rev up your engines today I'm gonna show ya how to fix a car that's running too
lean this Toyota rav4 just came over here the check engine light is on it's got
the code p0171 which means the engine is running to a lean now unfortunately
there's whole bunch of things can do this so you have to start logically
going to the hood and look at the most logical things first now running to lean
means that the combustion inside the engine is burning at too low a ratio
meaning either it's not getting enough fuel so it runs lean or it's getting too
much air and it's running too late now one of the common thinks for that is a
vacuum leak if a hose is come off if a gasket gets broken and sucking air into the
engine it'll run to lean so that's the first thing you look for and if
you're really smart and have just a regular scan tool you can get a $40.00
one that does this it's got the code that means there's data store so you go
to the section on your computer it's got freeze frame data here it is here view
freeze frame data so you look at you get tons of information there and the main
thing when you're running to lean is you want to look at when did it occur it will
show you the speed of the car if the speed of the car is zero and that code
tripped when it was idling that generally means it has a vacuum leak
because when the car is idling the engine is moving that fast so it has a
little less vacuum pressure if you get a vacuum leak and you're idling with the
low vacuum pressure that'll set it down quite a bit percentage-wise
can make it run lean than it trips the code realize that the codes are tripped
when the computer sees like 20% or more off value so it's got to be a reasonable
amount this lean code tripped when you're going 65 miles an hour
odds are it's not a vacuum leak because it's 60 the engine spinning like mad and it's
got tons of vacuum pressure it's got a little vacuum leak it's not gonna bother
it that much because the leak is gonna be a smaller percentage of what it is
when the engines only idling a much lower vacuum pressure so if it did occur
at lower speeds are at an idle you want to look all around for vacuum leaks and
on these Toyota's it's often a vacuum line it comes off a lot of times the one
back here behind the air filter gets pulled off and somebody changes the air
filter but that one's not bad sometimes they come off of the PCV system but
that's on nice and solid if you can't see or hear any vacuum
leaks when the engines idling use your ears and if you hear it sucking and
look around you can do like I showed in the previous video get a little wd-40
with the spray nozzle spraying around and if you get say on the intake
manifold and it starts to change the idle you know it needs an intake
manifold gasket but the cold tripped on this one when it was going 56 miles an
hour so it happened at a higher speed now if you got a running to lean at a
higher speed and you look at the trouble code freeze frame data it happening at
higher speed in this case 56 miles an hour
odds are it's not a vacuum leak but it's something in the fuel injection system
you could have a clogged filter you could have a weak pump you could add a
bad mass sensor those are the most common things to check for so the first
thing you do would be check the fuel pressure now here's a warning if your
fuel filter is easily accessible change the fuel filter first because fuel
filters if they clog up guess what after the filter the pressure will go down
make it run lean because you don't have enough pressure to spray the fuel
injectors correctly so if you do have a fuel filter that's easy to access go
ahead and change it now my old celica hey it's just two bolts you take off
your place of filter so that's what I would do but on this modern rav4
fuel filter is inside the gas tank now you don't have to drop the tank but you
got to take the back seat out then you have to take the excess panel then you
got to pull the fuel pump assembly out because the filters built in there now
Toyota generally wants to sell you the whole fuel pump assembly for six seven
hundred dollars with the filter built in you can buy a filter but in this case
hey you're not gonna just change the filter on the lark because it's such a
pain in the butt so we're gonna just check the fuel pressure it's supposed to
be between 44 and 50 pounds per square inch
just test it and if that's what it is well then we don't have to worry about changing
the fuel filter because the pressures coming out fine anyway since it's such a
job to get an air change the filter we're just gonna check the pressure on
this I'll get my fancy fuel injection tester chip and I do mean fancy because
Toyota over the ages they've been kind of a swine about checking fuel pressure
they never had test valves on them most of them don't anyways modern anyways
they all went their way it's cheaper to make it but you got to get a special
adapter you hook it on the fuel line and then check it with a gauge you're gonna
have to buy the special toyota adapter which isn't cheap so you might want to
pay somebody else to do this in this case it's fine it's about 50-51
pounds so in we know the fuel pressure is good so it's not that it's not getting
enough fuel next thing to check is the mass sensor mass airflow sensor now in
these Toyota's a notorious are getting dirty and giving false readings so they
can make them ron lean it's right here some thing to get to right here there it
is now you can only clean these things with mass airflow sensor cleaner
don't try anything else gotta leave no residue yeah this stuff costs a lot
sometimes these cans are like 10 12 bucks but they last for a long time you
don't need a much cleaner cleaner you just remove it from the vehicle
just find plugs you got squeeze the heck out of it then remove the two Phillips
screws that hold it in place they just screw out and the sensor wiggles and
comes out now clean is pretty easy there's a little mouthpiece here right
in here you want to clean it and there's also one inside so for that you spray it
in the front then you spray it on the other side of the hole and it cleans the
stuff on the inside and here comes a part that everyone hates patience
something hardly anybody has these days they're very volatile cleaner you're
gonna do it outside so you're not breathing it you want it to completely
air dry so there's no residue of vapors on it when you start it up because if
you clean it put it right in and start it off a lot of electricity goes through
here those vapors can short things out
and even worse don't clean them on the vehicle if you
take the hoses off and clean it from the inside then you got all that vapor in
there don't do that take it off and clean it most
cars it's not that big of a deal getting it out and like I say if you clean it
wait about half an hour because I've seen people who didn't they were in a
hurry or cleaned it inside and then boom the electricity hit the vapor burnt
things out they need to buy expensive sensor do it externally let it air dry
that way you can't hurt anything after half an hour so just put it back in its
hole the same way it came out make sure it's seated in because there's an o-ring
in there and you put the two screws one and two and of course don't forget to
snap the electrical connection in wow that was close the hood down erase the
codes just push erase codes yes this now erases the code so the codes gone and
take it for a good road test now sometimes codes take a long time to
come back but take it on the highway in town maybe half hour trip if the light
doesn't come back on then you just drive it and after or 2-3 weeks that doesn't
come back you fixed it in this case since this is a 2.5 litre engine when
it's idling the data the mass airflow should be somewhere around two and a
half grams per second that it's flowing when it's at idle in drive so I
checked it and it was our two point six four which is perfectly fine for this if
it had been really low like one point six that would mean it's giving it way
too little gas and if the reader have been really high like four point seven
then it would give it too much gas but then it would be running rich not lean
if it's running below the parameters then it's gonna run lean because it
thinks there's less air coming on so it gives it less fuel now in this case when
they get dirty they often give a false reading we're hoping and that's what it
is after the half hour drive it didn't come back on you're really like I say
give it a couple of weeks because these things can be very slow with picking
things up but if it never comes back then you know it was just a dirty mass
airflow sensor, so now you know how to fix a car that's running too lean in
this case also took was a few squirts of mass airflow sensor cleaner
so if you never want to miss another one of my new car repair videos, remember to
ring that Bell