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Walbro vs OEM Fuel Pump

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Old 01-03-2011, 03:24 PM
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Walbro vs OEM Fuel Pump

If you are to replace your OEM fuel pump with a higher flowing unit (walbro), will you need tuning?

(No performance upgrades)


In other words just simply swaping out the fuel pumps.



My moment of doubt here is all due to the way the fuel system works with the G35. I know OEM does not bring a return line so therefore the returnless system keeps pressure at a constant...


So my theory (please correct me if I am wrong) is if say XX amount of pressure is required with the OEM pump and it takes say 1 second to reach that pressure; Wouldn't it be achieved quicker with the higherflowing unit?


Or would the ECU not know how to handle that function?


any takers????
Old 01-03-2011, 05:18 PM
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I would think that if the pressure is the same (~61psi at warm idle) you should be OK.
The ecu will trim the fuel injection based on the A/F sensors. It may run slightly richer when cold (before engine is running in "closed loop" mode). My $0.02.

Last edited by HangUp n' Drive; 01-03-2011 at 05:23 PM.
Old 01-03-2011, 05:37 PM
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A high flow fuel pump is completely pointless on a stock engine. When people heavily mod their engine and use big injectors which use a lot of fuel, the OEM pump can't keep up with the flow and so pressure sags and you can't achieve your full power, so you upgrade the pump. You won't need tuning if the pressure is the same, and there will be zero benefit.

Your theory about how a high flow pump can help doesn't really make sense
Old 01-03-2011, 05:50 PM
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^+1. It won't help your performance, but it should work.
Old 01-03-2011, 05:57 PM
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Cool, I needed to know about this myself. For different reasons than the OP though.

So is it safe to assume that running a walbro pump without being tuned for it, will not impact the car negatively (besides running a little rich)?
Old 01-03-2011, 06:30 PM
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Should be OK. It might run a little richer when cold, when in closed loop should run the same as stock.
Old 01-03-2011, 10:45 PM
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Quote:
Originally Posted by marcinr View Post
A high flow fuel pump is completely pointless on a stock engine. When people heavily mod their engine and use big injectors which use a lot of fuel, the OEM pump can't keep up with the flow and so pressure sags and you can't achieve your full power, so you upgrade the pump. You won't need tuning if the pressure is the same, and there will be zero benefit.

Your theory about how a high flow pump can help doesn't really make sense
I made the thread to sound in a stock engine because at the moment I cannot calibrate the ECU. I have the EARLY ECU .


But my vehicle is extensively modified (OEM short block). I was just wondering if I replace the OEM pump with a faster pump would the ECU whom manages the output of the fuel pressure would actually handle it without needing to make a retun system or even ecu calibration.

As it is, I am running pig, so adding more fuel is NOT going to help if anything itll washout the pistons and cause havoc.
Old 01-03-2011, 11:53 PM
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I think the early ECU will adapt a little bit, but once you go too far out of spec, it throws a CEL and goes into the built-in closed loop maps, a sort of safety mode in case you lose a sensor or something (but it's been a while since I poked aroudn this stuff, I could be confusing it with my other car).
Old 01-04-2011, 12:30 AM
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I'd hate to be the crash test dummy, but I guess I'll give it a shot when I can...

Here is my theory:

I believe the pump is controlled by the solenoid that detects pressure on the top left passenger side by the fuel inlet (to the rail).

This solenoid reports to the ECU how much pressure is, the ecu then calculates MAF and throttle readings and engages the fuel pump on or off depending on what needs to be done.

Hence why I believe having a pump that can provide more pressure being under worked will be better? Although the OEM pump has been through 180k miles.... I guess if it's worth doing, it's worth overdoing.
Old 01-04-2011, 11:26 AM
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Every crash test dummy I have seen has been smiling

The ECU is going to control the A/F ratio by varying the pulse width (how long the injector is turned on) of the fuel injectors. This is based primarily on the readings of the O2 sensors but also includes MAF, throttle position, RPM, tempatures, etc etc.

So if the pressure at the fuel rail is the same as with the stock pump nothing will change. If the the pressure at the fuel rail is slightly different than stock the ECU will adjust the injectors to correct the A/F ratio.


If the pressure at the fuel rail is grossly different than stock, at some point the the ECU/injectors will no longer be able to compensate and will cease to operate closed loop (using feedback from the O2 to control the A/F ratio), and switch to an open loop mode with a predetermined fuel map.

During warm-up the ECU runs open loop, so if the fuel pressure is slightly higher, you will run a little richer.

I think the net effect of switching to a high volume pump would be, the pump won't run as hard as the stock pump.

Trivia: Did you know Walbro is a major manufacturer of weed-eater carburetors?
Old 01-04-2011, 12:24 PM
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Problem is I have the crappy ecu with no open loops.
Old 01-04-2011, 03:46 PM
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Open loop/Closed loop merely refers to the mode of operation, not the actual hardware.
Old 01-04-2011, 04:09 PM
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Quote:
Originally Posted by HangUp n' Drive View Post
Open loop/Closed loop merely refers to the mode of operation, not the actual hardware.
Not to sound like a dick...


I know very well the technological terms. The 2003 ECU is a problem because it is a open loop ecu.

It only controls fuel by air, throttle and load. It doesnt have the ability to control target fuel. (this is why NO ONE can tune the 2002-2003 ECU)
Old 01-04-2011, 04:50 PM
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Didn't know that, automakers have been using closed loop control since the '80s. I thought everyone did. My bad.

It may richen it up a little on the top, but I think it will work.

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