Lack of fueling up top... again
 

This is what I have:

NB1 converted to return style using a FPR from a European '99.
8mm supply line used for the return (full size).
Deatschwerks DW100 pump
Stock Wiring
Flow Force 640cc injectors
TD04L-13T turbo.

Some time back, I was seeing not enough fuel at high loads (100% DC) on yellow tops at about 12 psi. I replaced the stock pump (98K miles) with the DW100. That made things OK.

Then I realized I was still not utilizing the full flow of the turbo, so I upped boost and again ran out of fuel. Changed the Yellow Tops to the Flow Force.

Now at 15 psi, I'm running about 70% DC at 7k RPM's, which seems high to me compared to others running about the same HP.

This morning coming in, full throttle pull and my high end went quite lean (12.8 when should be 11.6 AFR). In the past, I haven't had fully consistent AFR, but never have I seen that much offset. Was a quick, 2nd gear pull, so AFR safety did not trigger.

It was cold (MAT = 40) but I have lots of extra fuel there, 6% extra (in fact, DC got to 78% on this run).

Thinking:
Bad Regulator
Bad Pump
DW100 is too small, though calculations say it should be fine
Bad wiring, including possible high resistance in some relay contacts.
Fuel Filter needs changing. This one has 10K-30K miles, I don't remember when I changed it.

One other data point. About 3 months ago, I started not getting a good priming pulse, whereas before it was OK.

What is the most reasonable trouble shooting procedure on this?

Add 10% fuel, re-test, double-check that DC% rises appropriately, and see if AFRs follow. If AFRs do not follow, then you have a fuel delivery problem, almost certainly on the fuel pressure side. From there, I would start with the easy stuff (fuel filter), and if that doesn't solve it, then move on to the fuel pump, which is marginal at your flow levels.

@ 17 psi I am flowing close to 650 cc/min @6k ( I rarely make it to 7). you could very well be at the end of that fuel pumps threshold.

Yeah, you can skip the test. My notes say that at ~60psi the DW100 will only support 500cc/min of fuel per cylinder. You're out of fuel pump.

What a dang waste that I bought that DW100. I was thinking that even the stock pump would handle my power need. OK, I'll turn boost down and order the DW200.

Just ordered one from the Fly-by-Night TSE place. Hope they ship it right out.

@Savington, I'm not going to have issues overpowering a stock FPR with the DW200, am I? I have heard it both ways over many threads.

Thanks for the help.

You should be fine. Thats about the biggest you can go though.

Im a bit confused though, as i was under the impression that FFs on stock pump were good to 300.

You should be OK.

Stock pumps are hit or miss due to their age. A healthy one is usually good to the 220-240whp ballpark. I've seen them give up as early as 180whp if it's the original pump to the car. The DW100 should flow about the same as a healthy, new stock pump.

I don't think stock pump will make 300.

I will change fuel filter first, then the pump... for science. Different calculation sites show different flow rates needed. ID's seems the most straight forward (realistic) and indicate that the DW100 might be marginal. It depends how much pressure drop is in the filter and piping.

It's easy math. Take injector flow in CC/min (640), multiply by duty cycle, and that's approximate CC/min per cylinder of required flow. Divide that number by 4 and you get the flow needed from the fuel pump for all 4 injectors in liters/hour (add a little buffer for head loss). Compare that to listed data from the MFG (DW100 is 120lph at 60psi) and see where you get.

I posted a quick list a while ago here of what each fuel pump would support in terms of injector flow, but I can't find it now, so here it is again. This is based on published MFG data and assumed 100%DC, so leave yourself some buffer from these numbers.

At 60psi of rail pressure:
DW100: 500cc/min
Walbro 190hp: 708cc/min
DW200: 938cc/min
Walbro 255hp: 963cc/min
DW300: 1271cc/min
Walbro 455lph: 1588cc/min

It was the fuel pump. Replacing with the new DW200 has fixed both the high load leaning out, and my starting problem.

I was having to run (2) prime cycles before the car would start quickly. Now I'm back to my standard procedure. Delay time of 0.300 seconds to prime. I can move key directly from OFF to START (no pause at ON), and the car starts right up.

Thanks.
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