Too much fuel pressure

[matt]

Hi, I am running a 2005 LS2 24 tooth engine in an Cobra kit. Runs great with no problems...except.... After it has been running a while and the engine is switched off it wont re start...just cranks over and over. I have noticed that after the engine has been shut down and after about 1 minute the fuel pressure gauge climbs from 60 psi right round to over 120 psi !!!! While the engine is switched off !!?? The only way to get it to start is to disconnect the fuel line in the engine bay, "very carefully" to release some pressure. Once the fuel line is re-connected it fires up with no complaint. And runs mmerrily at the correct 60psi. I have made all checks for leaks etc... I am 100% sure the fuel pump shuts down at the same time as the engine. There are no Fault codes in the ECU, Running a stock tune file. I have checked the tank vent pipes are not blocked. The engine never overheats and the oil temperature remains comfortably within operating limits at all times. Just not sure what is going on here??? Has anyone ver experienced this sort of thing??

[400ss]

Hi, I am running a 2005 LS2 24 tooth engine in an Cobra kit. Runs great with no problems...except.... After it has been running a while and the engine is switched off it wont re start...just cranks over and over. I have noticed that after the engine has been shut down and after about 1 minute the fuel pressure gauge climbs from 60 psi right round to over 120 psi !!!! While the engine is switched off !!?? The only way to get it to start is to disconnect the fuel line in the engine bay, "very carefully" to release some pressure. Once the fuel line is re-connected it fires up with no complaint. And runs mmerrily at the correct 60psi. I have made all checks for leaks etc... I am 100% sure the fuel pump shuts down at the same time as the engine. There are no Fault codes in the ECU, Running a stock tune file. I have checked the tank vent pipes are not blocked. The engine never overheats and the oil temperature remains comfortably within operating limits at all times. Just not sure what is going on here??? Has anyone ver experienced this sort of thing??

never hear something like this.. the fuel pressure cant jump from 60 to 120 with the fuel pump off, how can it be possible?

what kind of fuel system do you have? return or returnless style? what fuelpressurerregulator do you have?

[matt]

never hear something like this.. the fuel pressure cant jump from 60 to 120 with the fuel pump off, how can it be possible?

what kind of fuel system do you have? return or returnless style? what fuelpressurerregulator do you have?

Hi 400ss...... It really is odd... I have a return style system. A single Bosch 044 pump and Mallory 4305M regulator and Sytec 55 micron Bullet filter all mounted in the trunk. The bypass from the regulator is fed directly back into the tank. I have a non-return valve mounted in line between the output of the tank and the fuel rail. I have a Fuel Pressure guage mounted on the fuel rail, which is where my readings are taken. Using Braided teflon hose 7/16" from tank to filter and filter to pump inlet and 5/16" from outlet of pump through to the engine. I only get this problem after the engine has been running a while and evrything is quite hot, not overheating, just hot. The only thing I can think of right now is possibly that the tank may not be venting correctly????? The tank vents to the outside via the petrol cap and via a small pipe from the filler neck inside the trunk to the outside. I have pushed compressed air through the output vent pipe and the air clearly escapes from the cap and vice versa......Its really ticking me off having to lossen the fuel hose each time the engine has been running for a while.....If I could make a video to show you the guage creeping up after 30 seconds after the engine has stopped I would !! I would appreciate your input on this one.

[joecar]

Strange... fuel pump is not running and fuel tank is vented.

[EagleMark]

The only thing I could think of is when it's hot would expand pressure... but the regulator should release it! Having 60psi rise in tank is not possible... is it? Nah...

[joecar]

Is fuel line routed close to exhaust...?

[matt]

Is fuel line routed close to exhaust...?

Thanks for the replies guys...Good to know there are guys out there who want to help :-)

The fuel line is a long way away from the exhaust when it reaches the rear of the car and enters the tank. But....The fuel line is about 6-9 inches away from the exhaust high up in the transmission tunnel for the run up to the engine... There are two 2.5 inch exhaust pipes close to one another that run beneath the transmission tunnel all the way along the car where they separate each side of the gearbox to each bank with a CAT on each bank.....I am beginning to think that when the fuel stops flowing, the heat, and there is a lot of heat, rises straight up into the transmission tunnel and either expands or evaporates the fuel remaining in the line? Causing an over pressure and or a vapour lock? The only way to stop this I guess would be to remove the non return valve in the line and let all the fuel run back into the tank after the engine stops? Happy to hear what you think before I set about removing the valve?

[EagleMark]

The only way to stop this I guess would be to remove the non return valve in the line and let all the fuel run back into the tank after the engine stops?

Yup!

[joecar]

I agree, try it.

[darcy]

Can you explain your setup configuration a little more. The way I'm picturing it is:

Tank > Pump > Regulator > non-return valve > rail

Which isn't a return-type fuel system, but actually a standard-type dead-head arrangement (albeit you have move the reg from attached to the pump to outside of the tank, but still schematically the same), AND (critically) one whereby once the fuel has passed the regulator and valve it has no path of overflow/return to the tank.

If that is the case, then try removing the non-return valve as suggested.
Locate the non-return valve between the pump and the regulator - there it can still stop the reg draining out through the pump, but not stop the reg bleeding off pressure.

If I've understood the arrangement incorrectly, then dis-regard most of the above - but in any case the non-return valve should only be directly after the pump.