I suppose that makes sense: if adjusting the fuel map does not produce the expected changes to AFR, then one would suspect the fuel pressure is low. Adding a sensor array to my car was instrumental in diagnosing its problems and feeling okay about detecting future ones. I highly recommend the Zeitronix ZT-2, which is an AFR-sensor setup with inputs for boost (detect belt slip) and two other sensors; I use fuel pressure and IAT. And I will likely add another ZT-2 to monitor AFR in the other cylinder bank along with oil temp and pressure.
Dave Dozier [MENTION=4799]DDozier[/MENTION] recommended the Deatschwerks fuel pump over the Walbro. I liked what I was able to read about Deatschwerks as a company and about their products. There are a couple of tests out there that show pretty good flow performance and lower current consumption than others. I think it's difficult to draw a solid conclusion from anecdotal evidence, like someone getting a bad Walbro (e.g., ryu) notwithstanding buying from a reputable source (apparently fake Walbros are not uncommon, given their popularity). In the end I spend a number of hours scouring the interwebs to learn what I could and then went with the DW. The Denso pump from a Supra mkIV is a common choice, but is expensive, has high current draw, and the variations are a bit confusing. Aeromotive seemed pretty good and was on my list. I chose DW. At the time I was not using a piggyback and larger injectors, and I think the DW underperformed at 100psi (and I think it has a relief valve around that pressure), but it seems to be fantastic at the 40-55 psi I use now.
My car also has a relay for the fuel pump, thus the factory feed goes to the coil of the relay, which supplies power to the pump over higher-gauge wire. Others have reported voltage loss being an issue with some of the higher-current pumps. Because of this, I also removed the fuel-pump relay and replaced it with a jumper to bypass the fuel-pump resistor. I don't think that matters if you are using a separate relay for the pump, since the coil will be activated regardless of the resistor, but it's one less thing clicking behind my seat.
I hear you about oiled filters. I recently bought a paper filter and may try it out. I will see if/how it impacts AFR, which would be an indicator if it has an effect on power potential. Since I'm tuned with the K&N, I may stick with that. It seems to me that if the oil drips out, you put on too much. I haven't seen that though. With the foam unifilter, at least you can wear gloves and massage it to a certain extent with the aim of uniform distribution and to squeeze out any excess. And the filter area seems larger as the K&N filter element is a window smaller than the overall filter. Let me know if you want to sell your unifilter.
