Effects of Walbo Fuel Pump on Stock and Aftermarket Regulator.

[TurboStreetCar]

I have made a discovery today after the installation of my Aeromotive AFPR. Im running a standalone with no closed loop correction. It Runs directly off the same programed fuel map at all times.

I installed my Aeromotive AFPR and set it to 40psi with no vacuum. I set it this way as the service manual says 33-40PSI is stock spec. My car was running on the stock regulator so i wanted to get it running then adjust the fuel pressure to make the mixture correct so i would need to make minimal changes to the fuel map.

Upon turning the key the car was very hard to start. I got the car running kept the RPM up at about 1200 so it would stay running and i booted up the computer. I opened the Zeitronix program to find my AFR's in the 17.5-18:1 range. I felt that was slightly odd as i was just driving the car prior to installing the AFPR.

I increased the fuel pressure until the AFR's got into a reasonable range that the car would run on its own.

This is the Surprising part. I had to increase fuel pressure to 55PSI WITH VACUUM. This means without the approx 9.5psi of vac to the regulator, base fuel pressure would be 64.5PSI!

At first i figured maybe my stock regulator was a freak and was actually regulating fuel pressure to that level. I took the car around the block and at 5 psi where my AFR's are usually in the 13-12.5 range instantly dropped to the low 10's. At 10psi i was in the 9's.

Before anyone asks i have removed the J-Tube and the only things that changed were the regulator itself. The rubber hose that slips onto the hard line off the outlet of the stock regulator is slid onto a hose barb at the outlet on the bottom of the Aeromotive unit.

To all who run a Walbro fuel pump i would HIGHLY recommend changing out the stock regulator for a higher flowing unit. The stock regulator even with the J-Tube bypassed was restricting flow so much as to raise the fuel pressure 25+PSI untill the motor was consuming enough fuel to let the regulator operate as designed.

Running a Walbro should either be complimented with a higher flowing regulator, or keep the stock fuel pump resistor circuit in functioning order to lower the flow at low engine load.

 

[89supracrazy]

I have not changed my fpr out yet. I have installed my walbro and my vf reading on my safc II at idle is 4.7 volts and with the resistor bypassed to form the 12 volt mod it is 3.3 volts. I do not have a wideband yet just going by vf reading at closed loop. This is with 550 cc injectors. Also the readings that I posted is with the no vacuum at idle.

 

[TurboStreetCar]

Why do you not have the vac hooked up? Did you install the larger Lexus AFM? Do you have any correction programmed into the Safc?

 

[89supracrazy]

Why do you not have the vac hooked up? Did you install the larger Lexus AFM? Do you have any correction programmed into the Safc?

I do not have the vacuum hooked up because at idle it reads 4.7 with vac. and without it reads 3.3 volts. That is what the vsv does at wot it takes the vac. off to increase fuel pressure. I have my safc set to zero. Yes I do have the lexus afm. I need more fuel pressure at idle. I have my afpr from aeromotive I just have not installed it yet. The way I am running right now I do not have to even bypass the jtube if I choose not too. I am going to anyway. If you are running fuel pressure at 64 psi, you are on the border line of the injectors sticking on you. I read the injector could malfunction at 70 psi.

 

[TurboStreetCar]

No VSV takes vacuum away from the FPR at WOT. That would lower fuel pressure in boost as it is referenced to vacuum AND boost causing a lean condition in boost. Fuel pressure is raised at a 1:1 ratio with boost and vacuum. The Fuel pressure up VSV removes vacuum from the FPR only on hot startup. Leaving it disconnected will leave you very lean in boost. Vsv Operation explained here http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=45 Third paragraph down.

Something is wrong with your fuel system or you missed something in the Safc if your lean with 550's and a lex AFM on stock FPR with a Walbro.

If injectors failed at 70psi, anyone running 40PSI base fuel pressure and 30PSI of boost would have failed injectors.

Im running 40psi of base fuel pressure currently.

The point of me making this thread was to share findings of a potential problem with using a Walbro 255LPH fuel pump with a stock fuel pressure regulator.

 

[89supracrazy]

Ok. I am glad you are sharing your info. I read your link. Here is a link that I am going by. You will run lean with the afm and 550's if you don't have the sonic screw because you are getting alot of unmetered air. I do not have the sonic screw. That is the whole purpose of the adjustable fuel pressure regulator to increase fuel pressure to compensate for the unmetered air.:icon_bigg



http://www.cygnusx1.net/Media/Supra/Library/ToyotaTech/h22.pdf

 

[TurboStreetCar]

In that link it shows the proper function of the fuel pressure up VSV. The point of the 500cc injectors is to compensate for the unmetered air. Either way you understand your missing a part to complete the puzzle and running the engine with no vacuum line is inproper.

The regulator maintains a constant pressure differential across the injectors, With a walbro pump and the stock regulator that pressure differential could change at low load conditions due to the large restriction the stock regulator could create. This could create mixture control issues.

 

[89supracrazy]

Yeah. I am going to run the vacuum to my adjustable fuel regulator. At Idle I can get close with vf reading but in open loop I have know clue of what the ratio is. That is where the wideband steps in. I need to hurry up and get one. With the stock regulator you are not going to be able to tune much. Thumbs up for the afpr.