Brand new car, engine running rich?

[Noobie]

Brand new Chevy Spark with almost 3k miles.
Non turbo, non DI.
Car STFT is fine and is always close to 0%. However LTFT is ALWAYS 7-8% or more no matter if idling or cruising. Avg LTFT based in my observations is around 10%.
What could be causing this?

 

[The Critic]

Perfectly normal.

 

[clinebarger]

The calibration is not absolutely perfect, That's why fuel trims exist....So small imperfections in the calibration can be corrected.

 

[circuitsmith]

Consider that E10 gas adds about 3% to the trim.

 

[ARCOgraphite]

Brand new Chevy Spark with almost 3k miles.
Non turbo, non DI.
Car STFT is fine and is always close to 0%. However LTFT is ALWAYS 7-8% or more no matter if idling or cruising. Avg LTFT based in my observations is around 10%.
What could be causing this?

Bad fuel blend. How the ave fuel mileage? OK?

It may be covering LSPI afer max retard.

Is it a stick?

You got enough octane in there? That's a good running " classic" PI engine
Almost bought one for a grocery-getter when on sale for around $12,5- but there was not enough elbow room
for me. And the test vehicle was showing signs of front axle racket wheel bearing racket right out of the box.

I don't tolerate that poor off brand quality well in my old age. I walked.

Not that my Mahindra/Ford J.V. SCUV in my signature is any better.
Nice Indian Fabric and interior build adn design - very "Lincol-esque" quality inside for a BASE vehicle.
Killer sounding base stereo.
Add AWD and 2.0 L Miata "race- tuned: engine with a 6 speed traditional planetary auto.

and it was a must buy. only 16,5- before trade !

Nothing that "cheap" on the market - even used !

 

[Noobie]

We dont get Ethanol gas here where i live.
Its a CVT, i feel the fuel mileage is good enough considering i do 100% city driving. However i do put in the bare minimum octane rating required for the engine.
Now you have me wondering if that could be the cause.

 

[willbur]

The calibration is not absolutely perfect, That's why fuel trims exist....So small imperfections in the calibration can be corrected.

Swinging under and over stoic so that 3 way converter can do its job?

 

[gathermewool]

Perfectly normal.

10% is normal???

 

[The Critic]

10% is normal???

Is it ideal? No.
But +/- 5-10% is fairly normal for stock cars.

 

[clinebarger]

Swinging under and over stoic so that 3 way converter can do its job?

The ECM is having to add fuel too keep it at stoic (Averaged at), If it averaged more than 10% or set a P0171....Then there would be something to be concerned about.

The OP typed 10% which is Lean.....Negative numbers are Rich.

I'd bet money that the P0171 diagnostic's for this car states that up to 10% LTFT's is perfectly normal. And DTC set threshold is about 22%

 

[ARCOgraphite]

Swinging under and over stoic so that 3 way converter can do its job?

I don't think new wideband TF Lambda sense work that way.

And that is only at virtual NO load cruise. No enrichment.

Pull your MAF connector off and try to drive on the Lambda you will see.
I don't know why man cars are over-fueling so much. AND the linear E throttle programming is ridiculous.

The first 1/8 of travel should be construed as light throttle cruise and hold mixture at lean side of stoich
regardless of short term changes or positional changes. Looking at fueling you can pull back throttle and maintain SAME road speed and gain 20% in SSO mpg on many vehicles. What is WRONG with EM programmers?
They are missing out BIG TIME on fuel savings. Must be an Engineer > software dev. disconnect - and poor lead engineering.
______________

The OP, Noobie, wouldn't tell me his fuel mileage.

Better be in the low 30's mpg at WORST.

My near midsized Jetta achieved HIGH 30's around town with big power.

Noobie - what is the around town fuel mileage?

But I've really lost interest in a Spark with a CVT. How mundane.

C'Mon Man !

 

[circuitsmith]

What is WRONG with EM programmers?

I believe the 3 way converter can't reduce NOx if it's running lean.

 

[willbur]

I believe the 3 way converter can't reduce NOx if it's running lean.

It swings up and down relative to stoich to reduce or oxidize different contaminants in the cat. You're saying lean prevents this during cruise?

 

[Snowflake White]

I'd try changing gas brands just to see if there is any difference. Also try using premium and see if that changes anything.

 

[Danh]

Barring it not running right or displaying a CEL, this seems like a good thing to ignore.

 

[clinebarger]

I believe the 3 way converter can't reduce NOx if it's running lean.

But it isn't actually running lean as the Fuel Trims are not maxed.

 

[Noobie]

I made a big mistake. I was referring to NEGATIVE 10% LTFT average not positive.
Regarding my mileage, its around 30mpg full city driving, zero highway.

The reason why i started monitoring the engine is because after i leave the car off for a couple hours (Lets say, 6 hours or more) sometimes it would start smoothly then after 5 seconds of smooth idling it starts to choke for 5 seconds (RPM drops, engine feels as if its misfiring or stalling) then the ECU adds some throttle and it recovers and continues idling smoothly. So i started monitoring the engine to see if i could see anything unusual and as of now, the LTFT is the only parameter that i can clearly see a bit out of spec based on "Google" research.

Couldnt believe a brand new car is giving me rough idle issues. Previous korean econobox fared much, much better mechanically, didnt give me a single mechanical issue during the time i owned it.

 

[wolfox03SS]

https://www.aa1car.com/library/what...Trim to Diagnose,your engine is running LEAN.

It could be a faulty injector leaking down/ partially stuck open... You could check for this with a fuel pressure gage attached to the fuel rail test port. If it bleeds down in moments to zero after you engine-off + key off...gotcha!

Also, if you're a more visual learner?



Edit: OBD-2 systems will gently, slowly swing between rich and lean by small increments as a test of catalyst efficiency and post- catalyst O² sensor function. Your primary O² sensor will slowly cycle from low to high and back again, over and over again. Your secondary, post- catalyst O² sensor should simply read a dead on center constant voltage of about a ½volt if your sensor and catalyst is OK.

If your secondary sensor doesn't register voltage, or swings along with primary sensor? There's a problem, Houston.

 

[circuitsmith]

But it isn't actually running lean as the Fuel Trims are not maxed.

I was speaking in this context:

The first 1/8 of travel should be construed as light throttle cruise and hold mixture at lean side of stoich

 

[circuitsmith]

The reason why i started monitoring the engine is because after i leave the car off for a couple hours (Lets say, 6 hours or more) sometimes it would start smoothly then after 5 seconds of smooth idling it starts to choke for 5 seconds (RPM drops, engine feels as if its misfiring or stalling) then the ECU adds some throttle and it recovers and continues idling smoothly

You should try cold starting a carbureted car from the '70s, to put things in perspective.