[theonewithin]

Correction for the above.

A return is NOT required in all installations.

And there are many OEM setups that are returnless/deadhead.

[jonbill]

Chris, you're inventing problems I don't have. I have a return line. It works well, and the pressure at my injectors is constant.
fwiw, it also had a return line when it was on carbs. It's installed as per manufacturers instructions. https://aeromotiveinc.com/wp-content/up ... -0revF.pdf (single EFI fuel rail).

the problem I have is that the regulated pressure drops when the hot engine bay sits for a few minutes.
Do you know of a pressure regulator that won't have this problem? or shall I go back and rewrite the initial question as "how would you recommend I lay out my fuel system" and just forget my actual problem?

[jonbill]

Out of interest, I did go and look at a standard fuel injected car.
Here's the fuel rail and supply on my Toyota MR2.

mr2-fuel-rail.png (41.46 KiB) Viewed 3688 times

.
Seems that some of the minor OEMs thought it OK to not have a return on the fuel rail.

[Chris Wolfson]

You are free to do what ever you like. I do not invent problems, I solve them. I do not know of any temperature dependent fuel pressure regulators. I know a lot about defective regulators and cheap aftermarket ones that do not work correct or leak. Also saw in person what it looks like when a cheap regulator sprayed the engine bay and the fuel ignited. I do not start or tune any car if the fuel pressure is not constant at any time.
My experience is limited to Europe and cars running in Europe.
After 40 years in cars I do not know where to get a return less aftermarket pressure regulator for fuel injected cars. Have to go to school again, I suppose. Was so stupid to fit a return line to any car I converted to EFI. First one was in 1982. So just the 2 cent of an old idiot.
Sorry I bothered you. Good luck!

PS jonbill do you really think of a MR2 as a car? Strange idea...

[PSIG]

In performance applications, the fuel is typically routed through the fuel rails to the regulator, in order to flush any air bubbles and to maintain lower fuel temperatures. In this method, the main fuel tank is used as a giant heat sink. If your goals do not include max power, but may include minimum emissions, maximum economy (with emphasized tuning), and perhaps a slight cost reduction, then deadhead fuel rails can see a benefit, but just be aware there are side-effects to variable fuel temperature.

As OEM engine temperatures continued to rise (mostly for emissions, as higher temperatures make less power... damned science ), they benefit from better fuel vaporization. However, the running condition is not stable if allowed to heat, unless also monitored with a fuel temperature sensor for ECM compensation. In earlier Lambda 1 emissions systems, the CLT was used as a rough guide for fuel compensation along with O2 comp, but now rely almost exclusively on fuel sensors and newer catalytic converter designs that don't require Lambda 1.

With a simple "fun" car, where power or stable Lambda are not at the top of the list, deadhead systems can work, but be prepared for odd changes in your tune. Results that your Mom may not notice, but that we can see with our data streams and logging, or feel because we are into that type of thing.

Agreed, how or what you do is entirely up to you and your personal goals. For tuning simplicity and predictable performance, regulate after the rails. If the deadhead side-effects don't bother you, then stick with it and just have your fun.

[gpineau]

My pressure regulator is not on the fuel rail either. It is directly on the output of the fuel pump. The output goes onward to the fuel rail and excess is routed back to the the tank. But heat soak is not that big a deal on a motorcycle most everthing around the engine is exposed to free air.

[jonbill]

Thanks David and Chris, I'll get another metre of hose and move the regulator to the end of the rail and see what benefits I get. it'll place the regulator near the viscous fan so that might help cool it.
It seems to me that any regulator thats controlled by a metal spring will suffer a reducing spring rate with rising termperature and so variation in regulation. Is there a class of regulators that don't use a spring?

[Chris Wolfson]

See, if routed as usual (on all cars I know, Bosch, Weber Marelli and Siemens etc.) the regulator is constantly flushed with fresh fuel. So the question does not surface at all, what a regulator might do at 150°C, as the fuel will be gas at that point, anyhow. So no one can point you to a regulator for high temperatures.

Just to point it out again:
the fuel starts at the tank,
usually has a coarse pre filter,
passes the pump,
goes trough the fine filter,
enters the fuel rail at one side,
exits the fuel rail at the other side,
is pressure regulated by the regulator and
returns to the fuel tank.

This may not be the only way to do it, but it is the accepted and expected way to run fuel with an electronic injection system.

Because of the hot start problems, even many carburetor cars used this return system. Some, mostly x-flow engines, did not need it, but when the carb was directly above the exhaust manifold, without such a system you usually had to run the starter for quite a while. A fix was to use an electric fuel pump instead of a mechanical, but this was not safe in case of an accident. Even as it was used in cars coming fresh from the factory. Today we (have to) use an electronic relay that cuts out the pump after a few seconds without rpm signal. Just as the priming function of an EFI.

[PSIG]

Just a reminder that the FPR already flows constant fuel as it bypasses, so it should be relatively cool during operation. If it is in a position to be heat-soaked after shutdown, that is a different issue and should be addressed with location, heat shielding, etc. I did a quick calculation on your posted AFRs and fuel pressure, and the difference from 46 to 43 psi would alter the AFR by about 0.5 (e.g. 14.5 to 15.0), so it's not all about fuel pressure. Let us know how you get along.

David

[jonbill]

That's interesting, I suppose reduction in fuel density will also make a small impact. I've got some hose on order, hopefully it'll come in the next few days (even though ebay says 2 weeks).
What else could be involved? do hot injectors work less well?