kkbutler11

I just purchase my first RX-8. It's a 2007 auto with 83K miles. I am the third owner and long story short the first owner sold it to a young lady cheap and told her it didn't run due to the catalytic converter needing to be replaced. The young lady took it to a muffler shop and couldn't afford to get it replaced then sold it to me. I believe the RX-8 hadn't ran for almost a year when I purchased it last week. I was able to get for a great price and its body/interior seem to be in great shape. Not knowing any history on the RX8 i purchase it assuming I would be rebuilding the motor and expected the "no compression" issue.

First thing i did once i got the car in the shop was removed the cat. After removing the cat the RX-8 started instantly but would rev up & down for 5-10 seconds then die. It idle real rough and when giving it gas it would backfire. I then replaced the coil, plugs, wires, mass air flow sensor and air filter and it seem to make it start easier but still had the same idling issues. I am not pulling any codes other than the P0037 which i believe is because i do not have any cat or midpipe currently installed. I have reset the ECM with the brake peddle push and it seem to let the vehicle idle a little longer before it seems to just shut off.
I noticed through trouble shooting that when i pulled the plug wire on rear rotary it didn't make a difference on starting and still idle rough, so knowing that I tested the lead and trail plug for spark and was able to confirmed I had spark. Here is where I am confused. I had the air box removed today with the MAF disconnected and the accordion removed and I started the RX-8 and it started no problem, idle smooth just like a dream for about 30 seconds then it just died. The car would not start again until I plugged the sensors back in and it started back to a rough idle, seems to be running real rich then just shuts off.

I am in the works to get a compression test done on the motor, I know I need one. But at the same time the engine doesnt seem to be just stalling it's more like its just shutting off. Since I do not have a midpipe or catalytic converter installed right now with the O2 sensor being unplug could it cause the issue? It seems like something is causing the rear rotor to either not fire or the timing is off. I still in my head expect low compression in the motor but I feel like I should be able to get the RX-8 running smooth rather the compression is low or not especially since it ran perfect for about 30 seconds. Any help or suggestions would be appreciated.

Loki

iTrader: (1)

Which plug did you pull? Trailing (upper) plugs are not used when starting, and not super necessary when idling, so what you're seeing makes sense. Pull the leading (lower ) plug and you should see a difference. Also since you undid all the connections make sure the correct coil is connected to the correct spark plug position. There's a diagram you can google for. It's possible the shop or previous owner messed this up.

Put the intake back together and make sure it's airtight. No cracked or open hoses. Some instability while idling is normal after disconnecting the battery, but it should learn if you leave it alone for 5 minutes and go easy on the first drive. Watch the airflow value (grams/sec) and fuel trims on OBDm. If you can get a smooth idle, it should be over 5 g/sec and 0 fiel trims at 800 rpm. If it's not, report back.

Is the intake original? Are there any mods on the car? Was the catalytic converter actually broken or clogged?

It's not the O2 sensor, they're not used when starting or until they warm up, and the rear O2 doesn't make a difference anyway.

I would also check the baro sensor. See if it unplugging that (while the intake is assembled and MAF plugged in) makes a difference

kkbutler11

I pulled both rear plugs, trailing and lead wires and the vehicle starts and idles the same. Its like the rear rotor plugs aren't firing even though they both tested positive for spark. I've only found one good diagram of the plug wires but it seems straight forward from left to right on plugs to coils.1st and 3rd coils should be the front and rear rotary lead plugs.
I will try to get my readings but i have the original intake but the latches on the box are missing. The box seems to be closed semi-tight but i have held it tighter while running with no difference. I haven't ruled out a vacuum leak but I can't find one either.
I just gutted the cat today (dont judge) it was completely clogged and the car wouldn't start with it on. I placed it back on the vehicle just to keep the noise down while trying to start it. I intend to replace it but until i find out if ill be doing a rebuild i didnt want to spend the extra $$$.
There is no mods on the vehichle, all original and everything is clean under the hood for a 2007. No history on the car but it looks well taken care of mechanically under the hood compared to all the others ones ive seen.
I did unplug the baro sensor last week and it didnt make a difference but will try again soon.
My compression tester should be in tomorrow but I have several days or shift work ahead of me so it might be a little bit before I can get back at it.

My list of things to try:
Check for vacuum leaks using carb cleaner
Check fuel pump & filter
Check/clean Ecentric Shaft Position Sensor
Clean throttle body
And of course Test the compression
Please feel free to add anything to the list. I feel like at this point its about getting lucky. Thanks for the reply