Here is the story:
My old boost curve was 23psi starting to taper from about 3200rpm to 7000rpm in a progressive way, to 21psi. 2 weeks ago, I decided to retune it for a flat 23psi until 5500rpm and start to slowly taper from there, to 21psi at redline. Fuel map was retuned for new boost curve and was perfect. It added some midrange. Torque curve is much flatter than before.

My AFR target used to stay at 11.5-6 full boost and raise to 12.0 from 6k to redline. It always been very stable. Yesterday I saw 12.6 AFR on a WOT run. No knock. Fortunately I had a laptop in the car. So I connect it, and log a 3rd gear WOT run. This time AFR safety (thanks to tephra V7) which is set at 12.7 kicks in. So I open the fuel table and start adding fuel. Car takes it but in high RPM it started fluctuate between 11.7 and 12.7. This was not good. So I take the whole fuel map from 5000rpm and drop it by 2 whole points. I tell myself: if the fuel system is okay, IDC will raise to 120%(evoscan reading) and AFR will drop to under 11.0AFR.
Next WOT had exactly the same odd AFR swings. I conclude the engine is suddenly out of fuel.

I suspected the fuel pump, being not able to flow enough fuel for my new boost curve, making the fuel pressure swinging up and down from fuel starvation.
So tonight I'm installing a walbro 255hp with rewiring. I'm pretty sure this will solve my afrs.

So OEM fuel pump failure, at about 320whp, on a VIII 10.5. I know I pushed it a little in the last 2 years. I should have installed my Walbro sooner. And yes I knew that the VIII fuel pump were known to heat at high flow. I just trusted mine(?)

Don't trust your OEM fuel pump , it could suddenly start to fail!

 

The wally 255 is cheap insurance. Glad you got it in time

 

Yes!

Edit: Got the new pump in. AFR is rich but now very stable! (And I got lucky, my whinebro is silent)

 

Couldnt have put it better. Best under $100 investment I made.

 

The walboro 255 is essential when going beyond stock boost tables. Next step is to change the injectors.

 

Any reason for not going with the new walbros or duestchwerks?

 

a 255 is plenty for people that only run pump gas, or even E85 up to around 480 HP...

 

That^.... and it's cheap, reliable and proven.