Wandering afr

[PunkST]

Noticed tonight at low speed cruising on a smooth road ( 30 mph) my afr was wandering from 14.7. All the way down to 12.68 then back up. Doesnt do this at higher speeds or under loads.

Car has stock VT snorkel, stock airbox, stock filter, 2015 evap harness, stock turbo, CPE hotside pipe, MAP intercooler, stock cold side with symposer connected, stock cat, greddy evo exhaust, step colder ngk plugs and a cobb stage 2 91 octane tune.

No CEL or weird feels in how the car is driving. It most likely was doing the same before the crash i just never noticed it.

 

[TyphoonFiST]

Change the Tune if its a OTS tune to 93 and see if it still does the same thing. Also could be our awesome quality winter time gas ion the Midwest!

 

[PunkST]

I could flop to a 93 map. Its got 93 in it. That is a good point. And hey at least its not going super lean.

( i may try that cat cleaner stuff and see if maybe its crud in the cat making weird readings

 

[TyphoonFiST]

I had the Infamous p0420 Code roll through last week...Cleared it and Tossed in some Starbrite Ethanol fuel cleaner and ran it down to empty and filled up on 93 just to change it up! No return as of yet!

 

[AZSP33D]

Sometimes it wonders between one source for Lambda and another source within the ECU programming, but not having any more details, not sure what I can offer to help, it shouldn’t be an issue as the car runs fine momentarily low power 11-15 or so, just slightly different behavior and a few other things at either end of course.

 

[PunkST]

Well she did it at low load cruise at 60 mph. I wonder if its from it not being fully warmed up. I am not beating on a cold car. And ketting it get up to temp before getting into boost. Ill double check tonight on my drive home. If she does it near the house then its not temp related after a 40 minute drive.

 

[PunkST]

I think im gonna watch my pump pressures on the AP. Curious to see if that's what could be causing the wander.

 

[TyphoonFiST]

I think im gonna watch my pump pressures on the AP. Curious to see if that's what could be causing the wander.

How much gas in the tank?

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[PunkST]

Right now only a quarter. Thats normal near the end of a work week for me. I never let it get totally empty.

 

[TyphoonFiST]

Could be due to fuel sloshing around*

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[PunkST]

Im driving in a straight line on a smooth section of road. 🤷 it could be. But im doubting it. It makes me wonder if a pump is failing. Granted i drive a hell of a lot. But ive never had a pump die on me before so idk what that's like.

 

[AZSP33D]

I think im gonna watch my pump pressures on the AP. Curious to see if that's what could be causing the wander.

Are you having an issue that the AFR goes to 12:1 or that it goes to 14.7:1??? 12:1 means more fuel, it’s rich... meaning the ECU is commanding a target other than idle and low power.

Fuel pump pressure issues would happen under heavy load when there’s a lot of demand and the pump is unable to produce the required fuel flow to meet the high demand.

 

[PunkST]

Its dropping down to the 12 range and then back to 14.7 when cruising at light throttle. No input from me to ask for more fuel. Wasnt able to get a good test tonight since its raining. I was watching pressures thinking a pump was getting weak or about to die.

It could be the car still trying to warm up that last bit. I was sitting with the defrost on till it fully warmed so i could see to drive. Lol

 

[AZSP33D]

Like I said, dropping down to 12 is rich meaning there’s more fuel, not less. 12 is rich. 14 is lean. 12 is injectors spraying more gas. The 12 part of the air fuel ratio is air. Seems like you think it’s starving for fuel as it drops down to 12.

Technically it’s not showing true air fuel ratio but based on lambda for gasoline, But seems opposite of your interpretation. I will say no more.

 

[PunkST]

Inunderstand how afr works. Im trying to figure the reason why its swinging from stoich to rich and back.

 

[AZSP33D]

Inunderstand how afr works. Im trying to figure the reason why its swinging from stoich to rich and back.

I don't understand your logic of suspecting fuel pump is causing the AFR to "go down" to 12.

 

[PunkST]

Idk either. Other than car commanding the pump harder to try and make pressure. Only as a guess.

Hasnt done it the last couple run cycles. But ive been letting it fully warm.

 

[PunkST]

Bumping as its back now. Wandering from 12 to 15. I have a repair to make on my airbox and im gonna start looking at desired vs. Actual rail pressure. Maybe its a sensor.

 

[PunkST]

UPDATE: potentially resolved. I will be needing a new airbox lower half. Drilled out the two bad holes for some temporary zip tie action.

 

[Jason@dizzytuning]

I've been experiencing a similar issue in my 2016 with 2014-15 evap harness. Been like this for 30k, but recently I've been get afr in the 18's on cold start. Drops down to 15.7 after 2 minutes and stays there for 5 more minutes. Then comes down to 14.7. I'm not concerned with the 15.7, cause I believe that is normal on cold starts, but the 18's I can almost hear the misfires.

I've checked everything I can get my hands on, including replacing the evap harness. Still persists.