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Headers installed, now runs terrible under 3k

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Old 12-24-2015, 02:45 PM
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Default Headers installed, now runs terrible under 3k

Hey guys, just put a set of speed engineering headers, TR55s (.050 gap) and solid MWC mounts on the TA.. the car now misfires, surges and nearly wants to die.

I did some looking and figured it must be a bad new plug, or I cracked one when sliding the headers in, so pulled them all and they looked fine, put the ones that were in it back in to rule them out completely.

Now I'm starting to wonder if it's something with the o2 sensors. The front ones I extended (soldered and heat shrinked) and the rears I just put back in like the factory y-pipe is. Once above 3,000 rpms, the car pulls very well, just below that it's horrible. SES light flashes, but I can't read the code due to not having a scanner and not being able to drive it to Advance/O'Reillys.

Any help is appreciated, thanks guys.
Old 12-24-2015, 04:07 PM
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Just unplugged the rear o2s and got the no improvement.

Also I've noticed the first 1/2 mile or so of driving the car runs like normal even at lower rpms, then it'll just sputter out and misfire.
Old 12-24-2015, 04:48 PM
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Check the coolant temp sensor.
Old 12-24-2015, 05:10 PM
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Need more info here.
Did you use an off road ypipe, or catted one?
Is the car tuned after putting on the headers?
You need to get the car scanned to be sure what going on here.
Old 12-24-2015, 05:13 PM
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It's an ORY. Car has not been tuned at all, AIR system has also been removed so it definitely needs to get tuned to remove the codes from that junk as well.
Old 12-24-2015, 08:14 PM
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Inspect for vaccum leaks or anything you could have knock around or off. Check coil connections and plug wire connections.
Old 12-24-2015, 09:28 PM
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Sounds like a fuel trim issue. Be sure you don't have any leaks and it might be wise to swap the O2 sensors to rule them out. At higher throttle you O2's will be hotter and provide a better reading if there's a small leak, and at wot your ecu doesn't use the O2's for fuel trim tuning. Likely runs well for that first 1/2 mile because it's still in open loop.
Old 12-24-2015, 09:33 PM
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Originally Posted by Mongoose350
Sounds like a fuel trim issue. Be sure you don't have any leaks and it might be wise to swap the O2 sensors to rule them out. At higher throttle you O2's will be hotter and provide a better reading if there's a small leak, and at wot your ecu doesn't use the O2's for fuel trim tuning. Likely runs well for that first 1/2 mile because it's still in open loop.

Leaks before the front o2s? Or where else would really effect it?


Thanks for your advice.
Old 12-25-2015, 12:22 AM
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Originally Posted by WhiteLightningGTP
Leaks before the front o2s? Or where else would really effect it?


Thanks for your advice.
Before. It would have to be either pretty big, or very close to the O2 for it to be so noticable. It could be after the O2 but it'd have to be pretty close. If you have a leak at the collector, that might do it. It's probably making one side read leaner than it should and the ecu keeps trying to alter the fuel trims and is causing it to run poorly.
Old 12-25-2015, 12:36 AM
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You need to get the car scanned to be sure what going on here.
Old 12-25-2015, 11:34 AM
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Was able to scan for codes

P0171
P0101
P0174
P0300
P0418
P0420
Old 12-25-2015, 07:41 PM
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Pulling the rear O2s does nothing but adds codes. What
is the response to pulling the fronts, forcing it open
loop? Try that along with resetting the fuel trims (scan
tool, or disconnect battery) to see if false trimming is
your problem.
Old 12-25-2015, 09:27 PM
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P0300 is multiple misfire.

Couple things, flashing engine light means severe miss, don't drive it, it damage to cats from excessive fuel.

Your codes reveal 2 things.

1. Check the connections on your mass air meter. It's pulling a code for that. It's likely unplugged, or damaged.

2. You're getting a lean code. This means that you're sucking in fresh air before the o2 sensors. This will cause it to run pig rich. You have an exhaust leak (s)
Old 12-26-2015, 12:18 PM
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This ended up fixing the issue. I had the clamps sideways because it looks much cleaner, little did I realize that it pinchedthe side instead of the slots on the top and bottom. Car feels a bit doggy, but I'm blaming that on no tune and still having old plugs in it. Thanks all for your help.


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Old 12-29-2015, 09:51 PM
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It really shouldn't run that bad without a tune.. i ran the same set up without a tune for a few weeks and still had noticeable power gains..you still have misfire codes??



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