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OK, so I've read all the threads and talked to everyone I know. I am getting a P0420/30 error code and a rough idle after my boss manifold install. Ive had several re-tunes from steeda (through Stage 3 Motorsports). Everything kinda points towards a vacuum leak somewhere. I have taken it off and re-installed it with same results. A very rough idle, to the point sometimes it will stall and die. During install I realized that you cannot torque bolts down near as tight as the spec calls for, if you do the snap long before. Is this the problem? Who out there has been through this, any suggestions welcome.
 

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Get better bolts then>? That doesns't sound right. Grab a section of tubing stick it in your ear and move it around the engine bay/intake. You WILL notice it when you get close!
 

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Discussion Starter #3
Get better bolts then>? That doesns't sound right. Grab a section of tubing stick it in your ear and move it around the engine bay/intake. You WILL notice it when you get close!
I used both the bolts provided and the bolt from the old manifold after i snapped the new ones on the boss, they are both identical, no way to torque them to spec, cant believe im the only guy snapping these things off. i snapped one off hand tight not even cranking on it. the installed gaskets on the boss(and stock) look pretty weak, maybe use gasket sealer? I dunno, im a novice mechanic but refuse to let some mechanic screw me for something simple. I have listened and cant find a noticable leak, but still looking, thanks for the help
 

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What is the torque specs you're going by? I know a couple of guys here were trying to torque them to 89 ft. lbs. it's supposed to be 89 in. lbs.

To be honest, I didn't torque mine. I just snugged them down. But I've been wrenching since I was strong enough to carry one.

Did you relocate the purge valve? Have you checked it?
 

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I had a problem with a leak also but it wasnt on the intake, take a close look at your air tube, dont know what your running but I have the airaid cai and its made from cheap plastic that bends if you tighten clamps too much, and u cant see it unless u really inspect it...worth a try...
 

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What is the torque specs you're going by? I know a couple of guys here were trying to torque them to 89 ft. lbs. it's supposed to be 89 in. lbs.

To be honest, I didn't torque mine. I just snugged them down. But I've been wrenching since I was strong enough to carry one.

Did you relocate the purge valve? Have you checked it?
Really BIG +1^
 

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primer2tone said:
What is the torque specs you're going by? I know a couple of guys here were trying to torque them to 89 ft. lbs. it's supposed to be 89 in. lbs.

To be honest, I didn't torque mine. I just snugged them down. But I've been wrenching since I was strong enough to carry one.

Did you relocate the purge valve? Have you checked it?
I think you hit the nail on the head. The bolts shouldn't snap off like that even if there a little over tightened. Foot# and "#s is a world of difference. A little common sense goes a long way.
 

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i bought a boss intake sure i install the fuel rail with intake out of car or install intake and then fuel rail thanks
 

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Discussion Starter #9
Well thanks for all the suggestions, sorry I haven't replied, I have been away from the car for a while and havent had any time to work on her. Got back into it today and cannot find any vacuum leak, and I am only torquing 89 inches not ft (abut 7.9ft lbs). I have the Steeda intake and while it does not fit perfect I dont believe its leaking. Took it off and re-installed it a third time being even more meticulous than before, i just don't know. My tuner (steeda) says it has to be a vacuun leak or a more serious problem with the engine, but she rean like a champ prior to Boss install. It still idles rough and gives off the same P0420/P0430 Catalyst system efficiency below threshhold(b1)/(b2). I am planning on putting the old mani back on this weekend and hoping i can get the old car back. Might just have a really cool wall mount. I appreciate the help, just at a loss of ideas at this point. Thanks for all the suggestions.
 

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Discussion Starter #10
sorry to revive this thread, but really have never found any resolution. No vacuum leaks, no tuning problems found(same tune on similar mods anyhow). Old(stock)mani works like a champ so I don't believe it's a install problem, i torque them to same spec. Anyone else have a good looking boss 302 wall mount. Runs like **** with Steeda tune(stage 3). Love both companies but...
 

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Have you tried spraying small amounts of starting fluid or wd40 around the seal areas of the manifold? I used to use this method to find vacuum leaks. With the engine running spray small amounts and if you hear the idle change, that means it sucked in some of that spray and your leak would be in that area. Be sure your a/c is off.
 

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primer2tone said:
Have you tried spraying small amounts of starting fluid or wd40 around the seal areas of the manifold? I used to use this method to find vacuum leaks. With the engine running spray small amounts and if you hear the idle change, that means it sucked in some of that spray and your leak would be in that area. Be sure your a/c is off.
They changed the formula for WD40, it no longer works. We used to use it to start nitro bikes is how we found out, it no longer works.
 

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They changed the formula for WD40, it no longer works. We used to use it to start nitro bikes is how we found out, it no longer works.
Dang. I better check the expiration date on my wd40! I was using that method a few weeks ago on my dads pick up! Lol
 

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I'm having the same problem...

This is an old thread, but my problem is new. I have a 2013 GT that I recently swapped manifolds on. And yes, now it is giving me the P0420 code. Were there any advancements or solutions before I go tearing this things apart again???
Thanks
 

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If your manifold is seated well with no broken bolts, I would check to make sure the MAF sensor is clean and clear and then check the throttle body to make sure it is opening properly if you are having an idle problem. The 0420 could just be your O2 sensors though.
 

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I did not torque mine down either. I used common sense when tightening the mani. May be the tube slipping off?
 

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I torqued mine properly, and am not having issue with rough idle. Sorry to be in two threads, but I saw this one and then wrote my own. Sounds like I'm going to have to take the thing apart again and just double check everything. Going to stock and then reload the tune too.
 

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yeah same here bro, i just installed the mani a week ago and same thing happened. first off i also snapped one bolt while trying to torque it down to spec. and idle is running a little off, but i can hear a hissing noise. i used carb cleaner to verify nut i didnt hear any changes when i sprayed it. i checked all hoses and gasket. i have a 2015 GT
 

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There is no way you're snapping bolts if you are torquing them properly. Your TW might need calibration. It's a pretty low value and that's where torque wrenches get imprecise. I like to use a beam type for this kind of stuff as you can sneak up on the torque value visually.

Confirm a vacuum leak by doing some datalogging. If you have one, typically your long term fuel trim will be way off on the plus side.
 

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I see this thread is pretty old, but did anyone find the cause/problem ? I have a 2017 5.0 I did a boss manifold and I am having all these problems. Tuner says it’s a huge vacuum leak
 
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