Its a 6 speed. A used original intake is on the way. Will swap it out the K&N withe stock box and see if it makes a difference.
Failing that, what else could be up?

 

Failed ignition, clogged cat and poor intake are the main candidates. You've eliminated 2 of them assuming everything is connected correctly and there aren't pieces of cat downstream. So all eyes on that garbage intake.

Next step if that doesn't fix it, you'll want to get more detailed sensor data from the ECU: fuel trims, measured airflow. etc.

 

ive tried both v1/v2 of the k&n typhoon intakes very early on and neither gave me mpg that low

 

Nah, you definitely have something going on. I wonder if your fuel pump is creating too much pressure and you're just dumping fuel into your engine. It is possible you also have a stuck open fuel injector or even a vacuum or exhaust leak making the ECU think it's lean and giving giving the engine extra fuel.

Go buy a liver scanner (they are cheap on Amazon), and see what your short term and long term fuel trims are. If you see a high number, that would show you might have some sort of vacuum leak or exhaust leak. If it's showing a negative number, that could be something like a faulty fuel pump or stuck open injector.

 

8 MPG is definitely low for an RX-8, even with a modified setup. The strong exhaust smell suggests incomplete combustion, which could be due to a few things.

One possibility is that the stock catalytic converter (if it’s original) may not be performing as well as it should, which could lead to poor fuel efficiency.

Also, the high-RPM breakup might point to an issue with the fuel system, like injectors or fuel pressure. Since you’ve started pre-mixing, it’s a good idea to check for any carbon buildup in the combustion chamber as well, especially if the previous owner didn't pre-mix. It could also help to get a compression test to rule out any internal engine issues

 

The high rpm break up usually shows up with ignition problems.. but you just got new coils. Hmm
It could also be oil barfing into the intake in small amounts. Are the throttle or intake or intake manifold oily inside?

 

Stock cat seems like it was gutted.. Scroll up in the thread to see the pics.
I havent had the up high break ups in a while, or not obvious at least. I dont know what changed to cause that. It revs pretty clean to redline now as far as I can detect.

 

I have one of those OBD II scanners. Is there a best time or way to read the trims to get the required info? When cold, when hot, a particular rev, etc? And what is correct number I should be looking for both?

 

I pulled the K&N intake out this week, and there was a small trace of oil in there. I had installed a catch can, so I am not sure it was there from before or after the catch install. but as I had mentioned in about 2 posts up.. the break up is seemingly gone (so far). May have been the oil indeed.

 

So I got the stock air box finally. But before I got it and was running the K&N Typhoons, I watching my IAT closely from my OBD scanner. I normally just used to have my Coolant Temp, RPM and Speed displayed and paid attention to my coolant temp as my biggest concern. I was surprised to see how high it got, especially in traffic.. I live in Jamaica so its very tropical and HOT, abient temps currently running like 26°C to 29°C (79°F - 84°F). I saw IAT run up to as much as 80C / 176F, pop the hood and they fell back down qucikly.
I put in the stock intake box and I have seen it hit the same 80C on a very hot day. it seems like it takes a lil longer to get up there, but it will still get there.
While typing this I just went to look at it and saw that the pipe (ram air kinda thing) from under the bumper was connected to the front of the air box.. so it was still sucking up some hot air out of the engine bay. Will correct then and get back with the results.
On another note. My purge valve (valve in a silver metal case on the front of the manifold near the alternator) appears to be clicking for extending periods for lot of the time.. Could that be a part of the issue?

 

At low rpm/load IAT will be high, the air isn't moving quickly. When you go full throttle with the stock intake it shouldn't be more than a few degrees above ambient

 

Took this data screen shot this evening after I got home while idling. Did some pull a few minutes before on the way home. Mostly 1st and 2nd in some super tight corners. The IAT rose to 61C (from 55C) before I shut down the car after some idling.
Also just to be clear, I put the ram air pipe over the air box entry pipe..but it's not a perfect seal..the most of the foam is gone

OBD Data

 

Hmmmm this is while idling, correct? Your airflow is correct for 873 rpm, but your fuel trim is +15%. So for some reason it's not getting the fuel it needs while correctly measuring airflow and has to adjust. Possible your injectors are miswired, clogged or fuel pressure is low?
Stuck intake valves / solenoids could also cause the symptoms you have, but you'd have a CEL for that. Check them for freedom of movement by hand anyway.

 

I did have a similar problem and it was swapped injector wiring. Did you recently replace injectors?

A +15% LTFT indicates that you either have something going on with the injectors or have some kind of vacuum or exhaust leak making the ECU think it’s running too lean until it compensates for it (mostly).

Read my thread for more details: https://www.rx8club.com/series-i-tro...terity-276444/

 

Took a look back at the K&N intake today and saw that there was oil running down the front of the plate under the filter. So apparently there was still oil being pushed into the intake at high rpm. I used to keep oil level to full, I have been keeping the oil at about 3/4 full, so maybe that why there is less oil being blown into the intake during the 9k revs. It revs cleaner now as I said,. I will check the stock intake at a later date to see if it is still sucking up oil.

 

I just had the car a couple months. I personally have not touched the injectors or the wiring, I am not sure what was messed with before.
I guess I will be check ing out the wiring and checking out the intake valve movements by hand.
How are the primary and secondary injector plugs differentiated?

 

 

Thank you so much. Very much appreciated.

 

Update.........
I pulled the intake the checked the injector wiring, that seemed to be fine. I however noticed that the hoses that run to the 3 valves behind the intake were all brittle and cracking. And some of the wires to the connectors were chaffed. So sorted the wires and replaced the hoses.
I had removed the battery terminals during that process, so it seems the ECU data was reset. I made the car idle after restarting.. the Long Term trim started at 0., but if you look at the 2 attached obd screenshots, you. will see it's heading back up. Adding the short term and long term together gives about the same 14-15% as before.

 

I've never heard of adding the numbers. The LTFT is the biggest concern, but it's below 5% so it should be ok.