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Anybody experience fuel pump cavitation on the DW200 or DW300 fuel pumps? I'm running a returnless fuel system, basically from tank to DW110 10 micron filter, to an AEM FPR. FPR returns to tank and to fuel rail. Pressure is 43.5psi base and has a 1:1 rising rate with boost. Car is turbo BP with 12psi boost, E85, ID1050 injectors.
The install was initially with the fuel filter between the FPR and the fuel rail and with this the pump would cavitate pretty much all the time. You could hear it at idle, and see some bounce in the gauge on the FPR. Moving the filter to in front of the FPR helped this quite a bit, but the pump still cavitates at certain pressures. You can hear it by adjusting the pressure up and down on the FPR. At certain pressures you can hear the pump surging / struggling and the gauge starts to vibrate a bit.
At idle it holds pressure even if it's cavitating, but out on track it will cut in and out at anything above a few psi of boost. I log fuel pressure and fuel pressure will drop as low as 12psi (not good). System is powered from a 30A relay and 10AWG wire. This is with a completely full tank btw, so not a pickup issue.
I'm thinking of switching to a return system or PWM'ing the pump as the AEM Infinity ECU I have supports it and adding a SSR would be fairly easy. Just not sure slowing the pump down will solve it though.
I'm assuming this is an NB that originally had a factory returnless setup. Did you remove the factory in-tank fuel pressure regulator?
What is the peak pressure you are seeing, your log doesn't show the scale. Where is the pressure sensor located in your system?
Can you clarify how you have the lines plumbed? From your description it sounds like you have the fuel rail feeding off the return line to the tank.
That's definitely the wrong way to plumb it. It seems unlikely you'd have it set up that way, but I wanted to make sure I understood.
Only way you'd have pressure in this configuration is if you didn't remove the stock in-tank regulator
It's plumbed as your AEM picture of the correct setup shows. I originally had the filter between the regulator and the fuel rail, which seemed to make it worse, but putting it in between the pump and regulator, while better, does not completely solve the issue. This is a NA with a NB motor. For whatever reason it's plumbed as a dead head system instead of return system. As an NA chassis there was no fpr in the tank. The tank sock is the Denso 951-0001, so I've ordered the OEM Mazda one to rule that out as a problem. The tank outputs have AN6 bungs welded on, and it's AN6 stainless from the tank on. It's pretty much the Flyin Miata setup so I'm guessing the original builder just followed their directions.
I moved the FPR and filter to the trunk as having it under the car seemed weird to me and it's much easier to adjust and troubleshoot in the trunk. The DW110 filter and AEM fpr are connected directly to each other with a swivel fitting. The data log fuel pressure is directly on the rail
One thing of note is there are no dampers currently in the system at all. The one under the rail isn't there nor is the external one that you find in the NB system.
Base pressure is 43.5, it drops as low as 12psi and as high as 48psi. Basically the boost curve and the fuel pressure curve should follow each other I would think (shape anyways), and they do until they don't. The fuel pressure on the graph is min 0, max 60. I added some datapoints in red. Idle it sits at 34psi fyi. it is boost referenced.
My current plan is to convert to a return system lacking other explanations, move the fpr into the engine compartment and add a Radium Fuel Pulse Damper. It's a racecar, so overall that's not too difficult, but still a bit baffled (no pun intended as to why it's struggling. I'm also going to rewire just in case, but the wiring is extremely clean (think motorsports level wiring) and I don't think that's it. It's only dropping .35V from the input of the relay to the pump, which really isn't much for a 14A draw. (EE by trade).
A damper would only smooth out the pressure, the 20psi drop appears to be related to something else.
The DW300 has a pressure relief valve that triggers at 100psi. If you have a significant enough flow restriction prior to the rail that might be causing the pump outlet pressure to exceed 100psi which would bleed off pressure. However, it would be a tapering drop, not the sudden drop seen. Have you inspected the filter and made sure it isn't clogged?
Have you inspected the in-tank lines? Potentially a split line or loose clamp that's opening up at higher pressure. Most rubber line isn't rated for submersion in fuel and it can soften, swell or split.
Looking at the log, fuel pressure drop correlates directly to when you get ~10-12psi of boost. It doesn't occur until you hit that point and goes away as soon as you drop below ~3-4 psi of boost. Inspect the vacuum line going to the regulator for splits or kinks. Probably not the problem as it would only drop to baseline psi in that case.
Check the fuel pressure regulator, diaphragm potentially leaking under boost.
How old is the pump? You're well within the operating conditions of the pump. The only way you could be cavitation is if you had plugged the internal relief valve and were well over 100psi outlet pressure.
Have you reached out to DW, their tech support is pretty responsive.
Reached out to DW tech support, not a ton of help other than go to a return system. Pump is new. (brand new), but I was having some issue (similar) with a DW200 pump that this replaced. I've swapped them back and forth, with similar results. Filter is brand new as well, so not likely clogged. I thought about the rubber hose as well and tightened that up some more. I'll need to test as it's not easy to do in a racecar. I also lifted the assembly partially out of the tank to see if at least the top half had any leaks and it was good. Regulator seems ok, at least it doesn't leak under testing that I can tell. The AEM diaphragm is known to have leakage issues though.
Also see you have an LS7 Rx8. I used to have an LS7 RX7. Widebody, full race.
So converting to a return system . Ordered the Radium fuel pressure rail, direct mount regulator, and fuel pulse damper. Took a bit of work to get it all to fit, but looks like it should work.
Return system is probably the way to go, hopefully it sorts out the issue.
Radium makes some really nice stuff. They are super spendy, but they've got a few things like the pulse damper and a venturi pump that no one really makes. I've got a few bits from them on my projects.
LS7 Rx7 would be really nice. Did you keep it dry sump or convert to wet?
My Rx8 is my long term project; every few years I end up revamping it to make it a bit nicer.
I ended up swapping out the LS3 I had been running for a LS427/570 crate engine GM launched in late in 2020. Did it just in time as they stopped selling them last month.
So it seems to have fixed the issue. I haven't tracked it yet, but it sounds much better. I'm taking it to the track this weekend to see how it does. The Radium stuff was super nice from the standpoint you don't have to mount anything. It's all on the rail which simplifies a lot.
Rx7 was pretty much full race. Dry sump, LS7 stroked to 437, powdercoated chassis, all fiberglass or carbon where I could. Fun car but we called her Kandy and joked she had a slot for your money. Super fast, but also not exactly cheap to run.
02-07-2022, 11:40 AM
Fuel Pump Cavitation (DW300)
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as to why it's struggling. I'm also going to rewire just in case, but the wiring is extremely clean (think motorsports level wiring) and I don't think that's it. It's only dropping .35V from the input of the relay to the pump, which really isn't much for a 14A draw. (EE by trade).
