Hi all again. Tackling more issues on my RX8 project. I've turned to it's engine issues now, it failed it's emissions test at the fast idle, not quite certain why but my original theory was the cat. Ran the vehicle through diagnostics and there were zero faults found, I manually checked all sensors afterwards and everything shockingly was very good. I'm still having issues at the hot start with the engine however as well. Only thing I could blame it on was the catalyst so I did a temperature test on it, the main catalyst seems to be turning over fine readings, however the secondary cat is showing higher temperatures going out the cat than the temperature going into the cat. Not sure if that would be the issue though as I've not seen a car with two cats before however it doesn't have sensors in it so I guess it would make sense that it wouldn't cause any codes or anomalus readings. Any help would be appreciated

Thanks in advance

 

This car only has 1 cat?
Are you thinking of the front and rear O2 sensors? Yes it's normal for the exhaust temperature after the cat to be higher than before, it's oxidizing the remaining fuel and producing heat. Also the sensors don't really have a way to measure temperature, it's inferred from other parameters so O wouldn't count on it.

The best way to check the cat is to take it down and inspect visually. You may need a new front gasket donut from Mazda, they're not very reusable and sometimes leak after reinstalling

 

Yeah just realised I misinterpreted it a fair amount lol. Probably been working too late into the night on it. Yeah been measuring cat temps with a fluke infrared tester trying to figure out what I'm doing with it. Got told there's a chance of bad Injectors but judging by the fuel trims and O2 readings being fine I doubt it

 

Youe ignition could be weak. Spark plugs, wires and coils have about a 25k mile change interval. Shorter for spark plugs depending on how it's driven. It's the #1 killer of engines and it's silent.

What exactly are the hot start issues?

 

Sparks and leads were changed by the previous owner and had very little miles out on them, iridium NGK sparks on 8.5mm "performance" leads. Not sure about coils though. When it's cold it starts within a second no problem. When it's hot it starts struggling though, the engine will get hot, and then when shut off, it will start again but with extra cranks. Only under motorway driving will it refuse to start after (had to wait 3 minutes at a petrol station last time it did it until it would start again). When it does start though it has a tendency to puff black smoke a bit afterwards then it'll clear up and be fine, it does idle rough a bit sometimes but not all the time, it's very random and doesn't always happen.

 

You definitely want to replace the coils if you're not sure how old they are. Hot start issues are never a great sign, often indicate loss of compression, but combined with the failed emissions test, I would replace the coils so you get your MOT at least. What year is the car? Mileage? Does it have the updated starter? The 2kW starter from 2009+ could help with the start issues.

May want to look into a compression test to see what you're working with.

 

2003 with 70k miles on it. Got the new starter on it already. I was encouraged to blame it on compression but I was pretty certain the emissions failure couldn't have been caused by compression because it surely couldn't be that bad so I decided to see if I could find another problem. Gonna be a task to find a proper tester round here

 

I'm going to have a look at the coils in a few days on it and figure out what brand they are

 

Yeah just pulled the coils out finally now I'm back in the country. Looks like they're the original coils. How on earth they're still working at 69k miles is past me but I guess at least they're probably the issue for the emissions and hot start issues. Not sure why the previous owner put new sparks and leads but not coils, kinda weird

 

 

Been a while since I did anything with it, here's an update. I put new coils in it, it definitely runs better now and it won't ever fail to start hot however it is still hesitant to start hot and my long term fuel trim rarely goes below 6%, I ran it up to 2500rpm like what was done in the MOT to see what the whole fast idle thing was about. It reads between 0.04 and -0.03mA at the fast idle on sensor 1, apparently this isn't what would be expected of an RX8 at the fast idle? Not sure, as far as I've checked there are no vacuum leaks, exhaust is ok, so I'm presuming if there really is an issue and it's not compression it's either the sensor or fuel injectors

 

Hot starting issues does point towards issues with compression, so dont rule that out.

 

Yeah I'm leaning more towards that being the issue, however I noticed there's a faint smell of petrol in the car when it runs, I pulled the cover off the pump and as I suspected it's making a very strong smell of petrol only when it's running so I'd be inclined to say that's dropping fuel pressure

 

fuel pressure is easy to check