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I have a 2004 Mazda 6s MTX with prototype Injen intake and Magnaflow catback exhaust.

When I first got the Injen, around 30k miles, the engine light never went on. Once I hit about 120k miles or so, the light went on. I thought no big deal since it was probably the Injen finally throwing it off….

Recently I started blowing a couple of spark plugs on the lower/front, center part of the engine (not sure what cylinder number that would be). I thought that was weird.

Around that time I also noticed when I’m in a high gear, say 5th and am getting on a highway ramp about 35-40mph, if I don’t downshift and just try to keep the gas pedal down, the rev’s will jump up and jump back down (from 2.5k to about 4.5k and back) and I'll have a severe lack of power.

Now that I have 151k miles on it, I decided to check the codes with my reader. I’m getting P0171, P0174 (pending code) and P0431.

P0171 – System too lean (Bank 1)

P0174 – System too lean (Bank 2)

P0431 – Warm up Catalyst Efficiency Below Threshold (Bank 2)

My thoughts are this:
1) P0171 & P0174 codes probably from the Injen intake…..but since I went so long without tripping the CEL, why now?
2) P0431 – I will check the O2 sensors with a volt meter to ensure they’re functioning properly. If they’re not, what do I do next?

I plan on cleaning the MAF sensor and EGR valve. The Cat runs about $426 for the front and $650 for the rear per the dealer prices. I can’t seem to find them elsewhere because none are California legal.

How can I check the Fuel Pump to make sure that’s functioning properly?

Last time I changed my oil, I noticed the under carriage seemed “wet” with something. I’m pretty sure it was gasoline. Whenever I idle the car and have the heater on, I can smell gas.

Everything in the car is stock, including fluids, except for springs, brakes, serpentine belt, engine mounts, intake, axles, spark plugs and coolant hose. I've done all of the work myself except for axles, belt and mounts.

Any ideas anyone? Thanks!
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