I have question about fuel pump.
I am going to change new Walbro fuel pump.
There are 190lph and 255lph.
Which one is better for my 96 240sx stock KA24DE motor.

Some math , say you getting 10 miles per L , OK the 190lph will pump enough gas to go NINETEEN HUNDRED MILES in ONE HOUR .........................can you drive anywhere near's 1900 miles ......in 1 hour ???
Check my math though and of course .........YMMV

p.s. Output PRESSURE is most important match to what the little engine wants to see , right ? Fuel pressure regulators have a 'window' for proper pressure , could be a NARROW window that car ?

macgiver wrote: ↑

Fri Feb 18, 2022 2:23 pm

Some math , say you getting 10 miles per L , OK the 190lph will pump enough gas to go NINETEEN HUNDRED MILES in ONE HOUR .........................can you drive anywhere near's 1900 miles ......in 1 hour ???
Check my math though and of course .........YMMV

p.s. Output PRESSURE is most important match to what the little engine wants to see , right ? Fuel pressure regulators have a 'window' for proper pressure , could be a NARROW window that car ?

The engine will get more like 1 mpl at WOT, which is where volume matters. Even less when pushing top-speed air out of the way. So your math is off by maybe a factorial. Nevertheless, Daytona is the only place the car will ever go 190 miles in an hour.

Thanks , I'll go tell MAMA now She'll explain ' factorial ' to me

Thank you

You're most welcome. Happy motoring (Daytona or anyplace)!

I have one more question.
Which fuel pump is recommend for my engine?

Like Mac and I said, there isn't much point in using the bigger Walbro for your application. For most purposes a pump is a pump is a pump, as long as it moves enough volume to support WOT and you properly regulate the pressure to whatever the ECM and injectors expect. Regulation is just as important as having sufficient volume. The stock fuel system on your ride uses a regulator that varies the pressure according to engine vacuum, 34 psi under high vacuum conditions (idle) and 43 psi under low vacuum conditions (WOT). There's no Nissan spec for how much volume the stock pump moves, but the calculations above show 190 lph will be plenty.

Thank you for the polite explanation.
The reason why I asked the question with the fuel pump is that the check lamp on P0171 is on. Cleaning the air flow meter. Replace with a new O2 sensor. The most suspected air leak was no leak. The fuel pressure regulator was replaced with after parts two years ago. I replaced the fuel pump with after-parts 10 years ago, so I think it's time to replace it. Idling may not be stable every time when you stop at a red light after passing a curve at high speed or when you park on an uphill place. It will be cured if I step on the accelerator. Is there anything else you can think of?

If there's no leak, the next most likely cause for P0171 is dirty Throttle Body. Have you cleaned it? You could also have a bad PCV Valve, P0171 from that is pretty common as well.

Thanks I try that.

Where is the pcv valve located?

Thank you !

I have replaced new PCV valve and cleaned Throttle body.
P0171 seems to be fixed!!
Thank you!!

Happy motoring!

I wasn't sure whether to make a new thread or write here, but right after changed new alternator the P0171 is on again.
I cleaned Throttle body,O2 sensor, MAF sensor, checked air leak ( could't find leak ).
PCV valve and fuel pump have been replaced new just last March.
The Idling is stable but if park on a slight uphill after driving, idling becomes unstable and engine stalls.But it is not every time.
What else could be the cause?

Put a fuel pressure test on it and make sure the pressure regulator works. I think there's a fuel filter on a '96 also, check that.

Thanks VStar650CL for always.
I am also suspicious of fuel injectors though.

I have questions about fuel pressure test. Service manuals shows two locations to check .
after fuel filter and before fuel pressure regulator.
So have to check two locations?

Unless there's something wrong in the fuel lines, the only pressure that matters is what the injectors are seeing. Check at the engine, if it's low even with no vacuum to the regulator then check before and after the filter to eliminate it as the source of a pressure drop.

Ok thanks!

I haven't done a fuel pressure test, but first of all, after replacing the fuel filter on the 1992 300 ZX, the lamp was still on, so I installed an adjustable fuel pressure regulator and pressure gauge. I adjusted it to 43 psi at key on 34 psi at idle. With the key on, the pressure suddenly dropped so I checked the fuel pump and the hose clamp was loose. When I closed it, the pressure returned. I turned off the lamp on the obd2 scanner, but it started coming on again, and when I checked, I got p0171 and p0402. The idle is very stable and the engine runs well. What else could be the cause?

p0402 was gone after replaced broken tube but p0171 is still on.
The engine runs well but gas mileage is 17 mpg now. used to be 23~24 mpg.
Can someone help?