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5-speed swap PO171 code

3K views 21 replies 4 participants last post by  REM BROWN 
#1 · (Edited)
I have a 2002 v6 taco. About a month ago, I swapped out the auto for a 5-speed. The truck sat for about a month. I swapped in a 2002 v6 manual transmission ECU when I did the swap and depinned the wires that were used for the auto. Ever since I have been battling a p0171 code. So far I have replaced the front A/F sensor, and the MAF sensor. I have replaced vacuum lines and checked for vacuum leaks. Had it smoke tested by a dealer as well, they said there was nothing. I changed the fuel filter and put in a walbro 190 while I was at it. I also installed a URD AFR calibrator to try and trick the computer into a 14:7:1. The truck is supercharged as well. I'm out of ideas. Do you think the ecu is the problem? I can post the freeze frame data if that would help. Any ideas? If anyone knows of any tacoma experts in NC? I am running out of time. I can't pass inspection and it has expired last month. It is my daily. Thanks
 
#3 · (Edited)
When they smoke tested the truck did they Indicate it would pass an inspection or that the ecu was functioning. Any type of leak would cause the lean condition if there truely is one. The trick is gonna be figuring out if the ecu is trying to add fuel and running out of trim. How's the truck running?
 
#4 · (Edited)
It sounds like you just have an air leakage (vacuum leak) in the induction system allowing unmetered air in. Not sure if smoke testing is the best method for finding these kinds of issues. We would normally use smoke testing for finding issues in the EVAP system. Is your idle higher than normal? Usually listening for hissing when idling and a good thorough visual inspection should uncover any cracks or poor hose fitments. Did you do anything else to the motor recently? I don't think the trans swap has anything to do with this code unless it caused a hose to pop off somewhere. Attached is the diagnostics from the factory repair manual. It shows the possible trouble areas in order of likelihood. Also, I'm pretty sure you can plug in your original computer as a tester to see if the ECM is an issue. It should work..other than throwing additional tranny related codes...at least that's the way it was with earlier models
 

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#5 · (Edited)
Yeah I have the factory repair manual and have seen the diagnostics. The only thing I haven't replaced is the coolant temp sensor but my scanner says its getting a normal reading. I sprayed throttle body cleaner all around the motor as well. I have not replaced the intake plenum gasket and throttle body gasket since the supercharger install (about 2 years ago) so that could be a possibility but I doubt it. Idle seems normal. Bumps up from time to time but nothing crazy. Oil pressure is a tad high. I did a rear main seal and oil pan gasket when I did the trans swap but nothing else motor wise. Yeah the ECU is functioning with toyotas computers. In NC you cannot pass with any active CEL. Truck is running fine. I don't have a wideband unfortunatley but I'm going to order one soon.
 
#7 · (Edited)
Are you using the factory intake tube and filter..not aftermarket? I had an aluminum intake pipe on a Lexus GS300 and it would give a lean code because the pipe was a bit on the large side...some companies just make crappy products in a rush to get them to market. I ended up restricting the area inside the pipe around the sensor in order to get things back in spec and eliminate the code. This is something you might want to try just to pass inspection..then of course try to figure out the actual problem when time permits.If I had the original airbox and tube I would've put that back on.
 
#12 ·
Hey,
What is Key on Engine OFF for Mass Air. Should be close to .49.
Anything higher is out of spec. Mass air sensor will also set a Lean Code. Especially a dirty one! Running K&N? Oil drives them nuts. Also may be a calibration issue in ECM. Long Term Fuel Trim is way rich! Anything over 10% will set a code. Stored freeze frame data may help. Good luck, Mike :nerd
 
#14 · (Edited)
Found a vacuum leak on the back of the supercharger near the bypass valve. The leak got to the point where I could hear it and that is how I found it. Not too sure yet on how to fix that leak. Maybe some type of sealant? It is where the "horn" that has the bypass valve goes into the back of the supercharger
 
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