What does detonation sound like?

[scmguru]

Just got the 930 back from our new Porsche guy.

He told me the mixture was set too rich and he adjusted it from a CO of 8% to .6%.

A couple of problems now..

1. The cold idle is a disaster, it barely idles cold, backfires etc until it warms up.. didn't do that before, he suspects WUR or an intake manifold leak.

2. At a boost of .8 in 2nd gear, I'm hearing what sounds like a bunch of screws rattling around a tin can from about 4k RPM.

Does the 2nd issue sound like detonation?

Thanks Guys!

[turbobrat930]

Yep...sounds exactly like detonation....if you hear that sound...it might be already too late... if you hear that sound...let off the gas pedal....and find out what the problems is... unless you like melted pistons!!!!

[h20cooled7]

how can you determine melted pistons? will a leakdown test show this or are you tearing it down to look at the pistons

[turbobrat930]

Originally Posted by h20cooled7

how can you determine melted pistons? will a leakdown test show this or are you tearing it down to look at the pistons

HUH?

I am not saying he has melted the pistons... I am mearly stating that detonation is very bad. And prolonged detonation will cause broken ring lands, and if the temp gets high enough, there will be localized melting of the piston, commonly called "termite holes".

It is impossible to know if his pistons are melted or his ring lands are broke/ cracked, without a leakdown or teardown. I was letting him know the end result of detonation if the problem is not solved.....

[Shadetree930]

What does detonation sound like? It sounds like a great many large gold coins rattling through a large seive screen.

[h20cooled7]

I wasnt questioning your diagnosis,just trying to learn how diag nuked pistons.

[DDDD]

For some reason I always thought that detonation would sound more like the knocking and pinging you hear from bad or lower octane gas in cars sometimes?

Is it a totally different sound than that? Screws rattling in a tin can seems more dramatic than regular pinging, no?

Is detonation louder than the pinging you can get with low octane gas?

[turbobrat930]

h20... its cool... I guess I must have misread it..my apologies!

DDDD, I always thought that pinging was detonation.... just a very mild case of it... I could be wrong.

[A930Rocket]

Did anyone mention he needs to raise his AF ratio up to 3% asap?

[scmguru]

Originally Posted by A930Rocket

Did anyone mention he needs to raise his AF ratio up to 3% asap?

It was at 8% CO with the mixture screw still sealed from the factory..

Work Order states;

Timing at 26 degrees at 4000 RPM
Fuel Mixture came in at 8% CO, reset to proper .6%

Obviously it needs to go back..

[JFairman]

Originally Posted by Shadetree930

What does detonation sound like? It sounds like a great many large gold coins rattling through a large seive screen.

sometimes it sounds like little tiny metallic kernals of popcorn going off randomly to frantically inside the motor during big accelerations..

[A930Rocket]

Pull the O2 sensor when you set it at 3% to start with. Running it on a dyno or having a wide band O2 sensor will go a long way in making sure it's 100% correct.

[beepbeep]

Originally Posted by scmguru

2. At a boost of .8 in 2nd gear, I'm hearing what sounds like a bunch of screws rattling around a tin can from about 4k RPM.

Yupp, that's detonation, allright.

Your pistons might be OK but you have to check top compression rings. They have annoying tendency to crack even from slight detonation. Engine usually still runs fine but burns oil. I suggest running compression and leakdown tests. "Middle" pistons usually go first due to recieving more air from the intake pancake (thus higher AFR's). You might also have clodged injectors. Pull injectors and test them for spray pattern.

[h20cooled7]

none taken! possible turbo impellar hitting the housing?

[briankeithsmith]

Remember when Ross Perot said "You are going to hear a large sucking sound sucking the dollars out of America"

Detonation sounds the same, except "You are going to hear a large sucking sound sucking the dollars out of YOUR WALLET"

[purplehaze]

.....leave it to Brian, to spell it out in a simple language we can all understand! LOL

[NathanUK]

I've seen pics of those special 100 piece rings

[JFairman]

I think they're a little more durable than things are sounding here...