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Matt
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 21984
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a mazda rx8 reg YH05 EJZ after a while driving the engine

Customer Question

I have a mazda rx8 reg YH05 EJZ after a while driving the engine management light comes on fault code p0420 and the car stinks of neat unburnt fuel and loss of power I've changed the catalyst the spark plugs and wires not the coil packs though yet after I rest it goes off and stays off for a qhile but if stay drive from Wales to Manchester it'll come on near destination
Submitted: 1 year ago.
Category: Car
Expert:  Matt replied 1 year ago.
Hello
to get a P420 then the cat is suffering
probably due to overfuelling
I'd say the next step is to check the injector wiring for any signs of shorting out or other damage
and also remove the coil packs from the engine and check the underside for whitish burn marks as this shows where the coil packs fail and it certainly sounds like its not firing on all 4 plugs
it would also be well worth checking the compression pressures on cranking as if the engine has been running for any length of time like this it can have damaged seals
Customer: replied 1 year ago.
Thanks someone also said aomwthing about having to have the vacuum rebalanced or something after fitting plugs I've never heard this before at all have been doing conventional engines for years I build diesel vans Fox a living but rotary is different can you confirm this isn't the case and I'l try qhat you said am I ok come back to you if have any more queries thanks foe your time
Expert:  Matt replied 1 year ago.
Hello I can't say I've heard of that before? so don't worry about itgetting a compression pressure on these is a little different to a normal enginethis video showss howhttps://www.youtube.com/watch?v=k3mW8CzdDy8
Matt and 2 other Car Specialists are ready to help you
Customer: replied 1 year ago.
Hi again I've just removed the coil packs and I have what appears to be a really small white Mark on nunber 2 and the back plate they bolt too seems to be burnt it has soot on it where the other 3 have the original dirty but coloured surface
Customer: replied 1 year ago.
Thanks a lot for your help the coil packs had faiked 3 out of the 4 had white burn marks underneath I will definately recommended to anyone who need your help again
Expert:  Matt replied 1 year ago.
glad to help