Ok gang, correctly tested the MAF today and got 13.6mV. Reground the MAF and read 2.2mV. Problem is still there...WTF!!

Its like up until a little past mid throttle I get half-ass gas pressure then BAM, Im all squirly with spinning tires and full power. TPS tested at .613 and 4.38 at WOT. MAF, again is at 2.2mV, and I can hear the fuel pump turning on. One thing that Ben Davis and I were pondering is that I am STILL running the JWT ECU programmed for the 9.5:1 compression US DE, with turbo, on the new 8.5:1 DET block. With timing at 15, could this be the culprit?

I also pulled my 1 week old plugs and regapped them from .030 to .025. I am running stock boost and stock fuel pump. I am pretty sure it is fuel delivery related, since I have always had a slight backfire when switching gears since the FULL DET install.

Any advice is greatly appreciated, in the meantime, I will be setting the timing back to 8 and advancing it a few clicks to see if retarding helps since the ECU is not programmed for the 8.5:1 compression.

Thanks gang!

It could be something very simple like a dirty fuel filter! What pump are you running? How old is it? we had major bogging issues with Ryan N's car. The car would buck or lose power and then kick back on, the car would shut down and not start back up; turns out it was a very dirty fuel pump screen. We put a new pump with screen and it took the problem away.

As for the ECU, JWT has a more aggressive ignition curve with low compression than they do with stock 9.5:1 CR. Turbo vehicles tend to like more advanced timing either way! You may want to keep the timing set at 15 rather than turning it down!

Thanks Louis!

I am running the stock pump right now and I am sure its the one from the factory. I just bought the Walbro 255 for 94 bucks just to have incase I upgraded injectors and turbo later. I changed the fuel filter the day after I got my car about 11 months ago and I WILL do it again today.

One thing I was thinking, could it be the MAF is reading incorrectly unless a certain voltage is sent? I dunno, trying to cover all aspects here. I plan on doing a fuel pressure test the same time I replace the fuel filter just to see where I stand on that.

Also, after I reground the MAF and let it sit there and idle. After about 5 minutes, the idle dropped soooo much, almost to stalling, around 350 RPM or so. I know the S4's are lopy, but come on.

Thanks again Louis! :D