p1 fitted with walbro uprated fuel pump my fuel pressure used to sit on idle between 3.2-3.4 bar.now seems to be sitting steady at 3.6bar on idle and on boost at 1.3bar boost fuel pressure 4.6bar.any ideas about jump in pressure and shd the reading at 1.3bar boost be 4.9bar fuel pressure.set up aps fmic/cold air full decat hybrid vf28/walbro fuel pump and tek 3.do i need bigger injectors or better pressure regulator.when it was at 3.2fuel idle and 4.6 at wot this wld seem right it.

With the standard regulator, then 3.0 bar plus manifold relative pressure, but it might be a bit higher with an aftermarket fuel pump than before if the previous pump was struggling.

At idle you would expect 3.0 bar MINUS 0.6 to 0.7 bar idle vac, at 1.3 bar boost you would expect 3.0 bar PLUS 1.3 bar.

This is for the standard 1:1 static fuel pressure reg. Your idle pressure seems high, not dangerously so, and fine if intended and mapped around. I agree with your calculations on 4.9 bar being correct if you idle pressure is 3.6 bar.

The idea is that you have a constant 3.0 or whatever you choose bar perfusion pressure across the injectors with a static rate regulator.

[Edited by john banks - 1/23/2003 3:03:02 PM]

john car was mapped when fuel pressure at idle was 3.2-3.4 bar and this wld have been fine with 1.3 bar boost and 4.6bar fuel pressure.any ideas why fuel pressure wld jump to 3.6 bar on idle as at wot at moment i seem light on fuel pressure by 0.3 bar.havnt ruled out faulty sender but am guessing at other options as well.

Dodgy FPR? Would need to know if the fuel mixture is weak on full boost as well.

btt

Paul, the std fuel pressure reg gets overpowered by the Walbro pump and can act in a very variable fashion, even to giving the same fuel pressure for idle and 0.3 bar boost for example. I had a nightmare with mine until I fitted a decent pressure reg, now no problems, if the fp is varying as you say then a reg is essential to stabilise, should be adjusted to suit the fp at wot that the car had when it was mapped.

thanks bob i have sent u an email i had lost ur contact due to kids messing up computer and the whole thing had to be rebooted..paul

Hmm Interesting info Bob.

Skassa

I fitted a permanent fuel pressure gauge into the car (SPA) when I was having trouble ... quite an eye opener.

Wonder if this is part of my bother with inconsistent cranking times with the 550s and Walbro... idling one minute at normal coolant temp with -1 to +1% air fuel correction, next time pull up at idle it is at +7% or something. Starting from cold sometimes it only turns over barely once, other times a few goes, from warm more consistent, idle sometimes more uneven than I would like, but maybe 550 lack of granularity compared with 440s.

bob did u rcve my email.the fuel pressure at wot seems the same 4.8bar ish it is just the idle fuel pressure that seems to have jumped and thrown out the 1 to 1 ratio of fuel pressure and boost pressure ie if idle fuel pressure was 3.3bar then on max boost of 1,5bar fuel pressure wld be ok at 4.8bar

[Edited by myp1 - 1/24/2003 10:00:20 PM]

Hmm hmm,
Mayby i should not have sold the FPR i got from mark!!!.

Time to order a new one!!.

Skassa

Bob,

What PR are you using now? I've experienced the same fluctuating problems with the OEM one, and now have the same problem with an adjustable FSE reg I'm trying.

out of interest what are the symptoms with yours i spoke to bob this morning and he refered me to mark at lateral perf who does the cheap one and the expensive one.guess which one bob has