I think you should mount a go pro in the tank and see what it looks like at low fuel level.

Is it the stock hangar? I know there are some differences in hangars between the years.

Pretty sure he's diagnosed it extensively and still couldn't find the cause

I never saw go pro in tank video though. Which I actually am just interested in seeing :D

It's the stock hangar with the in-tank regulator removed. This means it's dumping the return fuel a few inches above the level of the bottom of the tank. I was concerned that maybe the fuel spraying out of that was pushing the fuel away from the pickup, so we ran an inspection camera down the filler neck and made a video of it when cycling the fuel pump (sitting in the garage). It really wasn't all that spectacular, though. I haven't done it while driving, but it didn't seem like a likely cause.

I know I posted this video on mt.net, but can't find it in my build thread. Maybe it was another thread. This is what a fuel pump prime looks like inside the tank.



--Ian

One Brembo RCC rotor costs as much as my car does.

--Ian

I was running this exact same in-tank configuration when I had the return setup, and I had no issues.

DW200 on OEM hangar, DW provided filter sock FWIW.

I could see this creating aeration in the fuel causing the pump to suck up some air? But beyond that you got me. Maybe order one of those fuel rail regulator adapters with the male AN fitting on it (because IIRC its the same bolt pattern) and throw an 90° fitting on it and shoot the return fuel off to the side somewhere. It may not accomplish anything, but for <$20 worth of parts it might be fun to test.

Of course, if this was the real issue, I feel like we would be seeing it more frequently.

Just a thought. :dunno:

I'm more curious to see if the sock sees air when in turns. Then you could compare it to a car that doesnt see fuel starvation, and see if the sock is seeing air then.

Indeed I have a return system, and indeed I have the same problem. 1/4 tank and below and I'm hosed. I can run it down below a half tank though, so it does sound like my fuel starvation issue is not as extreme as yours.

maybe just lengthen the return tube/hose so that it dumps right onto the sock? dunno

Ed also has the same return setup as ian in the tank. Fuel flowing from where the regulator used to be.

A change in the return configuration seems like a good idea to me. You must be picking up bubbles.

Try some of that Holley Fuelmat stuff?

I, too, wondered about return turbulence. I suppose we could weld up a flange and tube. However, this video, and other evidence is that bubbling is not the cause.

Another thing I noticed. When I pulled the original pump, it took about 5 seconds for the fuel to all run out of the expanded sock.

However, the old, stock sock was so loose on the new DW pump, that I used the one from DW, instead of re-using the stock one. Later, I pulled this assembly and the fuel ran out of the DW sock in about half a second.

Miata does not sell the OEM sock as a separate item.

I'm imagining a high g corner, most of the fuel is one one side of the tank, small layer over the sock. The fuel splashing back might bubble that enough?

Also, looks like when under high power, you are returning very little fuel to the tank. Is it possible you are running out of pump? 'Course that should change conditions much between full and empty tank.

EDIT: NVM. This is cycling pump. Duh… reading fail.

haha I was just thinking of this

Assuming you mean "Mazda", sure they do, I bought one. Looks like it's part # BP4W-13-ZE1 (at least, for an NB1, didn't check other years). "Filter, fuel pump."

I swapped out the one that had come with my Walbro for a new OEM one back when I was first investigating this problem last summer (a few pages back on the build thread). The OEM sock is held open with a spring, the Walbro one is not. The OEM sock went onto the Walbro input just fine, no rattling. Haven't tried a DW pump.

It didn't make any difference in the fuel starvation, though.

--Ian

@turbofan how did you get just a new OEM sock? https://www.miataturbo.net/race-prep...handers-89826/

Also, in above thread, Ian says he has an OEM sock, but pic on post 6 is not an OEM sock.

I'm not eager to dunk my GoPro in gasoline, or to have the fuel tank unsealed to the point where I can get the inspection camera inside while I'm out on track.

--Ian