Varying Afr's On Dyno

[jarrod83]

Hey guys i recently stuck my car in to get tuned, they reached about 9 psi and started to have issues with knockin.. etc scratched their heads for a while and worked out that the air fuel ratio was changing dramatically between runs without them changing any settings.. between high 10:1's to low 12:1's on boost

my mods are intank walbro fuel pump, power fc, fmic, full exhaust n a blitz ebc.. ive tried earthing the fuel pumps earth to the battery and the results remained much the same

any ideas would be greatly appreciated

Cheers

Jarrod

[GTR1993]

Put a fuel pressure gauge and check fuel pressures during runs?

[jarrod83]

yeh i would of liked them to have done this but i wasnt there as i was at work, had a mate take it up.. the ppl that dynod it turned out to be completely useless coz they could of chekd the coilpaks n pressures while it was on a dyno, n i don't want to have to send it to another place n another dyno just to get the problem resolved, just would like to know some of the most likely causes.. the earth wire on the in tank fuel pump is exposed n a little corroded.. that couldnt be causing the issue could it?!!

[R31Nismoid]

I reckon fuel reg is stuffed - without checking the fuel pressure (as per above) the dyno run was totally pointless.

[The Mafia]

yeap, and if the mechanics weren't smart enough to do that when they saw the fuel flucuating, then time to take it to another shop.

[Guilt-Toy]

where are you located?

[Sydneykid]

walbro fuel pump

That's my guess

Cheers

Gary

[jarrod83]

located in perth guilt-toy, thanks for the pointers guys ill probally replace the fpr first and over the fuel pump becuz its the cheaper one to replace... are they any fpr's that are direct replacement that dont need adjusting? is the sard one any good?

[green 33]

That's my guess

Cheers

Gary

Walbro x2

Edited May 1, 2008 by green 33

[R31Nismoid]

located in perth guilt-toy, thanks for the pointers guys ill probally replace the fpr first and over the fuel pump becuz its the cheaper one to replace... are they any fpr's that are direct replacement that dont need adjusting? is the sard one any good?

It goes in this order

Test

If broken

Replace

Dont just go replacing random parts dude, test them, find the problem and then fix it the first time rather than bringing more problems into the equation

[jarrod83]

okay well lets say i can borrow the fuel pressure gauge at the local car shop how do i test if its the fuel pump or the fuel pressure regulator at idle ?!

[R31Nismoid]

you said it was doing it under load, you must therefore test it in the same fashion

You 'can' do it on the street, but you wont be able to see the AFR's without a wideband and a proper read out.

Take it back to the dyno place and demand they do a semi-reasonable job. They did a half assed one last time

[jarrod83]

yeh i got a wideband with a datalogit.. i rang up the shop this morning n askd why they didnt test the fuel pressure n they claimed coz they were borrowin the dyno they didnt have their tools with them to do it ... so now i have the dilemma of sendin it to another shop with a dyno to diagnose.. why im tryin to just fix it myself coz all the shops in perth seem to be useless..

[STATUS]

fix pump, fpr is 9 times out of ten fine. Dont go aftermarket unless you have too.

[jarrod83]

anyone know if a 180sx fuel pump will work in a r33 gts-t?!? i borrowed a girl my stock one because she thought her one was broken n claimed several ppl said it was the fuel pump so after we installed the fuel pump for her we found out she had a kink in her fuel line, when and got home, i tested her fuel pump n it still worked.. id swap them back sooner but shes in bali for a while .. so would it be fine to test a 180sx one in the skyline for a run to see if the afr's hold more steady on the wideband

[R31Nismoid]

Just buy a decent bosch one, or nismo etc and dont cut corners

[dmr]

sounds like fuel pump. never heard of a OEM FPR stuffing up under such small load.

if funds are the issue, try and source an R32 GTR fuel pump. they're good for 250kw+

[jarrod83]

ahh think i might just buy the new fuel pump.. standard wiring isnt the best anyway the earth wire is exposed and a little corroded so ill buy a full replacement one... so tomei or nismo?!! i know you probally can't go wrong with either but what one would allow for more hp?

Cheers for all the advice aswell guys

[AdamsR33]

a genuine walbro should be fine, my tuner here is one of the best in sydney and installed my pump. Are you sure the walbro you got is genuine?

[jarrod83]

hey guys sorry to bring up an old thread but im still having afr troubles, i bought a new tomei fuel pump to replace the walbro, no change still playing up... bought a sard adjustable fuel pressure regulator.. same results...varies between 12 n 14.4 around the 6psi mark... and varies between 9.5 and 12.2 around the 10 psi mark... im measuring the results with a innovative motorsports lc-1 hooked upto a lap top... has anyone else got any other ideas that could cause the results to vary so much

Cheers

Jarrod

Edited May 16, 2008 by jarrod83