Cracking/knocking above 5k RPMs
 

I was driving my 8 yesterday and i was at WOT at about 5k RPM it started making a really loud rattling noise almost like a piece of plastic was loose. So i checked it out and there wasn't anything loose, so i called the dealer and told them what happened and they told me something about at high RMPs there are 2 other fuel injectors that kick on and a shorter intake is used. He told me that this could be malfunctioning. It's a 2004 GT 6spd with 65k miles on it. Can anyone help?? I'm kind of confused.:banghead:

Does it sound kind'a like a plastic bag flapping in the wind or spark detonation?
Railton

it sounds like if it had pistons, it would be a rod knock. Could too low octane gas cause it to do that? I changed out the spark plugs and that didn't help either

What octane are you using?

does it only do it in certain gears?

When my first motor went, At operating temp going uphill my car would not go past 65 mph. Took the car to the dealer and had the service manager test drive it and comfirmed there was a problem. That was on a friday, that monday he called back saying i am getting a new engine. When the car was hot the apex seals were not sealing right causing spark knock. I take it no CEL. Have the spark plugs and coils ever been changed and if so how many miles on them.

Mine too. I had the dealer do a compression check which confirmed the low compression.
Railton

Hmmm, new engine sounds nice

I think that's what it was. I was only using regular, :uh: now i'm using 96 and it goes great!

Sounds like detonation, on here we call it "MIAC" (Marbles In A Can) or blender. Low octane reg-gas will cause it among other things.

How low does the octane generally need to be before problems are experienced? Around here (Iowa), we can buy 87 octane, 89 octane (10% ethanol blend), or 90 octane premium. 89 is by far the most common, and is what I've generally use in my vehicles (even those that call for premium). My CX-7 doesn't seem to mind it a bit. RX-8 never seemed to mind either.
But just this past couple of weeks, I've been having issues. Rough/low idle (even worse than usual) - to the point that the car died on my wife one day while idling in a driveway. Apparent lack of power at times, too. I took it for a drive the other day to confirm the problems my wife told me about, and experienced the dreaded MIAC sound when revving past about 4K RPM. Car also threw a CEL (don't know which code, haven't had a diagnostic done). This is on a 2005 RX-8 w/ automatic trans with about 22K miles.
I'm planning on trying to get it to the dealership this week... should still be under warranty (we have an extended warranty on it). How worried should I be...?

In most casses 89 would be fine but some on here have to use 90+. You might have some carbon build up from a lot of short trips and not seeing the red line much. You might run a few cans of Seafoam, BGK44 or another carbon cleaner. Here is a "TSB" that the dealer can do...

http://www.finishlineperformance.com...4-08-1924g.pdf

Thx Old Rotor. I've called the dealership and will be taking my 8 in on Friday to have it looked at. I'll print off the MSP16 literature as well as the TSB you linked. My guess is they'll want to reflash my PCM per MSP16 first, see if that fixes the problem, and then if not they'll move on to the TSB. Could be a long day sitting in the dealer's waiting area...

OK, the dealership performed the MSP16 reflash and checked out my car. They determined that I need new sparkplugs, wires, and coils. Since it's under warranty, I'll let them start there. Once the ignition work is complete, I think I will ask them to run through some of the TSB, or at least do a compression test, just to make sure I don't have to come back for more work later.

i put 93 and half the time i still have to put .5 bottle of octain booster in the gas to stop the knocking... i wonder if the gas octain they sell here is a lie:suspect:

Things seem to have improved after the ignition work. I'd like to check the catalytic converter myself, too, just to make sure it's not having any issues (I've seen reference to looking for 'glowing' - can anyone elaborate on that)?

follow-up
 

Well, I ended up back at the dealership yesterday. Last Friday, I attempted to start the car, but it cranked and cranked without firing up (even after following the de-flooding procedure). Called roadside assistance and set up a date with the dealership. On Monday, roadside assistance showed up (no it didn't take them 3 days to respond -- there was a screw-up with the first company that was supposed to come out, so I called again and rescheduled for Monday :) ). Tow truck driver was familiar with Rotaries, having owned an RX-7, and by keeping my 8 hooked up to the truck's jumper cables and doing a lot of cranking, he was able to purge enough fuel to start the car. So I drove it around a bit, to get it up to temp and recharge the battery some before parking it for the night. Engine response felt a bit 'off', but I thought that might just be due to the after-effects of flooding.

Well, on the drive down to the dealership yesterday (a 45-mile jaunt), things weren't any better. Throttle response seemed off, power was EXTREMELY soft in the 2500-3500 RPM range (e.g. keeping up speed on even slight inclines required more throttle opening than I'm used to). Even high-RPM operation wasn't quite right... I remember the good ol' days when after the tach crossed 5000 RPM or so, I practically couldn't shift fast enough to avoid the "BEEP" (at least in 1st gear)... but now, the revs just lazily climbed, even with the throttle floored.

Well, long story short. They had already had me in several times for coil replacements. I had all the latest PCM flash updates and most TSBs performed. So this time, they did the full "lack of power" TSB - checked the cat, decarb'd the engine, the whole bit. Upon the follow-up test drive, it still failed the diagnostics, so... I'm getting a new engine.

The good news - hopefully she'll drive like new again once this is over, and in the meantime, Mazda sprung for a rental car for me.

The bad news - it's going to take at least a week to source the engine and do the swap, during which the rental car I have to drive is a light blue Hyundai Accent (quite possibly the fruitiest car I've ever set foot in).

No sympathy points for the rental car they gave me? Let me illustrate the situation, for emphasis!

(In all seriousness, I know I could have it a lot worse -- just trying for a laugh)