This has been fun. I feel like I've learned some things,,,,which I try to do each day. Sometimes I learn something new before even 8:00AM....and I can give my brain the rest of the day off .

Often this auto repair stuff isn't so much learning the science of things but, rather, just learning what everything is supposed to do, why it is supposed to do it, and recognize when it isn't doing it. For the life of me I can't understand how a diode actually works....but I know what function it performs and how to test it.

I admire someone like Leo who has enough knowledge and understanding of something to sit down with a pencil and paper and sketch out an illustration of it for the rest of us.

I'm reminded of my many experiences with OBDI and OBDII cars with trouble codes and live data streams showing us what the management system is seeing and doing. In the grand scheme of things OBD is a boon but it can also result in some serious head scratching...as what you're seeing must be interpreted. Sometimes differentiating between cause and effect was a real exercise, at least for me. You have to sort of mentally crawl into the ECU and view things from its perspective .

Many say that mechanics today "...just plug the car into a computer which tells them what to fix". In many cases, yes, but oftentimes not. There can be some real analysis involved. And even some seemingly cut-and-dried trouble codes can require lots of sussing out. There was one failure code on my XJR that required something like 27 diagnostic steps to narrow down the actual root cause.

Anyhow, I'm rambling....

Cheers
DD

 

So, HE XJS' fuel pressure should be ~28.25 psi at idle. ~36.25 psi at WOT. That's the net result of this discussion right?

I see closer to 36 psi at idle, 42 psi with no vac. Should I care? Based on the pressure difference, the same duration injector pulse will deliver 20% more fuel flow with my pressure too high. Perhaps my new Bosch FPR is wrong for this vehicle?

Realistically, I suppose the only reliable way to know what my individual engine requires is an air/fuel meter. The ECU is going to do it's thing regardless. If I can determine a fuel pressure that results in a proper stoichiometric mix ( in open loop ) then that's what I should use.

 

Simple answer yes.

As the rail pressure increases the injector will squirt more fuel for the same injector pulse width. So the idea of a variable regulator in the V12 is to provide the required fuel at WOT around 13:1 and up to 16:1 for cruising.

 

for your interest; you tube has some good information about FPR(fuel pressure regulators).

ron

 

There certainly is, I was interested in at how fuel pressure effects atomisation there was a good video done by a company that refurbishes injectors.

 

.

i have a good article about atomization

i'll look it up!

ron