2004 to 2020 Mazda 3 Forum and Mazdaspeed 3 Forums banner
1 - 13 of 13 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter · #1 ·
Hi!

Short version: P0171 on a 2014 Mazda 3, exhaust leak between the exhaust manifold and the downstream O2 sensor flagged as a possible reason, went to a weld shop to get it fixed, P0171 was still there. Mazda tech was not happy with the weld quality, and said that the joint is still leaking. Went to Monro Muffler as per Mazda tech's advice, and they told me that nope we can't fix it and you'll have to replace both (manifold and pipe).

The flange joint between the manifold and the cat pipe is gone now, and the exhaust also produces a throaty roar for a second occasionally. Leak was there on both sides of the flange I think).

Do I just need to find a better welder? Or am I looking at replacing both the exhaust manifold and the cat + pipe?

Automotive tire Motor vehicle Hood Automotive exterior Automotive design
Automotive tire Motor vehicle Hood Automotive fuel system Automotive exterior
 

·
Registered
2013 Mazda 3 i Hatchback
Joined
·
361 Posts
Ouch, that sucks. Looks like you got burned by the Right/Fast/Cheap choice. Of those three things, you can only have two, and it looks like the weld shop gave you fast and cheap, but it sure wasn't right. That said, if they removed the flange and replaced it with welded-in pipe, the flange was probably rusted out anyway and you would have needed to replace the parts that you are replacing now. But you are paying twice this way. Not cool.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #4 ·
Hie seem to have a similar issue. What other symptoms did you experience apart from the CEL (P0171). Am getting terrible gas mileage and cold start misfiring.
My gas mileage seems to be alright, maybe marginally lower. Mid-20 mpgs in city, probably mid-30s on the interstate, but haven't done a lot of long distance driving recently.

Other symptoms I have:

1. Idle is not super rough, but it is not stable idle. It probably cycles between the 650 rpm and 720 rpm range.
2. This is also aligned with my LTFT and STFT numbers, which I'm monitoring with an OBD scanner. My LTFT is 20%, and STFT cycles between 0% and 15% at idle. It gets better at higher RPMs.
 

·
Registered
Joined
·
5 Posts
I'll run a test over the weekend and share my fuel trim readings. Kinda puzzled now what the cause would be. I've checked for:
Vacuum leaks
Vapour canister valve
Cleaned MAF and O2 sensor
Changed my plugs
I'll have the exhaust inspected over the weekend and probably get the intake checked and cleaned too. Hopefully we'll diagnose it.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #6 ·
I'll run a test over the weekend and share my fuel trim readings. Kinda puzzled now what the cause would be. I've checked for:
Vacuum leaks
Vapour canister valve
Cleaned MAF and O2 sensor
Changed my plugs
I'll have the exhaust inspected over the weekend and probably get the intake checked and cleaned too. Hopefully we'll diagnose it.
Good luck! I've tried the MAF and O2 sensors, looked for vacuum leaks (mechanic couldn't find any visually, not sure if Mazda did a smoke test) - nothing. The car was with a Mazda dealer for 6 weeks (they were shorthanded and also working with the regional tech to diagnose it), found some exhaust issues, asked me to get them fixed from outside, I've done that and it's still there. Haven't done the valve or plugs.
 

·
Rubber side down
Joined
·
279 Posts
That is some very mediocre exhaust work. The bends alone are not done with care, I double the welding was either. MIG welding is NOT that difficult. Find a better shop who knows what they're doing and it may still be fixable, although the welding seems to be very close to the O2 sensor. I am hoping they took out the O2 sensor when they were welding so as not to damage the sensor.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #8 ·
That is some very mediocre exhaust work. ... I am hoping they took out the O2 sensor when they were welding so as not to damage the sensor.
They did not take the O2 sensor out. I don't know if it's damaged.

Since you seem to know a bit about welding, can you tell me if I should ask/insist on some way this be done? Should I ask for this bend to be chopped out, and some flange-joint welded in its place? A recurring problem seems to be that it's hard to seal the weld on the other side, and also the pipe they installed is a somewhat smaller diameter than the OEM stuff.

This is my first time dealing with exhaust work and I had no idea what to expect. I'd happily pay someone decent to fix this but in the Pittsburgh region, all I've come across until now is this sloppy work, another welder who was not impressed with this but tried to fix it half-heartedly (without dropping the pipes), and ended up leaving a gap on the other side, and another muffler shop that refused to touch the mess.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #10 ·
Can't you just buy a replacement and some new nuts and bolts?
CK
A replacement exhaust you mean?

I'd need to get both a new exhaust manifold and a pipe. That seems to be around $1200 in parts if I get the OEM stuff online. Then I'll need to find someone who'd be willing to install my parts, should be doable though.

I have one or two leads that I'm considering approaching, if not I'll bite the bullet. It just seems like a waste if most of it is fine.
 

·
Rubber side down
Joined
·
279 Posts
Junkyards/pick-n-pulls may have some of what you need.. you would need the tools to remove the parts and the ability to transport it though.
CK
I agree. If you cannot find a reputable shop that knows what they are doing, then find either a junk yard or maybe even Ebay. Ebay may cost a little more for the parts than a junk yard, but it is easier to find what you need without driving around and crawling under cars.
 

·
Registered
Joined
·
2,215 Posts
Try searching with car-part.com. it's a search engine for junkyards. They don't always list everything, so you may have to contact them and ask if if you can buy a part like the manifold. Many junkyards will pull the parts for you but they tend to charge a bit more for the service than a yard where you pull the parts yourself.
 
1 - 13 of 13 Posts
Top