Metallic Screech above 4,500rpm

[ATCO99]

My FED Elan M100 suddenly makes a metallic screeching sound under acceleration as the tach exceeds 4,500rpm...no symptoms below this point...I keyword searched 'screech' and read existing articles but this seems different. Turbo gives about 0.4-0.55bar boost most days, never more. My memory of my UK Elan is that it pulled harder, gave up to 0.9 boost as stock but 2 decades may have fogged my memory.

Mods on vehicle when I bought it (if relevant)
- Blow off valve for turbo
- Sports exhaust(recently checked on lift, good condition, no apparent leaks or cracks)
- ECM chip (subsequently removed and OEM replaced, engine not re-tuned but starts every time since and no more kangarooing or limp home mode)

Current theories (from people with more knowledge than myself)
- Turbo problem
- Drive belts and drive belt accessories

Any insights and remedies gratefully received.

[muley]

Does this happen only under load? e.g. if you rev engine on the driveway does it make the noise?

Is they any lateral play in the turbo? (take input hose off and wiggle rotor side to side)

[dapinky]

I understand where Jim is going with his questions.... the turbo will only boost under actual acceleration on a road (or rollers!) as there is an ECU input from the speed sensor, so if it happens on the driveway it is more likely to be something else (but could still be the turbo).

My thoughts are either alternator or PAS bearings if it happens static, but it could also be the timing belt tensioner, idler or water pump. With all of those items in a similar place it could be hard to isolate without stripping some stuff out. Try removing the PAS belt and see if it still happens, then remove the alternator belt and see if it still happens..... after that you're into whipping off the cam belt cover and looking at the bits inside there.

If it only happens when driving, then I'd suspect the turbo bearings are possibly worn and may be allowing the turbine blades to rub the housing - if you remove the inlet hose you can see the inlet turbine, grab the centre shaft nut and see if there is any sideways play, or longitudinal play..... and look to see if there is any scoring on the housing.

These would be my initial checks, but may or may not find the issue.

One other question, is the noise related to road speed or engine speed?

[HJ2]

I think your blow off valve needs a check on the setpoint of the spring.
It looks to me like the valve opens too soon .

[Hector2021]

switch as many electrics on as you can (headlights, main beam etc) and then see if the screech happens at a lower engine speed. It might point to an easy fix slipping alternator belt.

[HJ2]

[ATCO99]

Hi,

Sorry for delayed reply, time zone, work etc

Revved her on driveway just now and she sang all the way to 7,500rpm without screeching.

Will perform suggested inspections and a rolling rev test over the weekend and report results.

Thanks so much!

[Simon_P]

Exhaust cat ?

or Turbo bearings - they are floating bearings so there will be some play.

[ATCO99]

Hi,

Appreciate the help thinking this issue through, results of rolling rev test below

#1 - standing start, low beam headlights and dash for electrical load, screech quieter but still kicks in around 4,500-5,000rpm
#2 - rolling start, full beam, dash, radio, fog light, heater fan, screech quieter but still kicks in around 4,500-5,000rpm

Turbo inspection

Removed hose, reached in to touch impeller blade spindle and no lateral movement, however I noticed some discoloration (amber) on some blades and behind the blades the walls of the tube looked darker, possibly scored, I also noticed that the blades did not look right, it looked like some blades were hiding 3/4 behind other blades...I took pictures but struggled to embed them in the response.

Will attempt remainder of suggestions evenings this week.

Any new ideas or adjustments based on these findings gratefully received, thanks guys!