Fuel Pressure - What the jig?

[WildCards]

Richy Rich fitted my Adjustable Fuel Pressure Regulator over the weekend so I can now alter the pressure, but can anyone tell me whats the point? Are there any benefits or pitfalls to running high or low pressure?

Cheers

[Eurospec]

Higher presure = more cc's delivered per sec than the injectors are rated at. Turning the pressure up will therefore allow you to flow more fuel. The issue with this is you need to be mapped to take account of it, otherwise the ecu will essentially 'overfuel' in all situations. For example, say you need more fuel at WOT because you have the boost turned up past what the std injectors can cope with. Downside is, you will run rich at idle, unless you have an afc or something to control it. You can use this method to wince every last bit out of a certain size injector without going up a size, but to me i wouldnt do so. If you have more fuel requirements than the injectors can support, then go with bigger injectors.

Its horses for courses.

Lower pressure = the converse of the above, ie less fuel per sec of squirt.

Cheers,

Ben.

[Funkstar]

^^^^^ Great Info.

[Paul Beazer]

Which begs the question steve, if you're looking to sell why? Unless you go the whole hog, there doesnt appear to be much point?

[WildCards]

I already had the pump and FPR sitting gathering dust. Was going to Nicks over the weekend and thought I'd take them.

I am selling the car, just very quietly :curtain:

[Eurospec]

double post- sorry!

[WildCards]

The pump is a 255lph effort but not Walbro. What Hotwire thing?

[Eurospec]

^^^^^ Great Info. Thank you:happy:

Also, a decent aftermarket FPR will have a better response time than some stock ones. Hardly noticable at all but some people say they make the car a bit snappier.

If the pump is a warlbro 255lph one, did you do the hotwire thing?

Cheers,

Ben.

[Eurospec]

The warlbro 255lph pump, which a lot of people get (i think its model number is 341) actually flows LESS at normal voltages than a standard pump.

Mitsi fit a fuel pump relay which switches the voltage on the pump from about 8v at idle to about 11v or a bit more at WOT.

The warlbro pump, though it will flow more than the std one, is much more voltage sensitive. If you dont step up its voltage it will flow less than a standard pump.

http://img.photobucket.com/albums/v379/benh/flowtest-walbro.gif

It doesnt really show it on the graph, but you get the idea. The flow of the warlbro is very sensitve to voltage. At the normal say 8-11v you typically get at the pump, they do flow less than the std pump.

The solution is to hotwire it. This can be done 2 ways, firstly simply bypassing the original pump relay, thus feeding approx 12v all the time, or more correctly a complete bypass of that circuit using a second relay to feed the pump battery voltage (typically 14.5 volts when the engine is running). Then the pump will flow plenty.

Many of the warlbro pumps are noisey though, especially when hotwired. Infact the Warlbro 341 wont actually flow 255lph unless it is hot wired.

Cheers,

Ben.

[Kieran]

Has anyone done the Hotwire mod to a Legnum or a Galant? I've read up about the 3000GT method, so I'm familliar with the concept.... I just wanna know which wires to chop!:huh:

[valmes]

Benh already said everything there is about fuel pressure vs. injector flow etc. GTO guys know their stuff well!
/GJ

Although I would disagree that Walbro (I am using 342 model) would give you less flow than stock pump at stock, relay regulated, voltage... look at the attached picture.

I just wanted to add, how, you would go about raising fuel pressure with an afpr or in other words, what to set your base fuel pressure to.

Do it this way - plan ahead on how much boost you are aiming at, then substract it from 75 psi (recommended max stock fuel line pressure under boost - remember the higher the pressure in your rail, the less flow you will get from your fuel pump!) and that's where you will have to set your base pressure. Stock is set at 43.5 psi with vacuum hose disconnected.

Lets say you are going to run 15 psi (~ 1 bar) of boost. That gives you 75-15=60 psi of max base fuel pressure... I would even suggest some margin of safety and set it to 55 psi. So you would well be in spec for the fuel pump and your stock 390 cc injectors would flow 438.5 cc. That would equal to nice 70% injector duty cycle at 12.5:1 AFR at most load/rpm. More if richer, but still within reasonable limits.

Here goes link to engine calculator again... it's all in there (sorry if I repeat it too often... it just has all the needed calculations): http://four.fsphost.com/valmes/ecv1_2.htm

[valmes]

Has anyone done the Hotwire mod to a Legnum or a Galant? I've read up about the 3000GT method, so I'm familliar with the concept.... I just wanna know which wires to chop!:huh:

I've done it a long time ago... /Devil5

[Wodjno]

Has anyone done the Hotwire mod to a Legnum or a Galant? I've read up about the 3000GT method, so I'm familliar with the concept.... I just wanna know which wires to chop!:huh:

Don't Know ? Haven't read up on any ! But i would say you cut the Positive to the plug going to the pump and wire it straight to 12v ??

[Wodjno]

I've done it a long time ago... /Devil5

OOOOOOOoooooooooooooppppppppps :huh2:


Prolly Gonna be totally confused now.. And Rectified :rolleyes3

[Kieran]

I've done it a long time ago... /Devil5

I remember you mentioned that you had Val - Was it easy enough to do?

Tell me, pretty please:d :d :d /Wave

[Wodjno]

Also think i remember summat about, upgrading the wiring to take extra current being drawn :huh:

[valmes]

I remember you mentioned that you had Val - Was it easy enough to do?

Tell me, pretty please:d :d :d /Wave

I did it - "the simple way".
Got two thick "audio wires" and ran them all over the place... until it was hot and wired... /Banana
Ohhh... it's soooo early in the morning, let me think this one again... ahh, yes, now I remember! :beatnik2:

Two wires directly from the + and - of the battery to the fuel pump, bypassing the stock relay (but had to add additional relay, so it wouldn't work while car is parked /Nuuu) that's under your back sit (on the drivers side for RHD). 20 min job!

[Kieran]

Simple as that, eh? Cheers Val, that'll do nicely. I can figure the rest out with my multimeter!:D

[Eurospec]

Yeah, like valmes says, a way to do it (not being prescriptive here as i dont know where the galants std relay is without getting my manual out /lol ) is right there at the pump.

Get some nice heavy grade wire, like the stuff you use to drive an amp. I use 4 guage minimum (the fatter the wire the less voltage drop) and run it from the battery all the way through to the pump. In all honesty you probably dont need it to be this heavy, but anyway. Do isntall an inline fuse, i use 20 or 30 amp ones, as close to the battery as you can.

The reasson for the fuse is to stop the battery arcing out if you get a short. Remember all those BMW 7 series that brake down because the posative lead from the battery (under the rear seat) arcs out where it goes through the bulkead?!

Anyway, remove the pump inspection wire and identify the live feed to the pump. Connect 'the car end' of this wire to the coil input on a 40 amp relay. No sense putting a baby relay in when a bad boy that will more than cope with what you will throw at it costs about 50p more. Connect the other end of the relay coil to earth.

Connect the switched input to the big fat boy wire you installed from the battery, and connect the switched output back to the pump wire that you cut before.

Job done.:tiny:

This will give you about 14.5v at the pump and it will still all be controlled by the ecu, so it will energise when cranking etc, but importantly it will also shut off if the ecu kills the power, for example in case of an accident. Some methods which i have seen in the past totaly bypass the pumps original feed, thus preventing fuel shut off in the case of accident.

By the way, IMO, the standard toyota UK Mk4 'supra pump' is the daddy of these in tank pumps, its rated flow is 310lph. I have one in my gto, and at 16 volts it will blow enough fuel to support 6 680 cc injectors at 28psi of boost- you need a boost-a-pump (a lot like a stereo amp) to get the voltage up that high, but it does the bizzo and its simpler than the dual pump set ups you see. Dual pump is fine, but i have an irrational fear that 1 pump would fail and i would have enough fuel tokeep running, but only in an engine meltingly lean state! At least if my single craps out, i stop.

Cheers,

Ben.

[pezza]

Yup sounds simple enough to do.... I don't recall what gauge of wiring is used for the current stock pump.... is it really not up to the job? :thinking2

[Eurospec]

Yep, stock pump, stock voltage, stock wiring is fine. Bigger pump, then you get into issues of the pump characteristic of voltage vs pressure vs flow. The key is to match your components to achieve what you want. What you are needing to do is feed the pump enough voltage to get the flow you need at your max fuel line pressure.

Example:- (and forgive my ignorance as to the std pump voltage/flow/pressure curve of the vr4 pump) lets say the std pump can flow 140 litres an hour at 58psi. This is enough to drive 6 x 390cc injectors at 100% duty and 1 bar of boost. However, if it cant, say it can only flow 120lph at 58psi, then you will be lacking fuel and you will run leaner than you intended. Sure the injectors will open up, but the fuel wont be there to come out, so you run lean. IF- and like i say i dont know the characteristic of a stock pump- this is the case then you can hotwire the pump to give it a higher voltage, thus pushing it further up its curve and enabling it to flow enough.

The orignal post was mentioning an upgraded pump, and upgraded pumps have different flow/pressure/voltage characteristics which is why i was getting to the subject of hotwiring. After all its an important technique to get the flow you need from the pump. The warlbro 255 (model 341) wont actually flow anything like 255lph unless you step up the voltage. If you look in the chart its flowing like 225lph ish at base fuel pressure (ie zero boost) at 12volts. Most cars are running less than 12volts at the pump anyway- normally 10-11, maybe a bit more. So if you need 255lph of fuel delivery at say 1 bar of boost, then there is no way the warlbro can do it without being hotwired.

Conversely, the good news is that the same curve also tells us that the warlbro 255 pump at 12 volts will support 390cc injectors past 30psi of boost! Now by the time you have got there you'd have needed way bigger injectors anyhow!

These cars tend to run rich anyway when in open loop (WOT) so i dont think there is a generic fuel delivery issue. I'll drag out a data log and see what the IDC's look like for a standard boost, wide throttle pass.

The only time you need to think about changing stuff is if you need greater fuel delivery, for example if you are running more boost.

A few years back in the GTO world, lots of people suddenly became aware of the fuel pump hotwire mod and immediately began to take 'advantage' of it. People were posting up results and saying the car felt stronger etc. I'm not saying they didnt, but maybe they had old warn pumps which were under flowing, but in very many cases, when we did gas analysis of these hotwired but otherwise standard cars, we found they ran rich at idle. The reason? BEcause the standard fuel pressure regulator was unable to flow as much as needed at low throttle openings (most fuel is going back to the tank) and so the rail overpressures and hence the car runs rich! Thats the reason why Mitsu stepped down the voltage in the first place!

So, after the worlds longest post (lol) what it all means is:- If you need more fuel delivery, then you need to either hot wire your std pump, or get an upgrade, and maybe hotwire that, dependant on your fuel flow and pressure requirement. As soon as you are delivering more fuel to the rail than the std regulator was designed to cope with, you need to upgrade that to one that can handle the flow.

To me, and its just a personal opinion, i would only be doing fuel system mods if you need to do so, and the only reason i can think of to do that would be if you need to get more fuel in to the engine. The exception would be these snappy response pressure regs- although the difference would be minor IMO- just the manufacturers claim faster response.

Hope thats useful somewhere along the line!

PS, valmes, that engine calculator ROCKS!

Cheers,

Ben.

[Kieran]

Ben, that's a cracking post - Thankyou!/yes

Have some rep! :thumbsup:

[Paul C]

So is this the recommended way to hot wire the fuel pump?


12991

[Eurospec]

Yes,

I drew this for you just to be clear about the relay connections:thumbsup:

http://img.photobucket.com/albums/v379/benh/Fuelpumphotwire.jpg

Cheers,

Ben.

[Wodjno]

All understood nice and clear :thumbsup:

But now for the Stooooooooooooooooooooooooopid question../dunce

What does 1 of these relays look like ?? How many ins and outs do they have and where do i purchase 1 from ?? Pic of 1 would be much appreciated :afro:

PS ... And what sort of PRICE so as i know i'm not getting ripped off !!

[Eurospec]

All understood nice and clear :thumbsup:

But now for the Stooooooooooooooooooooooooopid question../dunce

What does 1 of these relays look like ?? How many ins and outs do they have and where do i purchase 1 from ?? Pic of 1 would be much appreciated :afro:

PS ... And what sort of PRICE so as i know i'm not getting ripped off !!

Its just a bog stanadard little black box with 4 connection pins sticking out of it. About the size of a match box, but square.

Should cost you about £3 or £4 in a motor factors or £7 or so in Halfords or wherever.

Its a std 4 pin switching relay 30 amp or 40 amp will be fine. I go with the bigger one just to be super safe.

Cheers,

Ben.

[Wodjno]

Its just a bog stanadard little black box with 4 connection pins sticking out of it. About the size of a match box, but square.

Should cost you about £3 or £4 in a motor factors or £7 or so in Halfords or wherever.

Its a std 4 pin switching relay 30 amp or 40 amp will be fine. I go with the bigger one just to be super safe.

Cheers,

Ben.

Cheers Dude :thumbsup: Much appreciated :d

[valmes]

"Off the shelf" part:

http://www.ipsmotorsports.net/product_info.php?cPath=2945_986_998&products_id=799

[Eurospec]

IPS are a great supplier too. Talk to Jeff.:smoking:

Cheers,

Ben.

[enigma]

I simply cant believe peoples blind faith in these regulators. To fit one without any method of assessing what you are doing to the AFR is not all that clever, fitting one where you have no way of assessing the AFR OR what pressure you are running is simply stupid. /JawDroppi

I am also shocked that some of the info in this post is new to people. Anything that adjusts the fuelling to your engine can and most likely will end in tears if you are not careful.

[WildCards]

I didn't know the gauge was faulty until it was fitted.

Bern's guide to fitting says the stock pressure is around 43PSi if I recall, and AFAIK he's had it fitted for a while with no repurcussions (sp?).

[enigma]

I didn't know the gauge was faulty until it was fitted.

Bern's guide to fitting says the stock pressure is around 43PSi if I recall, and AFAIK he's had it fitted for a while with no repurcussions (sp?).

Granted but at this point it should have been removed and the stock one replaced.

If you are running stock pressure............why bother? :stop: There are many areas that would benefit more from your hard earned.

[WildCards]

If you are running stock pressure............why bother? :stop: There are many areas that would benefit more from your hard earned.

Yes, but i'm just a sucker for Wodjies shiny head :end:

[Paul Beazer]

Yes, but i'm just a sucker for Wodjies shiny head :end:
Im really hoping you mean the one attached to his shoulders!

[valmes]

I simply cant believe peoples blind faith in these regulators. To fit one without any method of assessing what you are doing to the AFR is not all that clever, fitting one where you have no way of assessing the AFR OR what pressure you are running is simply stupid.
I am also shocked that some of the info in this post is new to people. Anything that adjusts the fuelling to your engine can and most likely will end in tears if you are not careful.

Were we talking pumps, regulators or fuel pressure in general?

For me getting upgraded AFPR was the only way to get my fuel pressure back to normal, after Walbro 342 install and "hotwire". Stock FPR was overrun... so were 3-4 more units we tried to work with.

Although I do agree that without some way of constantly monitoring fuel pressure and AFRs (Air/Fuel ratios) that's not a wise move... and I would say more - stock fuel in a good working condition is more than adequate for stock turbos! If you plan to upgrade your turbos - do the fuel first, if you don't - just check if everything works right, that would be enough! Yes, IMO, fuel pump, injectors and stock FPR will work just fine with anything stock turbos can produce! Put it this way - those aren't called "supporting mods" for nothing, what it means is - they will support higher HP levels, but they won't give you any HP increase by themselves! No point doing it, if you’re not going to need that extra fuel!

Here is an example of what a wise "stock upgrade plan" should look like (click on the text):

"Only five carefully chosen components separate this vehicle from a showroom stock version. They are a K&N FIPK, a Greddy Profec electronic boost controller, an A'pex Super AFC, an ATR 3-inch downpipe, and a Borla 3-inch cat-back exhaust." (http://www.stealth316.com/images/weltz-p2.jpg)

That would be enough to get the most out of the car without upgrading turbos... well, you might also want to upgrade the stock clutch...

[pezza]

All very interesting reading; since upgrading my fuel pump but still using stock wiring and stock FPR, I have noticed the AFR values have dropped the car appears to be running a little richer esp at higher loads / WOT periods..


At some point I should think about Hotwiring, as I plan to leave the car at 1ish bar, but will only do this at the same time as installing an AFPR to prevent overfuelling. I would also hate to think about the scenarios of burnt out wiring ... :anxious:

[kevin ap motors]

upgading the regulator,fuel pumpand hotwire mod is a must when using differnt turbos,injectors ect But if fitting to std car must have a/f/r checked and will more than likley need some kind of fuel controller or it will run rich at top end and at idel

[Oblivion]

Is it particularly bad if the fuel pressure doesnt rise as fast as the boost pressure? For example doing 3rd gear pulls on the dyno is fine, but when you shift up a gear when racing the boost comes on so fast that the fuel pressure momentarily doesnt keep up resulting in the pressure difference dropping below 3 bar. I'm thinking maybe this momentary drop might be running it lean in the short time that it drops and possibly also its cumulative effect is contributing to overheating.