2004 3.8L Struggling W/ P0175 Code For Months

SVT232V6

Member
just out of curiosity, are the new up and downstream sensors oem or aftermarket.

They are both aftermarket Densos. Though I recently saw a YouTube video by a guy named Scotty Kilmer who recommended to never use a maker other than the OE factory parts supplier.
 

Serpent

Active Member
that is why I asked. I have had that trouble with an aftermarket o2 before and have heard of others experiencing it as well.
 

6 Shooter

Well-Known Member
Your best fix is to replace the front O2 sensors with stock Ford sensors. Myself and others have had issues with aftermarket O2 sensors which have different calibrations than the Ford sensors. Be sure to get the front (Upstream) Motocraft O2 sensors with the GREEN pigtails. Should be able to locate them at 04 2004 Ford Mustang Oxygen Sensor - Fuel Injection - AC Delco, Bosch, Delphi, Denso, Motorcraft, NGK, Ramco, Replacement, Spectra Premium, Standard Motor Products, Walker, Downstream, Downstream Left, Downstream Right, Front, Rear, Rear Right, Upstream, Upstream Front, Upstream Left, Upstream Right - PartsGeek
 

Sam36

Active Member
that is why I asked. I have had that trouble with an aftermarket o2 before and have heard of others experiencing it as well.

It is not just O2 sensors either. I spent 10 years trying to figure out why my car would randomly start idling at 2k. At first I would replace the IAC valve (using OEM) and reset the computer. After a few years of that, I discovered if I just reset the computer (instead of also replacing the valve) that it would go back to idling normally for about 1-2 months. Eventually my automatic would sometimes start hunting gears when off of the gas and coasting down an off ramp from a highway. I messed with a lot of stuff... nothing ever seemed to help other than resetting the computer. I eventually remembered that about 2 years prior to the issue first happening (so nearly 12 years), I had replaced the TPS with a $10 one from autozone just because I felt like it. I went to ford, paid for an OEM one, swapped it and reset the computer... and it was a new car. That was probably 6 years ago, never had a high idle since :D

There are similar stories from other makes too. My general advice when it comes to sensors or electronics is to just go to the dealer and fork up the cash. It will save your sanity in the long run. Of course the irony is most OEMs don't make their own parts so you'd think an "aftermarket" part would be the same quality-wise. For instance valeo makes the OEM clutches for the mustang and ford just whitelabels them. The valeo kit on rockauto is $100 while from ford it is $600. Thought I could "beat the system" and went with the one from rockauto.... yet it gave me horrible vibration at 1.5k rpm.... so I got to change the clutch again.... You can snoop in my history to so those adventures... So even though ford and other OEMs whitelable parts, there is apparently some cruicial quality control specs that they must also pass. And I guess the ones that don't pass are still "good enough" for autozone, etc. :sleep:
 

SVT232V6

Member
that is why I asked. I have had that trouble with an aftermarket o2 before and have heard of others experiencing it as well.

That’s what I was thinking.

Your best fix is to replace the front O2 sensors with stock Ford sensors. Myself and others have had issues with aftermarket O2 sensors which have different calibrations than the Ford sensors. Be sure to get the front (Upstream) Motocraft O2 sensors with the GREEN pigtails. Should be able to locate them at 04 2004 Ford Mustang Oxygen Sensor - Fuel Injection - AC Delco, Bosch, Delphi, Denso, Motorcraft, NGK, Ramco, Replacement, Spectra Premium, Standard Motor Products, Walker, Downstream, Downstream Left, Downstream Right, Front, Rear, Rear Right, Upstream, Upstream Front, Upstream Left, Upstream Right - PartsGeek

That’s the plan. Before I order though, I’m going to try one of the sensors from my Mach since they’re the same part number and see if anything changes.

It is not just O2 sensors either. I spent 10 years trying to figure out why my car would randomly start idling at 2k. At first I would replace the IAC valve (using OEM) and reset the computer. After a few years of that, I discovered if I just reset the computer (instead of also replacing the valve) that it would go back to idling normally for about 1-2 months. Eventually my automatic would sometimes start hunting gears when off of the gas and coasting down an off ramp from a highway. I messed with a lot of stuff... nothing ever seemed to help other than resetting the computer. I eventually remembered that about 2 years prior to the issue first happening (so nearly 12 years), I had replaced the TPS with a $10 one from autozone just because I felt like it. I went to ford, paid for an OEM one, swapped it and reset the computer... and it was a new car. That was probably 6 years ago, never had a high idle since :D

There are similar stories from other makes too. My general advice when it comes to sensors or electronics is to just go to the dealer and fork up the cash. It will save your sanity in the long run. Of course the irony is most OEMs don't make their own parts so you'd think an "aftermarket" part would be the same quality-wise. For instance valeo makes the OEM clutches for the mustang and ford just whitelabels them. The valeo kit on rockauto is $100 while from ford it is $600. Thought I could "beat the system" and went with the one from rockauto.... yet it gave me horrible vibration at 1.5k rpm.... so I got to change the clutch again.... You can snoop in my history to so those adventures... So even though ford and other OEMs whitelable parts, there is apparently some cruicial quality control specs that they must also pass. And I guess the ones that don't pass are still "good enough" for autozone, etc. :sleep:

That’s quite some anal quality control!

I'd do some testing before replacing anything. No point in wasting money when you might not need to.

I’m going to first try swapping the sensor with one from my Mach and see if there’s any change. Gotta figure out how to electrically test these O2 sensors with my multimeter.
 

SVT232V6

Member
So changing the upstream Bank 2 Sensor 1 had no effect. Still Code P0175. ALTHOUGH the car did run excellent this afternoon on my way home from work. Only thing different was I gave it the SeaFoam treatment after my relief came. Short Term Fuel Trims were within +/-5% usually staying at -1.6 to 4.7%. Long Term Fuel Trims were consistently around -20%, but it did run and idle noticeably better. I did notice another clue relating to the high fuel pressure issue. When driving normally at partial throttle, the fuel pressure stayed at or under 40psi. If I floored to to get up to speed, or even revved the engine while in Neutral, the fuel pressure would start to climb seconds after.. Got up to 70psi at one point. The fuel pressure only seems to be increasing at idle or when not in motion. 37-41psi at speed/acceleration, 66-70psi at idle/stop.

On a thought, if the Fuel Rain Pressure Sensor is reading my fuel pressure relative to engine vacuum, and my fuel pressure increases with heavy throttle application, are there any lines or valves involved with that that I could check?
 
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SVT232V6

Member
UPDATE

While I was cleaning the injectors on my Mach earlier today, I took some SeaFoam spray can cleaner and started spraying every vacuum port I could find on the 6er. It ran terribly and had misfires on multiple cylinders for a bit then smoked out like crazy for a few minutes. I also remembered reading a thread somewhere that one guys fix was replacing his air filter with a non FRAM Unit. So I thought, why not? Certainly couldn’t hurt. So far, the popping noise is GONE. Car idles great. I will drive it the next few days and hopefully it stays so! Just a snap while monitoring parameters.
 

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SVT232V6

Member
seriously, a Fram air filter may have been the cause? wow!!!

Some **** you just don’t believe until you actually see it. Effing mind blown over here. Mind you that filter was new 3 months ago and the car didn’t even a 100 miles in that time ‍♂️

UPDATE

So first code P0175 went away and was replaced with code P0172 System Too Rich Bank 1. After a drive to work, car runs good and code P0175 is back. So both banks are rich but car runs great.. Is the Throtte Position Sensor adjustable? I know the TPS On my C4 Vette has to be set at a particular voltage to work properly.
 

Sam36

Active Member
Some **** you just don’t believe until you actually see it. Effing mind blown over here. Mind you that filter was new 3 months ago and the car didn’t even a 100 miles in that time ‍♂️

UPDATE

So first code P0175 went away and was replaced with code P0172 System Too Rich Bank 1. After a drive to work, car runs good and code P0175 is back. So both banks are rich but car runs great.. Is the Throtte Position Sensor adjustable? I know the TPS On my C4 Vette has to be set at a particular voltage to work properly.


With as much "fun" as I had with my TPS, I'd recommend just buying a new one from Ford or trying to find a used OEM one on ebay or something. And run a normal filter... sure fram will give you an extra 3HP at 5k rpm... but probably not worth it (lets not even start about the fact that oil analyst companies can tell whether you're using a fram air filter just by looking at your oil...). And a notable mention, clean your MAF sensor. Its in the plastic box behind the air filter. There's a small wire in it, I usually hit it with some carb or brake cleaner followed by a light draft of air from a compressor to dry it off. Something like this: youtube.com/watch?v=0JaN3Rzx7rA

But to be honest, not really sure if any of these sensors would cause your current issues... They are normally a royal pain as when they get slightly out of spec, your car does weird stuff but never throws a check engine light.
 

SVT232V6

Member
With as much "fun" as I had with my TPS, I'd recommend just buying a new one from Ford or trying to find a used OEM one on ebay or something. And run a normal filter... sure fram will give you an extra 3HP at 5k rpm... but probably not worth it (lets not even start about the fact that oil analyst companies can tell whether you're using a fram air filter just by looking at your oil...). And a notable mention, clean your MAF sensor. Its in the plastic box behind the air filter. There's a small wire in it, I usually hit it with some carb or brake cleaner followed by a light draft of air from a compressor to dry it off. Something like this: youtube.com/watch?v=0JaN3Rzx7rA

But to be honest, not really sure if any of these sensors would cause your current issues... They are normally a royal pain as when they get slightly out of spec, your car does weird stuff but never throws a check engine light.
Cleaning the MAF was one of the first things I tried because I had a MAF sensor voltage code. I traces he wore all the way to the ECU and there were no breaks. So I cleaned that one and there was no change so I ended up replacing it. Car ran good for a while, but started idling rough and misfiring after it was painted. Then I have this P0175 code that won’t go away. Now it’s P0172 and P0175. I’ve read a lot of threads that quote HO2 sensors, fuel pumps, fuel rail pressure sensors, fuel filters, leaking fuel injectiors, FRAM air filters, and even the harmonic balancer all as potential culprits. Just trying to figure this one out so future readers have info to use to fix their ponies.
 

Sam36

Active Member
Just trying to figure this one out so future readers have info to use to fix their ponies.

Indeed.. I just re-read the whole thread again. Somewhat puzzling. You haven't mentioned replacing the ignition coil. That usually only last about 200k miles or so before you start getting random misfires and rough idling. I would assume a "bank too rich" code would mean too much fuel in the exhaust. That makes me wonder if a bad/leaking exhaust valve could cause that code as well. Might want to do a compression check just for fun.

You mentioned "popping" sounds. Is that only at idle? Even when my car was new I would have some popping in the exhaust when revved in neutral while the rpms were falling. Only time I had popping during idle was when my coil was going out...
 

SVT232V6

Member
Indeed.. I just re-read the whole thread again. Somewhat puzzling. You haven't mentioned replacing the ignition coil. That usually only last about 200k miles or so before you start getting random misfires and rough idling. I would assume a "bank too rich" code would mean too much fuel in the exhaust. That makes me wonder if a bad/leaking exhaust valve could cause that code as well. Might want to do a compression check just for fun.

You mentioned "popping" sounds. Is that only at idle? Even when my car was new I would have some popping in the exhaust when revved in neutral while the rpms were falling. Only time I had popping during idle was when my coil was going out...

Yes, just replaced the ignition coil last week. There was no change in how the engine ran. If I haven’t mentioned it yet, car has 176K. I will do a compression test when I get home. Almost done with work.
 

SVT232V6

Member
So my girlfriend had me bring home this yesterday.. I have a complete donor project car that could be cross referenced! And this one’s fuel rail has a schrader valve!
 

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SVT232V6

Member
She’s amazing. Gotta give nurses a try lol And Then There Were 3
 

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SVT232V6

Member
Compression Test Results

Passenger Side
1 - 145
2 - 146
3 - 145

Driver Side
4 - 134
5 - 142
6 - 142

Cylinder 4 is a little low compared to the other 5. There was some gas in that cylinder while doing the compression test that I didn’t experience with any of the other cylinders. I’m going to retry cylinder 4 tomorrow after I let it air out overnight. Leaking injector? Too much fuel in that cylinder maybe?
 
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