OBS to LQ4 Fuel system

So I am helping a relative with this conversion and have a couple fuel system questions that I can't exactly find the answers too.

The stock system was a return system. It has two rubber lines by the firewall into some metal lines. I need to know if these rubber lines will be able to hold the new amount of fuel pressure or not?

The new engine has two lines coming off it for the fuel system. Can I use a return system on this engine or do I need to convert it over to a returnless fuel system? If so what do most people do with the other fuel line.

Also what type of connector is this on the engine? I looked at the 2003 tahoe and it looks like it's a push on style that automatically locks on the fuel line.

If anyone has any links that is always appreciated also. Read the OBS to LS1 conversion sticky and still need some help. Thanks in advance.

The single line is a 3/8" snap-loc fuel line that has an oring internal to the female connector. A dual line will have a 5/16" snap-loc connector. The fuel lines in non-vortec engine will only be safely rated for about 15 psi. What year truck is the OBS since the later models were setup for high pressure in the vortec engines.

The vehicle is a 94 suburban. The new engine is the 6.0L LQ4.

If the LQ4 has a single feed fuel rail, do the conversion to a Corvette style fuel filter as mentioned in the conversion topic. The filter will supply a constant 58PSI to the fuel rail and the fuel pressure regulator on the fuel rail will give you 50 PSI at idle and 58 at WOT. Cut the lines at the stock fuel filter and splice the Corvette filter in there. The return line is also there. You will have two lines on the back side of the filter and one line from the filter going to the engine. All the parts required to make it work are available from most any auto parts store. Be sure you use hose rated for 60 PSI or more.

So the fuel line on the engine looks like it has both a supply (before the regulator) and then a return line (after the regulator). If I run both lines down to the corvette style fuel filter then I would connect them to the two sides of the fuel filter. The supply line would then run into the fuel filter inlet. So now I am confused at where I would connect the return line that goes back to the tank.

On the tahoe it looks like both lines come off the engine and then run to that style fuel filter. And then the supply from the fuel pump goes to the inlet on the fuel filter. Didn't see a return line for the tank. However, maybe it is down there.

PS thanks for your patience.

Okay, if you have a supply and return line on the fuel rail then you can use both lines coming from and returning to the fuel tank, you will just have to alter the ends so that your connectors will lock onto the fuel rails. Did you install a high pressure pump in the fuel tank?

The high pressure fuel pump is on order at the moment.

Not quite sure what is the best way to alter those lines. Do all of the rubber lines need to be replaced? If so I was thinking of getting a pipe cutter and then using some fuel hose up to the connections at the engine. However if I cut the pipe is there a way to re-flare that end so I can get a good connection. Then at the other end pick up some of those snap-lock connectors to have a quick disconnect at the engine.

All the GM rubber lines are fine unless they're brittle. I've never had one fail, yet. Knock on wood. I don't flare the lines when I cut them, just double clamp each end of the rubber line on the connections. I don't use the worm gear clamps that cut up the rubber lines, I use the smooth wall clamps that have a nut and bolt through them to draw them up tight without cutting the surrounding rubber. Some high quality stuff like Russell connections and hose would be the best way to do your connections. Even a tractor supply company could build you some hose assemblies up for the fuel. NAPA is also a good source for the fuel lines, hose and custom crimping.

So I picked up some parts and the inlet side going to the fuel rails uses a 3/8 snap lock fitting. On what looks like the return side is a 5/16 snap lock fitting.

I checked out the corvette fuel filter and it has the same style fittings 1 is a 3/8 snap lock and the other was a 5/16 fitting. The other side said outlet which was really confusing to me what type of fitting would go in that side.

My understanding from your posts is do not cut the metal tubing but the rubber tubing leading up the firewall can be modified and install higher pressure fuel lines to the engine from that point.

No need to cut anything but the ends of the hoses that used to go to the throttle body on the old engine. You don't have a need for the Corvette fuel filter, the stock filter will work fine. Take your tubing cutter and cut the ends off the old connections, remove the threaded fitting and apply a piece of hose to connect it to the snap-loc fitting(3/8" to 3/8" and 5/16" to 5/16"). The stock return line will return excess fuel pressure to the fuel tank. Depending on how long your hoses are you could cut the rubber hose and use it or you could cut the metal tube and join it to the snap-loc fittings.

So we are going to cut right behind the old connectors. Right at the back of the block. Then install the snap lock fittings and run that to the rail. We may need to install an extension piece but it looks good. The old system was fuel injected but at a lower pressure I think it was 28-32psi maybe. Do you think those flex lines will be ok? They look fine but not sure if they will be able to take the extra pressure.

They should be able to handle the pressure. The lines at the fuel tank are made of the same stuff and all us guys with the OBS trucks have never replaced them that I know of.

very good info

So I was curious, if the OBS lines have been replaced with steel braided, don't know what PSI max though, they should be fine to run with a high pressure pump? Just convert the ends to match the quick connects on the rails? I'm doing a conversion right now and was needing to know the details of the Fuel system. Don't mean to butt in.

Braided hose should be good to 300 psi if I remember correctly

I used the factory braided lines from some undetermined year OBS and didn't have to cut any lines, spent less than $50.00.

800-078 + 800-058 = 3/8 line
800-079 + 800-057 = 5/16 line

http://www.ls1truck.com/upload/files/31/fuel.jpg

Quote:

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Originally Posted by r6z4o6

I used the factory braided lines from some undetermined year OBS and didn't have to cut any lines, spent less than $50.00.

800-078 + 800-058 = 3/8 line
800-079 + 800-057 = 5/16 line

http://www.ls1truck.com/upload/files/31/fuel.jpg

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How are them braided hoses connected to the nylon hoses?

800-078 + 800-058 = 3/8 line

http://static.summitracing.com/globa...NB-800-078.jpg

+

http://static.summitracing.com/globa...NB-800-058.jpg

= pressure side.

800-079 + 800-057 = 5/16 line

http://ecx.images-amazon.com/images/...500_AA300_.jpg

+

http://static.summitracing.com/globa...NB-800-057.jpg

= return side.

Is that rigid nylon hose rated for the pressure? I have only seen that used in vapor applications. Also looks like it is supporting the weight of the braided hose, may cause problems when it gets brittle.

Thats what i was thinking too. I think if i end up doing something like this i will build some type of support structure. I think the hose is fine for the pressure. Its used in fuel lines and clutch systems.

I tried it and it didn't work out for me couldn't get it to seal.