I am about to install a Walbro pump. Will this make me run richer (consume more fuel)? Or does it just provide the capability of more throughput when I need it? I would imagine that the ECU would control the fuel mixture and therefore the fuel pump.

I also checked out the cost of a new stock pump and that ran at $300+!!! Why is this so cheap in comparison? Is it just cos it does not carry Nissan logo?

 

During closed loop, you shouldn't be using anymore fuel... at WOT it may run richer (if fuel pressure is increased). DSM model should be a direct plug in. Do a search for additional info...

 

Before I installed it, I noted that the idle fuel pressure is around 32 or 33 psi. And at WOT, it went to around 41-42 psi. After the install of my Walbro fuel pump, idle is now at around 38 psi and WOT is at 49-51 psi. So the ECU didnt "automatically" reconfigure the fuel pressure. But again, I still have to reset the ECU, so that may have something to do with it. I will let you know what happens after the reset. Good luck, and be careful when playing with the fuel. Also, where some thick RUBBER gloves so your hands won't smell for days.

 

The ECM won't/can't lower the FP... it can only modulate the pulse duration...

 

What you say, Chunger makes sense. I guess the ECU will make shorter "bursts" at this higher pressure. So overall consumption should be approximately the same? I guess it may consume a little more since the ECU (computer) is tuned for lower pressure. I wonder if it is smart enough to correct itself?

Not a huge deal, I was just curious what would happen and whether anyone had experienced poorer fuel economy or performance differences because of it.

 

The reason is because your FPR can't keep up. Fuel pressure is controlled mechanically. Your ECU has no idea. Basically, you are running richer than you are suppose to.

 

Fat chance. Fuel pressure is purely controlled by the fuel pressure regualtor. ECU assumes 34psi at idle and 43 psi at WOT. The ECU fuel map takes these assumptions. At partial throttle, the ECU might make alittle adjustment via the O2 sensor readings. At WOT, the open loop fuel map will assume you have 43 psi. This same concept applies to injectors too. All ECU knows is to give certain voltage to the injectors at certain intervals. If you go bigger injectors, ECU will have no idea.

 

Well, no matter! I will be getting a fuel stand alone fuel pressure regulator. just out of curiosity do you know for a fact that this is true through your personal experience? If I were to hook up an air fuel ratio meter (which is my plan) would I see it running rich all the time? I honestly find it hard to believe that the ECU is that dumb. It should be able to control the amount of fuel input by controlling the on/off times or voltage to the fuel pump ... isn't that what the O2 sensors are for? I have read in other threads that when the O2 sensors go bad you run rich all the time. IF that is true, then the ECU IS able to control A/F ratio.

Anyway, the proof is in the pudding (as they say) I will monitor my fuel consumption for the next week or so. I just installed the pump. It took about 45 minutes (going slow). It was a piece of cake thanks to Synki's instructions. The hardest thing was pulling off the clip for the filter bag and that wasn't too bad!

 

Like I stated above, the ECU can controll A/F ratio at partial throttle/cruising condition via O2 sensors to a certain point/range. So, if an O2 sensor is bad. It goes into fail safe mode and triggers the CEL. The ECU will richen the fuel mixture by more voltage and/or longer duration at the injectors. It's designed to be safe than sorry. AT WOT, it goes by it's pre-mapped programming codes. It doesn't take into account any O2 sensor readings at WOT. It can't compensate for extra 5-10 psi of fuel pressure at WOT.

You won't able to tell if you are rich or lean with a cheap A/F ratio. It will say rich at WOT even when you are blowing up your motor. Best way to tell is to read your plugs, EGT and try to listen for engine knocks.

As for how I know fuel pressure is purely controlled by the FPR....think about it. How does ECU know anything that's happening on the car? By using sensors right? O2 sensors, crank sensor, water temp sensor...etc. What does the ECU use to reference fuel pressure? There is no "Fuel Pressure Sensor" on the maxima. If you want more proof, it says so in the FSM

 

BTW, nigelcmf...You ask some pretty good questions Keep it up. I'm glad the fuel pump install worked out.

 

where can i order the walbro pump?

 

Hehe! You're right about the A/F ratio. I have asked that before. I have bought a pyrometer (EGT) as well. Sorry to ask a dumb question. What is FSM? ... not that I still doubt what you say, but I would like to know exactly what FSM says (whatever it is) and if there is more info out there..... oh wait FSM = Factory Service Manual? I just ordered mine last week. Should be here soon!

OK so it sounds like under normal driving conditions the ECU should be able to compensate? Under WOT it's probably going to run rich ... did I interpret your response correctly? I can certainly live with that!

Thanks so much for the help!

Nigel