Fuel Pressure Setting??
Discussion
Depends on the car, i'm assuming its a flapper since i gather they don't work on hotwire, the stock settings are; 350i- 36psi, the 390se- 44psi.
I'd take these with a pinch of salt though because these may vary, my 390 requires 50psi.
I don't know if you can adjust the rising rate bit on these regulators but you're gonna have to set the fuel pressure for best compromise, you might have to run a touch leaner to get the correct mixture at higher revs or vice versa
I'd take these with a pinch of salt though because these may vary, my 390 requires 50psi.
I don't know if you can adjust the rising rate bit on these regulators but you're gonna have to set the fuel pressure for best compromise, you might have to run a touch leaner to get the correct mixture at higher revs or vice versa
Edited by B-Reight on Thursday 7th May 20:30
I've just picked up a fuel pressure gauge and will be maesuring the standard pressure and the stall pressure (as per steve heaths bible) this weekend in preparation to fitting a rising rate regulator. be interested to know how you get on and what pressure you set. I also have a flapper 350i
Carbonwedge,
I've always been lead to believe that the static pressure with a rising rate regulator should be set at 40 PSI... any more and the injectors start to weep fuel...
with the engine running and vacum pipe connected fuel pressure does vary (usually downwards)
I didn't pluck the value out of thin air, just can't remeber where I read it.
That's what my FSE has been set to ever since I fitted it some years ago.
Regards,
Brian (and a Red 350i)
I've always been lead to believe that the static pressure with a rising rate regulator should be set at 40 PSI... any more and the injectors start to weep fuel...
with the engine running and vacum pipe connected fuel pressure does vary (usually downwards)
I didn't pluck the value out of thin air, just can't remeber where I read it.
That's what my FSE has been set to ever since I fitted it some years ago.
Regards,
Brian (and a Red 350i)
The initial pressure was about 35PSI, so I've upped it to 40PSI, and checked the nut on the overrun valve as per the bible - which was already wound up tight. I've only been for a few short drives so far, and think it possibly feels a litle overfuelled.
I think the pump could do with replacing at some point as the stall pressure was a little on the low side, but i don't think it's affecting things. I guess it's possible the injectors could be weeping a bit at this age?
Going to try about 38PSI and see how that goes.
I think the pump could do with replacing at some point as the stall pressure was a little on the low side, but i don't think it's affecting things. I guess it's possible the injectors could be weeping a bit at this age?
Going to try about 38PSI and see how that goes.
CarbonWedge said:
The initial pressure was about 35PSI, so I've upped it to 40PSI, and checked the nut on the overrun valve as per the bible - which was already wound up tight. I've only been for a few short drives so far, and think it possibly feels a litle overfuelled.
I think the pump could do with replacing at some point as the stall pressure was a little on the low side, but i don't think it's affecting things. I guess it's possible the injectors could be weeping a bit at this age?
Going to try about 38PSI and see how that goes.
Paul, if you are running a bog standard flapper system with a 3.5 liter lump and original spec ECU it's not clear to me what you are expecting to achieve by setting the base pressure higher than 36 psi?I think the pump could do with replacing at some point as the stall pressure was a little on the low side, but i don't think it's affecting things. I guess it's possible the injectors could be weeping a bit at this age?
Going to try about 38PSI and see how that goes.
Everything in your basic system was optimised at 36 psi using a standard FPR which varied the fuel rail pressure between 36 and 26 psi.
When accelerating and at full load the ECU injects extra fuel on alternate cycles by triggering the acceleration and full load enrichment circuits.
So the ECU has the responsibilty to keep the stoichiometric ratio at the optimum level (typically 14.7:1). The FPR maintains constant pressure across the injectors at exactly 36 psi at all varying inlet manifold pressures and injector pulse width is calculated by the ECU to respond to the variable amount of air passing thro the flapper AFM.
By upping the base fuel pressure to 40 psi your overfuelling is now 4/36 ths higher or 11% too high. Definitely too rich for normal running on a bog std 3.5 flapper. The money supply also decreases at the same rate.
Sure the R/R FPR may be required to raise the fuel pressure under full load and during acceleration so that you get the sensation of more power (a kick in the pants) from a richer mixture, but dont forget that the ECU is already providing enrichment as mentioend for those two conditions.
To gain maximum benefit from the R/R FPR one would think that you might need a modified ECU that had inhibited internal enrichment and modified pulse width where necessary.
Now all of this R/R FPR stuff is completely foreign to me because I am only faniliar with the Bog Standard system, but I know one thing for sure, if you are atificially increasing the fuel pressure by increasing the base setting and the FPR is also doing the same thing, and the ECU is also doing its enrichment duties, then to make any sense of whats happening you have to bring in more air to get the mixture lean enough for the engine to be anything close to efficient under normal driving conditions.
That implies stiffening the spring inside the AFM to reduce the fuel being injected to weaken the mixture accordingly. Crazy.
But that also suggests a further problem! The AFM is matched to 3500 cc engine which will probably not breath any more air to get even bigger bangs unless it has been severely fettled or the capacity is increased.
So - as I say - its not clear what to recommend without knowing the objective.
Regarding the Over-run valve. It will have nil effect on any normal condition related to idle, cruise, acceleration or full load and has no working relationship to your fuel pressure machinations. It only affects the mixture on over-run.
It may be that some of the above will need further reading or clarification ( IE - fuel , blah, blah, blah) in which case go here for an index to all the parts mentioned and much more too:
http://www.vintagemodelairplane.com/pages/Rover_Te...
Regarding your objective, you may simply be wishing to improve your ancient system from where it is performing today in which case there are 15 things you can do to reduce efficiency losses.
Call it a magic elixer health check for the cost of - er - nothing much at all.
http://www.vintagemodelairplane.com/pages/Snippets...
honestjohntoo said:
Everything in your basic system was optimised at 36 psi using a standard FPR which varied the fuel rail pressure between 36 and 26 psi.
Thats for that explanation that makes a lot of sense, it certainly runs best at 36psi, so thats where i'll leave it. Just tried the 40PSI as per the bible and other recommendations - I don't honestly know what I was expecting!Regarding the overrun valve, the reason i'm led to believe for winding it in (strengthening the spring and requiring a higher vacumn to open it) is that the R/R FPR in overrun situation provides lower fueling than the standard FPR - therefore doesn't require extra air for compustion quite so readily.
.
[quote=CarbonWedge]the reason i'm led to believe for winding it in (strengthening the spring and requiring a higher vacumn to open it) is that the R/R FPR in overrun situation provides lower fueling than the standard FPR - therefore doesn't require extra air for combustion quite so readily[/quote
I had not come across that explanation before, but I suspect its something that may have crossed over from folks with newly engineered systems that are making proper use of R/R gadgets as opposed to just sticking one on a bog std system.
Thinking it thro' the fuel pressure 'across the injectors' is not normally less than 36 psi in any running condition, and the R/R gadget only raises pressure for peak demand, so to me, less fuel pressure on over-run does not seem a normal "physics class" result. But frankly I just dont know for sure.
Perversely, I came across another 'led to believe' side effect of screwing the nut right in. First the manifold vacuum never gets strong enough to overcome the increase spring pressure and allow in the needed air on over-run BUT it is strong enough to suck oil and gasses up the inlet valve stem guides on a worn engine allowing such fouling to get into places one does not really want it, creating some of the filth one sees in the areas below the rockers.
And of course the reason why its there in the first place, was to neatly allow combustion of the excess fuel vaporised by the high depression from that condensed on the plenum walls and thereabouts, preventing the unburned fuel getting into the hot exhaust system then igniting with percussive effect and flaming exhausts, just the job for boy racers and hot rodders but not so clever running downhill towards home after midnight and upsetting the neighbours. What? What?
[quote=CarbonWedge]the reason i'm led to believe for winding it in (strengthening the spring and requiring a higher vacumn to open it) is that the R/R FPR in overrun situation provides lower fueling than the standard FPR - therefore doesn't require extra air for combustion quite so readily[/quote
I had not come across that explanation before, but I suspect its something that may have crossed over from folks with newly engineered systems that are making proper use of R/R gadgets as opposed to just sticking one on a bog std system.
Thinking it thro' the fuel pressure 'across the injectors' is not normally less than 36 psi in any running condition, and the R/R gadget only raises pressure for peak demand, so to me, less fuel pressure on over-run does not seem a normal "physics class" result. But frankly I just dont know for sure.
Perversely, I came across another 'led to believe' side effect of screwing the nut right in. First the manifold vacuum never gets strong enough to overcome the increase spring pressure and allow in the needed air on over-run BUT it is strong enough to suck oil and gasses up the inlet valve stem guides on a worn engine allowing such fouling to get into places one does not really want it, creating some of the filth one sees in the areas below the rockers.
And of course the reason why its there in the first place, was to neatly allow combustion of the excess fuel vaporised by the high depression from that condensed on the plenum walls and thereabouts, preventing the unburned fuel getting into the hot exhaust system then igniting with percussive effect and flaming exhausts, just the job for boy racers and hot rodders but not so clever running downhill towards home after midnight and upsetting the neighbours. What? What?
Hi Paul, I took a measurment today and got 39psi. Thats with a standard fuel pressure regulator. Stall pressure was >90psi. I replaced the fuel pump a few years ago with a Bosch item so I guess I should have expected a decent stall pressue. This thread is becoming very interesting and making me think twice before shelling out for the rising rate FPR. Does anyone on the forum have any experience based on rolling road data with and without a rising rate regulator esp. for a flapper 3.5?
Hmm must get around to fitting my pressure gauge so I can get a baseline for my flapper 400.
Beginning to wonder if a RR reg is worth it, it's looking like an adjustable non rising rate is a better bet
I know the RR can help remove the lean mixture on Hotwire but I can't see any great benefit on a Flapper ?
Or have I missed something ?
Beginning to wonder if a RR reg is worth it, it's looking like an adjustable non rising rate is a better bet
I know the RR can help remove the lean mixture on Hotwire but I can't see any great benefit on a Flapper ?Or have I missed something ?
Edited by B@man on Sunday 17th May 17:48
Nigel_350I said:
Stall pressure was >90psi. I replaced the fuel pump a few years ago with a Bosch item so I guess I should have expected a decent stall pressue.
Crikey!!! Mine was more like 42PSI 
.I know the bible say anything less than 45 and you should think about replacing it, have you got a part number? Cheers!I have heard that the RR regs can be used to correct leaning out at the top end on flapper equiped cars, no idea if it actually works in practice.
You would really need to get your car on a dyno to see if you have a lean mixture problem anyway before installing an adjustable regulator of any kind anyway.
The flapper system is open loop so the effect of increaing or decreasing the fuel pressure using a normal adjustable reg will richen or lean the mixture across the entire range of rpm/load as the Pulse Width to the injectors remains the same.
Using a adjustable reg on a flapper is ultimatley a compromise, my car runs slightly rich lower down the rev range so that the mixture at higher revs is spot on.
I have no idea if the flapper ecu is reprogrammable/adjustable in any way. As i understand it, these adjustable flapper ECUs you occasionally see kicking around work by adjusting the resistance value in line with the temp sensor to increase/decrease the fuelling across the whole range as well.
You would really need to get your car on a dyno to see if you have a lean mixture problem anyway before installing an adjustable regulator of any kind anyway.
The flapper system is open loop so the effect of increaing or decreasing the fuel pressure using a normal adjustable reg will richen or lean the mixture across the entire range of rpm/load as the Pulse Width to the injectors remains the same.
Using a adjustable reg on a flapper is ultimatley a compromise, my car runs slightly rich lower down the rev range so that the mixture at higher revs is spot on.
I have no idea if the flapper ecu is reprogrammable/adjustable in any way. As i understand it, these adjustable flapper ECUs you occasionally see kicking around work by adjusting the resistance value in line with the temp sensor to increase/decrease the fuelling across the whole range as well.
Edited by B-Reight on Sunday 17th May 18:31
I tend to agree a rolling road set up probably makes sense. For now I'm going to stick with the std regulator. The car runs well with it and I'm reluctant to have it running richer than needed especially as I have no real way of measuring the mixture. The flapper ECU I believe can be altered by swapping out some resistors but it's not like the hotwire where a re-mapped chip can be used.
Good points,
I always thought the Hotwires ran lean at high RPM rather than the flapper ?
Flapper ECU is mostly analogue so it's not possible to re-map it by conventional methods however by messing with various component values and/or adding piggy back boards to intercept and modify internal signals you can change the fueling profile - Hence the Mark Adams Tornado ECU and while on the subject did anyone buy the one that was on ebay last week went for just over £100
Me and a mate who owns a LPG converted Scooby are going halves on a Wideband O2 sensor kit (probably techedge) so we can hopefully sort out his piggyback LPG ECU and run some tests on the wedge as it is before I start messing with the induction / ignition systems.
Once I've finished the other jobs
Yes Dyno sessions would be nice but if you are doing a lot of the tuning work yourself it's gonna cost a fortune to keep visiting the rollers so in this case the WB02 will very quickly pay for itself and help prevent engine damage if it goes really lean the real dyno session can be booked once the fiddling (sorry tuning) is finished !
A bit off topic but looking at the exhaust gas is really the only way to be sure that the AFR and therefore fuel rail pressure is correct for the engine.
I always thought the Hotwires ran lean at high RPM rather than the flapper ?
Flapper ECU is mostly analogue so it's not possible to re-map it by conventional methods however by messing with various component values and/or adding piggy back boards to intercept and modify internal signals you can change the fueling profile - Hence the Mark Adams Tornado ECU and while on the subject did anyone buy the one that was on ebay last week went for just over £100
Me and a mate who owns a LPG converted Scooby are going halves on a Wideband O2 sensor kit (probably techedge) so we can hopefully sort out his piggyback LPG ECU and run some tests on the wedge as it is before I start messing with the induction / ignition systems.
Once I've finished the other jobs
Yes Dyno sessions would be nice but if you are doing a lot of the tuning work yourself it's gonna cost a fortune to keep visiting the rollers so in this case the WB02 will very quickly pay for itself and help prevent engine damage if it goes really lean the real dyno session can be booked once the fiddling (sorry tuning) is finished !
A bit off topic but looking at the exhaust gas is really the only way to be sure that the AFR and therefore fuel rail pressure is correct for the engine.
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