Re: TBI, was Re: Hornet status

[farna@xxxxxxx]

That's not how the pressure regulator works. Basically it maintains pressure in the rail. The pump pushes fuel up into the rail against the regulator. Once pressure reaches 39 psi a valve opens and lets fuel flow back to the tank. The less demand by the injectors the more fuel goes back to the tank. The regulator has a vacuum control also. There is a spring that pushes against a diaphragm, but the spring is vacuum assisted. Less vacuum means less assist, so the spring is "harder" whne you punch the throttle and vacuum drops. Newer models (97+) have a simple spring pressure regulator in the pump body or mount (I haven't actually looked at one) in the tank itself, just like the oil pressure bypass in the engine. 

I'm running an external pump now. It just needs to be mounted as close to the tank as possible and preferably at the same level as the tank. I have mine mounted just above the tank on the right rear suspension rail, so it also has ~3' of hose to suck through also. Works fine, but I do need to remount it closer and/or lower in relation to the tank for longer life. Lower will probably be better, but will shoot for both when I get around to moving it. 

I don't think the booster idea will work so good is all. It isn't hard to mount an external pump near the tank. The XJ tank is close to the right size though. I may check on that, but the filler neck on the 63 wagon is in a rather unusual spot. Might take some creative work to fix that. 

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 -------------- Original message ----------------------
> >
> >I assume the problem is that whateverthepumpandregulatoris, that
> >it will "pump up" to it's highest-possible value when there's no
> >or little fuel being consumed; as soon as you "get on it" and fuel
> >is taken out the pressure will drop towards the lower end of the
> >regulated range, meaning the fuel pressure fluctuates with demand.
> >Not Good.
> >
> >The circulation business is basically a big "leak" that causes
> >"demand" all the time, so that the regulator can stay close to the
> >middle of it's range.
> >
> >So I'll just circulate back to the front of the booster pump, or
> >to the front of the mechanical pump. I see no reason why it must
> >go all the way back to the tank. It would help lower fuel

> >temperatures, but that's not a problem I see in my application.