Severe power loss, screeching, rally exhaust, and eye-burning death stink

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: __ 1990 Eunos Mk1
  2. I’m based near: __ Warrington
  3. I’m looking for technical help or recommendations on: __

I was driving a few days ago and noticed my mx5 developed a screeching sound. It happens when the revs are low but above idle, both when moving or stationary. It’s not clutch or brakes, despite it sounding a lot like brake squeal. Only happens after the engine has heated up. It’s intermittent and non-continuous.

Video of screech sound:

When driving around today to try and pin down the exact conditions for the sound, I suddenly lost power. Pressing the throttle gave 0-5% what I thought I was inputting. Car started to lurch and judder, and I couldn’t get above 10mph. I pulled over and the idle was extremely rough, (jumping between 250rpm to 2000rpm) and the exhaust had developed a throaty rally sound, and the exhaust fumes made my eyes and nostrils burn, and smelled like pure evil.

Video of exhaust of doom:

I got it home, tried to google for about 15 minutes with no luck. Started it back up to drive it into the garage and it started behaving normally again. Normal steady idle, drove fine, normal exhaust sound, and no death smell. Though the screech sound continues to be an issue.

The only thing that happened in that 15 minutes is the car cooled a bit, and the MAF sensor plug looked slightly off, so I re-seated that. Oil pressure and temp both seem fine. New spark plugs and HT leads 4 months ago was the last time I messed with the engine - not touched it since.

Any ideas:

  1. What that screeching sound is?
  2. What’s the cause off the loss of power?
  3. Why it suddenly came back to life?
  4. If the screech and power loss are somehow related?
2

I’d suggest the rough idle and death smell would be a misfire.
Regards the screech
I don’t think it sounds like internal engine noises. maybe an idler pulley, alternator bearing, water pump.
It sounds like metal rubbing on metal or a dry bearing.

3

I had some of those symptoms on mine which was due to an injector stuck open

4

Sounds like it’s a misfire then, fingers crossed it’s not a compression issue!

I replaced the idler pulleys and water pump 7 months ago, so I’d hope it’s not those but I’ll check regardless. I’ll investigate the alternator bearing too, that’s a good shout. If it’s not a dry bearing, are there any common places to have a metal on metal contact?

5

Think the misfire was a faulty AFM, replaced it and I’ve not had the issue since.

Turns out the screeching was inexplicably just belt squeal. I only found one other post with someone who has something similar, and the common thread appears to be a particular aftermarket V shape alternator belt from Mx5 parts specifically, that makes that sound when it gets loose. Most other belt squeal sounds nothing like that. Re-tensioning the alternator fixed it.

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