2006 Running rough, feels like its missing, gets slightly better when warmed up
 

Hey guys, been a long time since I've been on here, but I've been having some issues with my 8 and I was hoping to get some of your ideas.

2006 RX8, MT, 81k miles (purchased at 33k miles, I have never tracked the car). Short block replaced at 5k miles.

A little backstory:
About every 15-20k miles I would have an issue with my car starting to run rough and I'd take it to the dealer and they would replace the coils (I know to avoid the dealership now, but I didn't then). The last time this happened, the dealership said they replaced the plugs, but it was still running rough. The dealer that I normally went to closed down, so I went to one a few more miles away, they did a compression test and I was getting high 7's, low 8's. Here is where I can't be 100% because I never got any paperwork with this information, just some scribbles on the back of a sheet of paper and they didn't charge me for it.
On a recommendation from someone in socal, I went to Neptune Speed to have it looked at. They told me they weren't really sure what was wrong, but my sparkplugs didn't look new, so they replaced them and the car ran much better, but not quite 100%. They also told me my fuel injectors needed to be pulled out and sent off to be cleaned. I wanted to verify this before spending the 600-800 they wanted to charge me, but I haven't done that yet.

Ended up taking it to another mechanic who looked for vacuum leaks and did some other maintenance for me. He said he checked the plugs and replaced the plug wiring, which was the wrong harness for my car, so it was rubbing up against the block. While he was in there he checked the plugs and said they were fine.
So last night I bough new plugs and coils to install myself. Got home and replaced all the coils (the ones in the car looked fine, but I figured it couldn't hurt). Making sure I had the right tools I checked the plugs with the socket I had and found out pepboys sold me 4 completely rusted and used plugs, so I have to take them back today. The previous mechanic did check them less than 1500 miles ago when he replaced the wires, so I don't think they need replacing.

In any case, the issue persisted after I replaced the coils. Basically the car runs terrible at low rpms, and feels like its going to stall, especially when going uphill, until I run the car for about 10-15 minutes and then it runs better, but not well. Still sounds like its having a hard time chugging along like its miss firing (I can almost consistently get a P0301 code when I redline in 3rd gear). I plan on replacing the spark plugs anyway, just to make sure that's not the issue, but I'm afraid its the apex seals. Do they expand after warming up, so I would experience low compression until the car heats up and then I would have slightly better compression? Please excuse any ignorance, I just started getting comfortable enough to start doing some of my own repairs (which btw, was really fun!).

I'd love to hear everyone's thoughts on what could be going on and I'm happy to answer any questions.
If anyone is in the Southern Orange County area and wants to feel out the car, let me know.

Compression is better when cold than when warm. This is why marginal/failing engines stall and won't start when warm.

If you don't have one already, get a bluetooth OBD-II adapter and download a phone app so you can look at data.

I'd be interested in your fuel trims and MAF reading. Also, check out commanded throttle position. Have you cleaned the throttle body? Might need cleaning.

Thanks for the reply, here is some more information:
The car doesn't have any issue starting up when cold or warm. I just tested a warm startup as I don't normally get the chance to and it started up quick.

I have an OBD II to iPhone connector, but sadly the app I have doesn't record (I thought it was recording during my drive). I did make screenshots before I started driving and after, so here is some info from those:

MAF @ idle = 0 lbs/min
MAF @ ~4k rpms freeway driving ~= 8 lbs/min (this may be off, wasn't looking closely cause I was driving)

Short Term fuel trim (Bank 1): -1%
Long Term fuel trim (Bank 1): 1%

Another scan of fuel trim (after driving ~15 miles and then being at a complete stop)

Short Term fuel trim (Bank 1): -2%
Long Term fuel trim (Bank 1): 4%

Not sure what these are

Command throttle actuator: 3% (cold start)
Command throttle actuator: 1% (after ~15 miles highway drive)

Command Equivalance Ratio: 1 (after ~15 miles highway drive)

The throttle body was recently cleaned by a mechanic, and while I was replacing my ignition coils I got a look at it, and it looked really clean.

Pay the ~$10 for a decent app that will log. OBD Fusion is my favorite because you can configure custom PIDs and monitor things like tire pressure. DashCommand is also good but they don't let you configure custom PIDs. Both will let you log data.

If your MAF reading at idle is 0 lbs/min there's a huge problem. It should be about 5.5 g/s (or ~0.73 lb/min).

When was the last time you cleaned your MAF?
You know what? Don't answer that. Just go to your favorite auto parts store and get some CRC Mass Airflow Sensor cleaner. It should be < $10 and the process only requires a screwdriver to complete.
There's a DIY around here somewhere...

MAF sensor was cleaned 2 weeks ago. Was one of the first things I did as per a bunch of recommendations on this forum (did a little searching before posting).

I downloaded Dash Command as the other app won't work with the OBD connector I have.

I am posting a link to the log file, keep in mind this is when the car was already warmed up.

LGF file:
https://drive.google.com/open?id=0B7...DJrZ3JkNWVDLWM

CSV:
https://drive.google.com/open?id=0B7...lFpZjlPcmhDR2c


Let me know if I missed anything that I should have been recording and I can do another run tomorrow from cold to start to when I get to work.

Thanks again for all your help!

A 30MB file? How long did you log for? That's going to have to wait until I have time to deal with it.

Holy carp, didn't realize the csv was 30mb. It was only a 7 minute drive.
The LGF file is only 4mb, but it looks like you need DashCommand from this site to read it:
Downloads - Palmer Performance Engineering, Inc.

Next time, see if you can limit which PIDs it logs.

First thing that jumps out at me is that your MAF readings are low at idle. It should be around 5-5.5 g/s and your logs show <4.5 g/s.

I suspect that the fuel trims logged aren't actual. The RX-8 has 3 separate long term fuel trims for different conditions (idle, throttle tip-in, cruise) and they should all be a little different. Your logs show an LTFT of 3.1% throughout the entire logging period. Also, your STFT is too steady; it should be bouncing around a little bit.

Your throttle actuator control reading isn't right. The log shows it unchanging which can't be possible given the reported RPMs.

Since the problem that you're having is worse when cold, you need to log data while cold. See if you can limit DashCommand to log coolant temp, throttle, STFT, LTFT, Lambda, MAF and RPM.

Got a compression test done and my rear rotor is 2 Kpa lower than my front rotor.

Looks like I need a new engine :(

What's the average cost on getting a replacement?

You can get a Mazda reman for $3000 +$250 shipping. You'll have to ship yours back or pay a $1000 core charge.
ENGINE, SHORT M/T. ENGINE & GASKET SETS for 2005 Mazda RX-8. #N3H302200RV0

Omar at OJ Imports usually has a rebuilt Renny for sale on eBay for around $2500 plus shipping with a $500 core.

Alternately, he'll rebuild your engine for you.

I don't know of any other rebuilders in your area but there's always Rotary Resurrection (who's well respected and wrote the DIY on removing/reinstalling engines), Banzai Racing, and others.

Hi Tim which one? there are 100 for sale... just looking for recommendation.
thanks Carl