My 05 X-runner has been running ridiculously lean at WOT for some time. I replaced the fuel pump at a little over 200K miles with the Walbro kit from URD. This seemed to help a little but the truck still runs lean. To give some history, before changing the pump, the truck would lean so hard that it would sputter and backfire / cough when trying to accelerate. It has very few mods (long tube headers, gutted cats, old TRD intake and now the urd pump). when I monitor the OBD2 readings on my Torque app, it shows full lean at WOT (like 17.0 or worse). cruising it stays around 14.7, but under light acceleration, the fuel trims are always high (in the 20's). The motor was exchanged for a motor out of a 4wd 4runner back when the truck had 127K miles (original motor got rod knock). The new motor never seemed quite as powerful as the original, but it has progressively become worse over the years. The Walbro pump makes good pressure (tested at 50 psi with the low speed resistor on and around 55 or so with the resistor off). Could this be just bad injectors, or maybe a bad maf, or does the 4runner use different injectors from the xrunner all together? I tried searching for "lean" conditions to see if someone else has had this same issue, but I couldn't find anything comparable. what can I do to fix this issue? MAF calibrator? New injectors? cam control solenoid replacement (drawing at straws here). Any advice?
Truck running abnormally lean at WOT
- Thread starter Armond30
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So are you saying that you're logging data with Torque to determine that you're lean? Or are you just looking at OBD2 data on a gauge? That's always going to be delayed and you may not be getting real-time readings. Are you getting lean codes?
obd2 data on the gauge from the torque app. it's pretty blatant on both banks. when I go WOT for a full pull, it goes very lean and stays very lean and is obviously missing power (to be honest, I am surprised that I haven't melted something yet). I was thinking that it may be a dirty MAF as I have never cleaned mine. Hopefully it is this simple, but I have my doubts. I will check at lunchtime.
actually, it might have been as simple as cleaning the MAF. A quick WOT burst after cleaning it, and the App is showing 13.0 and High 12's A/F ratio (instead of 17+ like it had been showing). my mods list is very short. Old TRD intake, aluminum flywheel, Long tube headers, Walbro 255 LPH pump, O2 eliminator kits, gutted cats, replaced head gaskets (#6 leaked at 176K), denso iridium spark plugs. It is basically stock. I will take the expressway back home today and see how it performs, but I am actually pretty excited for my truck to have pep back in it's step 
actually, it might have been as simple as cleaning the MAF. A quick WOT burst after cleaning it, and the App is showing 13.0 and High 12's A/F ratio (instead of 17+ like it had been showing). my mods list is very short. Old TRD intake, aluminum flywheel, Long tube headers, Walbro 255 LPH pump, O2 eliminator kits, gutted cats, replaced head gaskets (#6 leaked at 176K), denso iridium spark plugs. It is basically stock. I will take the expressway back home today and see how it performs, but I am actually pretty excited for my truck to have pep back in it's step
Hope it's all sorted out for you! Keep us posted on how she runs
Looks like cleaning the MAF did the trick! AF is perfect at WOT now (goes from 13.0 at low RPM and gets to 12.1 by mid RPM up. power is back and truck feels like it used to years ago! I wish I had of thought of cleaning the MAF years ago
Gadget
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If you have the old style TRD intake you likely had oil contamination from the filter. You may want to consider switching to the dry filter:
https://www.urdusa.com/21-90044-afe-replacement-filter-prodrys/
https://www.urdusa.com/21-90044-afe-replacement-filter-prodrys/
