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Discussion Starter · #1 ·
So I have had the car for about 2 years now and bought it modified. Cold air intake, 3 inch downpipe with flowmasters, and what looks like a C&L bypass valve. Its tuned on a Bama X4. It has a CEL P0420 cuz of the high flow downpipe but has always ran fine with it. AFR would stick to 14.0 -14.1 at idle/driving.

I noticed last summer the AFR started to bounce up and down between 13.8-14.5 and I would have slight loss of power. My 0-60 times were consistent 5.2 but with the loss of power feeling best it could do is 5.6 seconds. The car at idle and driving does feel like its running a rougher too. It does this for both stock tune and modified tune.Before it would feel smooth and no micro-vibrations in my seat. Idid a ton of research and decided to replace the evap purge valve ,the low side fuel pressure sensor, and the spark plugs to no avail. Having no other vehicle to drive I just got used to it and drove it like that daily.

Then, randomly, today I was driving to work and the AFR was staying at a steady 14.0 on idle and while driving. The car felt smoother and came off of a stop easier. I noticed when I was traveling at 50mph and let off the gas it would coast and the MPH would VERY slowly start to drop. Before, when my AFR was running like poop the car would not coast that easily and would drop in MPH faster.
I have had multiple friends and family mechanics take a look but none of them could pinpoint the problem. I want to take it to ford and have them look at it but with my mods I doubt they can do much for me without returning everything to stock and I am left with a fat bill. Anyone got any ideas as to what I should check for next? Its been such a mystery for me lol.
 

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Cold air intake. Toss oem back on and test could be hot iat’s, maybe needs new plugs, or regap them. Maybe bad batch of fuel
 

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I’d put oem intake, and new plugs with correct gap, and try and get new fuel

but I’d try new tank fresh fuel first
 

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Discussion Starter · #4 ·
Cold air intake. Toss oem back on and test could be hot iat’s, maybe needs new plugs, or regap them. Maybe bad batch of fuel
I thought heat could be an issue as well unfortunately this has been doing it during winter and fall seasons as well when the air is cold. I replaced new plugs twice with correct gaps, new fuel as well and problem still persists.
 

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Discussion Starter · #7 ·
UPDATE: just came back from work. After starting the car up it held a steady 14.0 AFR. Driving home it was steady. Decided to give it a 60-80 pull at WOT real quick and after doing so the AFR started going whack again.
 

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2017 PP MT DD
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O2 sensors fouling
 
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2020 ecoboost base coupe,auto
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What codes is the computer giving besides what you gave in first post? Scan with your Bama tuner.
 

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Discussion Starter · #10 ·
What codes is the computer giving besides what you gave in first post? Scan with your Bama tuner.
P0420 is the only code that its giving me. Codes for Catalyst System Efficiency Below Threshold (Bank 1) which is from the high flow exhaust. Im getting a spacer for it to get rid of the code.
 

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no. That’s not from high flow exhaust.
You need new o2 sensors, look in your car to see if you have oem or aftermarket downpioe
If it’s aftermarket. Toss oem back on, with new o2 sensors

a regular catback exhaust, even straight pipe after the downpipe has no affect, but if you have aftermarket downpipe. Then there’s your issue

fouled up the O2 sensors

I did it recently
 

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Discussion Starter · #13 ·
no. That’s not from high flow exhaust.
You need new o2 sensors, look in your car to see if you have oem or aftermarket downpioe
If it’s aftermarket. Toss oem back on, with new o2 sensors

a regular catback exhaust, even straight pipe after the downpipe has no affect, but if you have aftermarket downpipe. Then there’s your issue

fouled up the O2 sensors

I did it recently
Its definitely aftermarket. Its looks like its a 3 inch downpipe compared to the 2.5 stock one. I seen stock downpipes and the cat is super obvious on it. This one doesnt have the big can looking cat. Heres a photo
39367

Mesh cat?
39368

I was under the impression these were high flows and that they will throw a P0420 code regardless unless I get a spacer. This is the source i got the info from: P0420 code
Also just wanna say thank you for taking the time to help me out I appreciate it!
 

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Yep the spacer will remove the code, you use it on the rear o2 sensor

not the front one. But unless you are tuned... yor car is not going to run optimal. Itl run worst than stock.

but you can get a protune. But a Cobb and get Ryan or adam to tune it
 

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That’s not a mesh cat, that is flex tubing. Post a picture of where your downpipe meets your engine. So we can see the downpipe and engine, take a few. I can tell you if it’s oem or not
 

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Edit

I just saw your photos, sorry I am kinda driving lol.

that is oem pipedownpipe,
Sounds like either need a new o2 sensor/one or both. Or your cat is clogged.
If it’s not burning efficient the rear o2 sensor throws that code

Aftermarket downpipes throw codes because two things

one, no cat, or two. Higher flow cat, and the o2 sensor says the cat isbad.

If you are oem, which I believe you are.

your cat may be culprit, but I would replace the o2 sensors first, 80 bucks for both of them from Levittown ford shipped No big deal

I reckon it’s the front o2 sensor thouth, since the rear is tripping the code, meaning the rear is working. It may be the cat itself or front o2 sensor.


but! Cat is under warranty, I think they are under warranty for something stupid like 100k miles! Sothis may be worth going to dealership, after you replace the front o2 sensor, if it’s still saying that cide

it’s possible your cat is bad
 

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Discussion Starter · #18 · (Edited)
Update #2 (oh boy this ones a doozy!)
I started the car up to get to work this morning and the AFR still fluctuated but much more slowly and not as bad. It goes from 13.9-14.2 now. The power is still there though??? Things I have noticed when the car runs right are
-comes off a stop smoother and with ease
-when the trans shifts it grabs harder and theres slightly more torque(Auto 6 trans)
-car feels smoother and runs smoother. Less vibration in my seat.
-it takes less throttle to bring boost up when cruising.(when the car runs fine or like crap I still hit peak boost at WOT. Peak boost is 22.48PSI)
-i have noticed my blow off valve makes more of a PSHHH sound than a stutut-pshhh at lower boosts(turbo flutter). Before if i let off the gas around -2PSI (or 2.0 inHG, fords built in boost gauge) the cars turbo would flutter. Now at -2PSI ( 2.0 inHG) the car does a crisp clean blow off sound with no turbo flutter at all.

all-in-all this is starting to make me feel like multiple things could be wrong. Is the turbo going bad? If so, why is it randomly working fine now? Would that mean the AFR is not causing the problem? Is my blow off valve going bad? That may explain the turbo flutters possibly. Is my intakeor throttle body gunked up and created less air flow and choking the power out, creating a rough ride? Or perhaps its all just the 02 sensors playing with the power? Lots to think about!
 

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Discussion Starter · #19 ·
Edit

I just saw your photos, sorry I am kinda driving lol.

that is oem pipedownpipe,
Sounds like either need a new o2 sensor/one or both. Or your cat is clogged.
If it’s not burning efficient the rear o2 sensor throws that code

Aftermarket downpipes throw codes because two things

one, no cat, or two. Higher flow cat, and the o2 sensor says the cat isbad.

If you are oem, which I believe you are.

your cat may be culprit, but I would replace the o2 sensors first, 80 bucks for both of them from Levittown ford shipped No big deal

I reckon it’s the front o2 sensor thouth, since the rear is tripping the code, meaning the rear is working. It may be the cat itself or front o2 sensor.


but! Cat is under warranty, I think they are under warranty for something stupid like 100k miles! Sothis may be worth going to dealership, after you replace the front o2 sensor, if it’s still saying that cide

it’s possible your cat is bad
I looked up stock cats for ecoboosts and I thought they looked like this
39371

they have more of a can-sized cylinder near the top. Mine doesnt have that, just that flex part in my previous photos. Thats why I thought it was high-flow with the P0420 code. (Sorry I am not the brightest when it comes with cars and mechanical parts)
 

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you aren't tuned correct? thats the issue, if you indeed have aftermarket highflown or hatless downpipe, you need a retune.

either snag a oem downpipe off someone, (prob can snag one for 100 bucks) ive seen people giving them away but that was before this new epa crackdown.

your car isn't going to run optimal til you get either a tune for that current set up, and a vibrant o2 spacer/defouler for the rear o2 (it WILL remove) the code. but, it won't make ti run how it should. it just tricks the sniffer o2 to think its running fine.

id look around and make a post asking for a oem downpipe on here and m6g and Facebook Mustang EcoBoost parts.-- thats the cheaper option.

the next option is, get a Cobb (300-400) bucks, then another couple hundred dollars for pro tune, but it'd run great, as it will be correct tuen for your gear.
 
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