P0172 code

Alright ive got a 97 tacoma 2.7l 5 speed. I changed injectors becuase one of them died and decided to replace all 4 with oem replacement ones and truck ran fine for a while. Now the truck is throwing a p0172 (rich) code. Both o2 sensors are reading .9v on a scan tool so they both seem to be working fine. I have cleaned the maf sensor 3 times and nothing has changed. I have smoke tested the intake for leaks and nothing to be found. Any ideas?

 

https://www.tacomaworld.com/search/14822625/?q=P0171&t=post&o=date

Numerous posts and threads about this. You'll probably find your answer.

 

https://www.yourmechanic.com/articl...-code-system-too-rich-bank-1-by-blake-griffin

P0172 indicates that there is too much gasoline being detected in the exhaust gases exiting the combustion chamber. The ECU uses a number of instruments, such as the mass air flow sensor (MAF), oxygen sensors, and manifold absolute pressure (MAP) to monitor the air-fuel ratio of the engine.

What causes the P0172 code?

• A dirty mass air flow sensor overstating the amount of air entering the engine which may cause excessive fuel delivery
• A bad oxygen sensor
• A leaking fuel injector allowing too much fuel to enter the combustion chamber
• A faulty fuel regulator, which may not be regulating the pressure of the going to the engine as it should
• A vacuum leak
• A possible fault in the coolant system such as a stuck thermostat or bad coolant temperature sensor
• Worn spark plugs

 

What's your MAF reading at idle after it's warmed up and RPMs are in the normal operating range? I'd take a look at your 02's performance as well - is it stuck rich? If you pull a vacuum hose does it respond by leaning out?

 

Maf idle reading is about 3.7-4.1 g/s idling at about 750 rpm and if you pull a vacuum hose the truck stumbles and sometimes will just cut off

 

Sorry, I meant that in the context of looking at the O2's. Do the 02's respond to a lean condition if you were to induce one by removing a vacuum hose? You said both 02's were at .9v - that's fine for the downstream but not for the upstream (B1S1), it should be switching. I would want to rule out a faulty O2 - they often get unresponsive and fail on the lean side however I suppose it's possible they could fail reading rich which is why I was asking to see if you could get it to react to a severe lean condition.

 

A couple of things come to mind… first check to see if the pcm is in closed loop mode. If closed loop mode is never reached you are wasting your time.

IIRC, 97’s still had the charcoal canister on the drivers side inner fender well. The black box with circular domes on top. Follow the vacuum line that goes to the intake and see if there is a strong fuel smell coming from the canister. There should be a vacuum switching valve to control the flow and that could be bad also. When and how long the pcm signals that valve to open… i have never investigated that.

if the injectors you bought were aftermarket that could be an issue too. Just because they are new does not mean that they are good. There are fake “factory” looking injectors. I dont know how you would test this in the driveway other than replacing them. Finding a shop would flow them and measure the fuel just doesnt seem practical.


Should have put this first… find the fuel pressure regulator and pull the vacuum line off and see if it is wet with fuel. If the diaphragm is bad you will be pulling raw fuel into the intake.