Hi,

I have recently installed a 35R turbo in my 2.0 Evo IX. I had a HO Walbro, stock FPR, stock fuel lines, fuel rail, 880cc Precision injectors, 91 Octane. When I ran 24-25 psi, the IDC was around 88% and AFRs were good, 11.4 at redline. But when I cranked up the boost to 27-28 psi, the IDC was 93-95% but the afr became 12.3-12.5 after 6500RPM. AFR value in the ecuflash map was pegged at 7.4, so no room to richen anymore.

I thought, surely my pump was on its way out. So, I got a new pump, modded it, installed it--nothing new. Same AFR.

Then I thought, lets change the injectors and fuel rail. So, I installed 1450cc FIC injectors and AMS Fuel Rail. Now the IDC became 65% by redline, but my AFR still starts leaning after 6500 rpm to 12.3-12.4, at any boost above 27psi. (Point to note: I richened my ecuflash map values to 7.4 (max) for all values 6500 rpm and above. Up to 6000RPM it is 9.0 with a corresponding AFR of 11.0)

Diagnostic checks performed:

1. Checked Fuel Pressure :
a) at idle (vac line on FPR) : 38psi
b) at idle (vac line off FPR) :45 psi
c) Peak fuel pressure (boosting 29 psi) : 68 psi

**Point to note: fuel pressure falls off above 6500 rpm, and by redline it is 57psi.
My boost is always increasing, (I have boost creep), so fuel pressure should also be increasing, not decreasing.

My question is:

a) Is it something mechanical? If so, what? Shouldn't be the fuel pump at such low power levels? (91 oct and 28 psi boost, 35R). I have tried, 3 different walbros, same result. Or is it the FPR? It shows no such sign at idle.

b) Is it something to do with electrical? i.e. the voltage dropping off or something?

c) Is it something related to the ECU? I have tried with both lean spool ON and OFF. No result.

p.s. I have already ordered the Buschur Double pumper. Lets see how it goes..

 

You need a bigger pump or 2 pumps, the walbro is maxing out

 

+1. Or a better single pump.

 

I am still a bit perplexed.. How can a single walbro 255 max out at only 27psi on 91 octane on a 35R variant turbo?

@mrfred: How can I change my ecuflash map so that I have more room to richen it. At the moment, I have my afr map pegged at 7.4 in rpms of 6500+. I have a lot of room with my injectors in terms of duty cycle, but no map room left...

 

27psi on a 35R is a lot of air and your injectors are not the best, I would also go bigger on those as well

 

Bigger pump. Walbro 400 or BR double pumper

 

I guess you haven't seen my threads on fuel pump testing and fuel pressure logging? I'm not the least bit surprised that the Walbro 255 is unable to supply the needed fuel. There's nothing that can be done in the ECU to alleviate this issue. Fuel flow through the injectors is driven by the pressure across the injectors. The standard pressure across the injectors on port-injected cars is 43.5 psi. What's happening with your Evo is that the pressure across the injectors is falling below 43.5 psi as the pump losses its ability to supply the needed fuel. As the pressure across the injectors drops, so does the amount of fuel. A better pump, or better wiring, or better fuel supply (larger diameter feedline that minimizes the additional pressure at the pump) is needed.

 

I have logs with VD results showing the limits of the Walbro 255 and a before/after when I upgraded to the Walbro 400. This was 30psi on a GTX3076r, but I think the limit is in the 450hp@wheel range.

 

I have observed the same on a FP Red car

 

This graph is where I noticed AFR not holding and then used my DEFI gauges to record fuel pressure under boost and saw the drop. Again, unmodified Walbro 255.

 

Thanks for the detailed reply. Actually, I have been reading on your fuel pump related threads before going ahead with the fuel upgrades. Helped a lot. I have been wanting to hardwire the existing pump or go with the 400 walbro. Its actually very difficult for me to change the existing lines to bigger diameter.

I have bought the BR Double pumper. Let's see how that goes. Might also install an FPR, if needed, to increase base fuel pressure. Will update this thread eventually.

 

You'll be fine with the double pumper. With no other fuel system mods, its good for at least 650 whp.

 

Mod the Wally, put it back in, and call it a day. If you're not going to be shooting for much more power that should be fine.

 

Don't forget about Squash...



Dual Walbro 400/450 or DW200/300, no drilled siphon goofiness, etc... We ship worldwide, too.

Andy

 

+1

Here is a short video of my Squash Double Pumper in action. Base pressure is set to ~45psi and the video is the car running 33psi of boost on a GTX3576r up to 8600rpm. The gauge on the far left is the fuel pressure and the initial bouncing of the fuel pressure was caused by compressor surge. Also, the boost gauge resets to 0psi when I exceed 30psi of boost. My setup runs twin Walbro 400's with second pump kicking on at 12psi.

Squash Double Pumper...33psi