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Hi guys, I'm having an issue that I cant seem to remedy after replacing my drivers side header. The story started last week when my check engine light came on and I went to get the codes scanned, I cant remember the code but it had to do with my driver side bank running too rich, funny enough once I got home my engine sounded like a lawn mower and I immediately suspected an exhaust leak. After checking I had found that the collar of the header that attaches to the mid pipe had cracked clean off, at this point I'm assuming a hit a bad speed bump bending the exhaust and slowly causing it to crack.


So I order a new header pull out the old one and replace it with the new one, here is where I screw up royally and I'm still kicking myself, when I put the header in I removed the spark plug cables and when I went to put them back I screwed up the order like an idiot and scratched my head for all of 5 min when I was getting nasty backfires, to make matters worse I noticed my error and rewired the spark plugs only the screw up a second time (I know right how the hell does someone screw up placing 3 wires into their proper holes twice).


Finally I get the order right and the backfires are gone, however at this point my cat is glowing red from all the fuel being dumped from the firing order being off, so I give it a few hours to all cool down before I come back. So now I'm faced with idle being completely erratic, while in park it is only slightly rough but rough enough to notice, when the car is put into drive the rpms immediately plummet to a near stall but recovers, this plummet occurs anytime the break is pressed when the car is in gear. If the car is in park and I turn on the AC the rpms will begin to dance up and down like a yo-yo repeatedly, never stabilizing.


I'm thinking that there is a problem either with air or fuel ratio at this point, Ive pulled off the throttle body, idle air control valve, and mass airflow sensor cleaning all parts scrupulously, Ive done several checks to make sure no hoses are lose or wires unplugged. At this point I'm stumped on what to do next, I suppose maybe the IAC valve or MAF sensor could have gone bad, but I'm sorta lenient on playing the game of buying new parts until the issue gets found. The thing that really puzzles me though is that this issue occurred right after replacing the header, unless of course my screw-ups with the firing order and backfires managed to damage something else.


My mustang is the 04 V6 Base Model.


Note:
The code that it was spitting out prior to me discovering the cracked manifold was P0174 indicating bank 2 being too lean which was most likely due to the exhaust being open to atmosphere. There no longer is any check engine light present once the spark plugs were properly wired.
 

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Unhook your battery for a few minutes. Then start fresh. Make sure you didn't damage any wiring while replacing the header. There's a harness that runs in close proximity to the header itself. If it hasn't cleared up after the battery disconnect, and your CEL is still on you need to pull codes. Guessing, and playing with other sensors probably won't help.
 

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Discussion Starter #3
Unhook your battery for a few minutes. Then start fresh. Make sure you didn't damage any wiring while replacing the header. There's a harness that runs in close proximity to the header itself. If it hasn't cleared up after the battery disconnect, and your CEL is still on you need to pull codes. Guessing, and playing with other sensors probably won't help.
Already tried, forgot to mention. I pulled battery and let car sit for a while as well as holding the break for a few seconds to insure complete discharge. No check engine light has come on after I got the spark plugs properly wired.

An idea that comes up is in relation to the oxygen sensor, could a damaged O2 sensor cause severly poor idle and if so could of the misfiring from the improperly installed spark wires caused damage to the sensors? The sensors are practically new, I installed them a year ago. There is a very nasty smell from when I got the cat red hot that's still lingering around and the exhaust dripped a puddle of black liquid out the tail pipe when I had it running, I'm wondering if I destroyed the cat.
 

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Discussion Starter #4
So this morning I had the bright idea to remove the cap that came with the replacement header to let exhaust gas flow into the engine bay and I started it up. Idle problem gone completely, so I believe at this point I can confirm there is indeed a blockage.
 

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Formerly LSNotch
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So you probably fouled the spark plugs and didn't change them? It may run better since the 02 sensor is not reading correctly with the "cap" off and the AF ratio might be lean. In my experience idle hunting is wrong fueling (rich) or too much timing.
 

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Discussion Starter #6
So you probably fouled the spark plugs and didn't change them? It may run better since the 02 sensor is not reading correctly with the "cap" off and the AF ratio might be lean. In my experience idle hunting is wrong fueling (rich) or too much timing.
So you believe fouled spark plugs are the issue? Its not only idle hunting but it just flat out isnt able to idle when in gear with the break pressed, it is at the point of stalling and is unable to raise RPM's.
 

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So you believe fouled spark plugs are the issue? Its not only idle hunting but it just flat out isnt able to idle when in gear with the break pressed, it is at the point of stalling and is unable to raise RPM's.
If it was running pig rich for a little bit and the spark plugs were old then there's a good chance they are bad. I would replace them just to ensure that is out of the way and it's not something else. Btw, did you yank or pull on the O2 sensor(s) by accident? I've damaged them before like that. Just another thought.
 

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Discussion Starter #8
If it was running pig rich for a little bit and the spark plugs were old then there's a good chance they are bad. I would replace them just to ensure that is out of the way and it's not something else. Btw, did you yank or pull on the O2 sensor(s) by accident? I've damaged them before like that. Just another thought.
Replaced plugs and O2 sensors last year, ive checked for loose wires or any damaged connectors over 3 times at this point. Ill check the plugs, if that's not it all I can think is the cat was damaged and became clogged, which means Ill either be replacing the entire exhaust or taking the car to a shop to get the cats cut off and new ones put on.
 

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Formerly LSNotch
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Replaced plugs and O2 sensors last year, ive checked for loose wires or any damaged connectors over 3 times at this point. Ill check the plugs, if that's not it all I can think is the cat was damaged and became clogged, which means Ill either be replacing the entire exhaust or taking the car to a shop to get the cats cut off and new ones put on.
Yeah the O2 sensor may look fine and still be bad. May not even throw a code. Did you pull codes after resetting the ECU?
 

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I don't have a scanner and the auto stores by me wont do a scan unless the check engine lights on, which it isn't.
hmmm you can have a stored code. Anyways, I would start by changing the spark plugs since they weren't firing at the correct sequence when you cross the wires and fuel was being injected. Also, when there's a misfire the O2 sensors normally read lean and ECU will inject even more fuel leading to foul plugs.
 

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if you want to DIY, get DIY tools

post 96 models have a powerful tool, use a scan tool to access what the ecm is seeing
 

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Discussion Starter #13
Well I seem to have a penchant for bad luck. The original pypes exhaust kit I ordered ended up getting back ordered so I snagged this for $180 with intentions of getting some cats for it in a month or so. I also got some cherry bomb mufflers and im doing exhaust dumps. While hooking it all up i noticed the flange on my passengers side header was loose and after taking the header off, it had cracked in the exact same way the driver side header had, it just hadn't fully separated yet. At this point I purchased these set of headers instead of going with the doorman replacements unfortunately while installing everything I managed to crack the egr pipe, i'm purchasing a new one but in the mean time I did a repair using fiberfix (its this fiberglass heat wrap that's impregnated with clay of sorts). After getting everything in and replacing the spark plugs I start the car up, idle goes to 1000 then levels off around 6-700 but I feel allot of vibrations, the engine is shaking but its shaking at a steady rate and in turn causing the car to shake a bit. After running for a few minutes however, it begins to backfire, and the backfire gets worse and worse until I shut it off.


Not sure what to check next at this point, I got both set of O2 sensors screwed in but the back ones are unplugged because i need an extension and I figured without any cats it wouldn't matter if they were plugged in or not.
 

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Discussion Starter #17
I'm beginning to think that I may be dyslexic, I had spark wires 4 and 6 swapped, after addressing that the backfire stopped and engine has settled, I drove for several hours yesterday and it runs wonderfully.

I do have 4 fault codes though, all seem to be relating to the second O2 sensors (it seems they are causing my banks to be stuck lean, I thought the upstream sensor was in charge of that?)

P0141 O2 Sensor Heating Circuit (bank 1 Sensor 2)
P0161 O2 Sensor Heating Circuit (bank 2 Sensor 2)
P2270 O2 Sensor Signal Stuck Lean (bank 1 Sensor 2)
P2272 O2 Sensor Signal Stuck Lean (bank 2 Sensor 2)
 
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