Backfire?

trader · Postby **trader** » Fri Jan 20, 2012 10:11 am

I went on a coffee run with a few other mx5's on Tuesday and while just cruising along I thought I got shot at or blew a tyre. We stopped but could find nothing wrong. Drove off and a few minutes later as we neared Bungendore it happened again - so no gunshot! I was doing 100 and not on over run. It hasnt done it since but wondering if a clogged cat converter would cause this. Cant imagine what else it would be other than a fuel explosion somewhere. Havent been able to do it on overrun which is weird to me.
Any ideas?

pcmx5 · Postby **pcmx5** » Fri Jan 20, 2012 12:06 pm

Perhaps you could get under the car and have a look at the exhaust.If a cat is blocked the exhaust will ussually ,but not always, run hot and the pipe(external) will show that ,by being different to normal, clean, or sometimes white. If the cat wasn't blocked for long then this won't show.If the cat is original then you can bet a new one would be a good purchase but on what you have said it is hard to say what is the cause.

Good luck,

Peter.

hks_kansei · Postby **hks_kansei** » Fri Jan 20, 2012 12:27 pm

Being an NA you can simply remove the cat and look.

It's flanged on both ends, just undo, take it out, and then shine a torch inside.
You should see a nice even mesh pattern all the way through (will likely have bits of carbon through it too)

note:
DO THIS WHEN THE CAR HAT NOT BEEN STARTED FOR A FAIR WHILE!!
Exhaust, hot, etc.
Plus, cat's tend to hold heat longer than the rest of the exhaust.

manga_blue · Postby **manga_blue** » Mon Jan 23, 2012 10:26 am

Backfire in the exhaust means that unburnt fuel has gone into the pipes and then been ignitied there. Typically it says that your injectors are feeding fuel OK but there are drop outs in the spark. Faulty coilpacks, plug leads or plugs are the main things that cause it.

Pic of a muffler from a Toyota with a faulty coilpack at the local exhaust shop might give you the general idea.

Toyota Exhaust.jpg