A Exercise in Critical Thinking Part 2



this is an interactive presentation design stimulate discussion and illustrate the importance of putting link it can be used by an instructor in a classroom or by individual if you cook yourself simply think about and respond to questions or you can see the next slide now let's think about these codes for a minute see how they fit now we have this lien Bank one code but let's think about that for a minute remember part of our complaint was that there's black smoke coming out the tailpipe that would indicate it's rich that we got a lien code now think about this it's a v6 engine so we got two sides the exhausts come down to a Y pipe and then there's an oxygen center so there's only one oxygen sensor so it's not lean bank one it's actually lean both banks equally because there's only one option sensor now if the lien codes showing that it's lean po1 71 reports that the whole engine is lean so how would you expect that the PCM would respond to this lean running engine but the computer will react to that lean code by trying to enrich it as you know the computer cannot add or take away air all it can do is add a takeaway fuel so since it's lean or there's too much air it's trying to add fuel to balance the air fuel mixture therefore the computer is dumping fuel into this and we have black smoke coming out the tailpipe now let's think about this peel 300 random misfire now the computer should be able to isolate a single cylinder if a single cylinder was the only miss that this is random which means there's multiple misfires now the engine is showing a lean code but because it's lean the computer is trying to add fuel to balance the air fuel mixture therefore it's actually running rich and we have black smoke coming out the tailpipe so our misfire is due to multiple sending cylinders so being rich this all makes logical sense right so explain why the fuel trims are negative if the computer is adding fuel the black smoke means the engine is running rich and that's evidence the fuel trims tell us the PCM is attempting to pull fuel away that's what you'd expect right the code indicates that it's lean the PCM should be adding fuel but instead it's pulling fuel away something is not making sense here are you ready to replace the o2 s now so we have oxygen sensors that are possibly not working right we'll need to check that we have the lean condition so the computer is adding fuel we have black smoke coming out the tailpipe it's all leading towards an air fuel balance mixture problem so now it's time to look at the scanner and see what the computer is seen and what the computer is doing you

12 thoughts on “A Exercise in Critical Thinking Part 2”

  1. For an experienced mechanic it would be easy to point out O2 sensor right away, but without understanding how to properly diagnose a bad O2sensor you can really screw yourself over because it still might not be an O2 sensor.

  2. I don't get the caption at 2:36. What are the fuel trims anyway? You don't reveal that. System is too lean because the o2 sensor is stuck low but that's also about fuel trims; fuel trim in a system too lean condition means that the car has detected that injector pulse width is 25 or more % greater for a certain amount of time. As the vehicle has p0171, fuel trims should be positive. Car is adding fuel in response to bad o2 but it's already running rich. I think this car has 2 problems – bad o2 sensor and bad fuel injector.

  3. I like your channel. I was wondering if you can cover a topic of lack of power on a 2005 tundra 5.7L. if feels like the it does not get enough gas and the pedal feels weak and it such up gas. the truck has no fuel filter. It had plenty of power before but on day on the fwy it started to stall out on me speed dropped i floored the gas pedal to keep moving and get to the shoulder of the road. the trk was bearly struggling to move, it felt has it was going to shut down. then trk began to pickup speed but it ran flat. still up to now it doesn't have the throttle response it hand before and the torque. what should I check as a possibility. the throttle sensor on the pedal or on the throttle body, could it be the fuel pump losing pressure, electrical issue or sensors? I have a Flowmaster exhaust and km air filter. hope you can make segment on this topic. if so I'm looking forward to watching it.

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