P0300 error code

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P0300 error code

Postby WIMorrison » Sun Aug 02, 2015 8:33 pm

I have been recommended to join and post my problem here by people on my usual haunt in the Volvo forums, I am sure that everyone will be as helpful as people are to each other there :)

My daughter purchased a Mazda MX5 Mk2.5 1.8 (2003) some weeks ago and it has started throwing up P0300 fault codes and the freeze frame has said Closed Loop(1) today and it was Open Loop(3) the other day.

If I clear the code it comes back after around 75mls, yet the car is always running smoothly.

Based upon what I was able to find in web searches, I have mchanged the plugs, replaced the HT leads and even swapped a coil pack over and yet the fault comes back :(

Any suggestions on what it might be, it is doing my head in.

Many thanks - all suggestions welcome.
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Re: P0300 error code

Postby drumtochty » Sun Aug 02, 2015 10:27 pm

I think you may have to wait until the part fails to find out what is the problem as all you are getting just now is something is not working properly sometimes.
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Re: P0300 error code

Postby joeytalent » Sun Aug 02, 2015 10:58 pm

Have you tried everything in this thread: http://forum.miata.net/vb/showthread.ph ... ight=P0300 ?

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Re: P0300 error code

Postby WIMorrison » Mon Aug 03, 2015 5:57 pm

Thanks for the replies chaps, took it to a local garage today and they haven't found anything either with their super,duper diagnostics tool - they were however very dismissive of my £7.99 app on the iPhone, though their's didn't show anymore that I already knew.

I guess it is keep reading the codes until something other than p0300 comes up and then I can fix that code.

Wasn't it great when all we had was points, a distributor, coil and a carburettor - I could fix all of them with ease :)
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Re: P0300 error code

Postby joeytalent » Tue Aug 04, 2015 5:13 pm

You've checked all the spark system - I'd try looking at the air / fuel as well. The fault code means it's randomly misfiring on multiple cylinders, so it's unlikely to be a single injector, so look at stuff that affects the whole engine:

Vacuum leaks - get some carb cleaner and spray around the hose joins to see if the engine dips when it's idling. Check the connections for the air flow meter (although that would probably be a different error code).
Fuel Delivery - is the fuel filter clogged? Are you getting good pressure at the fuel rail?

And yes, there's rarely anything the cheaper apps or scanners can't do that the more expensive equipment can. That's the benefit of more modern cars adhering to a proper standard when it comes to OBDII and fault codes. A lot of mechanics will have been introduced to fault diagnosis systems that you have to buy for each manufacturer though, as they were introduced through the 90s, so understandably have a healthy mistrust for anything that's cheap and claims to do everything.
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