LS3 Swap Fuel Delivery

[robby8388]

I'm looking for a little advice from someone who is more knowledgeable than I am.

I bought a vehicle (68 Camaro) with a LS1 already installed in it and it ran perfectly fine. I decided to go bigger and swapped in a LS3. I still have the existing in tank pump, regulator, and lines. I can't get the engine to turn over unless I put a tiny bit of gas in the intake. Once I do that it'll start and stay running. It's a little choppy like it's getting starved until I push on the accelerator a little and it sounds healthy. I'm assuming it isn't getting enough fuel and the initial no start is the only thing throwing me off. I'm ruling out injectors because it runs once it fires and then will run normal once I push the accelerator. This leads me to the fuel pump. I'm assuming it's not big enough to power the LS3 vs the LS1 I pulled out. I don't know what pump is in it or what regulator. I'm trying to pinpoint the problem before I drop the tank and switch the pump out. Any suggestions? Would it be wise to buy a fuel pressure gauge to check before I drop the whole tank? Thanks!!

[Rucumn]

Check fuse to be pump, verify pump has power when key turned to acc.

[andrewb70]

Going from a LS1 to LS3 is not trivial. What did you do for ECU?

Andrew

[cpd004]

Try hooking up a gauge to see what the pressure is upon turning the key. It should hold pressure for some time before dropping off. After it's running, check the pressure again. It could be 'bleeding' off so rapidly there isn't pressure at the rail until it is commanded 'on' constant once the motor is running.

[robby8388]

Thanks for all of the advice. It definitely points me in the right direction. I know it's tough to diagnose without knowing the parts.

The pump turns on to prime when the key turns on and stays on with the vehicle running.

The ECU is a LS3 swap standalone wiring harness and computer from PSI.

I'm going to grab a gauge today so hopefully that will give me some more info to go off of.

I'll post what my fuel pressure is when I get back

[71RS/SS396]

It sounds like the tune is jacked up to me. The pump you had in it for the LS1 should run it fine at idle low rpm unless something is wrong with the pump but I doubt it would run at all if that were the case. I would be careful dumping fuel into the intake, they're not designed to be wet and have a tendency to puddle the fuel in the bottom, I've seen people blow the intake off of the engine if it coughs with fuel in it.

[robby8388]

So I'm glad I didn't drop the tank and start replacing the pump or regulator. I ordered a fuel gauge and it's about 55 psi when I turn the key on and it primes and about 60 psi when running.

Thanks for the heads up about the gas in the intake, Tim. I think you're right about it being the tune. I got an engine code reader and it's throwing a P0106 MAP code.

[71RS/SS396]

So I'm glad I didn't drop the tank and start replacing the pump or regulator. I ordered a fuel gauge and it's about 55 psi when I turn the key on and it primes and about 60 psi when running.

Thanks for the heads up about the gas in the intake, Tim. I think you're right about it being the tune. I got an engine code reader and it's throwing a P0106 MAP code.

You may have the wrong map sensor installed, bad map, or a wiring problem. You need to figure out why that code is being set, it will definitely make it run as you're describing, it's probably really lean right now.