Failing 02 sensor

[toast]

My car ('14 with Edelbrock SC kit) occasionally runs like absolute shit. I can tell it is going to happen as soon as I start it when cold, the fast idle searches all over the the place from 1100 to 1700 rpm. I have been leaving the laptop in the car to try and catch it, but you know what that is like. It did it this morning, but by the time I got the laptop connected the fast idle period was over. I turned on logging as I was backing out of the garage and the car wanted to die after a few seconds with the clutch in. A blip of gas and it would cough and then run a bit. The log shows a couple things, very large (-30%) STFT but more importantly I can see the reported A/F ratio sits at 14.7 and then slowly drops down into the 12's with the clutch in and throttle closed. Since Ecutek sucks and you can't change the default logging parameters I didn't get injector pulse width but target A/F ratio is sitting right at 14.7 so I'm thinking the injectors and tune are doing what they are supposed to do. The large STFT is probably due to being on an untuned base map (v25, I'm waiting for v26 to come out before paying for more tuning).

I'm in port injector mode when this happens, so either I have a flaky injector or the wideband O2 unit is failing.

This only happens when cold - once the engine gets up to temp it never happens.

If I'm right the O2 sensor I need to change is the first one in the exhaust, correct?

If I want to upload a file for people to look at what is the preferred format? .csv is no good.

[tomm.brz]

datazap

[toast]

https://datazap.me/u/tshrey/stumblin...&data=22-23-29

log file

[steve99]

Looks ok in that log, manifold pressure at idle 0.3 bar doesnt look like intake leak


Ltft are low and afr and commanded afr fairly close.


Common issues with FI cars


Intake or exhaust leaks, check hoses BOV especially hoes under intake should be clamped.
Check for exhaust leaks at or arround header and 02 sensors. Cracked headers


Check the direct injection computer on side of motpr has all three bolts installed and all tight, these bolts provide groind to the unit,


Check maf sensor is clean and not contaminated with oil, check for oil in intake.

[toast]

The AFR drops to 12.4 with no throttle input while the command is 14.7 and the engine stalls. That's not weird?

Anyway, it happened again after work, so before the fast idle even died down I shut the car off and disconnected the battery. After the ECU reset everything is fine and car drives normally again. I think my tune is somehow walking itself into a bad spot after several weeks of running, that is why it is fine once it warms up. Whatever table is getting bad must reference coolant or oil temp.

[steve99]

Originally Posted by toast

The AFR drops to 12.4 with no throttle input while the command is 14.7 and the engine stalls. That's not weird?

Anyway, it happened again after work, so before the fast idle even died down I shut the car off and disconnected the battery. After the ECU reset everything is fine and car drives normally again. I think my tune is somehow walking itself into a bad spot after several weeks of running, that is why it is fine once it warms up. Whatever table is getting bad must reference coolant or oil temp.

i wasnt sure in that log if you turned it off or not



is you tune maf based or speed density
do you have bigger port injectors ?


has fuel trims always been -29%


does it only do this when cold

[tomm.brz]

Originally Posted by toast

The AFR drops to 12.4 with no throttle input while the command is 14.7 and the engine stalls. That's not weird?

Anyway, it happened again after work, so before the fast idle even died down I shut the car off and disconnected the battery. After the ECU reset everything is fine and car drives normally again. I think my tune is somehow walking itself into a bad spot after several weeks of running, that is why it is fine once it warms up. Whatever table is getting bad must reference coolant or oil temp.

but in the log there is accelerator pedal input, like 2 very short blips during the afr drop
you didn t touch the pedal? did you connect something like a wideband on the rear o2 connector? i d check also ground connections on di ecu as steve said

[Kodename47]

Seeing V25/26 referenced I assume a DT map? Have you checked the custom maps aren't doing anything untoward? Injector time/volume is a good indicator that more fuel is being asked for.

[steve99]

Avree with @Kodename47 its often very difficult to diagnose ecutek tunes as ghe tuner may be using speed density or a series of custom maps to control fueling in ways we dont understand or know about without access to the tune istelf.


Its certianly possible the o2 sensor is bad, its a little strange it only intermittent, usually thats a connection or earthing issue, but again possible it bad 02. Since they are fairly expensive best to cgeck out other possiblities first

[Kodename47]

Tried reseating the O2 sensor connectors? My AC crapped out the other day and that fixed it.

[toast]

Originally Posted by steve99

i wasnt sure in that log if you turned it off or not



is you tune maf based or speed density
do you have bigger port injectors ?


has fuel trims always been -29%


does it only do this when cold

Delicious tune, so MAF I guess. Stock everything except SC.

No, the fuel trims maxing out is new, normally it is about -9%. Definitely don't have an air leak anywhere. I'm running a Shorai battery now that it is warm, just to rule that out I put my big AGM winter battery back in and ran an 8 gauge wire right from negative terminal to the ECU.

I was wrong to get excited about the reset fixing it, stalled a couple times again this morning. Definitely only does it when cold, once the dash gauge gets to the middle the car runs great and fuel trims go back to normal.

I do have a Dbox and I've heard of those failing. I think I'm going to email Delicious and ask if I can have a normal v25 map without the Dbox adjustments and disconnect it just to rule that out.

[tomm.brz]

dt are all hybrid sd

[steve99]

Originally Posted by toast

Delicious tune, so MAF I guess. Stock everything except SC.

No, the fuel trims maxing out is new, normally it is about -9%. Definitely don't have an air leak anywhere. I'm running a Shorai battery now that it is warm, just to rule that out I put my big AGM winter battery back in and ran an 8 gauge wire right from negative terminal to the ECU.

I was wrong to get excited about the reset fixing it, stalled a couple times again this morning. Definitely only does it when cold, once the dash gauge gets to the middle the car runs great and fuel trims go back to normal.

I do have a Dbox and I've heard of those failing. I think I'm going to email Delicious and ask if I can have a normal v25 map without the Dbox adjustments and disconnect it just to rule that out.

That soumds like a good plan. It appears that deliceous dbox device modifys the signals from the maf and map sensors which could cause your issie if its not working correctly

[toast]

I think I may have caught it. Did a 15 minute data log of warming up partially in the garage and then driving. Oil and coolant were fully up to temp, sitting at a light and I can feel the car idle sounds funny. Looked over to the laptop and could see the AFR swinging from 12 to 14. Had to blip the gas a couple times to keep the engine alive and pulled over off the road for a minute. Then it all just went away and car was fine.

File is too big to upload to datazap so I have to figure out how to cut it up, but here is a screenshot of the area of interest. Throttle is zero, MAF is pretty constant. MAP starts going all over the place, fuel tries to keep up but then the AFR drops so the fuel drops. This continues in a cycle until I pull over and then when it goes away everything is normal. So either my MAP is flaky or the Dbox is (the MAP connects to the Dbox). From everything I see it looks like the primary O2 sensor is fine.