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So I bought a used rx8 with a rebuilt engine, they didn't tell me it was rebuilt until I had the check in hand but it drove great and the only issue was the engine coolant sensor light was on,which I neglected to fix immediately because of shipping time. The car drove fine until about a week and a half later when the check engine light came on with a p0420, most likely for the engine coolant sensor. I've been driving on the highway 30 miles out of town about 4 days a week for my job and the first time I noticed an issue was when it misfired once while getting ready to go to work. It started up after a minute of cranking and drove fine for a day or two then had a rough start again, then for a week it would drive and start fine for some days and some days have issues starting.
Now i'm at the point where its been 30 days, about 18 were driven out on the highway and the car is having bad problems starting up almost every time now and the part still isn't going to arrive for another week.
Did I blow my engine!? Will fixing the part help with starting?
After the car starts it drives and idles perfectly fine, and has good power still at full and low rpms with no stutters.
Car makes a grinding noise when misfiring, thinking because the ECT tells it to run lean so it has less fuel than needed to start.
When it didn't start at first it started off by not making any noise at all, just spinning noises then it'd randomly start. Now it spins and makes some chugging noises like it trys to start but wont.
P0420 is the catalytic converter, which, if ignored, will choke and destroy the engine.
However your symptoms don't fit that scenario yet.
Answer these questions please:
How long ago was the engine rebuilt?
Was it a DIY rebuild or Mazda?
Have the ignition coils been replaced in the last 30,000 miles?
Was the cat inspected or replaced at the time of engine rebuild?
Do you see white smoke on start up?
Is the coolant level stable? Did you fix the coolant light?
Has it ever overheated?
Did you or the previous owner do a compression test?
If you believe the computer is telling it to run lean, confirm this by reading AFR and fuel trim with the same tool you use to read codes.
It sounds to me more like you're seeping coolant into the rotor while the car sits, which then makes it difficult to start. It may have been poorly rebuilt or the previous owner may have caused damage. What do they have to say about these problems?
thank you I appreciate the reply!
the engine was rebuilt not to long ago, and it was a DIY im almost certain, the paperwork for the rebuilld is almost here.
Ill have to ask if they had the coils replaced in the last 30k and no the cat hasn't been inspected or replaced since rebuild but it is a aftermarket cat and theres only 80k miles on the car so Im assuming its still fine and the p0420 is for the engine coolant sensor since thats part of a p0420 code.
the car is currently sitting and not being drove until the part arrives to put in
theres been no white smoke, it smells a fair bit amount of gas right after starting and has kept a full tank of coolant.
the bar for the engine temp has never gone past half way, but Im scared that because the coolant temp sensor is broken that I possibly have been overheating it and not knowing because the temp guage doesn't work?
P0420 is catalytic converter. Google it. Did you mean p0420 or a different code?
Aftermarket cats don't live long attached a rotary, its highly recommended not to use them. Don't assume, clogged cats sre the #1 killer of RX8 engines. The original engine failed for a reason, and the original cat was replaced for a reason. These are indicators. Poor coils kill cats, cats kill engines.
Sounds like you're inheriting some of the previous owner's poor decisions.
DIY rebuilds are also not recommended, too many subtleties that if not done right lead to low life expectancy.
So if its indeed p0420, and your coolant temp sensor is fine, thats a good sign.
Do not drive it until the cat and ignition coils are confirmed good. If you start typing "I assume" anywhere on this forum, stop and think twice. See if you can get a compression test so you know where you stand.
Read through the "New and Potential Owners" thread, it has a lot more detail on how things work.
My coolant temp sensor is broken though,, theres a light for it on the dash saying its broken and Im scared Ive been driving it on a closed loop and been overheating it.
My coolant temp sensor is broken though,, theres a light for it on the dash saying its broken and Im scared Ive been driving it on a closed loop and been overheating it.
Do you mean the coolant level sensor perhaps? The light looks like a house or the Lincoln Memorial? There is no light for the temp sensor and the level sensor is know to go bad (along with the coolant reservoir, the sensor isn't really removable).
If the car thought the coolant temp sensor was broken, it would decide not to drive on its own and go into limp mode.
Yeah that sensor, it helps regulate how to send coolant through based on engine temps as well as helps let the computer know how much fuel to push through depending on whether it needs a more concentrated fuel mixture like on startups or less fuel mixture like when warmed up and driving,, and im scared it hasnt been correctly getting engine temps causing it not to be adequately cooled
Yeah that sensor, it helps regulate how to send coolant through based on engine temps as well as helps let the computer know how much fuel to push through depending on whether it needs a more concentrated fuel mixture like on startups or less fuel mixture like when warmed up and driving,, and im scared it hasnt been correctly getting engine temps causing it not to be adequately cooled
There is no light for that sensor. The light is for the coolant level sensor, which only measures the level in the overflow bottle.
Now it wont fire anymore and just gives a spinning noise with an occasional clunk of it about to start
If the ignition has failed, it's possible it has flooded. Google 'RX8 deflood procedure'
I would get the spark plugs out and see what the deposits tell you. You'll know right away if you're seeping coolant, or if a coil is not firing, or if it's flooded.
Ill try to get it in the driveway to remove the plugs,, is it going to be possibly to get them out with a normal deep socket ratched and extender or am I going to absolutely need swivel for the tool to get at it
Ill try to get it in the driveway to remove the plugs,, is it going to be possibly to get them out with a normal deep socket ratched and extender or am I going to absolutely need swivel for the tool to get at it
I've done it without a swivel, but I've also broken a spark plug that way. So... swivel probably best :/
Ill try to get it in the driveway to remove the plugs,, is it going to be possibly to get them out with a normal deep socket ratched and extender or am I going to absolutely need swivel for the tool to get at it
Definitely use a swivel joint. You will break the spark plugs without one. You should also do a compression test as well just to see how the health of the engine is. The coolant light being on can mean either low coolant (obviously) or the sensor is just broken. In the latter case, you will need to put a new coolant overflow bottle in. Did you see if you still have coolant in the car? Its possible it could have overheated if it was being driven with no coolant.
Thank you for the reply!
The coolant is definately full and has stayed full with no leaks
The part thats almost here is the coolant resivour which comes with a new sensor.
Is it possible that thats the issue though? Because that sensor helps the engine choose fuel ratio.
Looking at an ob2 reader the sensor is locked on hot Im pretty sure. And like mentioned above because the sensor thinks the engine is always warm im pretty sure it doesnt give enough fuel on start when engine is cold so it doesnt fire up
I did accidently take the coolant lid off when the engine was still pretty warm yesterday and a puff of smoke came out of the resivour, would that ne normal?
Thank you for the reply!
The coolant is definately full and has stayed full with no leaks
The part thats almost here is the coolant resivour which comes with a new sensor.
Is it possible that thats the issue though? Because that sensor helps the engine choose fuel ratio.
Looking at an ob2 reader the sensor is locked on hot Im pretty sure. And like mentioned above because the sensor thinks the engine is always warm im pretty sure it doesnt give enough fuel on start when engine is cold so it doesnt fire up
It wouldn't cause any real issues. I drove mine with that light on for months with no issue. Your problem is different. Have you tried to deflood it? When you take the plugs out make sure no liquids come out. I'm guessing it's either bad plugs wires or coils. If those aren't the issue, do a compression test and hope it passes. Might also be worth your time to change out the thermostat if you get it running again.
Last edited by CaymanRotary; 08-28-2019 at 11:19 AM.
If you're talking about this light on the dash it won't cause any damage to the car. It's just there to tell you the coolant level is low, most people will unplug the sensor to stop the light from coming on and just keep an eye on the coolant levels. No damage comes from this light
And last night after driving it home after a 30 mile drive I shut it off then tried to restart it to see if it would start back up and it wouldnt, so I dont know how it could be flooded
If the engine was warm when you opened the reservoir, a puff of vapor condensing rapidly (what you call "smoke" but really isn't) would be normal.
That light is the coolant level sensor. It's integrated into the reservoir. Drive with that light on all you want as long as you make sure the coolant level is correct.
The coolant temperature sensor is in the back side of the front cover near the thermostat housing.
And last night after driving it home after a 30 mile drive I shut it off then tried to restart it to see if it would start back up and it wouldnt, so I dont know how it could be flooded
Honestly, the engine could actually be broken if it wont start hot. You need to do a compression test and if it passes, do a block test to make sure you dont have a coolant leak.
08-28-2019, 02:22 AM
