I have been having a hot start problem for a while and put the car to the local mazda garage and told them what had been happening, they replaced the sparkplugs which had no effect. They then told me the compression was low so I changed both housings and internal seals. My car started first time and runs great but still has the same hot start problem. I then got a loan of a diagnostic machine which said the ECT sensor was reading -168 when the engine was hot, as such replaced the sensor. I then started the car and watched the ECT read out rise but when it reached 86 degrees the read then changed to -168. I then turned the car off and it would not start but when the engine had cooled and the read out on the diagnostic was 85 degrees the car started no problem. I tested the sensor in the correct fashion and found no fault I have now had the pcm inspected and no fault was found. Has anybody ever experienced this or got any ideas on how to fix?

Car is 04, 192bhp, 46000miles

 

Wow my eyes
I don't care if English isn't your first language ... holy wall of text Batman.
Phew ... ok
I'm guessing your car is a stock automatic.
Have you got the latest PCM flash?
There was a bad Flash for the 04's ... see last post here
https://www.rx8club.com/series-i-trouble-shooting-95/hot-starting-problem-185768/

Also .. I would get compression test done.

Have you changed the coils? 46k miles is more than enough to burn out a set of stock coils.
How about the starter?
Yes there is a TSB out there for an upgraded starter, the ones in the 03-05 RX8's were to slow.
The new starter will crank the engine faster.

How about plug wires?

While you are doing all this might as well clean the Maf and the ESS.

 

1. Have u tried the 20 stomp on brake pedal reset?

2. How long has it been since your engine rebuild?

 

Good one +1

 

Sorry forgot to add the car is manual,

I had the rebuild done a few weeks ago.

Not too sure which flash is on the pcm, the sticker on it is N3H8 so guessing that means its the N flash

Dont think it could be the starter as the car starts instantly when cold.

I did try the brake trick to clear the pcm memory after the rebuild

I will check the coils and leads over the weekend, but its the engine coolant sensor read out of minus 168 thats throwing me

 

I have that problem sometimes, not sure why because other times it starts just fine when hot. When I add oil to it when it's hot it doesn't want to start either. Anybody have any ideas?? I have a 05 6speed just replaced my plugs with the upgraded ones and coils and wires.

 

Who rebuilt it, I am assuming a local shop and not a dealer? Did you get another compression test done?

what upgraded plugs? You should be using NGK laser iridiums ie OEM plugs.

Also it sounds like your engine is dying, I'd get a compression test done.

 

The upgraded plugs Mazda says will help will starting issues. The hotter plugs. The only other thing I can think of is that I might need a new battery, because if I try to crack it over when it's flooded with the gas pedal in it will only crank it for about 9 seconds before it runs out of juice. Then I have to wait for about 10-15 minute for the battery to have enough juice to try to crank it over again. How much does Mazda charge for a compression test??