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12:01 AM
Something else to look at when seeing a lean condition is to look for a problem with the exhaust prior to the O2 sensor. If there's a leak in the exhaust, you can be getting a false lean. If your sparkplugs are really black from soot, this could be the issue.
my mech replaced all my plugs+boots in March as well
(well, he said he did and charged me for it...)
and I've only driven about 3k miles since then
@alexw - If your engine is running good, this could be an area to be looking.
Check your plugs. Even at 3k miles, your plugs would be black if it's actually running rich, but showing lean (false lean).
If your plugs are light tan white, then they are actually lean and the leak would be in the intake system
I might do this at my friend's garage tomorrow then
since he probably has a torque wrench
12:10 AM
Sounds like a good idea. Hard to see what you're exhaust looks like in the dark ;)
yeah that too :'-(
dang, thanks for the ideas
I know almost nothing about engines or fuel systems
exhaust leak does seem quite possible, especially if it's somewhere low to the ground
rust is a perpetual issue here in Indiana
oh, you're from NoVa!
I'm from Baltimore/DC
Awesome ... well, if you consider South Stafford (just north of Fredericksburg) NoVa, lol.
@alexw - Where about?
I mean I just assume that NoVa gains about 100 more sqmi every year
12:21 AM
And all this time, I thought it was shrinking because MD was consuming it all ;-)
Looks like a Mechanics.SE question
Q: How fast am I going?

Nick Replacing the SMD LED’s on my instrument gauge cluster in my truck with a new color LED. While attempting to remove one of the original LEDs, the solder pads came off from both the positive and negative contact points. One of the pads is salvageable (still attached to the light I removed), but th...

grew up in Pikesville, then went to UMCP
nah, MD is maxed out
@NickAlexeev - I guess, but wonder the reception. Send it over.
do you have a shop you run/work at?
@alexw - What I'm suggesting is, it seems a lot of people are moving out of MD into NoVA, which means it's becoming a suburb of MD ... without all the taxes ;) Actually, Governor Hogan seems to be doing a good job there.
12:24 AM
oh, yeah
@alexw - Just my garage (attached to my house)
NoVA == Southern Bethesda
No business.
@alexw - Exactly!
Actually, I like Bethesda.
ah ok, then I will not bring my car around next time I'm in town
Wouldn't live there, but I like it there.
@alexw - If you're down this way, send me a note on here beforehand ... if I'm available, I'd be more than happy to meet you some place and say hello.
12:26 AM
ooh, thanks for the offer :-D
I think I've met five people off of here, then a bunch of other people who use Stack Exchange.
I should have talked to you before I bought this Land Rover in July
Nah, you need to talk to @Zaid about LR's
I actually bought it in NoVA, then we convoyed back to Indiana
biiiiig mistake :-/
Oh, snap ... I'm sorry. You DID say you are from Indiana. I must be tired. When you said Baltimore, I was thinking something else.
12:29 AM
well, only lived here in Indiana for 5 years so far
almost naturalized but not quite
Well, I've been here in Virginia since 1992 ... but still call Montana home (where I was born/raised)
I drove through Montana on my cross-country trip
they had speed limits by that time, though
I might actually try to talk to @Zaid soon about the LR
all the parts are ridiculously overpriced, and I wish I had checked before we bought the thing
12:55 AM
@Pᴀᴜʟsᴛᴇʀ2 I've sent it over. Added an answer for a good measure.
@NickAlexeev - TY Kind Sir!
1:08 AM
@Pᴀᴜʟsᴛᴇʀ2 Hm... Someone downvoted. I wonder the reason.
@NickAlexeev - on our side?
@Pᴀᴜʟsᴛᴇʀ2 Yup
@NickAlexeev - Dunno why ... I fixed it though :o)
@Pᴀᴜʟsᴛᴇʀ2 Thank you.
I don't like when people downvote without a comment
@NickAlexeev - No worries.
Thanks for throwing a comprehensive answer on it.
2 hours later…
2:41 AM
@alexw search for "The Great MAF Experiment". What car are we talking about, and how many liters is the engine? I could crunch a quick number for you, although the confidence interval isn't that great
@Zaid for the Mazda?
or the Landie
Whichever one's MAF you're concerned about
(I don't have the context for your question handy as I'm on my phone)
I guess the Mazda?
well the Mazda is the one I've been looking at today
the Landie's problems I'm almost positive are related to the exhaust O2 sensors needing cleaned/replaced, if I can ever get them off
Is it petrol or diesel? Turbo or NA?
petrol, basic bae I believe
2:53 AM
Ok, then I can use the work we've done in the past to put together an estimate
oooh, you're a mech e
me too :-D
@alexw cool, I'm not sure if I've seen another ME on here before :D
The VE I'm getting for your Mazda is around 22%, which seems to be OK
haha, I don't do much ME these days
I tend to accrue degrees and then not use them...
Btw, you can't really tell much from short term fuel trims maxing out
@alexw volumetric efficiency
oh, that's useful to know
3:03 AM
Look at the LTFT values
The closer the LTFT's are to zero the closer the engines operation is to its intended design
you calculated this as a theoretical optimal value?
I got 4.7% today for LTFT
That should be fine
yeah it seems reasonable
the car has nearly 100k miles on it
3:06 AM
Do you have a question up on the site?
nah, there are plenty of good questions already about my error code, with pretty good answers
nothing specifically about my make/model though
So what's up with the car then?
oh, the check engine light came on the other night and I pulled a P0171: system too lean code
engine doesn't sound bad to me, though
Freeze frame info?
and I got my PCV valve, MAF sensor, intake gaskets, and plugs all replaced in March
sure, which values do you want to see?
actually I can take a pic
3:11 AM
Yeah, all of it would be nice
`APP_D = 7.8%`
`APP_E = 7.8%`
`TAC_PCT = 4.3%`
Actually, I think I have an explanation
But back to I was saying it's weird
P0171 is a system too lean
Which means there's too much air in proportion to the fuel that's being added to the cylinders
3:19 AM
And yet the STFT is maxed out, which I presume was due to moderately hard acceleration
no this was at idle
well, I guess I don't know how often that value gets updated
STFT climbs when there is an increase in load
Or at least a request for increase in load
Had you just come to a standstill?
when I took the freeze frame?
3:21 AM
When the code was triggered
so I wasn't there when the check engine light came on - I had loaned my car to a friend
she drops it off and is like "light came on just as I was getting back into town"
she could very well be a speed demon, idk :-P
but she claims that she drives relatively slowly
3:23 AM
This doesn't have to be due to aggressive driving
You'll see why in a minute
sits down
The point is that there was a demand for increase in load
Which the STFT duly obliged
You know what STFT is doing, right?
well I read the post about fuel trim
It's increasing the pulse width of each fuel injector to enable it to add more fuel to the engine
based on the readings from the MAF and O2 sensors, right?
normal acceleration demands should just affect the throttle, I thought
3:27 AM
So what I suspect is happening is that the fuel management thinks it's added a certain amount of fuel but in reality it's added less than that
so instead of "too much air", you think I have "not enough fuel"
I believe so
that makes sense...my mech replaced/cleaned all of the airflow-related parts, but didn't touch the fuel injectors
so maybe this is like the milk/cereal dilemma
Now you don't normally have to replace fuel injectors but they do get crud built up in them over time
So it's a good idea to use fuel injector cleaner every now and again
yeah I don't think I've done that
3:31 AM
There are other possible reasons for insufficient fuel but I think you'll find that this is what's affecting you
(In brief it's anything that affects fuel rail pressure)
@alexw what's that?
The dilemma, lol
oh, you pour your cereal and milk on top
I think I know what milk is ;)
then you eat your cereal
but there is leftover milk
so you add more cereal
then it's too dry and you need to add more milk
ad infinitum
3:38 AM
Well, it is sort of like that. The O2 sensor is the "dryness" sensor. The milk (air) is set by engine load and the cereal (fuel) is metered accordingly
ultimate ELI5 answer ^^
It probably exists already
yeah tons of things exist already, but they don't always get noticed
alright I'm gonna look into @Pᴀᴜʟsᴛᴇʀ2's idea about my exhaust first tomorrow, since that's the least invasive
if it's a true lean condition, I'll try the fuel injector cleaner
(and look for any obvious leaks, like a popped hose clamp or something)
One other possibility: it might have been bad fuel
That could do it too
seems unlikely but I guess not impossible
I had just refueled before I lent her the car
3:49 AM
You know where you live better than me. Where I'm at, bad fuel is really really rare
I just assumed y'all stick a straw in the ground and perfect premium fuel comes out
@alexw nah, takes some work to get from crude to gas
did you study in the States?
Me? Kinda
Texas A&M has a branch here
ah cool
my alma mater (UMD) had a big petro engineering program
lots of people from SA, UAE, etc came to study
4:02 AM
Yeah the US is a popular destination for the Arab demographic
Q: P0171 code with high fuel trim

jakester89741I have a 2001 toyota corolla. Lately it has been throwing the p0171 code system too lean. My short term fuel trim is normal at idle. +/- 5 % at idle and long term fuel trim is high at idle +18 %. When i rev the engine to 1500 rpm the short term stays the same and long term fuel trim goes down to...

^ @alexw this case is very different from yours. Here, LTFT is quite high which indicates a system problem
haha, what a coincidence!
4:21 AM
alright time for bed, thanks for the help!

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