Noob here, I read around on here a bit, or a lot, but maybe not enough so apologies if this is a dumb question.

I just recently got an 06 8, the guy I bought it from said he had it compression tested by Mazda about 13 months ago and they rated it an 8. 10 being perfect and 5 needing rebuild (as he put it). So theoretically the compression should be mostly alright, but I can't test it anyway since the car dies once it gets warm and cannot be turned on at all until it cools.
Car turns on very easily when it's cold and idles mostly fine but with occasional jumps or drops. Yet, once the car gets to normal temps it shuts off immediately unless I keep it above 1k revs.

If I keep the gas on the car will drive perfectly fine, but the second it hits 1,000 the car instantly dies and I have to wait about an hour until I can turn it back on, or a little longer.
It has a light that says it's misfiring, and maybe I'm inexperienced but I don't notice any issues when driving so that leaves me a bit confused. I've driven at 10 and 20 and even all the way up to 90, it's kinda slow but it will rev up to about 9,000 I believe.

So far I've done spark plugs, wires, cleaned the throttle body and intake (both of which had small traces of oil I think), cleaned the MAF, all of which didn't improve the idle, hot start ups, or "not shutting off" while hot at all.
I've also runned it and gunned it for a bit to see if it's the cat however I didn't see it glowing at all so I am unsure.

I'm thinking maybe getting 4 new coils and also taking off the cat and physically looking inside to see if it's clogged up. Is this the right direction or should I try something else first?
Sorry again if this has been answered before, I appreciate any advice, thanks!

 

You can definitely check the cat and replace the coils, but while shutting off can have many causes, not being able to restart again until cool only has 2: loss of compression or fuel pump dying. If it gets better with a full tank of gas, it's more likely the fuel pump. Otherwise compression. Compression isn't 1 number, it's 6 pressure numbers at X rpm. See if the previous owner can provide that. If he can't, either the dealer didn't know what they were doing, or he didn't or both.

Also 8kg/cm2 is good compression, but no car is at 10. They start between 8 and 9. 7 is borderline, 6.9 is failing. All numbers normalized to 250 rpm.

 

Ahh I see, it's likely the compression then. Car has half tank of gas so fuel pump is probably alright.
Would it even be worth the 200$ or so to do the coils or is there a way I can see for sure that they're bad? I'll check the cat either way, tho is there any possibility that fixing both the cat and coils (assuming they need replacing) could fix the shut offs?
And, since the car shuts off is there any way I'll be able to test for compression or no? I'd rather know for sure than just assume it's compression and start taking everything apart, but if that's what i have to do then I will.

Thanks for your reply and sorry for the slue of questions.

 

It shuts off warm right? Which means you can do the test warm
The engine doesn't need to run for the test to happen. Even a cold test will give you good indication, compression only decreases with temperature (which is why it stalls out).

Like I said, there are other reasons it might be shutting off, but mot turning back on is a pretty clear sign.

As for whether its worth it, it depends if you plan to keep the car and rebuild or scrap it and move on.

 

Where are you located?

Loki gave sound advice. You don't want it running when testing, so it can be tested hot or cold, though hot will give the most accurate representation against Mazda metrics.

Issue sounds like a compression issue, but any single or combination of issues could imitate the hot stall, such as reaching engine temp and going into 'closed loop', while a sensor is failing. I wouldn't buy ignition coils until you confirm compression is acceptable. If it is failing, best not to have spent the $120+ until you know what you want to do with the car.

 

If it's dying when it gets up to temp, then it's up to temp and ready for a test.
If the cause is low compression, it will be obvious in a compression test if you warm it up to the point that it dies.

If you want to go a step further, use the long skinny pedal to hold the RPM around 1,500 for a minute or two in order to make sure it's properly warm.

 

Okay, thank you both. I have a rotary specific compression tester on the way. I took the cat off yesterday thinking it could be clogged but it didn't fix it at all (ran it just out of the headers). I'll likely "keep it alive" with the gas pedal until I'm sure it's all the way warmed up and then test the compression.

 

I'm in Pinellas County Florida, this is my first rotary I'm gonna learn with this car.. Bought it knowing full well it likely had compression issues. Going garage it, build it, and possibly boost it all at once. This is my first project car I'm super excited.

 

Hi I just did a little more research and also talked to a couple mazda tech's on the phone. I can't drive my 8 to a dealership to get it compression tested due to it dying at idle so I bought my own compression tester to do it myself. Is that a bad idea or does anyone recommend certain testers to use? I saw one for around 340$ but this is the one I was planning on purchasing:
I also noticed in the new buyer's guide on here it said "You can only get it compression tested by taking it to Mazda". I'd really like to have my own compression tester since I plan to rebuild and build up the engine myself, so I'll need to have one handy since I'll be testing it multiple times.
I've also seen people mod regular compression tester's to test their rotary engine's but I feel like that would be quite inaccurate. Has anyone successfully compression test their 8 themselves or know of an accurate tool to do so with?

 

You can test it yourself, the 'buyers guide' is written for non-wrenchers. That tester on Amazon however is not suitable to testing a rotary engine. Reference: https://rotarycompressiontester.com/ -- not the only choice, but a sound one.

 

https://www.rx8club.com/rotary-compr...oupbuy-270189/