Let me start off by saying I know the rx8 is not a camry and its a sports car not a prius but let me explain.

Purchased my car in november with 84k miles on her, 05 winning blue gt 6 speed, immediately noticed I was getting around 9mpg with premium gas and highway was pretty much the same. Fast forward a couple months here is where I am.

Parts replaced.

Starter
Coils
Plugs
Wires
Engine
Clutch
Flywheel (light weight one)

Parts cleaned trying to track this down.
MAF
Air filter

Checked all fuses, checked for any el codes there are none, engine does not smell like it's running rich however I have noticed lately there is a tapping sound while engine idles almost like air escaping somewhere, looked at vacuum lines I could see and all seem fine. I am running out of options here on what it could be, I am thinking maybe clogged cat but dealership said my cat was fine last time it was in for service.

Best mileage ive gotten so far is 13.4mpg and that was for 84ish miles @ highway speeds.

I normally get less than 140miles for a full tank and this is just killing my pocket book on gas, my brother drives an 04 gt 6 speed and drives like a mad man and he says he averages 17mpg city, 20 highway.

Any help would be greatly appreciated, yes ive looked over the mileage thread and engine car thread, car just had an oil change and all the tune ups listed above.

 

Compression test? I barley get 250 miles to a tank. However, I have a real heavy lead foot.

 

i think the three largest influences on mileage are:

ignition condition; obviously, if the ignition isn't working, mileage is going to drop, i think a lot of cars are running around with 2-3 working coils, as the car will run like that.

cat condition; the best mileage i've ever gotten from an Rx8 was with a hollow cat, ergo a plugged cat will hurt.

engine condition; i've got one right now with a bad chamber/seal issue, and it consistently gets like 16-17mpg, and it doesn't matter how or where i drive it. my other car has a good engine, and it gets about 1-2mpg more.

as a 4th, you might want a scanner, there are things like the coolant temp sensor, that can cause bad mileage if its bad (although it should turn on the CEL too), or maybe a slow/dead 02 sensor

 

 

Just had a full tune up on coils/plugs and wires, just had a new (reman) engine put in less than 1000 miles ago, are the remans really THAT bad?

 

it should be fine, actually i'd suspect something is installed incorrectly

 

Got an appointment scheduled tomorrow (10th one since i got this car i swear to god) and I gave them very specific instructions to do a compression test AND check my cat and check for vacuum leaks. If I can't get this resolved I might have to part with my 8 this is just getting out of hand.

 

Easy things to screw up, that that might have hosed...

Plug cables going to the right plugs.

Reset ECU with 20 stomps.

Questions:

Do you have something like an ultra gauge that will show you things like fuel trims?

How is power, related to your brothers?

How long is your drive?

Where are you?

 

I am going to double check the plugs again tonight and try the ecu thing since I doubt the people who did the work knew how to do that power wise I would say they are about the same but then again my brothers doesn't have any of the same problems mine does but I feel a lack of power in mine after about 3k rpms almost like its bogging down and I never noticed that in my brothers that's for sure.

I live in Indiana,USA and my work commute is only about 5 miles a day but for school i typically drive 40miles both ways every friday plus normal around town drives.

I have noticed there is a good bit of condensation build up (white stuff) when i check my oil, to the point where it takes at least 3 dips with the dip stick to even see my oil level because there is so much condensation.

EDIT> No AP or Ultraguage however I am installing a nexus 7 in my dash (just ordered everything I need) and using a bluetooth odb monitor I can see those readings from the ecu but that will be at least a week or two before I can get around to installing it.

 

02 sensor?

 

Bogging down around 3K could be something hosed on the SSV. That will hurt. SSV is like a tuned intake. If it is tuned wrong, things will not work. How about the rest of the RPM range up to 8K or so?

Also, when you get the tools, look at CAT temp. If it is really hot, above 1600 degrees, there might be an indicated that you are way too rich.

The mileage will suck for the 5 mile part of things. Especially that far north. The engine will not warm up at all. That is why you still have the condensation. I was recently in GA right around freezing. After a 15 minute drive, I was still at 160 degrees. My mileage was not that low however. What oil are you using?

Might want to check and make sure they hooked up the vafd. If it is stuck closed, you will be breathing through a small hole. However, if I remember correctly, that does not open until 4,500 rpm.

Can you hook up your ODBII adapter and collect data without mounting the Nexus 7? I am in Florida, so loaning the UG is a little tough.

I seem to remember someone getting the fuel injector cables crossed. Ran, but bad. It is amazing what the computer can adjust for. The second set of injectors does come on around 3K (I think).

Best I got for now.

 

Double check the spark plug wiring:

 

Car is in the shop right now but when I get it back I will update and let you guys know what they come back with, i'm starting to lose faith in my local mazda dealer... I'm still waiting for the odb adapter to come in the mail but the minute it does I will hook it up asap, from 3-5k it runs really rough like it doesn't want to go and then from 5.5-9k it feels like she opens up a bit. With it being cold I typically let it warm up just a little bit before I drive her, sometimes I let her warm up completely other days I wait until my water pump isn't working so hard and the rpms have dropped back down to idle.

 

The dead spot from 3K to 5.5K sounds like something hosed on injectors. I cannot remember the issue exactly, but it was either the wrong one installed in the wrong location, or the wires crossed. The other thought was that the thermostat was hosed and the car never really warms up.

The SSV has a sensor to check and see if it worked, so that is not a likely a problem. However, if a fuel injector is squirting fuel in a runner that is not getting any air, there will be issues.

There is also a chance that the dealer is an idiot.

 

The water pump works exactly as hard cold as warm ...

 

Maybe i should have been more clear, I have an upgraded water pump that whines on startup for about a minute as it works into overdrive mode if you will to pump as much water as possible during startup.

 

The water pump is spun by the belt off the front main pulley. It is not possible to push more water at 750rpm when cold vs 750rpm when hot. Same speed. The only way you will change the volume of water you push where the only factor changing is water temp, then you will push far more water when the water is above the freezing point than you will when it's below the freezing point.

If there is whining, then your water pump belt is slipping. Since your alternator is also on the same belt, it might be causing alternator current delivery problems.

Another possible source of the "whining on startup" is the air pump, since it only runs on start up briefly. If you know the whining is your water pump, then it's actually the belt.

 

You are right, my mistake turns out it was my air pump making the noise but got her back and here is what the dealership has to say "Nothing wrong at all."

Compression test results:

1. Rotor 1 - 8.8 , 8.8, 8.9 @ 288rpm
2. Rotor 2 - 9.2 , 9.1 , 9.0 @ 290rpm

Diagnostics results:

1. Response Lean to Rich - Min: 0.292 Max: 255.992, Value: 1.949
2. Response Rich to Lean - Min: 0261 Max: 255.992, Value: 1.425
3. H02SB1S2 Monitor - (Empty on chart)
4. Low Sensor Voltage for switch time calculation - Min/Max: 0.299V, Value: 0.299V
5. High sensor voltage for switch time calculation - Min/Max: 0.400V, Value: 0.400V
6. Rich to lean sensor switch time - Min: 0s , Max: 0.080s, Value: 0.032s
7. Catalyst monitor bank 1 - (Empty on chart)
8. Rear to front switch ratio - Min: 0 , Max: 7.999 , Value: 0.960
9. EVAP monitor (large) - (Empty on chart)
10. Evamp Monitor Large Leak Check - Min: 0.618mA , Max: 255.996mA, Value: 2.089mA
11. Evap Monitor 0.040 inch - (Empty on chart)
12. Evamp Monitor 0.040 inch leak check - Min: 2.085mA, Max: 255.996mA, Value: 2.089mA
13. Purge Flow monitor - (Empty on chart)
14. Purge Flow Monitor blocked evap system line check - Min: 0mA, Max: 18.648mA, Value: 18.621mA
15. secondary air monitor bank 1 - (Empty on chart)
16. secondary air functional check - Min: 0s, Max: 4.992s, Value: 0s
17. misfire cylinder 1 data (rotors #1) - (See Below)
18. ewma misfire counts for last 10 driving cycles - Min: 0, Max 65535, Value: 5
19. misfire counts for last/current driving cycles - Min: 0, Max 65535, Value 9
20. misfire cylinder 2 data (rotor #2) - (See Below)
21. ewma misfire counts for last 10 driving cycles - Min: 0, Max: 65535, Value: 7
22. misfire counts for last/current driving cycles - Min: 0, Max: 65535, Value: 30
23. Thermostat Monitor - (Empty on chart)
24. Engine coolant temp - Min: 71c, Max: 6513c, Value: 74c

I feel like the most recent drive having 30 misfires is a little high but maybe I am wrong plus my engine temp seems a little low too?

I think their logic at the dealership is that no check engine code means my cat is good.. I will have to figure out a way to test it properly they also said me letting the car warm up could be using all that extra gas which just seems a little absurd to me.

Thanks again guys for helping me out, I hope this provides enough data for now.

 

165 degree F max ECT? After 30 miles? Way too cold --> thermostat stuck open.

 

I think you might be right, I have noticed the car takes quite a while to warm up in the mornings however I have no baseline for where you get your 30 mile number from since they did not provide any insight as to how they tested that.

 

yeah thermostat, 74c is too cold.

the misfire count is probably ok, but 30 seems high enough that it might be worth cleaning the ESS, and doing the 20 brake stomp reset thing.

 

ESS? I tried the brake stomp thing but I can never be sure there was any affect from it, I will be getting the thermostat replaced asap and see if that helps, the dealership was really reluctant to provide me the diagnostics list or even a copy of the service record which was a huge red flag to me

*Edit - Got an appointment scheduled for saturday to replace the thermostat with a local carx (people who seem somewhat competent) with a fail-safe version that won't ever close shut on me , hopefully by time that is all done I can get some results if not I will have my odb monitor setup and can provide more information soon.

 

Just an update, I did the brake stomp thing a couple times until last night I finally saw my oil pressure gauge spike up and then go back down during the process which didn't happen before, so I think I reset the ess sensor finally and we will see how it goes, right now I am getting according to my rough calculations this morning just barely 12mpg which is a hell of a lot better than 9 but still not right.

 

Progress,

Could be a lot of crap to burn out of a lot of places... 9 to 12 is 33% increase.

 

Hell if I can go from 12 to 15 I think that is much closer to factory specs and I would be happy with that, hopefully after my new thermostat install tomorrow I can run through another tank and see how she does I do know I won't be taking my car back to my local mazda dealer since they didn't seem to want to admit there was a problem with misfires or low engine temp.