Engine knocking noise on premium fuel

[Benjamin Choi]

Often when I'm going up a hill, applying throttle at say 25mph in 2nd gear, I get an engine knocking noise that's very sharp like a metal-on-metal noise. Tap-tap-tap. My indy and dealer confirmed that the noise is engine knock. I can reproduce it on this local stretch of road near my home. It happens at lower revs and when I apply the throttle say after a shift from 2nd into 3rd. Less so on the 1 to 2 shift since I usually shift at higher revs (4K ish). I've never been able to reproduce the metal tap noise with aggressive shifts at higher rpms whether it's WOT or partial.

I run premium fuel all the time no doubt. Chevron or Shell here in Seattle. I asked them if this is something that I should be concerned about (wear and tear) and both places said not so necessarily so, just keep driving and keep the revs up.

Is it Seattle fuel, my particular engine, or what? I'd rather not have this noise. Running race gas to mix is impractical for me. I have a life outside of my car so going out of my way for it is just plain nonsensical. Based on my search, it looks like it's none too common with the M96, though I have heard of another local M97 owner experiencing the same thing.

I want to just enjoy the drive with peace of mind.

Thoughts?

Edited April 7, 2009 by Benjamin Choi

[C2951]

Whey they say "engine knock" are they really trying to say "spark knock"?

If so, I think you need a second opinion because the knock sensors and the DME should prevent you from hearing that in a properly functioning system.

Based on the symptoms, I'd look for something in the transmission, flywheel or clutch, drive shafts, differential, wheel bearings, engine and transmission mounts, chassis cross brace and maybe even suspension bushings in the rear.

I don't believe they'd send you on your way if they really thought there was metal to metal contact in the engine, so we won't even go there.

Edited April 7, 2009 by C2951

[Benjamin Choi]

Whey they say "engine knock" are they really trying to say "spark knock"?

If so, I think you need a second opinion because the knock sensors and the DME should prevent you from hearing that in a properly functioning system.

Based on the symptoms, I'd look for something in the transmission, flywheel or clutch, drive shafts, differential, wheel bearings, engine and transmission mounts, chassis cross brace and maybe even suspension bushings in the rear.

I don't believe they'd send you on your way if they really thought there was metal to metal contact in the engine, so we won't even go there.

Clutch and flywheel are only 5K miles old. Engine mount is new for the heckuvit. The noise is like clack clack noise and usually accompanied as a set of two or three or four really quick clacks and goes away.

[phillipj]

Driveshaft? :huh:

[demosan]

Often when I'm going up a hill, applying throttle at say 25mph in 2nd gear, I get an engine knocking noise that's very sharp like a metal-on-metal noise. Tap-tap-tap. My indy and dealer confirmed that the noise is engine knock. I can reproduce it on this local stretch of road near my home. It happens at lower revs and when I apply the throttle say after a shift from 2nd into 3rd. Less so on the 1 to 2 shift since I usually shift at higher revs (4K ish). I've never been able to reproduce the metal tap noise with aggressive shifts at higher rpms whether it's WOT or partial.

I run premium fuel all the time no doubt. Chevron or Shell here in Seattle. I asked them if this is something that I should be concerned about (wear and tear) and both places said not so necessarily so, just keep driving and keep the revs up.

Is it Seattle fuel, my particular engine, or what? I'd rather not have this noise. Running race gas to mix is impractical for me. I have a life outside of my car so going out of my way for it is just plain nonsensical. Based on my search, it looks like it's none too common with the M96, though I have heard of another local M97 owner experiencing the same thing.

I want to just enjoy the drive with peace of mind.

Thoughts?

Ben,

I have experienced the same type of noise in my Saab Aero and found it was the plugs needing replacement. The car manual said I could use regular as well and I tried mid-grade as well as premium ( Chevron as well) and still had the noise until the plugs were replaced after only 15K miles. Never had the the problem in my 02 C4S running Chevron premium fuel FWIW. How many miles does your current plugs have on them??

Good Luck!! Dave :cheers:

[Benjamin Choi]

Often when I'm going up a hill, applying throttle at say 25mph in 2nd gear, I get an engine knocking noise that's very sharp like a metal-on-metal noise. Tap-tap-tap. My indy and dealer confirmed that the noise is engine knock. I can reproduce it on this local stretch of road near my home. It happens at lower revs and when I apply the throttle say after a shift from 2nd into 3rd. Less so on the 1 to 2 shift since I usually shift at higher revs (4K ish). I've never been able to reproduce the metal tap noise with aggressive shifts at higher rpms whether it's WOT or partial.

I run premium fuel all the time no doubt. Chevron or Shell here in Seattle. I asked them if this is something that I should be concerned about (wear and tear) and both places said not so necessarily so, just keep driving and keep the revs up.

Is it Seattle fuel, my particular engine, or what? I'd rather not have this noise. Running race gas to mix is impractical for me. I have a life outside of my car so going out of my way for it is just plain nonsensical. Based on my search, it looks like it's none too common with the M96, though I have heard of another local M97 owner experiencing the same thing.

I want to just enjoy the drive with peace of mind.

Thoughts?

Ben,

I have experienced the same type of noise in my Saab Aero and found it was the plugs needing replacement. The car manual said I could use regular as well and I tried mid-grade as well as premium ( Chevron as well) and still had the noise until the plugs were replaced after only 15K miles. Never had the the problem in my 02 C4S running Chevron premium fuel FWIW. How many miles does your current plugs have on them??

Good Luck!! Dave :cheers:

My plugs have to be less than 5K miles old. OEM.

It may be called "detonation". As you can tell, I'm no engineer.

[SH-GT3]

My guess since we're all playing :) = perhaps lugging the engine is causing excessive heat causing detonation/pre-ignition?

[Benjamin Choi]

But I promise you I really don't drive like a wu$$. If shifting at 3-4K is lugging the engine, well, then I'm guilty as charged. :D