What I've got:
* 2002 Corvette
* Converted to return-style fuel system
* Walbro 400 pump
* Hydramat pickup.
* Racetronix pump wiring upgrade
* Aeromotive 10-micron fuel filter w/ 8AN fittings
* 8AN fuel supply lines and rails,
* Fore fuel pressure regulator
* 454ci LS, Dart block, naturally aspirated

...and I'm seeing fuel pressure drop at full throttle / high RPM (6000 RPM+). This cut the dyno tuning session short at 550whp, and the engine should do 600 or so.

Is that pretty drop to be expected with that combination? Or does this suggest that the filter is clogged or something else has gone wrong with my fuel system?

Basically I'm wondering if I should upgrade the pump or ditch the filter.

Is there any point keeping the filter, or should I just trust the hydramat to be the fuel filter?

 

What is target fuel pressure and how much of a pressure drop? Is the regulator vacuum referenced?

Do you have a data log showing fuel pressure, manifold pressure and system voltage?

Which part number/size Aeromotive fuel filter are you running?

Regarding the filter question - no, the hydramat is just a prefilter for the pump. It is far too coarse a filter for protecting the injectors (and probably even the regulator).

 

Target pressure is 58psi, not vacuum referenced. (Same as stock.)

No logs, but we could see it happening on the dyno.

It doesn't happen on the street because the max-throttle-vs-RPM table is now set up to limit the throttle opening, it starts tapering at 5500 and is 40% from 6500 and above, and that prevents it from getting to where the engine needs more fuel than the system can provide. It would probably be fine at 75% throttle but I wanted to be absolutely sure it doesn't become an issue.

The filter is part number 12377.

Thanks for any insight, I really appreciate it.

 

Before you limited the throttle opening, what was fuel pressure dropping to at peak power rpm?

 

Sorry but I don't recall. The tuner was behindi the wheel (with the car on his dyno) and he took his foot off the accelerator as soon as it dropped.

I probably should have mentioned that I have a fuel pressure gauge on the A-pillar (AEM X-series). The fuel pressure is normally very stable, but the drop was obvious during those pulls.

 

The reason I ask is that some pressure drop under full load is fairly common for a few reasons including regulator design and the location of the fuel pressure sensor vs the location of the regulator and the restriction that may exist in the system between the two at higher flow rates.

If your target pressure is 58 psi (4 bar) and it drops to 55 psi, I wouldn't be worried about it. Your effective injector flow rate change from that pressure drop is only around 2.6%. But if it drops to 48 psi then I would be worried as now your injector flow rate has effectively dropped by around 9%.

And the reason I asked if it was vacuum referenced is that if you have an inlet restriction that generates higher vacuum at peak power (lets say barometric pressure is 98 kPa and your inlet pressure/MAP is 92 kPa) then the regulator will lower the rail pressure in relation to the atmosphere to maintain the differential pressure (if it is vacuum referenced) so your pressure would drop 6 kPa (roughly 1 psi).

If they are running the vehicle on the dyno, they should have logs, even if the aborted the run. That is sort of the point of testing on the dyno. Make sure they are recording data the next time you test. And if you have a way to record data yourself (HPT, EFILive etc), doesn't hurt to do so as well. Fuel pressure isn't visible to the ECM in that year vehicle (no fuel pressure sensor) but you could likely data log the fuel pressure going to your gauge if you wanted.

The reason for asking for data logs is I have seen issues where charging voltage drops at high RPM due to alternator pulley speeds or alternator voltage is erratic due to charging system issues caused by using non-resistor spark plugs and/or spark plug wires. And if you aren't data logging the vehicle data you might not realize that your fuel pump is now seeing 10 or 11 volts due to those issues instead of 13.5 volts and that is the cause of the flow issue.

 

Before you consider (removing) fuel filter; I recommend that you LOG or monitor actual DC Voltage at the fuel pump connector (Tank HAT)
My suspicion is that ( as ProServ said above) you are NOT getting the full 13.8 volts needed AT the PUMP.

 

The tuner was logging when it happened, but he was only logging from the PCM and from his wideband, so his logs don't have fuel pressure. Might have voltage, but that would be system voltage, not voltage at the pump.

I have the ability to log from the PCM plus fuel pressure, oil temp, knock sensors, RPM, and dual widebands... but my logger only makes CSV files, and can only log about half as many PCM parameters at a time as HP Tuners, so it's not great for dyno tuning.

Voltage at the pump would be really interesting, and it's definitely a prime suspect, I'll need to run some additional wires to make that loggable, or at least visible. And find a way to make ful power without a dyno... between cold air and wet roads, that might not be possible for months. It's too cold for nice tires, and with all-seasons it'll spin the tires at full throttle in third gear. (Which is kinda fun, but it's impossible test 550whp when wheelspin starts at 500.)

Anyway, since nobody seems to think that the pump is undersized, I guess I can cross that off the list.

 

Voltage at the pump would be best but voltage at the ECM is a good start - if that is low then voltage at the pump is low.

To confirm it is the filter you can add another sensor or put the existing sensor before the filter and test. If it has 58 psi before the filter but significantly less after the filter then the filter is the cause (seems unlikely).

CSV data is easy to view in Excel and many graphing programs. And you don't need a lot of variables - just need fuel pressure to be one of them. So the fact that you have a way to log that is a plus already.