I was having the same problems on my 2004. The cat looked new from the one side, however, it had broken up from the back side and pieces were rattling around going into the muffler pipe. After getting all the rubble out of the muffler pipe and totally emptying the cat making it a straight thru pipe..(I took all the material out of the cat myself) It was amazing. All the rattling stopped completely and past around 7000 RPM I actually get a big boost of power.

 

UPDATE:

Summary of what I've done:
Coolant changed
Oil changed
Transmission fluid changed
Differential fluid changed
spark plugs have 15000km only, coils the same.
Radiator fans working
MAF cleaned (no oil blowback)
Intake filter checked (clean and not oily everywhere)
Throttle body cleaned
battery voltage checked.... 12.7 to 12.8 when engine off
alternator output anywhere between 13.6 and 14.1. It tries to maintain 14.1, goes to 13.6 whenever something has just started for a brief second or so.
one (1) can of BG44K ran into the tank.

I swapped the coils back to my old set which were NOT failed (no CEL). I wanted to see if the current set with 15,000km had gone bad. The old set had 70,000km on them. The result is the same. Also before I said the noise appears when the temps are above 90C, well that's also not true because it happened when it was back down to 82 - 85C as well.


Noise starts happening around 5000 - 6000 under load at WOT. If you were to drive with light throttle in those RPMs, there is NO NOISE. The noise only happens after driven for awhile.

AFR's are 15.1 or so at idle
14.7 at cruise

Engine has vibrations that travel into the cabin. I opened the hood and turned the A/C on at idle to watch it cycle on and off. The whole engine shakes a lot when it turns on. Is that normal?

Again, I have NO CELs.... I'm down to the following which I think are relavant:
1) dying CAT (no glowing red though)
2) bad engine mounts (nothing to do with the powerloss issue, but nonetheless is bad)
3) overheated fuel pump? (but it does that when the gas tank is full too)
4) low compression, new engine required? (But I don't have idle problems or random stalls)

 

Stuck Shutter Valve?

Mine worked fine until the engine warmed up, then it'd stick and I'd get the "raspy" noise and a flat spot in power from 3,500+, and generally only noticable at full throttle.

 

The SSV is something I'm reluctant to check. I saw JON316G's video on how to remove it, it looks like a pain in the *** to remove and check....

is there no way around it? Will seafoam clear the SSV? My last option really is to take on the huge task of removing the SSV. The video just scares me removing all those items.

 

MariesRX8,

Did you replace or clean your SSV and fixed your problem?

 

My dealer replaced it after replacing the engine, and yes... no more rasp and no more power flat spot. He at first thought the SSV was fine, as he could move it freely by hand I believe before the engine was replaced, BUT that was on a cold engine.

Once the new engine went in and they were testing it, he noticed the SSV stuck when hot.

 

If the SSV was stuck when hot, shouldn't it throw a CEL?

I have no CEL... and can Seafoam unstuck the SSV?

 

Okay, I inspected the SSV and VDI without removing anything. I simply took a long screwdriver and tried to move the valves. They all move freely and returns to their original position fine without slowing down or anything. The SSV makes a little squeak though as its moving. The VDI does not.

I guess having done this, I don't need to remove it to see if its gummed up then.

I'm trying a can of seafoam in the 1/2 a tank of fuel right now. I think I will try the induction method of mazda zoom zoom cleaner next.

 

Make sure you check the SSV when the engine is hot. My mechanic said mine moved easily when cold, but froze shut when hot.

 

Okay, I'll check it out tomorrow morning after the drive to work

 

Reason I'm going for a manifold change is the looseness of the SSV. You can feel quite a bit of radial and axial play in it, plus it makes quite a knock when you move it about:

http://www.youtube.com/watch?v=UahOn-XS_m4

 

Okay, I inspected the SSV and VDI after the morning drive. Engine is hot.

Both move freely using a long screwdriver, and return to their positions when let go. This rules out that I have a stuck SSV or VDI.

Manicmechanic, are you saying that the loose SSV is contributing to your rattling sound? Or are you guessing that this is whats causing the noise?

 

The noise it makes when you shake it by hand sounds just like the rattle you get on the move. Plus when I rigged up a bodge with some rubber bands to pull the SSV away from the manifold slightly in use, the noise lessened noticeably.

 

Is the play there when hot and cold or only when hot?

 

Both. I'm still not 100% sure that the SSV rattling is the cause of the problem or a symptom of something else though.

 

When are you replacing it?

 

Manifold arrived today - took two months to get here from Idaho via Canada!

Probably be fitting it in a couple of weeks when I've got some holidays. Need to get gaskets and seals too.

 

Please update me if this fixes your issue

 

Will do. It seems there are a few of us with this problem and nobody's found a fix yet.

 

A few more observations made from running with the Ultragauge fitted.

Lambda voltage is around 0.8v flat out, so not running weak - fuel pump should be ok.

Ignition advance runs around 25' and doesn't back off when rattling, suggesting it isn't detecting pinking - backed up by Haywards diagnosis.

Mass air flow peaks at around 175 g/sec when the car is warm, but not hot. When the rattle occurs, WOT air flow drops as low as 130 g/sec at the same RPM/load.

Water temp runs around 185 - 200'f (85-93'c) whether cruising or caning the bejesus out of it.

CAT temps run around 1500'f (815'c) at cruise to an absolute max of 1735'f (945'c) when at full load.



I'm really guessing now, but decreased air flow suggests the engine can't draw any more in because:

..Exhaust under pressure is being forced back up the intake as the port opens as it can't escape through the exhaust, causing the rattle on the SSV and VDI

..or compressed mixture from the compression cycle is leaking past the seals back into the intake cycle chamber.

..or some random fluttering of the SSV/VDI valves occur sometimes when hot, limiting the air flow. There is a distinct shiny worn dimple in the SSV actuator arm, suggesting it has either hit the stop a lot very hard or may be chattering. Gonna try jamming it full open and see what happens.

Any clues, even odd sounding ones, are welcome. I may even resort to changing the oil injection lines and nozzles when I'm doing the lower intake manifold swap. Another pop at premixing should prove or rule this out though.

 

Thanks to advice from this and the UK forum, I think I might finally be getting to the bottom of this.

Chucked 150ml of 2 stroke oil in with a tankful of petrol and the problem appears to have gone away completely. Granted it hasn't been screaming hot weather recently, but the car idles and drives much smoother - plus the mass air flow g/sec is improved at higher rpm. I'm showing 150-160g/sec at 6000 revs where it was only seeing 140 before. Peak air flow looks to be 170g/sec, but it will bounce higher as you slam carelessly into the rev limiter...
Previous attempts at premixing weren't good, but I have changed a few parts since then including most of the ignition system!

So it looks like it's a lubrication / oil injection fault.

It's early days to close the book on it completely for me, but in 100 miles it has been perfect.

 

It's a wear\compression issue.

 

I'm not so sure. Compression test:

 

Are you 100% sure that they prformed it properly? Contact Shifty to know how his second test looked like. Don't be stubborn!

Premix generally band-aids the situation when the apex seals aren't perfectly flat because it makes a taller film. The key word being "band aids". 150gr on 50l is nothing, try 200\220grammes.

 

I'm planning on trying different amounts, in honesty I feel I should use less rather than more if it still runs ok. 125ml oil for 45 litres fuel is what I've seen recommended when using Protek-R.

Compression test was carried out by a well respected rotary specialist called Hayward North.

Priced up new oil injectors and lines. Over 400 GBP, wow.