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Rear Exhaust Manifold


Synesthesia
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Originally posted by "ken inn"

 

for the last year and a half, i have been getting the p0421 code. it has been getting more and more frequent, changing out the o2 sensors did not make a difference. so, today, i changed out the rear exh manifold. engine is a 2.3. all references to bolts/nuts is the head size.

after searching the net, the best price i found for the manifold was 423. checking albanymazda, the new list price is 416. since i get an employee price, it was 358, delivered. i also got the exh manifold gasket, 2 Y pipe gaskets, and 2 ring gaskets. i found out later that a 3rd one is needed(main cat to resonator). here is what i did. first off, i have access to a lift, and a friend to help.

 

pull the right wheel, and splash shield(all 10mm bolts, and 1 screw clip). unbolt the left splash shield, and you can let it hang. this will give you access to one of the bolts on the y pipe to main cat. pull the front post cat o2 sensor(it is in the Y pipe), and drop the Y pipe, 2 3 bolt flanges, 14mm, and 1 2 bolt flange, which goes to the main cat. unbolt the main cat from the front resonator(2 17mm nuts), unbolt the resonator from the rear exhaust. you will need to pull all 3 pieces. pull off the rubber hanger on the rear of the resonator. the main cat is supported by 2 hangers, but they are attached to a crossmember, held on by 2 14mm nuts/bolts on each side. dont bother disconnecting the hangers, just unbolt the crossmember, and drop it with the main cat(here is where a helper is needed). it took a while for us to figger this out. pull both sensors on the rear cat. if you pull the egr pipe first, getting at the pre cat sensor is a bit easier. the nut size on the egr pipe is 23mm, i used a box/open, but i think a 23mm crows foot would work better. then pull the heat sheild, 3 10mm bolts.

 

there are 5 bolts and 2 nuts holding the exh manifold to the head. the 2 nuts are top center, the rest are bolts, all 12 mm. what i do is first loosen them all, then pull the bolts, and leave the nuts for last. be careful with these nuts and bolts, they are some different alloy, or stainless, not mild steel. most of the exh side stuff is not magnetic, or just barely. i have these little parts trays that are magnetic, but some of these did not stick.

 

the manifold is a real bitch to get out. my friend john, who owns the shop where i go, does this every day. he was convinced he could get it out, and after about 15 minutes, we did get it out. there is a LOT of stuff in the way, esp the power steering lines. i even loosened a bracket holding the lines, but even then they barely moved. i was ready to pull the jack shaft, then it would have dropped right out. here again, 2 pairs of hands got that sucker out. pulling the jack shaft would probably have added about an hour to the job, but it would have made it way easier. the new manifold went right in. i left it hanging, and took a water break.

 

there are no tricks to reassembly. mazda has used a lot of special alloy stuff, so there was nothing much rusted. it all broke free pretty easily. i have a special o2 sensor socket, and some really long extensions and universal joints, which came in handy. i have all 6 point sockets, some with universal joints, and they also came in handy. sears box racheting wrenches were perfect for some of the nuts/bolts. the top sensor is tricky, i used a 8" extension on the sensor socket, then another 12" extension on that, and it works perfect.

 

i cannot imagine doing this without a lift. the only air tools i used was for the wheel. the next time i do this, i think pulling the jack shaft will be a lot easier, and it will certainly give about twice the room in there. when we pulled the manifold, it was still quite hot. all told, it was about 4 hours, i took 2 good breaks. i think it can easily be done in 3 the next time, but the cats will be really hot.

the black car has been throwing a p0173 code, next week i will probably pull the intake, and replace all the tees and vacuum hose. that job looks a lot easier, but might take longer.

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