Missing In Low Revs In 1St, 2Nd And 3Rd After Fuel Pump Install

[rondofj]

Remember my car was initially running dangerously lean a/f of around 13.7 and up with the stocko item, so now this new fuel pump has hopefully brought that down to 12ish a/f ratios by supplying the required amount of fuel, hence 'making' the power that shud have been there. yes its in low revs then fine, my sock has got a bit of play, i was thinking that maybe the pump doset have enough pressure in low revs cos of this - then on higher revs, it has built up the pressure??

[DVS JEZ]

Just putting a fuel pump doesnt increase the power in the car it just enables it to run more power just like a front mount,you will however make more power when you combine it with such mods as turbo injectors where you require more fuel to be pumped out so not sure what your talking about there.

The problem does sound strange as it is missing then working fine, would have thought it was surging from maybe mounting the pump to high but your saying it in low revs and then its fine.

Yes and no. If the afr was leaner than about 13.5 he would be losing power.

You really need to rewire the pump before the tune. U cant do it after or the tune will be out again.

[StealthX]

Remember my car was initially running dangerously lean a/f of around 13.7 and up with the stocko item, so now this new fuel pump has hopefully brought that down to 12ish a/f ratios by supplying the required amount of fuel, hence 'making' the power that shud have been there. yes its in low revs then fine, my sock has got a bit of play, i was thinking that maybe the pump doset have enough pressure in low revs cos of this - then on higher revs, it has built up the pressure??

Dude, 13.7 isn't that lean at all... Besides, a bigger fuel pump won't change anything, the stock regulator is keeping the fuel pressure the same, and the injectors are still opening the same amount, so your AFR won'tt change from a fuel pump swap. I reckon the pump isn't receiving the right voltage, the fuel pressure is dropping and the "misses" are lean spots, but it probably wont detonate at those low revs in that situation, it'll just miss instead...

when is it reading that AFR? under boost? on idle?

and how were you measuring it?

[89CAL]

13.7 is lean on boost....

[StealthX]

13.7 is lean on boost....

Yeah he didn't mention that, my bad.

Regardless, re-wire your fuel pump, and if it still happens, ask your tuner what's going on.

My x-trail does the same thing, I've tuned it myself, played with EVERYTHING possible to fix it, and have no idea what's going on. It just randomly goes lean and misses, if you apply the throttle @ 1700rpm, worse when cold, I think i've narrowed it down to intake turbulence. But yours sounds like a fuel pump voltage issue...

VERY interested to hear the outcome, good luck dude.

[eightsixboy]

Get the car on a dyno and have someone check it out properly. For all you know you could have a dodgy afm or blocked fuel filter, it could be anything. It prob has nothing to do with the fuel pump at all.

[rondofj]

It has to do with the fuel pump dude, before changing to the walbro, this issue wasnt there at ALL, I reckon re-wiring is the go - will get my tuner to do that - how much shud I be paying for that??

I know its simple - relay, and then wire from batt positive etc, grounding, but nobody has any pictures anywhere - I need to know things like how the modified wiring goes into the tank, at what point it is cut and where in the chasis it is grounded etc, as u know the battery in the R34 is in the bonnet not boot. I already got amplifier wiring running from battery + to boot with its own fuse (amp is out), can I use that??? Just connect the relay etc.. Does the relay need to sit in bonnet beside battery?

And I saw the a/f ratios after driving on 2nd to 7000rpms and it showed around 13.7 everywhere on the tuners laptop running nistune. Didnt get it tuned then, and yeah on idle it is around 15, normal driving on boost is high 12s to mostly mid 13s..

[DVS JEZ]

Yeah he didn't mention that, my bad.

Regardless, re-wire your fuel pump, and if it still happens, ask your tuner what's going on.

My x-trail does the same thing, I've tuned it myself, played with EVERYTHING possible to fix it, and have no idea what's going on. It just randomly goes lean and misses, if you apply the throttle @ 1700rpm, worse when cold, I think i've narrowed it down to intake turbulence. But yours sounds like a fuel pump voltage issue...

VERY interested to hear the outcome, good luck dude.

Post a pic of ur maf sensor in its current position.

Also what ecu are u running to control the fuel pump voltage for ur returnless fuel system. This is very important for ur setup and a fuel pressure gauge must be input to the ecu.

Yes u can rewire the fuel pump using the amp wiring. But get a relay with a fuse in it. Connect the amp power to the power in of the relay think its pin 30.

Then the current trigger of ur fuel pump ( is r34 neg trigger? Im not sure)if its neg trigger cut the negative going to the fuel pump and connect the ecu side of the cut to connect to pin ? (mental blank. Its the earth pin)

If its positive trigger cut the positive to thr fuel pump and connect the current power in from ecu side of the cut to pin?(mental blank, its the other power in NOT PIN 30)

then pin 87 power out goes to ur fuel pump positive the other half of the above cut wire.

Then negative of the fuel pump wire should be grounded to the chassis. U dont need to remove the fuel pump to do any of this. Use the stock wiring approx 300mm of it anyway.

I mount my relay on the right side of the boot well half way up the side.

[StealthX]

Post a pic of ur maf sensor in its current position.

Also what ecu are u running to control the fuel pump voltage for ur returnless fuel system. This is very important for ur setup and a fuel pressure gauge must be input to the ecu.

Don't have a maf sensor, it has an EMS stinger 4424, uses map sensor for load source.

pump has a constant 12v supply, still running the standard fpr, i'm going to install a aeromotive regulator and reference it to boost, the more stable fuel pressure might fix the missing porblem @ 1700rpm... If I want to run more than 12psi, I need a better fpr anyway, and I think it's generally not up for the job at all.

the stinger has no fuel pressure compensation values, it's got air temp and water temperature compensation tables for timing and fuel, anti-lag, two step, 15 other customisable outputs.

And a fuel and ignition map "override", never learnt to use this.

Can you elaborate on why pump voltage is important in a returnless setup?

PM me if you don't wanna clutter this thread!

[DVS JEZ]

returnless systems sometimes rely on the ecu to control voltage to the pump depending on a feed back on what the fuel pressure is at the rail, but because yours has a fuel pressure regulator this might not be the case.

is your wiring to the fuel pump stock ie 12volt constant? did your factory setup have a sensor on the fuel rail?

Returnless setups are a good idea due to the facts that you dont get fuel splash when the fuel returns to the tank and the fuel will stay alot cooler as its not travelling through the hot fuel rail then returning to the tank constantly,

but as we all run a return type system it will work for your setup too.

[DVS JEZ]

ok now that i am half awake,

-Pin 30 is power in from your amp power wire

-Pin 87 is your power out ( this goes to the positive side of the fuel pump)

-Pin 86 can be connected to the earth trigger, or if its positive trigger connect 86 to the chassis

-Pin 85 can be connected to the positive trigger or if its negative trigger connect this to a switched ignition 12v source

-then connect the fuel pump earth to the chassis,

doing this will give the fuel pump full battery voltage, but still be controlled by the ecu incase of an accident where the engine stops the fuel pump will stop, and wont pump a tank load of fuel all around the car if the line is ruptured

[rondofj]

Hey Jez, thanks very much man, you have been extremely helpful, now all those pins, where are they, are these the pins -30, 85, 86, 87 etc, on the plug going into the white fuel pump plastic cap that seals the tank?? Theres 2 plugs and 3 hoses there. So that means I dont have to open that plastic thingy and take out the fuel pump with bracket as it can be done from above, right? And how do I know which is the positive / negative trigger, and by 'switched ignition 12v source' - that is the battery, right?? Sorry for being such a noob, but in all my DIYs I find this the most confusing as theres no real pics I could find, just diagrams..

[DVS JEZ]

When u buy a relay with a fuse in it. U will see on the packet the pins of the relay 30,87,86,86 and there inputs. Ill write more later

[rondofj]

cheers bro - I will be headed to jaycar soon

[rondofj]

A 60A Horn relay with a 30Amp fuse is what I need right?

[DVS JEZ]

Yep sounds good.

[SiR_RB]

Hey jez should I do this direct battery feed for my sard fuel pump? Or just get u to do it when I c ya next

[rondofj]

Theres so many relays in www.jaycar.com.au - this is the only one with a fuse: can I use this?

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[DVS JEZ]

Just go to supercheap. Get the same

Basic relay with fuse. Get some crimp terminals and a crimper if u dont have one.

Yeah michael i can do that for u

[rondofj]

Jez, if u were in Sydney, I might ask u to do this for me..