I've finished up my 3.4 swap a couple of weeks ago and the only code I'm getting is the P0171. My engine is from a 2000 4runner with a 4runner ECU. The engine is running a little rough at idle and is running very rich. Constant black smoke at idle and when I rev the engine. I can clear the code and the smoke almost goes away, some might be from build up in the exhaust. When the CEL comes on it starts running rich again. I've cleaned the MAF and ruled out the Coolant temp sensor as my scangauge reads 184-190 fully warmed up.
Would this be fixed with a new MAF? I haven't seen where a P0171 would cause a rich condition.

 

That's an odd symptom of a P0171 code. P0171 is bank 1 running too lean. You said you cleaned the MAF, there's a way to ohm out the MAF to see if it is functioning properly (check the Factory Service Manual (FSM)). Other than that have you tried unhooking the battery to do a memory "reset" and reconnecting it? Sometimes when the computer is allowed to recalculate all the data, it can adjust the fuel trims properly.

Other than that, check your O2 sensors to ensure that they are all functioning properly.

 

Yes I've had the battery disconnected several times working on other things so it should have reset.
I went ahead and bought a new MAF sensor and instantly got codes P0100,P0110,P0450 and P0450. Also with a very rough idle. So I went back to the store and got my money back with my old MAF sensor.
I'll have to test my O2 sensors. I'm thinking they might be covered in soot and getting the wrong reading.
I am also wondering if it running rich is even related with the P0171 code.

 

Next i'd test the 02 sensors like you said. Running rich is NOT a symptom of P0171.

 

Yea I'm going to have to search how to test the O2's after I get done working on some awesome drum brakes.

 

Alright I took out both O2's and they were covered in soot. I cleaned them off but I don't have a torch to test them so I put some codes in my scangauge as that's all I have and here is what I got.
Engine temp 184-188 degrees F

O2 sensor data
Bank 1 sensor 2 0% (That's the only one that showed anything so I'm guessing it works.)

Air fuel ratio
Bank 1 Sensor 1 14.5 open loop (at start up with warm engine)
14.7-14.8 closed loop

Fuel trim
Short term bank 1 19
Short term bank 3 27
Long term bank 1 39
Long term bank 3 48

The engine runs fairly smooth at start up (warm and cold in open loop) and no exhaust smoke even when revved. On my scangauge when it hits closed loop the idle is rough and black smoke starts coming out of the exhaust.
Also still the only code it's throwing is P0171, so no new codes.

 

 

Searching around and it seems like my fuel trims are high, way to high.

 

Vacuum leak (post 41 below for one spot)?
https://www.yotatech.com/forums/f2/p...17/index3.html

 

Thanks for the reply, just went out and checked I don't have any vacuum lines around my power steering pump like in the thread you posted. I've checked for leaks with starter fluid, spraying all of the intake with the engine running and found none.
The engine only runs bad in closed loop, thinking it might be the air fuel ratio sensor or O2 sensor.

 

A/F or O2 sensor could be the issue. Use only Denso or one from the dealer... Lots of Toyota dealers sell online for significantly cheaper than at the counter. Bosch, etc. does not play nice with these engines.

 

Thanks on the tip to only use Denso stuff never had a toyota before.
If my a/f and/or O2 is bad could that cause the fuel trims to be high but not get a check engine light?

 

When I say A/F or O2, they could be a contributing issue if they are sluggish and not responding with a good signal. Typically, they bounce between 0.1 to 0.9V with a lean condition changing at 0.55V or less and a rich condition changing at 0.44V or more.

An interesting read:
http://www.4x4wire.com/toyota/4Runner/tech/O2_Sensor/

Generic P0171 info:
http://repairpal.com/OBD-II-Code-P0171-and-P0174

Have you double checked all your wiring from the swap? The MAF was pulled from the same rig as the engine?

 

Thanks I was reading over the one on 4x4wire a few hours ago. I'll have to "check" my MAF meter how its mentioned in the second link.
I know swimmer boy said the P0171 and the engine running rich are not related but it seems to me like if the engine sets a lean code wouldn't the ECU put the engine in "safe mode"and over fuel since running a engine lean is bad?

 

Yes all sensors are from the donor I bought a complete running 4runner. I even have the stock 4runner exhaust on the truck.

 

From the 2000 5VZ-FE FSM:

P0171When the air fuel ratio feedback is stable after engine warming up, the fuel trim is considerably
in error on the RICH side (2 trip detection logic).

Trouble Areas
Air intake (hose loose)
Fuel line pressure
Injector blockage
Heated oxygen sensor malfunction
Mass air flow meter
Engine coolant temp

 

To bad I don't know anybody local with a 3.4 4runner or taco that would let me "borrow" there sensors just to see which one fixed the problem. I don't mind if I have to buy MAF or a O2 but I don't have the money to throw around at parts that don't need replacing.
I am still thinking how I am going to test the O2's as I don't have a "back probe" or a propane torch. I will test my MAF tomorrow per in the link and see what it shows.

 

There is no fail-safe mode for P0171--it just goes high on the trim. See Paragraph 4 here:

http://tacoma.site40.net/4Runner_96-...zfe/preche.pdf

You did not mention PCV valve. That's the first check on the P0171 flow chart(p. DI-53 in below):

http://tacoma.site40.net/4Runner_96-...e/cip0171p.pdf

 

I tested the PCV and it functions like it should but it is dirty, I will go ahead and replace it. I've also checked to oil fill cap and dipstick as they are apart of the PCV system to.
I removed the TB and when disconnecting the hoses on the bottom, the IAC I believe, a little bit of water came out probably not a good thing. I also removed the plugs and they are covered I soot.








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