Severe AFR Wandering causing car to almost stall

[Bushhy]

Hey everyone! Before the issue, I want to give a bit of back-story to hopefully clear a bit of things up.

So last week, I drove my car to school, and when I went to start my car when I was leaving, the car would start, and then stumble and stall. It gave the P0087 code when hot, and P008B when cold. I had the car towed home, and let it sit while I ordered parts. I ended up coming to the conclusion that the low side fuel pressure sensor was bad, as it would sit at 108psi while idle, and while revving, basically confirming that the sensor was bad. I replaced it this morning, and it now reads a more normal amount, around 80-100psi depending on RPMs, and no longer stalls like it was before.

However, now I am noticing my AFRs are a bit weird. When revving the car in neutral, the AFR will stay close to 14.7, then shoot up to 30-40, and slowly come back down. However, it will dip well below 14.7, around 11-12, and then try and recover. This causes the engine to almost stall, as you can see in this video :

View: https://www.youtube.com/watch?v=1YkzLNeiWOA&ab_channel=Bushhy


It continues to bounce between 11-12 and 16-17 until it eventally settles back to 14.7. When I was replacing the fuel sensor, I had to remove the beginning of the intake, the soft plastic part between the airbox, and the hard tube. I replaced the two "vacuum?" hoses (the ones with the green tabs), and the other hose. Noted with the red arrows in this photo.



At this point, the only thing I can think of is the upstream o2 sensor? I have had a p0133 code for a long while now, and last time the car was in for service, they mentioned something about a spacer being on the front o2 sensor, however the car never had issues like this until now. I am not too sure where to begin with diagnostics, as I do not want to hurt my car by running it. I have a spare o2 sensor that I had bought when the car started having the stalling issue, as it was a fairly cheap part on RockAuto(I got the motorcraft dy1285), so I figured I would throw that in tomorrow morning, and remove the spacer they were referring to.

Any other tips would be greatly appreciated!

 

[Ford ST]

How many miles? If under 60,000 this should be covered under your powertrain warranty. Did you buy it used or new?

Regardless you are not going to have correct air fuel ratios with a malfunctioning upstream O2 sensor that is what it does. Install the new sensor clear the codes and see what happens.

Sent from my LG-LS997 using Tapatalk

 

[D1JL]

The spacer should never be on the upstream O2 senser.
The spacer is only used on the downstream O2 senser when the CAT has been removed or is bad to pull the senser out of the mainstream.
Now a tip, after many years of doing smog repairs, I have never found O2 sensers that worked as well as those supplied by the dealer.
I can't explain why but when using others, the work always came back.

 

[Bushhy]

How many miles? If under 60,000 this should be covered under your powertrain warranty. Did you buy it used or new?

Regardless you are not going to have correct air fuel ratios with a malfunctioning upstream O2 sensor that is what it does.

Sent from my LG-LS997 using Tapatalk

Hey! Thanks for the response! The car is a 2017, with 24k miles. It is outside the 3/36 warranty, but within the 5/60. The car also has a catless downpipe, but was tuned for this. I guess it is probably a good idea to just replace the sensor anyways, especially considering I have an OEM one laying new in a box right now.

The spacer should never be on the upstream O2 senser.
The spacer is only used on the downstream O2 senser when the CAT has been removed or is bad to pull the senser out of the mainstream.
Now a tip, after many years of doing smog repairs, I have never found O2 sensers that worked as well as those supplied by the dealer.
I can't explain why but when using others, the work always came back.

Hey D1JL! Thanks for the response! Yours came in as I was typing the answer above. The car does have a catless downpipe, and was tuned for this. I do have an OEM upstream sensor, so guess there is no reason not to replace it.

Would it be easier to replace that sensor coming from above, or from under the car? I do not have the heat-shield on the downpipe, as it got a bit... mangled during removal haha.

I did also notice what sounded like a light pinging noise coming from under the car. Im not super advanced in diagnosing cars, but it does seem like there is a possibility of an exhaust leak? I did have to get the car towed home, and the driver really strapped the car down, so there could have been a chance it bumped a bit on the bed of the truck and maybe knocked the exhaust around a bit.

I just walked out to the car to listen to it again, and noticed this noise coming from the exhaust. Sounds like a rattle to me? Could actually be the real issue I am facing now?

View: https://www.youtube.com/watch?v=eMnWOP4GSMw&ab_channel=Bushhy

 

[Bushhy]

So, heres an update. Exhaust rattle is still there, can't really figure out where the hell it is, so I am just going to say screw it and let it rattle until I do a cat-back.

I pulled the upstream o2 sensor, and like Ford had mentioned, it had a defouler/spacer on it. This was probably a large part of my actual issue. Car seemed to run fine, and pull hard. Went ahead and did an oil change today, as I was close to the 4k mark anyways(ive read something about these cars doing 10k intervals???)



Here's some pictures of the upstream o2 sensor. Definitely got its butt kicked the past 15k miles or so. Im assuming the car ran ungodly rich for a while, so its making me start thinking I may need to get my injectors cleaned and do some plugs...

Either way, car seems to run a bit better today. Going to drive it to get some food, and see how it does. Also going to go ahead and log some data and send it over to my tuner, and see if the tune is off because of this issue.

Incase anyone was wondering about that defouler, what I believe happened was when my turbo was replaced, Ford removed the downpipe and o2 sensors. When it was put back together they must have put the defouler on the front. Either way, I can live with the P0420 code when I am running the stock tune. Bit of electrical tape always does the job.

 

[SteveS]

Oil changes could be at 10k miles or so if you go by the dashboard indicator for oil changes.

 

[Intuit]

........ it will dip well below 14.7, around 11-12, and then try and recover. This causes the engine to almost stall, .........

There's little bit of lag in the readings on my motorcycle. Sounds like it's the same there as well. Rather than low AFR causing the stall, it is the stall causing the low AFR reading. Low means rich. An engine miss results with more unburned fuel being sent out of the exhaust. An engine miss, will naturally result with a rich reading. Need to find out why it's missing. Check/read the plugs for starters.

 

[Bushhy]

There's little bit of lag in the readings on my motorcycle. Sounds like it's the same there as well. Rather than low AFR causing the stall, it is the stall causing the low AFR reading. Low means rich. An engine miss results with more unburned fuel being sent out of the exhaust. An engine miss, will naturally result with a rich reading. Need to find out why it's missing. Check/read the plugs for starters.

It seems that now since the o2 was replaced, and ECU Learning was reset, the car is learning again, and driveable. Was able to drive to the store without any issues, and sent some logs over to my tuner. Lets hope this is the end of that issue!