87 Octane Fluttering Engine Sound

[pinchemateo]

So I recently swapped in a 20V blacktop and put in the 87 octane fuel instead of 91 on accident. I am about a little over 1/2 through the tank now and I have started to hear a "fluttering" noise coming from the engine at 3k to 4k rpm. I have put in octane booster just for peace of mind but it doesnt seem to be changing much. Not sure if its pinging from the lower octane fuel or a greater issue. I can replicate the "fluttering" by revving up to 3k-4k parked. Has anyone else experienced this by putting in a lower octane fuel or is there a greater issue? Any thoughts on this? Thanks

[Deuce Cam]

Is this the first tank of gas on the swap? Have you drove it hard with the low octane? (If so stop until you get the right octane in the tank.) I would just put around like a grandma until the tank is near empty (or drain/refill if you're really paranoid). Octane boosters rarely do anything unfortunately. You'd be better off adding some unleaded race fuel, but it's really expensive ($8+/gallon) if you can even find it locally.

I doubt it would ping in neutral with no load applied, but it's hard to say for sure.

[pinchemateo]

Is this the first tank of gas on the swap? Have you drove it hard with the low octane? (If so stop until you get the right octane in the tank.) I would just put around like a grandma until the tank is near empty (or drain/refill if you're really paranoid). Octane boosters rarely do anything unfortunately. You'd be better off adding some unleaded race fuel, but it's really expensive ($8+/gallon) if you can even find it locally.

I doubt it would ping in neutral with no load applied, but it's hard to say for sure.

This is the 2nd tank I have driven on it. First time owning a premium gas car so naturally it just slipped my mind the next fill up and I put in 87 oct. I have not driven it all that hard on this current tank so I am doing like you suggested and putting it around until I can put premium in it. At rpm's lower than 4k it doesnt make that noise I was referring to so until I put premium ill avoid it. Thanks for chiming in.

[jondee86]

Pretty sure that the BT has a knock sensor, so it should pull timing if there
is any knocking/pinking caused by the low octane fuel. You would feel that
as a loss of power in the engine speed range where knocking occurred.

EDIT: Probably there would be a loss of power across the whole engine
speed range. Once the engine stops knocking, the ECU will gradually restore
the timing to normal, providing there is no more knock.

Cheers... jondee86

[pinchemateo]

Ok so I put in 91 octane gas and the "fluttering" sound was still there at 3k and onwards. I then did some research and thought it was the click of death and my pulley was not working correctly. I did the 12v power to the VVY solenoid test and it didnt make the sound go away. I revved at 3k to replicate the sound and then had someone spark the solenoid and nothing happened. I couldve sworn the sound my engine was making was the same as this guy's 20v https://www.youtube.com/watch?v=e0WjRSAo5Vs. Any thoughts on this should I be worried? Thanks!

[jondee86]

Fluttering is not a term commonly heard to describe engine noises.
Knocking, tapping, squeaking, whirring, whistling, scraping, graunching,
clunking... yes, even rattle and hum <-- for the old school dudes
So kind of difficult to pin down. VVT pulley knock is mostly noticible at
idle, and as you know, there is a simple test to check if this is a problem.
Tiny, very rapid tapping/ticking noises are more or less normal for cams
hitting buckets, and it usually only becomes a problem if one valve gets
way out of adjustment, and ticks louder at a slower rate.

If this is a high mileage engine, then you may have a timing problem
caused by a loose cam belt. The tensioner is hydraulic apparently, and
they do fail and need replacing. Cam timing being off can cause strange
gasping or choking noises to emanate from the intake side... kind of like
the noises Bart makes when Homer was both hands around his throat

There are other things that can cause strange noises, but it is near
enough impossible to diagnose them without having the engine running
and a stethoscope to narrow thinks down.

Cheers... jondee86

[pinchemateo]

So just wanted to give an update to everyone. I took my car to my mechanic and we used a stethoscope and found the problem. It was actually a bad alternator and one of the bearings was messed up. Since the bearing was slightly damaged it was vibrating and making noise at higher rpms. Just wanted to update everyone thanks! Also just took the 86 to the track and it was a blast.