Civic4metoo

Got a 2004 Civic Ex engine that blew up in my sons car...my son and I swapped in a JDM D17a engine. Just cant beat the deal on those motors. Looks brand new with super tight compression. Oil still looked new in it....we swapped it out easy enough with lots of reading on this site. Car runs really nice but gas mileage seems to be below average. Only code it throws is a PO420 bank 1 catalyst (o2 code I believe) Any idea if we need to throw in a different o2 sensor because of the swap? Kept the Ex harness ,ecu etc.....think we only had to change out the oil press switch,harness and oil pan on the jdm engine. This swap was for economy and longevity only....not trying to make it faster.Thanks in advance for any help

ezone

No, that's a catalytic converter code

Civic4metoo

Thanks Ezone....was hoping you would reply! I could tell from reading on this forum that you definitely know your stuff with these cars. From some reading I have done on other forums I thought I read that you might have to switch the secondary o2 to a wide band or narrow band sensor after a jdm swap......I will hook up to the car tomm and try to get a reading on the o2's . I guess it would be a bad o2 or cat.....or small exhaust leak maybe. Fun fun fun.....just bought my daughter an 03 civic lx but the trans is going....gonna try a jdm trans swap with that. She will just have to live with the cel going from bmxa to slxa...might try and rebuild her trans after its out also. Thanks bro

ezone

Did you reuse your original exhaust manifold and pipe and cat and both sensors?



Assuming you reused the original parts,
How many miles on it?
How did the last engine fail?
Did it have cat code before the last engine blew up?
Did the engine failure cause the cat to fail?

Civic4metoo

Yes we used the original manifold,cat and o2 sensors. 212k on the old motor...he basically overheated the motor a few too many times(head gasket). Was gonna just try throwing a new gasket on but with the miles on the engine and the cost to do the head properly....I just went with the jdm. A little bit more than doing the head but geez...the inside of the jdm versus the original was night and day. Jdm literally looked brand new inside and out while the old one was coated with carbon/sludge inside. I should have taken pics and posted them up when we did it. Oh and there was no cat code prior to swap. Thanks Ezone!

ezone

Erase the codes. Drive it a few days. See how long it takes for the code to return.

If it resets a few times and you erase codes a few times and it keeps returning, then look into fixing it

The mileage alone is plenty to wear out the cat.
Antifreeze ingestion from a blown head gasket/warped head can ruin a cat, and ruin sensors too. (but you don't have codes for sensors, sooooooo)
Oil consumption can slowly ruin the cat as well.

If there are no exhaust leaks between the engine and cat, the computer is in control of the fuel, no codes related to the sensors themselves, I'd punt the cat. Beware of cheap cats.

Civic4metoo

Sounds like a very good plan--will do. Thank you much for help!