I just r2placed a 2.5 with high miles and bad head gasket in an 03 legacy with a jdm 2.0. The car ran perfect for about 2 days. Now it threw a po420 code and barely runs. The check engine light is also flashing.

 

I've never had that code change how a car runs. I'm thinking coincidence, and something else is going on, but there are no other codes.

 

Any suggestions.

 

Thanks

doesn't seem like a an exhaust leak!

 

if the CEL is flashing, should be more codes than the P0420

 

front O2 sensor or MAF or maybe clogged exhaust ?

 

you may need to start with first principles; check for slipped timing, A:F sensors, vacuum gauge testing, look at live data......

Edited June 1, 20178 yr by 1 Lucky Texan

I've had a flashing check engine light with no misfire code before. I think it take a little bit to set.

^^^ didn't know that could happen.

I had it happen on a Chevy once and just thought it was specific to Chevy or maybe domestic. But then my buddy who has a 03 wrx said he occasionally gets a flashing check engine light, and when I pull the codes, there are none (same drive cycle and with SSM) So I'm not missing any, there aren't any. At least according to the factory scan tool.

Misfire = flashing CEL, and converter was probably already bad from the old engine, etc. We see that all the time. Car comes in for major repair barely running - comes back a few days later with a 420 code. Probably not related to the misfire on the new engine per-se.

 

GD

Converter seems good. Now that i have glanced at it. The power steering pump has leaked all down the front of the motor. Tomorrow i am going to open up the timing covers and see how much fluid is in there.

 

Maybe jumped timing because of a lot of atf fluid on the belt?

The power steering leaks never seem to get one the belt despite that appearance.

 

What do you mean by the cat "seems" good. You can tell from looking at it. Check inlet and outlet temperatures. Outlet should be about 100 *F higher than inlet. Otherwise it's not working.

 

GD

Edited June 3, 20178 yr by GeneralDisorder

It was a misfire with no code, just flashing engine light. New coil pack fixed it.

 

Thank you all for the input.