wardie

This is my first post so apologse if I mess this up.

I've had my hi-power 6-speed manual RX-8 for about 2 months now and clocked up roughly 2500 miles on it. During the first 1000 miles or so I never took it over 5-6000rpm and everything was fine.

Since then I occasionally take it further now up to around 8500rpm or when the beep cuts in before teh redline. Most of the time it is fine - smooth and more power flows on and on.

However sometimes (say 7 or 8 times) I've noticed that as soon as I hit above roughly 6500rpm accelerating I getr a rattling noise from the engine and not much more power (like feeling like you need to change up in a normal cylinder car!). It certainly does not happen all the time, and seems to happen more the first time I take the revs high when driving it - although I always ensure the engine it warmed up first. Obviously I back off when hearing this. The noise sounds like a value or flap is bangin open and shut very quickly, or like very bad version of tappet-like clanking on my old MX-6 when it was cold (a known "feature I understood").

When I then later try again, it works fine, but may occur again later that drive without predictability. At no time have I seen the Check Engine light come on and the oil level is kept full regularly.

Having looked through the manuals I'm guessing it is something to do with the hi-power engine design that comes in at these rpm e.g. aux ports or variable intake.

I am wondering if this is something quite normal with running it in that eventually will go away or something that I need to get seen to by the dealer when I next go in, or sooner if it sounds bad. It doesn't make me feel confident about driving the engine in the way that makes it unique... :-(

Has anyone had anything similar? Any advice much appreciated.

i3man

I wouldn't worry about it. There is going to be slightly more vibration at 8000 RPM than at 4000 RPM. Unless the car feels like it's breaking apart like on those super sonic speed tests, I think you're fine.

rex

iTrader: (2)

The fact that this is an intermittent problem is suspicious.

Loss of power after 6,500? I do notice a reduction in acceleration at that point but it's more like a temporary hesitation and it always behaves the same way at the same revs. This is a symptom of the over-rich AFR in US spec cars. Not sure if that applies to Euro spec. There's definitely no rattling though. That's not right. Take your car to the dealer and see if the PCM logged anything. I could be a fuel injector, a problem with an air intake port actuator or worst of all an apex seal. You want to get it looked at.

sferrett

The exhaust note changes a little when you are pushing past 6000 rpms, but I wouldn't describe it as rattling - just a sharper note (a little more like a sport bike imo).

If you're concerned with it and can reproduce it reliably (especially if it doesn't happen all the time) take it to the dealer and have them listen to it. It's difficult to get advice on sounds via an internet forum since nobody can hear what you're hearing.

JCC

[QUOTE]Originally posted by wardie
[B]This is my first post so apologse if I mess this up.
<snip>
However sometimes (say 7 or 8 times) I've noticed that as soon as I hit above roughly 6500rpm accelerating I getr a rattling noise from the engine and not much more power (like feeling like you need to change up in a normal cylinder car!). It certainly does not happen all the time, and seems to happen more the first time I take the revs high when driving it - although I always ensure the engine it warmed up first.
<snip>

This sounds exactly like the abnormal combustion problem or "pinging" here in the US. The knock sensor probably will not set a code or reset very quickly so get to the dealer as soon as you can after it happens. Ask the dealer if your car has the hotter leading sparkplug mod - this could cause problems with some gasolines. I suspect that rotor carbon build up could be why the noise and power loss is intermittent. Let us know what the dealers says

Omicron

Another possibility: The secondary/tertiary intake runner valves open up somewhere around that RPM. Could be they are sticking.

Regardless, definitely a problem to have your dealership take a look at. Try to see if you can figure out a way to make the problem replicatable, eg, does it always do it when the engine is cold, or in cold weather? After it's been sitting for a while? After you've been running it hard? Etc, etc.

wardie

Thanks guys for all your help! I'll try to answer at once.

Regarding if it is normal or not, I've driven the dealer demo car and it definitely does not do what mine does so I think it is a real problem and not me being a rotary rookie... And it id definitely in the engine not down the drivetrain or exhaust.

So yes I'll definitely take it in to the dealer when I can to get this looked at and let you know what happens. So far I have not found a way to reliably repeat it, but it tends to be the 1st time the revs go high for that run.

Hope it is nothing serious as otherwise I just love the car and am still amazed at the value-for-money in the UK market against competitors(?).

Does anyone have a link to a thread/info on the "abnormal combustion / pinging" problem mentioned, especially if this is a common fault?

Cheers!

zoom44

others in the uk are experiecing just this situation on their cars also. it seems to be a uk specific situation.

JCC

Try forum searchs on "pinging", "knock" and "detonation" and you will find many treads with no real conclusions. This rattle sounds like very noisy piston engine tappets or gear rattle on acceleration. It has been reported in all markets with both low and high power and all transmission options including a JDM 5 speed manual Some people in the US have stopped the noise with higher octane fuel. The tuner Canzoomer mentioned on the Canadian forum someone in the US doing an ignition profile reset by pumping the brake pedal many times with just the ignition on - an official US Mazda procedure! I think the transmission rattle theory can be disproven by the noise happening in auto boxes with planetary gears.

My personal feelings are the noise is not very harmful but the power loss is not good. Excessively lean fuel mixture from varnished up secondary injectors when the extra ports open could be part of this too.

ashmason

I just had this problem with our US spec Auto with GT package. I tried to duplicate the problem and managed to once but couldn't a second time. Yet when my wife drives the car (and it's her's not mine) she gets the rattle again. Problem is unless I can replicate it then I know I am wasting my time at the dealer.

My speculation is that the spark plugs are getting fouled by low intensity driving, she sits in bumper to bumper LA traffic every day, because as soon as I get behind the wheel and give it some beans, the problem goes away.

So far it's only done it once with me and twice with her so I will just have to keep an eye on it. Oh and we only have 1600 on the clock.

Artifex

I took my car to the dealer regarding this issue. They didn't acknowledge the problem and claimed they couldn't reproduce it. The very same day I picked up the car, it happened. The dealer said theres nothing they can do because the computer says the car is ok and not to worry about it.

attn JCC: my car started doing this about 3 weeks after sevenstock when you told me about it. I am now running hotter leading plugs and I still experience it. It's kinda scary because its a crap shoot on whether or not the power will be there when you floor it!

Anyway your not alone on this one, hopefully Mazda will stop ignoring it.

JCC

Hi Artifex, I'm not suprised as noting was found on my car either. A service writer said that Fords don't store knock sensor history and he didn't think the Mazda would. I am not convinced that the problem is preignition and it could have something to do with exhaust interference between rotors. The fuel effect may be from different burning speed which Union 76 says is independent of octane. Oxygenates slow burning time and one rotor is at high exhaust pressure across the shared center port with the other rotor. This other rotor is finishing the exhaust cycle and is in overlap with its intake port! If burning exhaust gets mixed into the intake cycle there could be power loss and noise.

wardie

I took the car to the dealer yesterday and they took it for a long test run and also looked at the diagnostic computer. In common with Artifex above, the engineer could not replicate the problem at all and the computer didn't show any faults logged and the CE light hadn't come on at all.

They advised me to bring it back if it became more frequent or repeatable reliably - otherwise there is not much to do. The problem has not come back in the last day or two since they saw it fortunately.

The only thing I can think of is that it is caused by periods of low-intensity driving, which of course they could/would not do on a test run I guess.

I'll let you know if this continues and I manage to get anywhere with the dealer, or if it just disappears with miles.

kristopher_d

no overlap between intake and exhaust in the renesis (thank you side port exhaust). This sounds like a sticky aux-port actuator. If one rotor's aux port opens slower than the other, the engine will experience significant vibration. One of the actuators is probably sticking the first time you rev it up, then actuates smoothly after breaking lose. Consistant use of the aux ports should help wear them in and result in smoother operation.

Edit: BTW, that means rev the hell out of her every chance you get. That's what rotaries like.

JCC

If you look closely there is a small amount of exhaust - intake overlap in the Renesis that even the extra cut-off side seal does not prevent. Both the secondary (common to both low and high power engines) and barrel valves have their shafts and actuator linked so both rotor's intake will be synchronized when either system opens. I do think sticking can be happening but it should effect both rotors. Your idea about the vibration would rattle things for sure though.

kristopher_d

Well, the actuator bit is news, but I haven't really looked under the hood on my 8 much. The 6 port 13B had seperate actuators.

As for the overlap, Mazda claims several degrees of dwell.

In any event, if you don't run her up to red-line fairly regularly, you are almost definately getting some sticking in the tertiary (aux) port actuators.

I suggest you take a full day, find a nice twisty road, and excercise the hell out of those secondary and tertiary port actuators. A full day of going from 5K to 9K and back should losen up the almost gaurenteed gasoline-lacquer build-up resulting from 1K miles of dis-use. After that, she should spin up like a charm.

Remember, your rotary powered car is like a woman, make scream and she'll treat you right.

zoom44

OOH YOU SAID TERTIARY PORT! THAT WILL MAKE WAKEECH VERY HAPPY