If you try premix on one tank and the problem goes away, it gives you an area to focus on rather than guesswork though.

 

Just seafoamed the car. Will monitor for changes. There are already noticeable differences in power and idle. The sound is a little different too. Will see if the core problem goes away

 

ok is there an update here...seafoam work??? compression test?? plase help i ahve this problem and am ready to freak out

 

Core problem is still there..

Will perform a second seafoam, and then change the coils/plugs

 

Nonsense, really nonsense.

You had a seafoam, nothing changed and now your plan is to seafoam again and throw away $$$ for coils and plugs?

Why don't you simply try premixing 250-300cc (like 8-10oz maybe) in a single tank as Manic Mechanic and bse50 suggest? Simple and near-zero cost. If the rattle ceases then it's a bad sign, cause it means that some seals are going to heaven and sooner or later you'll need a rebuild or a new engine.

 

I have no symptoms of low-compression at all..... no bad idle, no hard starts, no hard starts when hot... it is not a compression issue.

 

The noise is only happening under WOT load above 6000 rpm, only after the car has been driven for awhile.

Something is changing with heat...

 

Yes fella, you're describing my symptoms. I really can't understand why you won't spend $1 to try premix on one tankful. Mine has no compression issues either as verified by a test at the specialists.

If it helps to set your mind at rest, I've just had the CAT off mine when I changed the clutch - I've been premixing 150ml per 45 litres for the last few months - sometimes a little more - and the CAT still looks like new.

Mine may be an oil metering issue, but the symptoms are completely eliminated with a little premix.

 

UPDATE:

I did some more investigation... here is some background info on what I have done and where I am now in the investigation.


- Seafoamed
- Coils/Plugs/Wires changed at 72k km, currently 94k km (Coils have been checked with inductive timing light to ensure they are operating)
- No CEL
- No stuttering
- No hard start issues cold or hot
- Optima Red Top replaced stock battery at 90k km (after 4 years on OEM original from dealership)

I've also recently did the coolant restrictor mod and confirmed it has gotten rid of the MIAC noise.

I've asked a passenger to ride in the car to listen to where the noise seems to come from to get a second opinion. The noise does not appear to come from the back of the car. It sounds like it's coming from right where the feet are, which to me points to either the exhaust manifold or the CAT portion.

To recap, the CAT had been taken out and examined from the front end, looks normal, no deformation. There is 1 line of material that goes across the honeycomb thats gone, but upon closer inspection, that hairline crack does not extend past the first 2mm of the honeycomb. Shaking the cat and knocking on it does not sound like any parts in it are loose.

Mazdaspeed dual-canister exhaust checked for chunks rattling, none present.

Here are the recent findings:

Noise is coming on in the upper RPM's after the CAT has reached around 850+ Celsius. This temperature is obtained using Scangauge II. I verified this by driving around for a while to get everything up to temp. I parked the car and shut it off to allow the CAT to cool for 5 minutes. I started the car up again, coolant temps are still around 85 C so it was safe to rip it immediately. I drove off and at this point the CAT was "rewarming up" to about 450 C. I ripped it to redline several times in 1st/2nd/3rd, and there was absolutely no noise. AT the end of the run, it was back up to around 780 C. I did it again and watched the CAT temps go up towards 910 C, by the 3rd gear redline, the rattling noise was apparent.

Diagnosis: Something is expanding with the heat causing the rattling. Although last checked, the heatshield wasn't loose, perhaps once it gets up to 900C, it expands at certain gaps and areas enough to cause rattling. Looking at typical thermal expansion values for stainless steel, I find that a change in temperature from 0 C to 900 C can result in change in length of approx 15mm. If multiple parts near the CAT and exhaust are changing their dimensions, it is entirely possible for some parts to be touching.

I am going to try to take some $5 hose clamps from Home Depot and clamp down the CAT heatshield as a first attempt. I don't know which piece is expanding and rattling at this point. It could be the exhaust down pipe, the CAT, or the CAT-back Mazdaspeed Exhaust.

What do you guys think? And again no, it is not a compression issue.

 

Ask somebody to lend you a properly working catalytic converter.

 

You're still describing my exact symptoms dude, be a brave soul, go against your instincts and try 99c worth of premix.....

You can always go to confession later.....

 

premix does not explain temperature related noises though.... how do you account for that?

 

Nope but may alleviate the problems caused by your stubborness.
6 pages of thread and you're still running in circles because you refuse to follow the various advice given to you.

Have fun finding your problem on your own.

 

Ok I forfeit. Good luck Footman.

 

Maybe I could end up proving all of you wrong... slim chance, maybe... we'll see.

My reasoning for not following some of the advice here is because there is no factual evidence to prove it. The advice given is a shot in the dark. Whereas, I am actually getting data to go along with my symptoms.

Still NO one could answer that question... why would premix fix a temperature related issue? Everyone else is just saying "try premix" with nothing more than anecdotal evidence.

 

Dude, I admire your perseverance with this but you're just making yourself work harder for no reason at all.
No factual evidence? Exactly the same symptoms on mine with the same info/research you're posting but you won't try what fixes mine. Which leads me to think you haven't read the thread. I know and have posted that the premix doesn't fix whatever the root problem is, but it's probably oil injection related. The reason I haven't pursued this to provide you the facts you crave - have you seen the price of 4 x oil injectors, lines and a new oil metering pump? See in this thread for the checks I've done on the oil system by the way.

Along your factual lines, why do you think it's a temperature related issue? You've proven the cooling system is working correctly, the coolant is running at the right temperature - so it's not a fault there - it's just something that happens when the engine is at normal working temperature. Like mine.

I too, will unsubscribe from this thread. Good luck fixing your problem and the very best of luck 're-inventing your wheel'.

 

Hey mines doing the same thing it threw an error code p0302 misfire cylinder #2

 

it is a heat related issue, when engine is up to temperature it is important to avoid apex seal chattering and proper lubrication becomes more critical. Added to the fact that renesis have a bad oil injection design for the first gen models premixing is a well known fix to this engineering mistake. This is well documented.

Since your car is old and never premixed your engine has developed more and more grooves in the middle part of the housings and has some apex seal wear that causes chattering and power loss at high rmps under load and during high temp conditions.
There is no solution besides premixing or reflashing to full on for OMP max delivery.

I guess if you take a look on how the renesis engine design has this flaw you can relate to what we are talking about.

You need not change the engine, but do not expect to think that its 100% perfect.

 

so does anyone know how this story ended?? I want to know who was right!!

for my 2 cents....it sounded like when the cat gets hot and expands, maybe the element inside might become loose and vibrate..?
had that happen on a van i used to drive....drove me nuts till i changed the cat.

 

Mine's still running great with 150mls of premix, no other symptoms. The CAT is intact and passes a UK MOT for emissions every year ok.

mperformance, sounds plausible - but how does it pass a hot compression test ok? There's also a few more UK drivers with the same issue, one even has the issue with a rebuilt engine.

 

I took mine in to the dealer I spent the money.... They puged her up to the scanners and computers figured out ive got bad ignition coils and plugs. Swapped them out problem solved and tech said the only time u would ever premix is when the oil injectors are failing

 

Has that tech ever opened up an engine and inspected housings after 100,000miles? I have 3 engines in my shop right now, all of them with worn paths in the middle part of the apex contact surface most likely due to low injection.

I hope your engine is the newer one which has no issues unlike the older ones with only 2 oil squirters instead of 3 per housing.

Ahh I forget techs at mazda do not rebuild engines they get them reman...


FOOTMAN what are your WATER temps when this situation occurs? you posted catalytic temps, see if you are over 100C coolant temp when the issue happens. You will not see the temp needle move, nor will you have low compression issues with a healthy engine, but it will rattle for sure and you will get low power. I have a car with the same exact symptoms due to a bad radiator placement!!! Its mounted Horizontally! except here the rattle is exagerated and very easy to recreate due to spiking temps (NO boilover nor dash needle moving)...

 

different issue...but thanks for reviving the thread

 

Figured why it passes hot compression test...

Problem with hot start is wear from sideseals, apex seal groove in the middle affect high rpm contact path which might not show in the compression test.

I just figured this out by premixing a badly hurt engine that passed all compression test, yet it would not rev pass 5000rpm and had the rattle and low power issue. Just tested it today after a decarbon and heavy premixing and the rattle went down about 80% and now it doesn't stall and can be driven hard. So I guess this engine is bad...