Critique my fuel system
 

I thought my fuel system would be good for my goals, sub 350whp@250kpa, but it looks like I'm leaning out up top and MS is showing 120% duty cycle.

Specs:
'96 Miata stock lines
'99 fuel rail
ID1000 injectors
Aeromotive boost referenced FPR @ 70psi base pressure
Walbro 255

Can I just raise my fuel pressure another 10psi or is the Walbro 255 going to start giving up on me? Am I going to need a new pump something like a DW300 or Walbro 400? Or am I getting to the point that I need to think about a fuel rail or aftermarket fuel lines?

my bet is on the pump failing or not having enough juice (voltage) or something
dw300 should hit 350 no problem, even on e85
if that doesn't solve it, then you have a problem, because that setup should be good for 400

Thanks, Vlad. It looks like 90-100psi is where the 255 starts taking a dive in flow rate. I was hoping I could push it a little harder and get enough flow. Good know the lines aren't necessary though, that seems like it'd be a big expense. I'm sure a $150 pump is getting off easy by comparison.

and you can get one for super cheap with all the sales right now

Get a fuel pressure sensor. That will tell you a lot too

North of 300whp, I think a fuel pressure sensor is pretty much a requirement. Between the need for better wiring, the balance between flow and pressure from the pump, and nearing the limit of the injectors, you really need to know what the fuel pressure is doing.

I found some $20 0-100psi pressure transducers I'm going to be testing out. Should work with MS awesome.

Wally is boarderline at that power, drop your base pressure to 45psi and it'll be way happier or step up to the wally 400e85 like soviet and I.

Measure voltage at pump. If you didn't rewire it already, it's probably not getting full voltage which means the pump isn't pumping as hard as it could be. I had over 1.0V voltage drop at 12V battery voltage, that's A TON.

My advice is start there. If you look at the pump specs (flow vs pressure) you'll see cranking the pressure isn't doing you any favors, and that's assuming you got the HP version. If you don't have the HP version, you need it or a better pump.

E85 or gas?

FWIW, I'm doing 340 rwhp on gas with a walbro 255. I have -6 AN lines and an FM dual-feed fuel rail, though.

Fuel pressure monitoring via MS highly recommended, yes.

--Ian

I did 359 whp on e85 with a walbro 255. Stock wiring, stock rail, stock regulator, stock lines, with ID1000's. This was a 1.6 though.

Fuel pump rewire is MANDATORY if You want a constant 12V at the pump plus it free the engine of sensors that regulate the voltage to the pump. Read about wire length and thickness and how it affects voltage drop.

Thanks for the feedback guys. This is on E85, I forgot to specify that.

I bumped pressure up another 10psi (which looks like about the limit on the 255) and it still leaned out so it looks like the pump just can't keep up. I ordered a DW300 that should be delivered today, hopefully that fixes the problem.

I'll have to look into the voltage drop issues. I guess that's the next thing to address if issues continue.

If the pump flows 30% of it's rated flow at 100 PSI and you're running lean, bumping up the pressure doesn't fix anything, will just wear the pump out faster.

id1000s are also marginal for 350rwhp on E85, IMHO. I'm seeing low 60s for duty cycle on my id1000s w/ 340rwhp and gas, add a third to that and you're into the mid 80s.

--Ian

Mid 80s are maxed out, but not unsafely so. You can also add base pressure at 350whp without stressing the pump too much. I made ~350whp at ~87psi rail pressure on E85 with a Walbro 255HP and ID1000s.

My logic is that one of two things were happening:
A. My pump couldn't hold the pressure I needed it to run for my injectors to properly fuel the car.
B. My injectors weren't big enough to properly fuel the car at the pressure I was running.

Bumping the fuel pressure gives my injectors more flow, assuming the pump can hold the pressure. This didn't fix the problem so I assume the pump can't hold pressure at the flow rate I need and I bought a better pump.

Sure I can lower the fuel pressure to 43psi and the pump will easily hold pressure, but then the injectors can't flow enough and I'm still leaning out. That 2 minutes of extra wear on my pump was the test I used to help confirm the issue.

* Edit - I really miss props. Thank you to all those who have helped out and provided data from their personal experiences. I can't imagine the money I'd be throwing at this car if it weren't for all your help.

Yeap you got it.

When I rewired my pump, that bought me a bit of headroom in boost since the pump could pump a bit more up top with higher voltage. Even if you put a new pump in, I recommend it. Thread here where I posted voltage drop data on my 99.

https://www.miataturbo.net/general-m...-1999-a-83478/

https://www.miataturbo.net/attachmen...ine=1426489987[/QUOTE]

^ Thanks for the link, I was having trouble finding info when I searched.

New DW300 arrived today, DOA. Installed it and it did nothing. Uninstalled it and wired directly to a battery and still got nothing. So more waiting for another one now. Good thing I paid more to get 2 day shipping, blah.

DW is garbage. Ive had them fail in 2 seperate cars in one year.