had to remove the fuel rails so I could get the intake plenum cover painted. I reinstalled the fuel rails with existing injector o-rings since the engine doesnt have but 1200 miles on it. Regardless, I have noticed that if the engine sits for 2-3 weeks it will not initially crank. I typically have to hook the battery charger up to it and let it turnover more than normal especially for a fuel injected engine. When the car is running I cannot visibly see any fuel leaks anywhere. Could it be possible there is still a leak causing the cas to drain from the fuel line back to the tank? Any help would be appreciated!!!!

[andrewb70]

It won't crank or doesn't start? Is the battery being drained?

What ecu and harness are you using?

Andrew

[brgarris]

Andrew, thanks for the reply!! I should have been a little more detailed in my initial write up. The ending will turn over, but will not crank until it turns over for a while. I do not believe the battery is being initially drained, but it does get weak after trying to start for a while. The ECU/harness is the OEM harness from GM. I ordered the engine and harness from GM performance. For some reason I feel the fuel line is draining back to my fuel tank after a period of time. I have the detroit speed tank with internal fuel pump. It comes out to a corvette style internal regulated fuel filter (one side has the supply from pump and return to tank, the other side has discharge to intake). I am not sure what the internal of these filters look like, but is there a way that the filter is leaking by thus allowing the fuel supply line to drain back to the tank? Could there be a leak internal to an injector causing the issue? I would assume that if an injector o-ring was leaking it would be very apparent on the outside of the engine since there is 60 psig of fuel pressure at the injectors.

It would make sense to me that something is causing the fuel line to drain back to the tank after the car sits for a period of time. That would explain why I am having to contantly allow the motor to turn over before it cranks. In my mind the fuel line is purging itself and the air is being evacuated through the injectors. Just a thought. Again, any help would be much appreciated!!

[andrewb70]

Andrew, thanks for the reply!! I should have been a little more detailed in my initial write up. The ending will turn over, but will not crank until it turns over for a while. I do not believe the battery is being initially drained, but it does get weak after trying to start for a while. The ECU/harness is the OEM harness from GM. I ordered the engine and harness from GM performance. For some reason I feel the fuel line is draining back to my fuel tank after a period of time. I have the detroit speed tank with internal fuel pump. It comes out to a corvette style internal regulated fuel filter (one side has the supply from pump and return to tank, the other side has discharge to intake). I am not sure what the internal of these filters look like, but is there a way that the filter is leaking by thus allowing the fuel supply line to drain back to the tank? Could there be a leak internal to an injector causing the issue? I would assume that if an injector o-ring was leaking it would be very apparent on the outside of the engine since there is 60 psig of fuel pressure at the injectors.

It would make sense to me that something is causing the fuel line to drain back to the tank after the car sits for a period of time. That would explain why I am having to contantly allow the motor to turn over before it cranks. In my mind the fuel line is purging itself and the air is being evacuated through the injectors. Just a thought. Again, any help would be much appreciated!!

The ECU is programmed to prime the fuel system right away, so I don't see a loss of pressure from sitting to be an issue.

At this point I would do some basic trouble shooting:

1. Is the ECU throwing a code?
2. What is the fuel pressure?
3. Double check all the wiring. Do you have good grounds? Do you have a good source of power to the fuse panel that came with the harness?

Andrew

[brgarris]

I havent checked the ECU but will do that. I dont have anything rigged up to check the fuel pressure right now. I know that the driver side fuel rail has a connection to be used for checking fuel pressure. Do you know what type of fitting I would need to use this connection? Grounds should be good and there is a good power source going to the ECU.

[andrewb70]

Something like this will work to check fuel pressure:

http://www.amazon.com/OTC-5630-Fuel-...tester+kit+otc

It screws into the shredder valve that is on the fuel rail.

Andrew

[brgarris]

oh ok thanks.....I believe the LS engine needs to have 60 psi of fuel pressure before it will start correct? What should I see on the fuel pressure gauge once the engine is shut down? does it stay at 60 psi or will it slowly bleed down? What is normal will assist me in troubleshooting. Thanks again!!

[andrewb70]

oh ok thanks.....I believe the LS engine needs to have 60 psi of fuel pressure before it will start correct? What should I see on the fuel pressure gauge once the engine is shut down? does it stay at 60 psi or will it slowly bleed down? What is normal will assist me in troubleshooting. Thanks again!!

Fuel pressure needs to be 58-60 psi. I've seen the Corvette filter/regulators run anywhere from 55-60 psi. It doesn't matter what the pressure is when the engine is shut down. This is the reason the ECU primes the system for 5 seconds as soon as you put the ignition key in the "Run" position.

One other thing to check is to make sure that when the engine is cranking, the ECU sees a full 12 volts. Where did you tap into the stock harness for ECU power?

Andrew

[jlcustomz]

I have an inline fuel gauge on mine, which is a help if something is not right. Sometimes it stays full pressure after shutoff for a long while, sometimes not. But it always pops up to full pressure almost instantly.

Fuel leaks on gas & diesel engines can be strange things. Injector to manifold seals can spray fuel out when running, but injector to rail or fuel line seals could possibly have a reverse leak & empty the system during sitting without finding a running leak. These mysterious types of leaks can either go away or suddenly show their ugly head. Or sometimes both.

On most efi vehicles when you turn the key to on , the pump will run for a few seconds & then stop if not cranked. You should be able to hear it if its anywhere near quiet where youre at.
If you are having an issue such as yours, you can turn on the key, wait a few seconds , shutoff, & repeat a few times before cranking. This helps prime a troubled system without running your battery down. Same procedure as should be done after running out of gas.