'08 V6 codes nightmare

[inscarguy]

This is a long read, please be patient.

My vehicle is a 08 v6 4runner with 172k on it. Bought in may of this year needing some work and maintenance. Got all the needed things done. Been getting a p0456 code since day one and replaced everything related. Also got a bad stumble on start up when warm after sitting at least 1hr. Took it to a friend who is a real good mechanic and has knows the ins and outs of a vehicles systems. He found both upstream o2 sensors very lazy so i changed them with a comparable non oem sensor. After 1 day got code p2197 on bank 2. Cleared code and it came back. So I ended up changing MAF with a denso unit( oem supplier) and ordered a denso o2. During the down time I did some diag and found #5 injector leaking so i changed all the injectors and related gaskets with densos. At the same time I installed the new o2.

I Took it on a decent ride yesterday and it was running sooo much better. Very smooth, no stumbles, no codes. On the way home about 2/3rds the way the lights came back on. The code was p0174. WTF!

All new vacuum lines, tuneup, MAF, upstream o2s, plenum gaskets, gas cap, checked canister and replaced assoc hoses, cleaned TB.

I never got these codes until the o2 sensors were changed

Any thoughts?

 

[AuSeeker]

I know you said you replaced all the vacuum lines...but you could still have a vacuum leak, use some carburetor cleaner and spray it all around the intake and the vacuum lines while it's running, if the idle changes you have a leak in that area.

 

[Trumpet]

Also may be a faulty O2 sensor. Just because it's new does not mean it is properly functioning. Damhik.

A obd scanner will show running parameters, that may help some.

 

[81runner]

Could be a PCV valve, could be the gasket for the intake, could be weak fuel pressure. The engine THINKS it's running lean. That means you either have a vacuum leak throwing readings off, you have a fuel delivery problem, or a sensor reading incorrectly. When you replaced injectors, did you replace the fuel pressure regulator? As others have stated, real time data will be quite useful in narrowing this down. The question here, what are your long term fuel trims? If they are both off the charts, I would lean towards a pressure problem. If one is ok and one is off the charts, I'd lean with the down stream sensor/s, I believe you already changed the upstream sensors.

 

[inscarguy]

The pcv is new along with the hose. The short and long fuel trims are perfect all within .3 to .5 of each each other between banks well under where the light would get triggered. I dont remember the numbers at this time. down stream o2s are within .1 of each other. Fuel pressure is right where it is supposed to be.

Press reg was not replaced as these codes only came into play when the o2 sensors were changed and different codes on each bank 2 sensor changed.

 

[81runner]

Do you remember what your fuel pressure was tested at? And how much fuel was in the tank during test? Was the light on during tests?
Another issue, when you did the up stream sensors, were the harness plugs dirty and oily inside?

 

[techno]

It sounds like you know your way around the engine and ways to troubleshoot things, but have you read the FSM pages for the p0174 condition? Perhaps this could help out?
http://4runnerclub.com/i/4r_files/f...7toyrm/07toypdf/07rmsour/4runnerr/0050027.pdf
Note the 2 trip detection logic for the code. This would explain why the CEL didn't come on immediately. The condition was there, but it needs to happen twice before the computer thinks there's an actual issue.

 

[inscarguy]

Thanks for that.

I checked for fluid in ecu and o2 sensor plugs - none
Checked pins for alignment - ok
Checked intake - no leaks
Fuel pressure between 41-42
Tank was half full

 

[81runner]

Is there a way you can get an OBD2 reader to get some live data? If you can, find out what you long term and short term fuel trims are. Measure at idle, 1500, 2500, and 3000 rpm. You will need to have a cel or you won't be able to figure out anything

 

[UrbanRunner651]

08 v6, got the code off and on occasionally last year and tracked it down to a crack in the header manifold. replaced it with some stainless shorties and haven't had issue since.