Hey everyone! I'm new to the chat. I have an 83 el camino with an 5.3 LM7 swap. I have an LS6 intake, LS6 injectors and aftermarket fuel rails. Here's my question. If I haven't started the car in a week a or so, when I go to run the car on it takes a little longer to crank and turn over than normal. However, if I turn on the ignition and let the fuel pump run for MAYBE a second then crank it the car starts right up. The car drives perfectly fine. No misses or lack of power. I'm a bit of a novice and I'm learning as I go on this car (I didn't build it). The issue is I don't have a schradar valve to test the fuel pressure so I'm guessing I have to buy a cheap in line fuel pressure gauge? My question is do any of you think I have a very very very small/slow fuel pressure leak or am I overthinking it and the electric fuel pump just need a second to build fuel pressure before I crank the engine over?
LM7 fuel pressure question
- Thread starter lolthisisnuts
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Very normal and expected to have the rail lose pressure while sitting. The OEM's resolved this with a pump that has a check valve of some nature in the supply line, and some returns have it as well. Most aftermarket pumps do not have a check valve anywhere.
Let the pump run for a second or two and all will be well.
Let the pump run for a second or two and all will be well.
Thank you for the help! I was driving myself nuts over this haha. Felt like I was chasing a ghost.
Hey All
I have a 2005 LM7 out Silverado. I have a returnless system. Electric fuel pump is brand new (in tank), fuel filter is brand new, lines are brand new, fuel rails are brand new. I have LS6 injectors. My question is why is my fuel pressure higher after starting the engine.? When I turn the ignition on I hear the fuel pump and the fuel pressure gauge reads about 57-58 psi and doesn't hold pressure for a long period of time. There is no evidence of any leaky fuel lines. When I turn the engine on the fuel pressure goes up to about 61-62 psi. The car drives fine and no issues idling or with acceleration. I'm thinking I have a slow injector leak but I was curious if anyone else could shed some insight on this?
The returnless system w/ corvette regulator causes this if your fuel pump is too big. I think 255 is about the biggest you can use without overpressurizing the regulator and pump head. My buddy had a Kemso 340 feeding thru the vette filter. He read 66psi. Car ran fine but I bet this caused that cheap pump to burn up 2x. There could also be a restriction in your return line but doubtful.
Interesting. Any reason why it doesn't hold pressure well before cranking? Or are you saying that is related to the oversized fuel pump?
I agree with nailheads post regarding pressure before you start it. Its normal. I was talking about after its running. I figured that regulator can't handle that much flow. So the pump is forcing fuel into the regulator faster then it can send it back. Forcing the pressure to go up and be erratic.
Disclaimer: I'm not a mechanic.
Disclaimer: I'm not a mechanic.
The Corvette Filter regulator is only good for 255lph or less as indicated by RabbitholeSS. Anything over and above that could drive pressure over the set point due to the regulator not being able to bypass the excess fuel flow.
Depending on the pump you have it could have a check valve in the outlet or not. If it does have a check valve then it is designed to hold line pressure between the pump and the next thing which in this setup is likely a regulator. If during start up there is no smoking or raw fuel smell, it would lead me to believe that the fuel injectors are not leaking down.
What could be happening is either:
a. the check valve in the pump (if it has one) is sticking or has debris in the check valve seat
or
b. the regulator is dumping its pressure
Depending on the pump you have it could have a check valve in the outlet or not. If it does have a check valve then it is designed to hold line pressure between the pump and the next thing which in this setup is likely a regulator. If during start up there is no smoking or raw fuel smell, it would lead me to believe that the fuel injectors are not leaking down.
What could be happening is either:
a. the check valve in the pump (if it has one) is sticking or has debris in the check valve seat
or
b. the regulator is dumping its pressure
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