Potential fuel issue?

[bg2013]

A little over a month ago I had both turbos replaced with new oem turbos, hollowed out the front 2 cats and straight piped the 3rd cat. ( no emissions testing in Indiana and the failing turbo had leaked oil into them and clogged them) got the car back and it drove great until last Friday when it started to feel like it had an intermittent misfire, it would happen when I would be cruising in low rpm on the highway, try to give it a little extra gas and it would feel like it was misfiring, if I push the throttle further it would get worse, back off and it went away. It does it in every gear unless i absolutely baby it. I initially thought it was related to the work I just had done on the turbos so I took it back to the shop for them to check it out…. Well they just called and told me that there are zero codes for anything besides p420/430 from the gutted cats. Looking at live data they say that the turbos are building boost as they should, and that the only thing that looks off is the fuel trims. They are telling me that because the cats are gutted the vehicle isn’t figuring out the proper fuel mixture and that’s the issue I’m experiencing. Is that even possible? I thought it was the pre cat o2 sensors that controlled the fuel mixture, and they are working and not throwing codes.

In summary; I thought these cars would function properly without cats, was I wrong? And if I wasn’t, any thoughts on where to start diagnosing this issue?

Thanks!

 

[kryptto]

Downpipes or Cat Back Exhaust

Which one should I install first, Downpipes or a Cat Back Exhaust?

shoforum.com

 

[BradM]

A little over a month ago I had both turbos replaced with new oem turbos, hollowed out the front 2 cats and straight piped the 3rd cat. ( no emissions testing in Indiana and the failing turbo had leaked oil into them and clogged them) got the car back and it drove great until last Friday when it started to feel like it had an intermittent misfire, it would happen when I would be cruising in low rpm on the highway, try to give it a little extra gas and it would feel like it was misfiring, if I push the throttle further it would get worse, back off and it went away. It does it in every gear unless i absolutely baby it. I initially thought it was related to the work I just had done on the turbos so I took it back to the shop for them to check it out…. Well they just called and told me that there are zero codes for anything besides p420/430 from the gutted cats. Looking at live data they say that the turbos are building boost as they should, and that the only thing that looks off is the fuel trims. They are telling me that because the cats are gutted the vehicle isn’t figuring out the proper fuel mixture and that’s the issue I’m experiencing. Is that even possible? I thought it was the pre cat o2 sensors that controlled the fuel mixture, and they are working and not throwing codes.

In summary; I thought these cars would function properly without cats, was I wrong? And if I wasn’t, any thoughts on where to start diagnosing this issue?

Thanks!

I agree the downstream O2 sensors are there to monitor the health of the cats and they don't impact fuel trims. How far off are the trims? Short term or long term or both? Both banks? Have you changed gas stations recently?

 

[bg2013]

I agree the downstream O2 sensors are there to monitor the health of the cats and they don't impact fuel trims. How far off are the trims? Short term or long term or both? Both banks? Have you changed gas stations recently?

I’m not sure on the exact numbers the tech just told me they were “all over the place” I’ll try to get specifics when I pick it up tomorrow. The day the issue started My low fuel light was on and I had just stopped and added $25 of 87octane from a gas station that I occasionally stop by after work. Then when I got on the highway probably 3-5 minutes later is when it started acting weird.I have been running regular gas since I got the car back because the bill to replace the turbos nearly broke me. I always ran 93 before that but I’d been running 87 since getting the car back for over a month with no issues.

 

[BradM]

Well the computer sees the issues with the backs and the wide spectrum front O2 start to adjust the fuel going in. I didn't explain it through.

I respectfully disagree. https://www.walkerproducts.com/o2-sensor-training-guide/troubleshooting-oxygen-sensors/

 

[BradM]

I’m not sure on the exact numbers the tech just told me they were “all over the place” I’ll try to get specifics when I pick it up tomorrow. The day the issue started My low fuel light was on and I had just stopped and added $25 of 87octane from a gas station that I occasionally stop by after work. Then when I got on the highway probably 3-5 minutes later is when it started acting weird.I have been running regular gas since I got the car back because the bill to replace the turbos nearly broke me. I always ran 93 before that but I’d been running 87 since getting the car back for over a month with no issues.

87 wouldn't be an issue but water would. When you get the trim numbers, please share.

 

[bg2013]

87 wouldn't be an issue but water would. When you get the trim numbers, please share.

Will do! Thank you for the info

 

[Texas Marauder]

Well the computer sees the issues with the backs and the wide spectrum front O2 start to adjust the fuel going in. I didn't explain it through.

I disagree, the rear O2 sensors only monitor the cat efficiency. They do not affect the way the engine runs. The front sensors control the air fuel ratio.

 

[SHOdded]

mainstream tuners wont ignore o2 codes due to epa regulations and enforcement. your state does not do emissions testing, so idk if there is leeway there.

with properly designed hi-flo cats, o2 codes are not triggered. you could add an old school part to fool the rear sensors. that would be the cheapest fix if the problem is due to the o2's. with these in place it probably wouldn't matter if you have oem/normal airflow cats or hi-flo cats (which in essence you have created by hollowing them out).

 

[kryptto]

@BradM and @Texas Marauder I am still learning myself thanks for correcting me. Thanks for the correct info. I was under the impression back from the Tuner I used back when I used the HP Tuner. I either misunderstood, which is very possible. Or to my own detriment I believed him. I will blame my misunderstanding.

I will bow out and watch the masters at work. So until the numbers come in it could be bad gas?

 

[Junkyard_Mad-Scientist]

I also have an intermittent misfire that usually happens at cruising speed (1500 rpm or so) it will sputter almost and if I lay in to it it'll trip an engine light for misfire, if I back off and and then lay into it to drop a gear it passes 1500 and smooths right out and the problem goes away for a while. my car is completely stock exhaust and turbo wise, I have been convinced I have a slowly dying coil pack. That said its worth looking into as a just incase because I've seen a failing ignition cause fuel problems, but if for any reason there is air making its way past the o2 sensor like a leaking manifold, loose sensor, bad weld, I know that can cause an o2 sensor to freak out. with your trims being "all over the place" I'm guessing she's neither consistently fat nor lean, so something is aggravating the fuel system. if you have a scanner with the ability to watch live data Id watch your sensor readings while running and hot, or even try to match the conditions that cause the problem and see if anything is flickering or out of normal range. if you don't have one amazon has them for $20 and as cheap as it sounds it does pretty good and lets me see live data. I don't leave home without it

 

[bg2013]

87 wouldn't be an issue but water would. When you get the trim numbers, please share.

Ok so I got the car back today. I have a cheap Bluetooth obd adapter and an app that lets me see some live data. I monitored LT and ST fuel trims of both banks and here are the values I got. I’m assuming minimum and maximum is what we’re looking for?

Bank one STFT min. -12.51 max 10.9
Bank two STFT min. -15.625 max 10.93

Bank one LTFT min. -4.688 max 8.594
Bank two LTFT min. -5.469 max 7.813

I decided because I had the scanner on it that this time when it started doing the “misfire that’s not a misfire” I would throttle into it for a moment rather than let off instantly. Well I did that and got a Flashing CEL, pulled over and scanned it and got a cylinder 2 misfire code! Left the engine running while it was scanning the codes and it idled completely normal and the CEL went away. Drove it the mile back to my house gently but nothing felt worse than when I started the drive.

Do those fuel trim numbers tell you anything?

I’m wondering now if maybe it could be a coil/spark plug/injector ?

Yeesh ‍where should I start?

 

[kryptto]

Well time to pull that plug and another couple and look them over a send some pics.

Sounds to me like a bad coil pack. How many miles, might be a good time to replace them all, plugs and coils.

 

[Junkyard_Mad-Scientist]

Ok so I got the car back today. I have a cheap Bluetooth obd adapter and an app that lets me see some live data. I monitored LT and ST fuel trims of both banks and here are the values I got. I’m assuming minimum and maximum is what we’re looking for?

Bank one STFT min. -12.51 max 10.9
Bank two STFT min. -15.625 max 10.93

Bank one LTFT min. -4.688 max 8.594
Bank two LTFT min. -5.469 max 7.813

I decided because I had the scanner on it that this time when it started doing the “misfire that’s not a misfire” I would throttle into it for a moment rather than let off instantly. Well I did that and got a Flashing CEL, pulled over and scanned it and got a cylinder 2 misfire code! Left the engine running while it was scanning the codes and it idled completely normal and the CEL went away. Drove it the mile back to my house gently but nothing felt worse than when I started the drive.

Do those fuel trim numbers tell you anything?

I’m wondering now if maybe it could be a coil/spark plug/injector ?

Yeesh ‍where should I start?

Same thing I got, same cylinder too! Checked the new plugs, still new, I moved my coil pack to cylinder 5 to see if the problem followed the coil and it has only tripped once since and didn't log a code so I'm still in the dark but the issue became way less frequent (go figure). I agree with @kryptto coils couldn't hurt but I'd try what I did and relocate the pack to see if the misfire follows the coil and definitely check the plugs while you're in there.

 

[BradM]

Ok so I got the car back today. I have a cheap Bluetooth obd adapter and an app that lets me see some live data. I monitored LT and ST fuel trims of both banks and here are the values I got. I’m assuming minimum and maximum is what we’re looking for?

Bank one STFT min. -12.51 max 10.9
Bank two STFT min. -15.625 max 10.93

Bank one LTFT min. -4.688 max 8.594
Bank two LTFT min. -5.469 max 7.813

I decided because I had the scanner on it that this time when it started doing the “misfire that’s not a misfire” I would throttle into it for a moment rather than let off instantly. Well I did that and got a Flashing CEL, pulled over and scanned it and got a cylinder 2 misfire code! Left the engine running while it was scanning the codes and it idled completely normal and the CEL went away. Drove it the mile back to my house gently but nothing felt worse than when I started the drive.

Do those fuel trim numbers tell you anything?

I’m wondering now if maybe it could be a coil/spark plug/injector ?

Yeesh ‍where should I start?

It sounds like you've located a bad plug or coil. As for the fuel trims, the mins and maxs don't help. You would need to see the real-time fuel trims once the car was warmed up.

 

[bg2013]

Well time to pull that plug and another couple and look them over a send some pics.

Sounds to me like a bad coil pack. How many miles, might be a good time to replace them all, plugs and coils.

Ok I’ll get them out and get pictures tomorrow after work. It just crossed over 150k last week, I’ve owned it since 119k and haven’t changed plugs or coils since I’ve had it, not sure about previous owner.

It sounds like you've located a bad plug or coil. As for the fuel trims, the mins and maxs don't help. You would need to see the real-time fuel trims once the car was warmed up.

Ok thank you for the reply. I am able to see live data while driving and the vehicle was warmed up when I tested previously. What would be considered the “ normal “ range for the fuel trims?

 

[SHOdded]

oem coils rarely fail on the ecoboosts. possibly due for spark plug refresh. also check what gap they should be set at per tuner. if you can do coils, great, retain originals as backups unless they test bad.

what app are you using to monitor data? forscan lite at minimum and preferably torque pro esp if using custom PIDs, if no tuning device is in use. i get 30ms resolution with forscan line and obdlink mx+/mx. a tuning device can get you down to 10ms iirc.

 

[BradM]

Ok I’ll get them out and get pictures tomorrow after work. It just crossed over 150k last week, I’ve owned it since 119k and haven’t changed plugs or coils since I’ve had it, not sure about previous owner.


Ok thank you for the reply. I am able to see live data while driving and the vehicle was warmed up when I tested previously. What would be considered the “ normal “ range for the fuel trims?

As close to 0 means everything is perfect and the left bank and right bank should very close to the same values. Any imbalance between the banks would help you identify possible causes. In your case, I was wondering whether you may have an exhaust leak before one of the 02 sensors since you recently changed turbos and had your cats off to hollow them out. But get that misfire addressed before looking at trims.

 

[bg2013]

I pulled the plug from cyl 2 today and compared it with cyl 6 and they both looked ok. So I swapped the coils and went for a drive. The misfire followed the coil to cyl 6 so I think it’s safe to say that coil is bad? I don’t believe they are oem coils (unless they came from the factory with MSD) but they’ve been on the car the whole time I’ve owned it.

 

[BradM]

I pulled the plug from cyl 2 today and compared it with cyl 6 and they both looked ok. So I swapped the coils and went for a drive. The misfire followed the coil to cyl 6 so I think it’s safe to say that coil is bad? I don’t believe they are oem coils (unless they came from the factory with MSD) but they’ve been on the car the whole time I’ve owned it.

Your diagnosis is correct. MSD is not OEM and I've heard folks complain about MSD coils.