Erratic Idle after header replaced - Ford Mustang Forum
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post #1 of 13 (permalink) Old 10-02-2019 Thread Starter
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Erratic Idle after header replaced

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.


Edit

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.


Last edited by letumeternum; 10-03-2019 at 12:57 AM.
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post #2 of 13 (permalink) Old 10-02-2019
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You might want to check your O2 sensors.


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post #3 of 13 (permalink) Old 10-02-2019 Thread Starter
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You might want to check your O2 sensors.

So that was another thing I was thinking, could the O2 sensor have been damaged from misfiring, they are all pretty much 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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post #4 of 13 (permalink) Old 10-03-2019 Thread Starter
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On an updated note after some reading about base idle I'm finding that the engine should idle just barely with all electronics off and the IAC disconnected. Upon disconnecting the IAC the engine immediately dies and is unable to start without the IAC connected.

Im not seeing how installing the new header could have effected the base idle but im sort of grasping at straws short replacing sensors one at a time.

Last edited by letumeternum; 10-03-2019 at 01:37 AM.
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post #5 of 13 (permalink) Old 10-03-2019 Thread Starter
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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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post #6 of 13 (permalink) Old 10-03-2019
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Red Hot is not good. I would add to the list; check the cats for clogging.

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post #7 of 13 (permalink) Old 10-03-2019 Thread Starter
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Red Hot is not good. I would add to the list; check the cats for clogging.
Im pretty sure there is a clog somewhere at this point, the engine runs perfectly (maybe even better than before?) with the cap that came on the new header removed. I.m gonna go ahead and take this opportunity to upgrade the entire exhaust with high flow cats and an x pipe.
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post #8 of 13 (permalink) Old 10-27-2019 Thread Starter
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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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post #9 of 13 (permalink) Old 10-29-2019 Thread Starter
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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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Quote:
Originally Posted by letumeternum View Post
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)
Sensor two just reports rich or lean. It doesn’t do anything else. So you have something going on upstream causing it to run lean. The rear sensor is a monitor only.

Last edited by 90lxwhite; 10-30-2019 at 01:02 PM.
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post #11 of 13 (permalink) Old 10-30-2019 Thread Starter
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Sensor two just reports rich or lean. It doesn’t do anything else. So you have something going on upstream causing it to run lean. The rear sensor is a monitor only.
Voltages from both upstream sensors cycle between 0.9 and 0.1 when driving, which appears to be normal.
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Originally Posted by 90lxwhite View Post
Sensor two just reports rich or lean. It doesn’t do anything else. So you have something going on upstream causing it to run lean. The rear sensor is a monitor only.
Voltages from both upstream sensors cycle between 0.9 and 0.1 when driving, which appears to be normal.
Further upstream. The rear o2’s are just telling you that the air to fuel ratio is “off,” which could be due to just about anything.
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post #13 of 13 (permalink) Old 11-03-2019 Thread Starter
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So I got the new cats in as well as the downstream O2 sensors, CEL is gone and there are no longer any trouble codes. However the emissions readiness s/DTC is showing that the Catalyst and EGR system are incomplete, before installing the cats only the catalyst was marked as incomplete. The upstream O2 sensors oscillate between 0.1 and 0.9 (sometimes staying high or low for a little bit), the downstream O2 sensors sit at 0.04 or lower sometimes drifting up slightly followed by going back down.


Any ideas for the Catalyst and EGR system being marked as incomplete? I'm thinking I just need to drive it more for the ECU to register things.
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