[jonbill]

Hi -
I've got a bit of a problem with heat soak - when I restart the car after a shortish stop (5 to 20 minutes) the engine runs lean until I've been moving for a few minutes. By lean, I mean AFR 16 - 18 where normally it'd be 14.0 to 14.5 at idle.
Normally, my FPR regulates at 46 psi, but when I have this lean problem, my FPR is regulating at 43psi, so I guess that explains why it goes lean. I'm not sure if the problem is the consequence of hot fuel in the FPR, or a hot FPR per se.
How would you address this?
A better FPR?
relocate FPR?
Fuel cooler?
Fuel temperature compensation in Speeduino? (which doesn't exist yet, AFAIK)

TIA

[LPG2CV]

Before messing with the FPR, take a look at the IAT temperatures.

[Chris Wolfson]

Most cars injected, many carbureted too, have a fuel return line. This, together with carefully routed fuel lines, should flush out any hot fuel in the first seconds of running or even earlier, during priming.
If your regulator is not constant in pressure (check with vacuum hose off! It lowers the pressure during idle) it is simply broken.
Get a new one.
Makes no sense to compensate in the ECU software for mechanical faults.

If you want further hints, do some good pictures of your installation and post them.

[jonbill]

Before messing with the FPR, take a look at the IAT temperatures.

Yes, IAT does go up to 30s which doesn't help because of the IAT compensation pulling a few %, but even making the IAT compensation 100% across the board I still have the problem, so it's definitely the drop in pressure.

[jonbill]

Most cars injected, many carbureted too, have a fuel return line. This, together with carefully routed fuel lines, should flush out any hot fuel in the first seconds of running or even earlier, during priming.
If your regulator is not constant in pressure (check with vacuum hose off! It lowers the pressure during idle) it is simply broken.
Get a new one.
Makes no sense to compensate in the ECU software for mechanical faults.

If you want further hints, do some good pictures of your installation and post them.

the FPR is normally pretty constant, its only when the engine bay temperatures soar that the pressure drops a few PSI.
The return line is at the FPR so I could move it to the end of the fuel rail, but that won't make much difference if its the FPR body getting hot that causes the problem.

DSC_0066.JPG (3.44 MiB) Viewed 4872 times

[LPG2CV]

Do you have a map regulated FPR. Is it feasible that for some reason you are getting increased map, which is pulling the pressure down.

[jonbill]

Do you have a map regulated FPR. Is it feasible that for some reason you are getting increased map, which is pulling the pressure down.

No, no MAP attachment - it's 46psi all the time, except when it gets very hot.

[Chris Wolfson]

From the picture I can not see where how your fuel lines run. The usual plumbing is tank, fuel pump, filter, injectors, regulator, return line, tank. If your regulator changes pressure with temperature it is defective. That is a fault, not a feature.
As far as I can see you have a filter in the wrong place, in front of the regulator. Does your feed come from the left side to the fuel rail and the excess exit to the right ? If not, you got the plumbing wrong and gas bubbles will not be pushed out of the system.

[jonbill]

Thanks Chris. The filter is after the pump and before the regulator which is before the rail. There's also a swirl pot before the pump and another pump at the tank.
I think I should probably move the filter to the tank before the first pump, but that's not this problem.
And my recent relocation of the FPR to the far side of the engine bay (away from the exhaust, to make it cooler) has created a larger volume of fuel in that hose that will get hot and can only be released through the injectors, so yes, I probably should relocate the regulator to the end of the fuel rail. But, it'll still get hot there and so I'll still have this problem.
so - what adjustable regulator is impervious to heat? any recommendations?

[Chris Wolfson]

See, the regulators I know have to be located at the exit of the fuel rail. The fuel pump pushes fuel into the intake of the rail with maximum delivery rate. When the required pressure is reached, the regulator opens and any excess fuel goes back to the tank. . That way you have a constant flow of fresh of fuel trough the rail and 100% constant pressure.

What I can see is that you did not install this system. The pressure you get installing the regulator wrong is random.

Have a look ant any fuel injected car and you see that it works the way I described.

Your mistake is often made in conversions from carbed engines, as they have no fuel return line. A return is essential for a working injection system, no trick to get around it.