The Pitstop - 2018-10-23

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Pᴀᴜʟsᴛᴇʀ2

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.

hmm

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

Pᴀᴜʟsᴛᴇʀ2

@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).

oooh

Pᴀᴜʟsᴛᴇʀ2

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

Pᴀᴜʟsᴛᴇʀ2

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

Pᴀᴜʟsᴛᴇʀ2

I bet

oh, you're from NoVa!

I'm from Baltimore/DC

Pᴀᴜʟsᴛᴇʀ2

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

Pᴀᴜʟsᴛᴇʀ2

12:21 AM

And all this time, I thought it was shrinking because MD was consuming it all ;-)

Looks like a Mechanics.SE question

0

Q: How fast am I going?

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

Pᴀᴜʟsᴛᴇʀ2

@NickAlexeev - I guess, but wonder the reception. Send it over.

do you have a shop you run/work at?

Pᴀᴜʟsᴛᴇʀ2

@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

Pᴀᴜʟsᴛᴇʀ2

@alexw - Just my garage (attached to my house)

NoVA == Southern Bethesda

Pᴀᴜʟsᴛᴇʀ2

No business.

@alexw - Exactly!

Actually, I like Bethesda.

ah ok, then I will not bring my car around next time I'm in town

Pᴀᴜʟsᴛᴇʀ2

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

Pᴀᴜʟsᴛᴇʀ2

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

Pᴀᴜʟsᴛᴇʀ2

lol

Nah, you need to talk to @Zaid about LR's

I actually bought it in NoVA, then we convoyed back to Indiana

biiiiig mistake :-/

Pᴀᴜʟsᴛᴇʀ2

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

Pᴀᴜʟsᴛᴇʀ2

Well, I've been here in Virginia since 1992 ... but still call Montana home (where I was born/raised)

ooh

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.

Pᴀᴜʟsᴛᴇʀ2

@NickAlexeev - TY Kind Sir!

1:08 AM

@Pᴀᴜʟsᴛᴇʀ2 Hm... Someone downvoted. I wonder the reason.

Pᴀᴜʟsᴛᴇʀ2

@NickAlexeev - on our side?

@Pᴀᴜʟsᴛᴇʀ2 Yup

Pᴀᴜʟsᴛᴇʀ2

@NickAlexeev - Dunno why ... I fixed it though :o)

@Pᴀᴜʟsᴛᴇʀ2 Thank you.

Pᴀᴜʟsᴛᴇʀ2

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

2.0L

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

:-O

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...

VE?

Btw, you can't really tell much from short term fuel trims maxing out

@alexw volumetric efficiency

oh, that's useful to know

ah

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?

No

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

user image

`APP_D = 7.8%`
`APP_E = 7.8%`
`TAC_PCT = 4.3%`

>:

Weird

Actually, I think I have an explanation

But back to I was saying it's weird

ooh

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

yup

3:19 AM

And yet the STFT is maxed out, which I presume was due to moderately hard acceleration

no this was at idle

Ok

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

ahhh

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"

:D

she could very well be a speed demon, idk :-P

Cool

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

ohhh

interesting

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?

milk/cereal?

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 ^^

Haha

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

oooh

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

Qatar?

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

cracking!

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

1

Q: P0171 code with high fuel trim

I 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...

toyota corolla p0171

^ @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!

Seeya

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