strange experience twice now

[michaelb]

Hi all

96 RBBathurst.

I had a strange experience twice now on the motorway. Straight after all is fine.

It only happened when I was in 5th gear pushing the car acceleration wise as fast as it can go. I heard a grinding noise( not a bang ) for a split second and the car defiantly pulled back…Quite a nasty noise possibly coming from somewhere behind me under the car.

The car starts perfect and idles fine. Has huge amount of pulling power for practically a stock car, turbos work wonderful.

Any other time I accelerate flat out up to 3rd and all is fine….

The engine was rebuilt about 2 years ago and the car just had an engine service at Rotechnics.

Any ideas ?

Regards,
Michaelb

[Carl]

Detonation almost certainly.
If it kind of sounds like a rattling in the exhaust then that is likely what it could be and it definitely sound like it to me.
What are all of your mods?
Regards
Carl

[Red and Single]

Ouch, I hope you are wrong Carl, they don't like detonation too much :(

[michaelb]

Hi Carl

It does not sound like rattling; it last half a second, loss of power, car pulls back and it is all over in a split of a second. It sounds like a low, metallic sound….

What is detonation? I hear it all the time on this forum and I am not quite sure of the meaning….

Regards,
Michaelb




Detonation almost certainly.
If it kind of sounds like a rattling in the exhaust then that is likely what it could be and it definitely sound like it to me.
What are all of your mods?
Regards
Carl

[kev-yorks]

Sounds like it could be detonation mate. Detonation is the self ignition of the fuel air mix, because it is self ignition its not a timed/controlled explosion of the mix and tends to happen at the wrong time in the cycle hence the damage to the engine. Carl will probably come on shortly and give you a more detailed expanation.
Kevin

[michaelb]

Hi

Does it always mean a blown / damaged engine? The cat drives and pulls superb, starts in all weathers and idles perfect. Is it still OK?

RE Mods:
I have Tein suspension; HKS back box and a blitz dump valve…The car has not been de-catted…

Regards,
Michaelb

[kev-yorks]

You may be lucky some people get away with it others blow there motors first time. Its one of the reasons why some fit 3mm or ceramic seals to give a bit of protection.
Kevin

[royston1xx]

More than likely it's fuel/boost cut.

[Carl]

If it was fuel or boost cut then it would do it in the lower gears.
In 5th gear at high speed the engine is put under more load and for a longer duration at the rpm where det could occur.In the lower gears it maybe detonating but driving through it quickly and not noticeable.
Kevs explanation is more than adequate about what occurs.
Of course it could easily be something else,but from the way it has been described it sounds like det to me.
Regards
Carl

[royston1xx]

Exactly, in 5th gear there is more load which would also give more time to boost creep slightly and hit fuel cut. This is exactly what used to happen to my car 7 years ago while i was still close to stock - fine in the lower gears and fuel cut in the higher gears. Take it as you will :)

[michaelb]

Hi

What is the best way to avoid detonation ? Better fuel ? Installation on Apexi PFC and a map? Sometimes the exhaust backfires but I have been told that is quit normal with the size of the box I have...

Regards,
Michaelb



If it was fuel or boost cut then it would do it in the lower gears.
In 5th gear at high speed the engine is put under more load and for a longer duration at the rpm where det could occur.In the lower gears it maybe detonating but driving through it quickly and not noticeable.
Kevs explanation is more than adequate about what occurs.
Of course it could easily be something else,but from the way it has been described it sounds like det to me.
Regards
Carl

[royston1xx]

What fuel do you use?

[Carl]

Hi

What is the best way to avoid detonation ? Better fuel ? Installation on Apexi PFC and a map? Sometimes the exhaust backfires but I have been told that is quit normal with the size of the box I have...

Regards,
Michaelb

Hi Michael,
A power FC would be good.
It would also depend on what mods you have.
Regards
Carl

[kev-yorks]

what ever the cause i think its safe to say you aught to be going to see a rotary tuner to get it sorted before it goes pop, as fuel cut if thats the case isn't a good thing.
Kevin

[royston1xx]

Also, when did you last change the fuel filter and plugs?

[michaelb]

it does feel like a sudden fuel cut....no power for 0.5 seconds and back to normal...but I am stepping on it big time in 5th gear
Regards,
Michaelb



Exactly, in 5th gear there is more load which would also give more time to boost creep slightly and hit fuel cut. This is exactly what used to happen to my car 7 years ago while i was still close to stock - fine in the lower gears and fuel cut in the higher gears. Take it as you will :)

[Carl]

I heard a grinding noise( not a bang ) for a split second and the car defiantly pulled back…Quite a nasty noise possibly coming from somewhere behind me under the car.


The engine was rebuilt about 2 years ago and the car just had an engine service at Rotechnics.



Regards,
Michaelb


Did it sound like someone dropping a load of nuts and bolts into the exhaust?Like a mettallic loud rattle? If so it to me would still be det.
Regards
Carl

[michaelb]

I had a service at Rotechnics about 5 weeks ago...

Also, when did you last change the fuel filter and plugs?

[michaelb]

Hi Carl

no rattle just a deep grinding noise for 0.5 sec..
Regards,
Michaelb


Did it sound like someone dropping a load of nuts and bolts into the exhaust?Like a mettallic loud rattle? If so it to me would still be det.
Regards
Carl

[royston1xx]

Sorry, i missed that bit. Does it happen around 5500-6500rpm and feel a bit like the rev limiter?

[royston1xx]

Sorry, i missed that bit. Does it happen around 5500-6500rpm and feel a bit like the rev limiter? As that is where my car used to do it.

[michaelb]

it has only happened twice in the last 8 weeks not all the time...it does feel like a limiter but it is not...
Regards,
Michaelb

Sorry, i missed that bit. Does it happen around 5500-6500rpm and feel a bit like the rev limiter?

[Carl]

Royston could be right about the problem then.
I do think that you should either stop doing 150 mph,or get it tuned with a power FC!
Regards
Carl