USAFPilot11

iTrader: (5)

Hey all, I got some questions about some of the problems I have been having with my 8 lately. Most of these I have tried to mitigate, but have been unsuccessful. Some might be caused by me.

1) Gas mileage 15.6 or less
I installed a new BHR ignition system and new spark plugs about 1.5k miles ago. Since I installed it, my gas mileage has dipped as low as 14mpg! Recently, my mpg was 15.6, which is better, but a far cry from my avg of 17-18 that I was getting about 20k ago. Is this just because it's getting older?

2) Oil in the intake system.
I am almost positive I accidentally overfilled or added oil too quickly to cause this. Is this going to cause more issues? I very thoroughly cleaned it out, and haven't seen any oil return as of yet.

3) Idle RPMs very high for long periods of time after initial startup. This is usually worsened with cold weather. Basically, when I first start up the car, the idle RPMs are about 1500-1800 then will drop to 1200 and sometimes bounce slightly. Once the car warms up it will stay about 900-1000. Is this where my MPG is wasted? One of my grounds in my chassis isn't exactly perfect (I'll upload a pic later once I get off work), it has some corrosion on it. Could this be the issue?

4) I also haven't had the MSP-17(the computer reset to add more oil, I think that's the name) flash done yet to my car. Dealer schedule hasn't worked with mine, and they are ********. Planning on getting it done very soon. Would this cause any problems as well? Sometimes at very high RPMs (7-9k), I hear a subtle what I think is knocking. I always buy premium gas. Is this a result from not pre-mixing or having the reflash?

Thanks guys! Really appreciate the help!

Some info about my 8: 2007 GT, 68K miles, don't pre-mix, though I am going to start. Live in west TX where gas quality seems to be low and octane is 91 at highest.

RIWWP

iTrader: (2)

1) Huge number of things that can cause a mileage loss.
- coils
- plug wires
- plugs
- engine compression
- Front O2 sensor
- Rear O2 sensor
- clogged cat
- clogged air filter
- engine block grounds
- fuel trims
- vacuum leak
- MAF fouling
- ESS fouling
- brake pads dragging
- tire pressures far too low
- engine coolant temps at cruise
- Driving style

2) Yes, it can cause problems with the intake valving and MAF fouling. I recommend cleaning it up.

3) High idle RPM is most probably a vacuum leak, probably a severe one. The idle bypass is a fixed amount of air that the engine gets even with the throttle closed. If the engine is getting even more than that all the time via a vacuum leak, it could easily produce a high idle.

4) Running without MSP-16 done is directly shortening the lifespan of the engine. It's pretty critical. I am not aware of any impact on mileage other than what the resulting low compression would cause.


In short, find and fix your vacuum leak first, and then go from there.

USAFPilot11

iTrader: (5)

Thanks for the great and quick reply, RIWWP. How would you recommend troubleshotting for the vacuum leak?

RIWWP

iTrader: (2)

Lots of methods out there. The fool proof one is getting the intake tract smoked, see where smoke comes out of.

A quick check should be done on the LIM service nipples and the vacuum hoses post-throttle body. A vacuum leak pre-throttle body isn't great, but usually won't lead to a high idle since it's still throttled by the closed throttle using the idle bypass. A vacuum leak causing a high idle should be post-throttle body. The LIM service nipples would be the most likely candidate. It could be anything though, including a cracked UIM.

04Green

iTrader: (1)

you did not say how old, but if you are looking at the 04 to 06 vintage, there are some potentially useful things in the $100 link below, after you look for the vacuum leak.

USAFPilot11

iTrader: (5)

Sorry, I put it in my edit at the bottom of the post. I should have put it at the top.

My car is a 2007 GT with 68K miles.

I actually did a few of the things in your post when I first bought the car in 2010. Some of the things I did were cleaning the MAF, insulate the A/C lines, A/C reamplify, vacuumed cabin air filter, and I of course just installed BHR ignition coils, new plugs and wires.

I am planning on buying a grounding kit, because everytime I unplug the battery for maintenance and plug it back up, I get a huge increase in ingnition, but over time the ignition starts to take longer and longer. I think this is a grounding issue.

Thanks!

USAFPilot11

iTrader: (5)

Here is the picture of one of my grounds in question. Does this need to be cleaned?

I have bought an NRG ground kit from ebay. It should arrive by this weekend.

I tried to find the vacuum hose leak but was unsuccessful. So I uploaded a couple videos to youtube concerning the issues with my car, in hopes that someone may have some more info for me.

This video, is starting my car a couple months ago in the early morning going to work when it was around 30 degrees. My car starts much nicer than this now since it is warmer. My thinking is that the crack in the vacuum hose expands in heat and closes the crack making symptoms less obvious.

Video of starting:
The second video of my car with the key turned to ACC and not ON. I know some noise is acceptable but this noise seems excessive. Does anyone know what it is?

Video of noise:
Thanks for the help guys! Taking my car to the dealership this weekend for the MSP16 reflash and possibly a new clutch based upon the recall 2 years ago on it (my clutch is making funny noises that can be heard from the outside of the car). IDK if I am going to have to fight for that or not. I'm not really enthused about having to take my car to the stealership. Anyway, thanks again!

USAFPilot11

iTrader: (5)

Last question, if you notice in the startup video that my coolant light is on. I know there is a problem with many 8's with this. My coolant level is just fine and I just flushed it 1000miles ago.

Should I bring this up to the dealership? I did a few years ago at a different dealership and they blew it off and said it wouldn't do anything. It's just more or less annoying to me.

RIWWP

iTrader: (2)

From the first video, I suspect that your starter is near death. It sounds really weak.

The idle speed looks fine for a first start to me.

The high pitched noise from the solenoid might be troublesome, might not be. It's hard to say which one of yours is making that noise, but opting to replace it may be the right thing to do.

The coolant light is the known sensor problem, you have to replace the coolant bottle to replace the sensor. The dealer will do it for you, but they will also charge you for it. You are out of the bumper to bumper warranty that might have covered it for free.

USAFPilot11

iTrader: (5)

Thanks for the reply again RIWWP. The main thing that confuses me about the starter, is that if I unplug the battery and plug it back up, the starter starts the car very quickly, then over time it reverts back to a weak startup after a couple weeks. I guess that just means it is on it's way out?

I found 2 different parts for the starter, do you happen to know which one it is? (N3H1-18-400R-0A) or (N3H2-18-400R-0B)

The thing about the idle speed is that unless I let the car sit and warmup for 5 minutes, the RPMs will throw a little bit of a fit when I start driving when I throw in the clutch or go back to idle at a stop sign etc. RPMs will shoot sometimes to 3. Then very slowly work it's way back down. Vacuum hose?

Just filled up again and got 15.6 mpg again. This is almost all city miles, so I guess 15.6 isn't too abnormal.


Thanks again, this forum is awesome. I hope to learn enough to be help to someone someday as you have me. Slow progress though.

**Was searching around and found a cheaper and stronger (advertised stronger) starter. N3Z1 starter, have you heard of this? Is it worth it?

RIWWP

iTrader: (2)

I think the B is the newer and better starter. Google search the site with site:Rx8club.com <part number> to see the references to each. Should be simply to figure out.

Yes, 3,000rpm is too high for a cold start idle unless you have subzero ambient temps (I assume Texas does not right now).

15.6mpg all city is in the acceptable range. Do a 100% highway tank to really get a better measure of mileage health.

USAFPilot11

iTrader: (5)

Just wanted to give you guys a heads up. I had a compression test done today at the dealership (Apparently the MSP-16 flash was done in 2008 but they didn't put a sticker on it).

The compression test came back saying the rear rotor had significant compression loss and the front rotor had some compression loss. Out of 7 the front rotor scored between 6 and 6.5 and the rear from 5.5-6.3. I forgot what the scale was, the tech said it wasn't PSI.

The dealership said that a reman engine would be covered under warranty but wanted my records for oil changes. I have had some oil changes done at a dealership but most I have done on my own. I am seriously OCD with this car, I love it like it was my kid. Is there any chance they would deny the warranty because I don't have oil change records? Does anyone have any advice. They said they would get back with me on Monday.

RIWWP

iTrader: (2)

If you have any records, even of your own work, you can put them in the owners section of MazdaUSA.com. many dealers accept a printout of that

USAFPilot11

iTrader: (5)

Great thanks. I will put my records there. Unfortunately I haven't saved all my receipts from oil changes though.