Yep... stock pump won't cut it

[huguetpj]

OK. Short story. Bought a used BEGI FMU from Structure240 (thanks by the way) as a temporary band aid for my lean AFs while I either crack the ECU or fork out the dough for the emanage.

I installed the FMU last Saturday before a competition I had and set it up to 58PSI at 0PSI (the instructions said 48 but I misread the little marks on my gauge). I'll move it to 48 as per the instructions and finish setting it up on the dyno later.

So the fuel pressure jumps from 43PSI at almost 0PSI (stock reg) to 58PSI no problem whatsoever. Then as the revs go up the fuel pressure stays at around 58PSI and slowly starts going down to around 48PSI at redline, and this is a 7:1 FMU. I haven´t tested the pumps pressure capability at idle as the FMU instructions explain, but this behavior seems to me like the stock pump won't cut it. So it seems that the Walbro that's been sitting in my room for the past months is going in this Saturday.

I'll make a few tests on the stock pump first if I have time, since I have another track day Saturday and drag racing Sunday... busy weekend as you can see :ylsuper

Just wanted to share

[j-z]

when using an fmu, your suppose to run a high pressure inline pump. your ringlands will crack if you continue to boost on just an fmu and no pump. trust me, i know. play it safe man why risk it, its stupid.

[tony/ka24de]

I ran just a fmu with 7psi of boost for a year with no problems and a good af mixture according to the gauge. I am still running this with no problems. What do you mean by ring lands?

[WDRacing]

What he means is that you could suffer from detonation. Not that your ring lands will all of the sudden crack because they found out you weren't running an after market fuel pump. The BBk 255LPH is 100 bucks. Hardly worth not buying.

WD

[Structure240sx]

is it a fuel pressure gauge inside the car or engine bay? are you revving it under load while boosting? im guessing yes. and yea the stock pump shouldnt be able to keep up. the walbro takes about 30min tops to install

[C-Kwik]

A OEM pump in good working order should be able to supply enough fuel for about 7-8 psi using an FMU with 270cc injectors. Sounds like you have a pump that isn't quite up to par. With a 7 psi, the FMU will want to bump up the pressure to about 92 psi total. However, some unconfirmed sources tell me the stock pump will dish out to about 80-90 psi before it can't keep up with the flow. If you are maxing out at 58 psi before the pressure starts to drop, you're pump should be replaced.

[MikeMurphy]

interesting

[Jookmasta]

walbro or 300zx fuel pump and u'll b good

[huguetpj]

For those of you who say to play it safe... I know I know :pface I just want to find out what the stock components can take. And I had been running with a stock fuel system for over half a year now... ****ty AFs but no probs. Hell... if I hadn´t spun a bearing last year my motor would still be stock.

Anyway, I installed the Walbro last Saturday and it took about 45min (give or take a few 10min chitchats with my buddies). And definitely the stock pump wasn't cutting it. But I now have a new prob. I lowered the 0vac point to 48PSI of fuel pressure. And now when I floor it fuel pressure jumps to 48PSI... ok... starts climbing to about 60PSI... ok... but then it stays there up until redline. I thought it should go up to 80PSI since:

5PSI * 7 = 35PSI fuel pressure, 43PSI+35PSI=78PSI

The vaccum line is the same as the stock FPR and SBC. So I'm pretty sure it's getting 5PSI of boost signal. I'll check the lines again to see if there is some kind of problem or kink, but anybody have any ideas? I'm also gonna check the max fuel pressure the walbro can give at idle. And the BEGI online instructions say to check the check valve, gonna do that.

By the way, the needle valve is all the way in.