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OBXT with P0171 lean

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I have been intermittently getting P0171 lean code. It comes on while at freeway speed.


Here are the facts:


  • Bought car 2.5 years ago with 114k (now has ~160k).
  • Came with Cobb air filter (no box) with Denso 22680AA31A MAF sensor (stock sensor I think).
  • Unknown if ever tuned (Sport & Sport# mode have always had issues under hard accel).
  • 2 years ago: added Grimmspeed Lightweight crank pully, F1 clutch & lightweight flywheel.
  • Stock downpipe (but cat gone since clutch job).
  • Removed and checked the passenger motor mount (looked good - so probably both are fine).
  • New plugs this past winter.
  • Just swapped in a used MAF sensor (same as above) with no noticeable change (see data table image).
  • Cold start, freeway load, & hot idle data snapshots in table below.
  • Gas mileage/power seems unaffected but for a while, I've been noticing sometimes it shudders from a stop (clutch wear out?).
  • What feels like drivetrain linkage slop at low rmps with no load (lightweight related?), or maybe one side of clutch is worn more and grabbing less and low RPM accentuates the effect?

I doubt that clutch wearout (if that is what I'm feeling off the line) would cause a false lean condition at freeway speed.


I thought maybe I was over oiling the air filter and ruined the MAF sensor but the one I just got off an N/A OB from the junk yard looks exactly like mine (slightly tarnished) and looks nominal (only one trip so far).


Any suggestions to troubleshoot this? I've sprayed carb cleaner around the motor (but only at idle) with no results.


I have a Tactrix Openport 2.0 but can't find decent instructions or any related forums alive for help (should have saved for AccessPort).


Thanks in advance!

Here's my live ODBII snapshot data

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issues under hard accel and at cruising highway speeds, to me, sounds like a fuel pump that can't provide enough fuel. check fuel pressure at idle and wot.



also, check your intercooler for separation. oily residue and bent back fingers indicate failure.

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Thanks for the reply.



Fuel pump makes sense. Fuel pressure isn't coming up on my OBDII outputs (using EngineLink which has lots of other outputs, just not fuel pressure). What's the easiest way to check this?




BTW, my P0171 light cleared two starts after I got gas yesterday. I suspect maybe this has been a trend I haven't noticed but will watch for it now.



As I understand O2 sensor info, there is only 1 bank since exhaust is combined. So "O2 Sensor 2" is downstream and "O2S1" would be upstream?



S1 (lambda is the only output I have) is always close to 1.

S2 (Voltage) seems to move around more between 0 and 1V when before with the P0171 light, it seemed to rail between low and high (no middle ground). What is normal?



How do you think my catless exhaust with untuned stock O2 affects things? I read something while researching this that indicated it could be a big problem to run without tuning for catless.

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Your gutted down pipe (and no tune) could be your issue.


You basically let the engine breathe better without making changes in the tune.


This is assuming you were tuned for the Cobb intake. If not, that will cause a lean condition as well.

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I wouldn't doubt it except that it had no issues (no CELs at least) for well over a year, maybe 18 months until the extra clutch shudder near idle began which I assume is from clutch wearout but could be many other factors.




Now reading about boost creep and potential catastrophic damage from running lean.




Is there any way to tell if it has an aftermarket tune? I have an Openport 2.0 but cannot find clear up-to-date instructions on how to use it. Accessport is not in my budget right now.




If I have a local shop check for vacuum leaks, clean the injectors, check fuel pressure and these all check out, would Brentuning work with my gutted cat? I read that it could be tuned out. Is their cat requirement simply a legal disclaimer?

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Get over to the tuning sub-forum and do some reading about opensource tuning to find out how to check if the car has been tuned. The guys that frequent that sub-forum are much better equipped to help you figure out if your car has been tuned. You'll need a laptop to go with your tactrix cable.


Your best bet (for the last question) is stopping by Brentuning and asking face to face. Without an AP you will need a shop that is willing to do some opensource tuning. These days many shops are not equipped to properly tune a car without an AP.


As for the P0171 look at your upstream O2 and make sure there isn't any obvious damage. You issues in S and S# make me think you are NOT tuned though.


Also the combination of LWCP and LWFW are likely what is causing your shuddering. That is a combination that has been known to not play nicely together on these cars. I don't know anything about F1 clutches but no clutch should wear out in 2 years.

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