So I am having an issue with my 1999 4.0 Ranger with 189000 Miles. This is my first vehicle and I don't know much about fixing cars/trucks so I thought I would reach out to a forum before I go out spending a ton of money on parts. The issue is there is a really strong gas smell coming from the exhaust, and when I turn the truck off white smoke will continue to come out of the exhaust for another 15-30 Seconds and the smoke reeks of gas, I don't know if smoke is supposed to keep coming out of the exhaust pipe even after the vehicle is shut off but I thought I would mention it. I get bad gas mileage (about 10mpg) but I do a lot of city driving, and I have a check engine light on. So the first thing I did was scan the check engine light with an OBDII scanner it came up with 4 codes. P0136, P1132, P1151, and P0172. I did some research about the codes and they all had to do with oxygen sensors and the engine was running too lean or too rich. I was about to pull the trigger on buying the new o2 sensors but before I spend a bunch of money on them I want to know if there's anything else I should check that would solve my problem that would be a little cheaper. I've already tried cleaning the MAF Sensor and changing the Air filter but that didn't help. Any feedback is greatly appreciated and thank you for reading :)

 

Welcome to the forum

Post definitions with the codes since you looked them up, makes it easier for getting answers
P0136 02 Sensor Circuit Malfunction (Bank I Sensor 2)
P1132 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Rich – Bank No. 1
P1151 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Lean – Bank No. 2
P0172 System too Rich (Bank 1)

If you have a V engine there are 2 Banks
Bank 1 is Passenger side
Bank 2 Drivers side

On 1995 and newer vehicles there are Upstream O2 sensors and Downstream O2 sensors
Upstream O2s are close to the engine, and are called Sensor 1, you have two, Bank 1 sensor 1 and Bank 2 sensor 1, they are BOTH Sensor 1's
Downstream O2 is after the Catalytic Converters it is called Sensor 2, if you have a single exhaust tailpipe then you just have the one, Bank 1 sensor 2, a Dual exhaust system would also have Bank 2 sensor 2, these Downstream sensors check that Catalytic Converters are cleaning the exhaust

The Upstream sensors are used to set Fuel Trims

P0136 02 Sensor Circuit Malfunction (Bank I Sensor 2)
So this is the Downstream O2 sensor, Sensor 2
And "malfunction" can means a few things, most likely is that the wires came unplugged or got melted on exhaust pipe check for that first, and could be O2 sensor has failed


P1132 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Rich – Bank No. 1
P1151 Lack of Upstream Heated Oxygen Sensor Switch – Sensor Indicates Lean – Bank No. 2
P0172 System too Rich (Bank 1)
These are all Upstream O2 sensor codes, sensor 1's, and these codes mean the O2 sensors are WORKING, no malfunction, computer is seeing them and they are reporting data, so WORKING

Because of the symptoms you could have a stuck open fuel injector on Bank 1
Or if you had any engine work done recently the tech could have accidentally reversed Upstream sensor plug ins

But lets test for leaking injector first
All fuel injection computers have a Clear Flooded engine routine
Turn on the key
Press gas pedal down to the floor, at 0 RPMs and WOT(wide open throttle) the computer will starter Clear Flooded Engine routine, which shuts OFF fuel injectors
Now, holding gas pedal DOWN all the way, crank engine
It should NOT START, or even fire, there should be no fuel

If engine fires or starts then fuel is leaking in, you can then unplug one spark plug at a time on Bank 1, and repeat above test, when engine stops firing then unplug cylinder has the leaking injector.
You can also pull out spark plugs on bank 1 and look for the Darker one, it should be the one with the leaking injector

1998 and up Rangers use a Returnless fuel system running 55psi fuel pressure
On the fuel rail, what the injectors are plugged into, there will be a Pressure Damper and it will have a Vacuum Hose attached to it
Although unlikely this Damper can leak, the vacuum hose is there to prevent gasoline from spraying on hot engine if it does leak, so find the Damper and check its vacuum Hose for gasoline
This would generally cause Rich on BOTH Banks, not just one, but free and easy to check it


Upstream O2 sensors should be changed every 100-125k miles, downstream 300k miles, these "see" cleaner exhaust so last longer
So at 190k it wouldn't hurt to change the upstream O2s, but this is NOT the problem, so find the problem BEFORE changing O2 sensors