Too big fuel pump maybe?

[nick.parker]

Hi,
I put a 255lph Walbro in my SC14 supercharged AW11. And have been having issues with apparently not enough fuel delivery considering the large injectors (550cc rx7).
On EarlyRolla's advice I fitted a cheap ebay fuel pressure gauge, and at idle I get 50psi fuel pressure which is insane! And it doesn't change much when I blip the throttle like I would expect.

At idle, it should be (36.3psi - 9) = 27.3psi. (My idle is at -9 psi approx). Has anyone had experience with this sort of thing before and can anyone recommend a suitable regulator or any other reason for this high fuel pressure? Does anyone know if a stock JZA80 (GTE version) regulator is the same style as the 4AGE regulator?

Thanks, Nick.

[roadsailing]

what management are you running?

I can see my way to a high flow high pressure capable pump, but not like you are describing. running rich i can understand, but not running lean.

Maybeye try disconnecting your FPR manifold line and see if you can notice a difference? it should take care of pretty much any fuel pressure.

[nick.parker]

Hi,
Custom management. I have a wideband sensor and have a basic fuel map running fairly rich at max boost (12psi) - my injectors would be near 95% duty running 0.8 lambda at 7000rpm, with only around 165rwhp, and maybe 40hp for the SC the total output would only be 220hp or so, and my injectors are 550cc.

So I have two problems - not enough high boost fuel, too much idle pressure.

I really want to know if other people have observed overly high fuel pressure with stock regs and high flow after market pumps. I am under then impression numerous people have installed this sort of gear and have read on various forums thats stock regs are usually very adequate for much more fuel than stock requirements.

It seems logical that if the regulator was a restriction to a high flow pump then rail pressure would be too high.....

Regards, Nick

[mullett]

Hey Nick...is there a way of accurately measuring the flow through the reg when it's fully open? Maybe alter the voltage to your pump or something (at idle, or maybe jog the pump with the engine not running?), see if the pressure drops off as the pump slows down. Terrible explanation (I'm stuffed) but I think you get what I mean.

RM.

[nick.parker]

Hi Robin,
Good plan. Actually there is a power connector I can access - I could put a series resistor inline with the pump power. Thanks for that.
Cheers, Nick

Edit ::
Just tried that. I activated the pump with engine off, and it generates about 40psi with pump running and sits at 33psi with pump not running (after rail is pressurized).

Amazing but true, startup current must be a few amps as 1.1ohms in series with the pump wont let it start up (just draws 6+ amps and makes horrible slowly rotating noise) But running with no resistor in series it runs and draws 5.4A with running (with engine off and atmospheric reference to regulator).

Tommorrow morning I'll try jumpering the resistor and then remove the jumper when pumps is running, but I'm too tired now to do anything!

[mullett]

haha, no worries, one of those late night flashes of inspiration I guess. I'm going to bed before I have another one

RM.

[oldcorollas]

Just tried that. I activated the pump with engine off, and it generates about 40psi with pump running and sits at 33psi with pump not running (after rail is pressurized).

Amazing but true, startup current must be a few amps as 1.1ohms in series with the pump wont let it start up (just draws 6+ amps and makes horrible slowly rotating noise) But running with no resistor in series it runs and draws 5.4A with running (with engine off and atmospheric reference to regulator).

40psi is about what it should be.. it seems unlikely that the reg is bot flowing enough... it could be that the return line is not flowing enough, but then with engine off, it would have same issue.

seems strange for the rail pressure to go UP 10psi instead of going DOWN 10psi with engine idling...

ok, when engine off.. 40psi
engine idling 50psi

take off the vacuum sense line from FPR when engine is idling, and it should go down to 40psi (since it is same as engine off)....

if it DOES go down, there is something screwy as it should be other way around, and not the pumps fault.... does the fuel pressure reg have two ports???

wait.....
where is the manifold pressure line coming from for the FPR??? is it actually from the manifold (between head and throttle) or???

what exactly is the setup of TB, SC and sense line??

oh, and 5-10amps is expected current draw....

[nick.parker]

Hi,
oldcorrollas, the pressure ref line comes off the inet manifold itself to the pressure reg. I start the car up and it idles with about 50psi fuel pressure.

I was thinking the 40psi I see with engine off may just be in part due to the pump running on slighltly less than 12V, where as with the engine running and alternator generating eetc there is 14V on tap so I get 50psi. This might indicate a fixed restriction in the fuel return or the reg is faulty maybe.

Get this :: pulling the VAC line off does not change the fuel pressure - it stays at 50psi with engine idling. I tried blowing with my mouth to the reg line, (I know I can strain and just blow 3psi!) this also does not increase fuel pressure at all.

The air leak where the reg's ref hose was on the manifold changes the idle quality slightly, so I know that is not blocked. I have another stock ZE press reg I will try.

Cheers, Nick

[Cruiser97_80]

Sounds like your pump is putting out to much flow for your regulator or return lines to handle.
That would be why you see no pressure change when removing your vacum line off the regulator.

[oldcorollas]

what size return line is there???

can you temporarily try a larger line, going to a jerry can or something?

if you get a big syringe (ike 25/50ml) from chemist for likr $3 or whatever, you can try to get higher pressure in the ref line... or a bike pump with one of those conical fittings... if by putting pressure on reg, the gauge pressure _doesn't_ go up.. i would start to suspect the gauge. it is reasonable to think the return restriction could increase pressure, but pressure on the ref line SHOULD increase any pressure further....

it's also possible that the pressure gauge is incorrect... can you possibly try on someone elses motor? or borrow a different reg and just connect pump to it and see if pressur ecomes down (and also measure the fuel volume coming out...the pressure vs flow graphs are available on the net somewhere)

with the 190L walbro (155 at 40psi) i had no issues using a ... 3SFE? pressure reg or a 4AG reg... the 250 is about.. 210-220 at 40psi or similar?

[nick.parker]

Hi,

I have no reason to doubt the gauge yet. Just tried a second regulator and had the same issue. Looks like a return line restriction thing. Maybe something got pinched when I installed the pump 6 months ago, but everything from tank to engine bay is metal. I guess the fuel return is bloody restrictive to 4 litres a minute though, given the tiny banjo fittings as stock etc. Atleast the fuel supply line to the rail is a fair bit bigger. The tank is a bastard to remove, and I cant drive it anywhere (i.e to a hoist) at the moment . I will try disconnecting the far end of return line and pointing that into a jerry can.

Thanks, Nick

[nick.parker]

Just been scouring the net, and I found a lot of forums where people were saying that your FP goes up if you install a Walbro 255. It appears that the common cause (given the highly increased fuel flow) was the stock FPR! The stock FPRs were usually unable to bypass enough fuel and some people solved it simply by fitting an after market reg. Fingers crossed it is not my return lines then!...Now...does anyone know of a reliable and not too expensive (NOT NECCESARILY ANODISED ) fuel pressure regulator?
Cheers, Nick

[mullett]

For the really good stuff, call Go Gear in Osborne Park. They've got an amazing range of stuff in there, and I'm sure they'd have FPRs. Or try Aston at Jshop...just been told he does adjustable SARD ones for *I think* $199.

RM.

[30psi 4agte]

hey nick.

I use a malpassi (non rising rate) fuel pressure reg with a bosch motor sport pump on my setup. They are about $120 from memory

I have had no probs at all with it . No pressure drop off at high rpm etc.

I use a 6mm return line. - so you should be sweet with that .

[camrygt?]

I have a 255 walbro in the camry with a digital fuel pressure gauge. In my setup with the pump at full speed the pressure goes too high at idle about 45-50psi.
I run the pump on a slower speed with some resistors (sorry can't remember value I could check if you want but its low, like about 0.5 ohms). Using the standard 2 speed output on the 3sgte ecu and a relay. The stock ecu gives full speed to start the pump anyway. I get about 33psi at idle with this setup

Mine still over pressurised with a stock ST205 fuel rail and reg but sv21 return lines which arn't huge.
I know the fuel flow from this pump is massive compared to a standard pump, I turned it on with no line connected to the tank and before I could turn it off fuel had sprayed a wall about 2 metres away and left a fair sized puddle on the floor.

Also with less than 1/4 in the tank I can hear this crazy swirling noise from the tank which I am pretty sure is the return fuel as the car doesn't loose fuel pressure for at least another 150km after the noise starts