I wondered if someone has any idea what this problem could be:

A while back my rx8 started to dramatically lose power at high rpm, being accompanied by an unpleasant rattle / grinding noise almost like a tin can being dragged and crushed around. This would only really happen once the car had been running for long periods (after one very long journey the car became pretty much powerless) . After doing some searching I though that this might be a bad cat so I put a decat pipe on - this seemed to solve the problem.

Several months later I'm getting the same problem, although not as badly as before (see video). Also the engine light came on, after scanning this showed up as P0410: Cataclyst System Efficiency Below Threshold (Bank 1).


My questions are:

1) Any idea what this could be if not related to the cat(s)

2) Does a 2004 rx8 have a precat in the manifold? could it be due to bits rattling round in here? If so will it pass an MOT with this gutted?

3) Why did P0420 show up so long after I decatted?

Thanks in advance to anyone who tries to help with this

 

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The code is because you do not have a CAT, the ECU finally figured it out. It can take a bit.

If the issue shows up when you are deep into a trip, is the fuel level low? I would look into the fuel pump...

 

A long time since my last post but thought I would bring this back to life as I have still not found the problem to this.

I was about to change the fuel pump recently but thought I would do some more searching first. People with the same issue that sorted it have said that one of the following was the cause of their problem:

- Shot vacuum pipe
- Bad battery - Oil metering fault (solved by premixing fuel with oil)

Others are sure that it is a bad SSV valve:
I would love it to just be the fuel pump but dont want to replace this for nothing - I understand why this would be a cause for the power loss after warming up but what about the rattling noise? Also cleaning the SSV seems like a big job. Really do not want to end up doing all the above for nothing if it is an oil metering fault!

Any further advice on what I should do first? Or anyone with experience of the same problem? Thanks

 

Heat Shield???

 

It does just sound like a heat shield but there is also a loss of power. The power loss gets worse when the noise kicks in and the two only happen when the car has been running for a long time

 

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Recently changed the oil, battery and disabled the VFAD (variable fresh air duct) and this problem seems to have gone away. The car used to have to get pretty hot for it to appear and I went on a pretty long drive recently and the car is behaving like a car of its spec should do, both hot and cold! So it looks like the problem was either:


VFAD: I disabled this because the noise seemed to kick in at around 5,500rpm (from what I found this is exactly when the VFAD opens up). From what I understand the only purpose of this is to make the engine quieter at low rpm – disabling it just keeps the fresh air duct open permanently with no bad effects (just a slightly louder engine and if anything, a performance gain). The VFAD requires vacuum to close. Capping the vacuum line running to it, or more simply just reversing a one-way valve on the line keeps the VFAD permanently open: see https://www.rx8ownersclub.co.uk/foru...ic.php?t=53537


Oil Change: Worst case scenario is that the problem was due to clogged metering oil nozzles. A few people with what sounded like the same problem found that the ussue went away after premixing the fuel with 2-stoke oil. I’m thinking that it’s possible that the fresh oil (being less viscous than old oil?) would pass through any clogged oil nozzles more freely and might be a cause of the fix. From now on I am premixing 250ml of Castrol Power1 Racing 2T oil per full tank of fuel as a precaution (when the noise went away I had not started premixing so only the oil change could have been the fix if this is the problem).

Battery: I saw one reply to a video of a similar problem saying that a new battery fixed it. I couldn’t understand how a bad battery could affect anything once the car is running unless it is completely dead but I’m probably wrong on that. My battery was definitely on its way out and would go flat after 2 weeks of the car being left.


Anyway, hope this helps anyone else with the same issue. Would be interesting to pin it down to one of the above. Thanks to anyone who tried to help with this.

 

I had a very similar noise at one point as well.
it was intermitent and I experienced a loss of power when it did occur.
only after having the VFAD replaced has the rattling sound completely disappeared and the car runs beautifully now.
I don't completely understand why or where the rattling sound was coming from but it hasn't returned.