Hey guys, I have a 2000 tacoma 3.4 to which I have done the deck plug mod to the air box and the ISR mod to the intake tube. This was done about 2 years ago but recently I have had the check engine light one and the code is P0171 (bank 1 lean). It has been at my local dealer for the past 3 days and the best they could come up with is the mods are causing the code. Some how I do not beleave this. Mainly because I am only getting 7mpg and if I park the truck against a wall I leave a nice black mark on it from my exhaust, which would indicate to me that I am running rich? Does any of this make sence to you guys or have any of you had a similar problem? I have changed both O2 sensors and the Mass Air Flow sensor as well as the filter itself. I am now officialy lost.

I think that you are correct as is the OBD2 computer.

Suppose you have a plugged injector on bank 1. The O2 sensor will read a lean condition for the enitre engine and boost fuel to the whole engine because there is only 1 pipe that the O2 is sniffing.
The problem is that this will not change the O2 reading much because you still have 1 cylinder that is pumping O2 out the tailpipe. So the computer will do it again.
Eventually the O2 will be happy but the injector pulse width will be outside of parameters.
The engine will then kill fuel to a bank at a time and sniff with the O2 sensor. Bank one will show lean where bank two will sniff good. The computer then throws a code saying that you have a lean condition on bank 1.

I do not know that this is your problem but I would be interested to find out what it was.

No leaks in the exhaust before o2 sensor is there? Probably not but it the only thing I could come up with. Exact same thing was happening to my buddys 94 22re. His problem was that his o2 sensor was not tight agains't the rednecked flange that a muffler shop installed. My next move would probably be to replace the injectors. How many miles on the motor?
Rob

According to the dealer the injectors tested fine for flow, not sure how they checked them but that is what they say. It seem that just after I hit 100,000 miles the thing just gave up. As for the exhaust I'll check that today and see what I can find. I should add that it's also been changed to a 3" exhaust with a high flow cat and a flow master 3" single in dual 2.5" out. Also this has been in the truck for over a year now. Thanks for all the help guys and I'll post more I as I find out.

Any news?

Well so far I am still scratching my head. I checked the seal around my O2 sensors and everything is fine there. I've also spent some time looking for things disconected but everything seems to be in order. The dealership did mention something about when they had the factory air box back on the air/fuel mixture sensor was reading like it was about to go. Can anyone clarify this, maybe point me in the direction where it would be located? (I didn't think such a sensor existed.) I keep going over what Toyota said about ti getting too much air but if TRD has as supercharger for this motor then everyone with that would have a similar problem I would guess.

I battled this same code for quite some time, and as a result, I changed out the O2 sensors, the MAF sensor, the catalytic converter, PCV valve, a half-dozen other things that the dealership told me to change (including the gas cap, WTF???), and checked everything else along the way. The problem ended up being a small air intake leak causing too much air to be drawn into the system behind the MAF sensor. I had checked the system for leaks before, but didn't check my supercharger very well, which was exactly where the leak was occurring. Some high-temp silicone fixed the problem, and the truck ran much smoother, and the check-engine light went out. It's now been driving great for about 4 months, and I got my MPG back.
After being raped by dealerships and being fed their BS for way too long, my advice is to see if you can locate the problem yourself first. Check thoroughly for intake leaks, make sure that MAF sensor is clean, and read the 4X4wire article about PO171 trouble codes. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Oh yea, one more thing: the dealer will ALWAYS tell you that your mods are causing the OBDII codes to show up. 98% of the time, that's just their way of hiding behind the fact they don't know what the problem is. <img src="/forums/images/graemlins/angry.gif" alt="" />

Just for clarification, where did you have to put the silicone - where the throttle body attaches to the supercharger intake?

Actually no (that's where I originally checked for the leak). The spot that was leaking was back here, approximately where the image is pointing to "Boost Line 1":


Where that L-shaped port connects to the back of the impeller housing, there was a lot of freeplay. It seems as though that port had come loose somehow and could easily be wiggled. Excess air was then being sucked into the intake (I think). I noticed that after I sealed that connection up (right where the port fits into the cast impeller housing), the truck ran much smoother at idle, and the code cleared itself after exactly two drive cycles. AWESOME!

A year and a half worth of dealership BS, expensive parts, and many many nights laboring away under the hood of my truck was cured by a $5 tube of hi-temp silicone!!!! <img src="/forums/images/graemlins/notooth.gif" alt="" />