I recently bought a '96 Legacy GT with 195,000 miles from a friend. It has a history of the dealer changing the EGR valve. It is now showing the codes P0304 ( cylinder #4 misfire) P0400 ( EGR flow malfunction) P0420 (catalyst system efficiency below threshold). It runs good but mpg and pick-up seem a bit low. My question is if these could be related and what problem should I tackle first.
Thanks, Ted
At this mileage you're probably due for the 2nd possibly 3rd front (at least) O2 sensor. Possibly new cat converter - some mechs have a pressure test for the cat using the O2 bung hole.
Not clear in your post, but if the other codes come back immediately after clearing them they could be real second and 3rd issues, but I have read about bad cats causing misfires/pinging/loss of power etc.
If you want a lot of info and help on tackling these problems yourself check the forums at
Carl
1 Lucky Texantedt wrote:
The "low catalyst efficiency" is usually caused by air entering the exhaust system where the headers bolt to the head (exhaust manifold). Buy new gaskets, studs, and nuts and watch the torque. You might be able to get away with just gaskets but chase the threads on the studs and nuts if you do it that way otherwise the torque readings will be insufficient to seal things up and additional torque will break a stud. TG
err, I see this is a fairly old post, but could you explain "chase the threads ..." for this old feller?
Thanks,
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