Rasp from engine...help!

[warpc0il]

If the air meshes in the intake are damaged or misaligned, then it doesn't impact the breathing as such, what it does do is mess with the airflow over the MAF, which means that the PCM receives incorrect data and the fuelling goes all over the place.

Worse case it can run lean enough to cause mechanical damage but more commonly the engine just runs rough and noisy, often at particular revs/load.

[Rotaryjon]

Makes same sound with both air filters (AEM and standard).

2nd bottle of redex used up and now on 3rd. So far the noise now seems to be limited to when the engines under heavy load (e.g. going up a hill in 2nd gear). I'm starting to wonder if the gradient of the car is a factor (as if the exhaust is somehow 'pulling' apart).

Side note, other than the noise, engine is better than ever , faster, nippier and start seems much smoother on rev dial (not as much dipping in first few seconds)

[Rotaryjon]

P.s. for the redex test I've only been using 95 crap petrol e.g. your usual tesco , Sainsbury's , indipendant stations (not shell or bp)

[Rotaryjon]

Update, noise still active but not as bad as before now I've been using redex in every tank (an 8th bottle I think now).

No dynamo info but HP feels much higher

[ChrisHolmes]

Which Redex product are you using?

[Rotaryjon]

Sorry for late reply, was just the standard redex https://www.eurocarparts.com/ecp/p/car- ... gIZ8vD_BwE

Sadly sound has got worse over last 2 weeks.

[New Duke]

My money would be on Pete's guess from the second post. Your video of the underside showed what's left of the heat shield on the exhaust manifold is rusted and flakey. But in the video you guys didn't shake it hard to test.

My manifold heat shield has rusted the fixing bolts loose (even though the shield itself is intact) and it sounds like someone shaking a bag of nails, even after I've strapped it tight. Probably down to the joys of heat expansion. Makes the car rattle over bumps, but also rasp under heavy load. Less heat shield remaining might = a more subtle noise like you have.

If the noise was engine related I doubt it would still be driving, especially after all this time. Which is a plus.

Unrelated: That video you took of the underside, was that immediately after an oil change? Or does your sump have a leak?

[ChrisHolmes]

Sorry for late reply, was just the standard redex https://www.eurocarparts.com/ecp/p/car- ... gIZ8vD_BwE

Sadly sound has got worse over last 2 weeks.

When people mention Redex that is generally assumed to be the original engine cleaning product which worked fine in piston engines but “ate” seals in the rotary. Time has moved on and Redex is now simply a branded range whereas initially it was just one specific product.
The product your using is in my view unlikely to cause any issues.

[ChrisHolmes]

https://www.rx8ownersclub.co.uk/forum/v ... 25&t=75466

[Rotaryjon]

Well it's fixed (touch wood).

In brief, my alarm started going off a few times randomly. Couldn't work out why, put it down to sunlight hitting the sensor somehow.

Then few days later my car wouldn't start (flat battery). Jumped it and continued as usual.

Few weeks later (aka this week), my car battery died every time I tried to start and had to be jumped. Not a biggy I thought and ordered a new battery.

Now the interesting bit, I noticed after jumping that the engine didn't make the dreaded noise.

Got a new battery yesterday and dropped it in, POOF the rasp has gone and HP is back to normal (I didn't even realise how much HP I'd lost until I put my foot down pulling into motorway).

I can only assume the 'rasp' was the engine not sparking every other rotation or so due to the sparks not getting enough juice to ignite the fuel??? (Would also make sense why high quality fuel made less of a rasp).

[NickyL89]

Hi all,

I am new here and have this same noise! Not long bought the car but the battery was replaced not long ago. Car was down on power and didn’t make this noise, replaced coils, leads and plugs and suddenly I have this noise! Not sure if it’s the ignition coils that are requesting more amps and the battery can’t provide it? I personally don’t think it sounds like bearing failure and it would be a coincidence that bearings fail as soon as I have replaced the ignition system. Coils and leads from Essex rotary and plugs are from Ryan rotary so I doubt they are the issue. It’s a rasp noise, almost like a screamer pipe. Cat doesn’t appear to be blocked. Any help would be appreciated, even if it’s a way to test if the battery is up to it, or if there is a specific battery that should be fitted.

Thanks

[NickyL89]

You can get mechanical-sounding noises from the ignition system if;
- one (or more) of the HT leads aren't clicked firmly onto the plug tops. The spark arcs between the connector and the plug
- one (or more) of the spark plugs are loose, cross-threaded, cracked or swapped (Leading/Trailing) so you have combustion gases escaping passed the plug.

I'm not saying that's the cause of the problem in you case, but it wouldn't be "the ignition coils that are requesting more amps and the battery can’t provide it" as that isn't a thing.

FYI Battery info here
viewtopic.php?f=25&t=36434

[98of400]

I had a 'rasp' sound, at higher revs (>4k) with a loss of power. Cat and ignition system were ok. Spoke to a couple of rotary specialists who both (and independently) said the same thing, which was it could be carbon building up in the combustion chambers, getting hot and causing early ignition. They recommended using Super Unleaded (97 or better still 99 RON) which I did, and I've not heard the noise since.

[NickyL89]

I always use Tesco momentum which is 99 so should be ok but I know it isn’t as good as v power so I will try v power. I also have some sea foam as I have read that it could be carbon igniting also. Pretty sure all coils and plugs are in properly but will double check

[NickyL89]

If you've got good quality HT leads with proper rubber caps then sometimes they grip the porcelain of the plug tight, before the contact locks on.

A spray with silicon oil, or wipe with silicon grease, can make all the difference.

[NickyL89]

Yes I’ve got MSD leads on it, brand new. I see what you’re saying, will whip them off and double check tomorrow. I’ve just checked the coil plugs and the HT leads on the coils and they’re all fine.