P0171 & p0174 Lean Codes Question

S

ssmd

New member
Hi Everyone,

Are there any v8 owners who have had leaky exhaust manifolds cause the p0171 & p0174 lean codes?

I know it can be related but haven't seen anyone post conclusively that their cracked manifolds caused the codes.

I've ruled out all the sensors vacuum leaks. It's down to the manifold leak or a weak fuel pump.
 
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Is this a recent issue with you or have you had this issue a while?? Just had similar experience in my Civic.....all due to one bad tank of gas. Rough idle, would sometimes stall, CEL on with "lean" codes. Took me half a tank to realize it started with a fill up. Dumped a couple ounce of Marvel Mystery Oil in tank and it got better until I used up the gas and got some good stuff.....been running great since. It was 100% due to the gas I got that day.
 
slyfox75 said:
Is this a recent issue with you or have you had this issue a while?? Just had similar experience in my Civic.....all due to one bad tank of gas. Rough idle, would sometimes stall, CEL on with "lean" codes. Took me half a tank to realize it started with a fill up. Dumped a couple ounce of Marvel Mystery Oil in tank and it got better until I used up the gas and got some good stuff.....been running great since. It was 100% due to the gas I got that day.
Click to expand...

It has been a few months now, I ran a few bottles of fuel additives/injector cleaners in it and still no results.

I'll have to check for vacuum leaks again and find someone with a EVAP smoke tester. Maybe its a stuck open purge valve, brake booster, or EGR. :noidea::noidea:

If I can rule out vacuum issues I'll get the fuel system pressure checked next. Not looking forward to dropping the fuel tank to swap a bad fuel pump if that is the problem.

At least I know all my sensors work.
 
Hi Everyone,

I wanted to post an update to this thread so that it may be useful to someone in the future.

I ended up buying the fuel pressure gauge kit on Amazon and tested the fuel pressure. It read about 30PSI which is low for this car. I think it should be around 45PSI.

Bought a new fuel pump assembly and new gasket for about $300 and spent a few hours swapping the pump. It sure was a pain in the rear but I finally got the tank back in and now my fuel trims are reading as it should for both long term and short term. I cleared the CEL and will monitor it and will check back in if it comes on again.

Hope this helps someone out there.

The truck had about 120K miles when the fuel pump went bad, however the truck had drivability issues for a few months before the CEL came on.

Peace
 
I am getting a PO171 and PO174, I've replaced the air filter, MAF, I took it to a shop and they smoke tested it which showed it needed the PCV & it's hose, intake manifold gasket set, fuel injector O-ring and fuel injector cushion ring-lower which were all changed and still getting PO171 & PO174. The shop tested the fuel pressure and it was within spec.

The only thing I can guess is the O2 sensors?

2005 V-8 4.7 4Runner SR5 2WD 157,000 miles.

Any ideas?
 
Last edited:
another-bill said:
I am getting a PO171 and PO174, I've replaced the air filter, MAF, I took it to a shop and they smoke tested it which showed it needed the PCV & it's hose, intake manifold gasket set, fuel injector O-ring and fuel injector cushion ring-lower which were all changed and still getting PO171 & PO174. The shop tested the fuel pressure and it was within spec.

The only thing I can guess is the O2 sensors?

2005 V-8 4.7 4Runner SR5 2WD 157,000 miles.

Any ideas?
Click to expand...
As of today are you still having this issue ??...171 and 174 would have me thinking VACUUM LEAK right away...vacuum leaks usually go away at higher RPM's and the engine runs better...have you looked at your O2 sensor waveforms if you have a scantool...if your 02's are lean spray carb cleaner or similar into the intake...if 02 sensors start to go rich (higher MV's) they are probably good...I have a 2016 and I don't know if the older 4 Runners like yours use AF sensors...AF's run around .3 Mv ...there are excellent videos out there for this...Scanner Danner is the Jedi Master of auto diagnosis...watch these videos !!...let me know if it's fixed and what you found !!

https://www.youtube.com/watch?v=3RFTS22w6tM&t=1061s
https://www.youtube.com/watch?v=9gJoH5_Thaw&t=5s
 
rwrobs777 said:
As of today are you still having this issue ??...171 and 174 would have me thinking VACUUM LEAK right away...vacuum leaks usually go away at higher RPM's and the engine runs better...have you looked at your O2 sensor waveforms if you have a scantool...if your 02's are lean spray carb cleaner or similar into the intake...if 02 sensors start to go rich (higher MV's) they are probably good...I have a 2016 and I don't know if the older 4 Runners like yours use AF sensors...AF's run around .3 Mv ...there are excellent videos out there for this...Scanner Danner is the Jedi Master of auto diagnosis...watch these videos !!...let me know if it's fixed and what you found !!

https://www.youtube.com/watch?v=3RFTS22w6tM&t=1061s
https://www.youtube.com/watch?v=9gJoH5_Thaw&t=5s
Click to expand...
Forgot to ask...did your shop just check fuel pressure at idle or under load...with the engine at idle if you "blip" the throttle fuel pressure should NOT drop...if you're not getting good volume...lean codes !!...now you said you changed the MAF...did you check power and grounds to it...you can have a new one but it's still bad...usually has a 12 Volt power,ground,5 volt reference signal to PCM...can have more wires, can be wired with MAP too !!...not familiar with your truck !!
 
rwrobs777 said:
As of today are you still having this issue ??...171 and 174 would have me thinking VACUUM LEAK right away...vacuum leaks usually go away at higher RPM's and the engine runs better...have you looked at your O2 sensor waveforms if you have a scantool...if your 02's are lean spray carb cleaner or similar into the intake...if 02 sensors start to go rich (higher MV's) they are probably good...I have a 2016 and I don't know if the older 4 Runners like yours use AF sensors...AF's run around .3 Mv ...there are excellent videos out there for this...Scanner Danner is the Jedi Master of auto diagnosis...watch these videos !!...let me know if it's fixed and what you found !!

https://www.youtube.com/watch?v=3RFTS22w6tM&t=1061s
https://www.youtube.com/watch?v=9gJoH5_Thaw&t=5s
Click to expand...

Finally took it to the dealer and their more in depth code scanner showed it was running at a 40% mixture. I was advised to not drive it. They isolated the PCV valve which I had replaced with one from Autozone and they pointed that Autozone is Autozone. Was supposed to pick it up today but the fuel pump was low so it will have that changed Monday. What a mess, and I thought my BMWs required a lot of attention...
 
another-bill said:
Finally took it to the dealer and their more in depth code scanner showed it was running at a 40% mixture. I was advised to not drive it. They isolated the PCV valve which I had replaced with one from Autozone and they pointed that Autozone is Autozone. Was supposed to pick it up today but the fuel pump was low so it will have that changed Monday. What a mess, and I thought my BMWs required a lot of attention...
Click to expand...

What was the final verdict? Did the dealer get you fixed up? That code gone for good?
 
Having a hard time attributing the lean condition to the PCV valve... just can't seem to make that connection in my head. It's gotta be something else.
 
I just got these codes in my truck as well, but only after replacing thr throttle body with one from Rock Auto. Truck runs fine, but first time these engine codes have come up.

And I’ve had cracked manifolds for a while.
 
ssmd said:
Hi Everyone,

I wanted to post an update to this thread so that it may be useful to someone in the future.

I ended up buying the fuel pressure gauge kit on Amazon and tested the fuel pressure. It read about 30PSI which is low for this car. I think it should be around 45PSI.

Bought a new fuel pump assembly and new gasket for about $300 and spent a few hours swapping the pump. It sure was a pain in the rear but I finally got the tank back in and now my fuel trims are reading as it should for both long term and short term. I cleared the CEL and will monitor it and will check back in if it comes on again.

Hope this helps someone out there.

The truck had about 120K miles when the fuel pump went bad, however the truck had drivability issues for a few months before the CEL came on.

Peace
Click to expand...

could you point me in the right direction, the specific fuel pressure kit you bought off amazon. trying to track a high LTFT P0174 issue on my truck
 
earthrealm said:
could you point me in the right direction, the specific fuel pressure kit you bought off amazon. trying to track a high LTFT P0174 issue on my truck
Click to expand...

Actron CP7838 Professional Fuel Pressure Tester is the one I picked up. If I remember correctly this kit came with everything I needed. I pulled up a youtube vid for the 4runner to get the proper procedure.

Good Luck.
 
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