Low RPM Hard Acceleration - Pre-detonation

I have looked about and have had a bit of a hard time finding info about a noise I am getting at low RPM when I accelerate hard (lug the engine). I think I found a few threads that imply that this can cause some strange noises. Was hoping for some more information.

So my problem is NOT pre-det - it is in fact VANOS clatter... If I run the factory 241 software, the problem goes away.

The noise is present when running Stage 1or Stage 2 programs and it is present when lugging at low RPM at wide open throttle. Higher octane fuel seems to help, a lot, and that is odd...

But with some great help from Alex, the problem has been narrowed down to VANOS adjustments. I can now run a Stage 2 tune with normal Stage 2 timing advance and I no longer get the rattle/clatter at low RPM WOT after Alex changed the VANOS advancement back to stock.

This has been a bear of a problem to diagnose as my car never threw a single code. It just made bad sounds. But, Alex helped a lot to get this figured out.

Cheers,

Do you have a video clip of the sound?

Mine does a lot of weird VANOS noises, but that's usual and the whine of the gears might be part of the all the noises you're hearing.

Get a video and post back up.

-M

I took a video, then realized the camera was pointed squarely at my crotch... So I ripped out just the audio

https://vocaroo.com/i/s1dEWMceQUOe

The clicking/rattle happens a second after I hit the gas then stops right after I stop accelerating.

This was in 4th gear at 40KM/hr - ~1800RPM to 2500RPM ishish.

Thanks again for the help.

Cheers,

A little longer would have been much more appreciated lol!

Where is it it coming from? Engine bay, finder wells, back, front?

It almost sounds like you have something possibly in the intake or the air filter - as you suck in and open the throttle, it starts to rattle. Any loose wiring that might move around under load or anything like that under the hood?

I'd really need some more information my dude - I faintly hear it but a few runs of acceleration say 5 runs might be sufficient to help diagnose.

Also, where do you hear it in the car? Really need to try and pinpoint a general area.

Let us know, thanks!

-M

DukeofAlexandria wrote

A little longer would have been much more appreciated lol!

Where is it it coming from? Engine bay, finder wells, back, front?

It almost sounds like you have something possibly in the intake or the air filter - as you suck in and open the throttle, it starts to rattle. Any loose wiring that might move around under load or anything like that under the hood?

I'd really need some more information my dude - I faintly hear it but a few runs of acceleration say 5 runs might be sufficient to help diagnose.

Also, where do you hear it in the car? Really need to try and pinpoint a general area.

Let us know, thanks!

-M

Yeah, posting in a rush is always awesome...

The noise seems to be coming from the engine bay area. It only makes that noise when lugging hard at low RPM. Once it hits 3K, it goes away.

I have looked in the bay and cannot see any loose wiring. I take a look at the exhaust and make sure nothing is rubbing etc. but it does sound higher in the engine area, not below the car.

I will also see if I can get a better set of videos!!

Cheers,

Hmmmm, interesting.

Have you take the plenum off and also the breather box/air intake? Honestly could be something in there that you aren't able to see on the surface level.

-M

I resolve that with new spark plugs and using 93 oct exclusively. On the 2nd tank with 93 the noise disappear.

Eme 3 wrote

I resolve that with new spark plugs and using 93 oct exclusively. On the 2nd tank with 93 the noise disappear.

What!?

Resolve what? He doesn't even know what the issue is yet, lol!?

What was the root cause of your issue? Did you have a loose spark plug, or pre-detonation occurring?

I'm a little confused here, as just 'changing plugs' and using '93 oct' would resolve such an issue as rattling below the 3K RPM mark, especially without determining the root cause of the issue.

-M

I'm not sure if it's the same sound you're experiencing, but check this thread out

https://www.m3post.com/forums/showthread.php?t=603650

I have looked through that, might be the same - it is hard to tell. I will put it on jacks and check the exhaust too. I will also try to get some better audio samples. I have just been crazy busy.

Thanks,

I know the noise you on about but cant make it out myself. It's either the LSD plates slipping and doing there job. Or maybe the clutch springs if you have a manual like me or maybe it's just another one of "those noises" we pedantic M owners have trigger our OCD. fml

Took a mechanic out for a test drive - immediately said it was pre-det. Might be I got some bad fuel.

I had to buy gas today so we will see if that sorts it out.

Cheers,

I KNEW IT!

LOL!

Get a fuel injector cleaner, but you'll ultimately want to find out why it's doing that.

Either advanced timing to early/late or really is bad gas.

Good luck man!

Our gas quality has gone down the toilet. I bought one of those ethanol strips and found 18% ethanol in my gas and the car ran like shit.
Loved going to PA to fill up with non ethanol gas. The car felt like a different animal. I just think these motors are sensitive to bad gas.

DukeofAlexandria wrote

What!?

Resolve what? He doesn't even know what the issue is yet, lol!?

What was the root cause of your issue? Did you have a loose spark plug, or pre-detonation occurring?

I'm a little confused here, as just 'changing plugs' and using '93 oct' would resolve such an issue as rattling below the 3K RPM mark, especially without determining the root cause of the issue.

-M

d

Duke:

What I was trying to say is that I resolved similar symptoms that our friend described as:
"In my case, I notice a intermittent pinging when I accelerate hard when at lower RPM. Not something I do a lot but from time to time you have to react to other "drivers" and a gear change is not practical. Once I get over 3K RPM, all is good. Engine pulls to redline no problem. This does not sound like rod knock to me (not to mention I hit redline daily and have not had any parts try to escape yet). Also, it has been happening for some time and does not make any noise when out of gear at any RPM."

After spark plug change and my second 93 oct tank, pinging noise disappear. Good luck!

Ahhhhhhh, gotcha!

Sorry, it just read a little weird and I wasn't sure where you going, gotcha!

Thanks for clarifying and appreciate it! :-D

-M

I updated the original post. Issue is pre-det under heavy acceleration at lower RPMs. Was wondering if there are any things to check if pre-det is a problem. Plugs look good. I run Shell 91. Bearings are BE and car has ~44,000KM on the clock.

Any help would be greatly appreciated.

Cheers,

Scharbag wrote

I updated the original post. Issue is pre-det under heavy acceleration at lower RPMs. Was wondering if there are any things to check if pre-det is a problem. Plugs look good. I run Shell 91. Bearings are BE and car has ~44,000KM on the clock.

Any help would be greatly appreciated.

Cheers,

My car does predet at times at around 2k. I bought the car at 17k and it sits at 27k now. Right now about time to change the spark plugs so that might contribute. My view is that these engines simply are tuned for high rev. Try driving in traffic between 2.5 and 3.5-4 rather than 2 and 3 for example like in the usual 5.5k max rpm toaster oven utility car.

m3jala wrote

My car does predet at times at around 2k. I bought the car at 17k and it sits at 27k now. Right now about time to change the spark plugs so that might contribute. My view is that these engines simply are tuned for high rev. Try driving in traffic between 2.5 and 3.5-4 rather than 2 and 3 for example like in the usual 5.5k max rpm toaster oven utility car.

Issue I have is that it is really quite bad at low RPM and I am getting some pre-det at 5K+ too (not much but a little) when running a tune. When running factory, it is all normal.

Just wondering if there is something that may lead to pre-det - fuel filter? Coil packs? I am not throwing any codes...

Good times...

Scharbag wrote

m3jala wrote

My car does predet at times at around 2k. I bought the car at 17k and it sits at 27k now. Right now about time to change the spark plugs so that might contribute. My view is that these engines simply are tuned for high rev. Try driving in traffic between 2.5 and 3.5-4 rather than 2 and 3 for example like in the usual 5.5k max rpm toaster oven utility car.

Issue I have is that it is really quite bad at low RPM and I am getting some pre-det at 5K+ too (not much but a little) when running a tune. When running factory, it is all normal.

Just wondering if there is something that may lead to pre-det - fuel filter? Coil packs? I am not throwing any codes...

Good times...

I know you said spark plugs look good but when were they changed?

Is the air filter clean and no blockage?

Filter is pretty clean. The plugs have about 13,000KM on them.

:|

Thanks for the help, keep the ideas rollin:)

Question: would O2 sensors cause pre-det issues and not throw codes?

Typically the engines I've seen the exhibit this have a fair amount of carbon deposits on the piston crowns and exhaust valve faces. The intake valve faces also to a lesser extent.

The carbon deposits hold heat and can create hot spots, so that on compression of the fuel air charge, it ignites prior to the spark event.

Most often, using a high quality 93 octane or higher (Shell seems to do well at this) will over a few tanks remove some of the deposits and improve things. Sea Foam in the intake may be of use here as well.

Test the theory with a cheap Harbor Freight borescope camera and 90 degree attachment down the spark plug hole and look at the piston crowns and valve faces.

I suspect oils which are noted having lower consumption also reduce the carbon build up as well.