Very nice, that's a good test and not everyone thinks to perform it. I like the suggestions from others to watch for temperature and/or cavitation problems. I've heard of tuners who won't do dyno runs unless the tank is full or nearly full. This next one is weird, but I've heard of a big-power car like a 2JZ having fuel pressure problems that were fixed by installing a larger fuel return line. Apparently they had upgraded the fuel feed line and the pump but the OEM size fuel return line was causing problems in unexpected ways. Also if there's an easy way for you to check the vacuum line going to the pressure regulator, that's a good idea too. The regulator won't keep the fuel pressure high enough if it's not seeing the same pressure as the intake manifold.

If your testing suggests the pump is the problem, it's possible you got unlucky in terms of your fuel pump. Unfortunately it's hard to guarantee that quality of aftermarket parts will be consistent, especially if the suppliers are being asked to keep prices low. It's quite common for overseas manufacturing to build the first batch to good quality standards and then save cost by reducing quality of future batches. And it's unlikely the people selling fuel pumps are testing every single one before it goes out the door. You could try running the pump with engine off, have the fuel return line feed into a bucket and measure the flow rate. If you measure how many seconds it takes to fill a 2-Liter container, you can calculate the pump flow rate from that and compare to the manufacturer's rated flow numbers.

 

Another very common cause of fuel pressure drop/ overheating fuel is-

Many people use -AN male fittings in the sides/ of aftermarket fuel pressure regulators because they screw right in...

FPR require -AN ORB fittings.

The flare end of a male -AN fitting will be so close to the inside of the FPR body that it creates a huge restriction and overheats the fuel causing cavitation at the fuel pump inlet.



Male end on Left and ORB on Right side of this fitting.


Typical aftermarket FPR. If you zoom in you see how the flare restricts flow in the blind machined hole.

 

no all my FPR fittings are orb no problem with that thanks

 

we do this with the carbureted engines, Mazda gives us a spec, the race cars want 1.5L per 30 seconds, so you need a good size container.
i like to do a couple/few tests too, just to get an average.

ive found that the pumps ive tested usually don' come close to their advertised flow rate...

 

thanks for sending me your map and two logs. the first two screens show the two logs in their entirety, 10 and 12 minutes. i highlight, of course, differential fuel pressure. as the minutes fly by the trend is clearly down... in the first, from 49 to 45. the second log was just a few minutes after the first and starts out at approx where the first run ended at 45. it doesn't drop much but the direction is lower. i am certainly not an expert on this but to me it looks like it is probably a defective pump. whether the pump is just mechanically defective or the defect heats the fuel is for others to opine. i do not think it is electrical.






here we see the system under stress. it appears that the fail is especially dynamic. sort of an initial slippage when asked to deliver and then regains a bit of traction. start with 2.4 boost, 44.4 psi DFP at 5:29.688



at 5:29.822 with boost on the rise to 2.6 we see a fail as DFP is now 38.3.... pump slippage gets my vote. but notice some recovered traction after the fail.



at 5:30.630 with no boost we are back to 44.4

all this in less than a second! and of course if you didn't have a digital fuel pressure sensor you wouldn't know. i have always felt a digital fuel pressure sensor was second only to an AFR sensor.







my bet is either a counterfeit pump or a slight tear in the fuel pressure regulator diaphragm.. perhaps others may find the data helpful in finding the answer.

here's a real Ti Automotive/Walbro pump.

 

That is what I was seing on my logs also very kind of you and I have to thank you man not you of trying to sort things out for me and spending your time.

The pump is getting changed next week so we will see if thats the problem.
Also one other thing I forgot to mention is that my fuel pressure sometimes when i test the pump throught the pclink my pressure reaches to base pressure and drops really slow sometimes it drops really fast, dont know if this plays a role but thought it was good to mention it.