Pre - Ignition

[91five-o]

Took my car to get it dynoed and a chip burnt however the tuner couldn't do it as he said there was pre ignition when he had it on the dyno. I have had the car on a dyno before I installed the supercharger so I guess it's fair to say the problem is a result of the install ? Mechanic says there can be a lot of causes, one being leaky head gaskets. Anyway, anybody experience this problem. Is there anyway I can change / test things so see if they are the problem without having to put the car back on a dyno. I'm at a loss and need help here ! Thanks.

Ian

 

[HISSIN50]

Are you really sure it's pre-ignition and not detonation? I dont ask to be rude - many people incorrectly interchange the two terms (they are different).

If pre-ignition, reducing cylinder head temps can help (easier said than done). The easy thing to try is running a colder plug (that might be recommended with your set-up anyhow).

Good luck.

 

[91five-o]

I have never heard of pre-ignition.....only detonation (pinging). The mechanic/tuner says it's pre-ignition and apparently this is much worse than detonation. My real problem is not knowing if doing all the possible changes will fix my problem without putting the car back on a dyno. Would hate to spend a bunch of money not knowing if it helps or not. Possible causes I'm told of pre-ignition are:
EGR valve
spark plugs
head gaskets
carbon build up

Ian

 

[HISSIN50]

For pre-igition specifically (the spontaneous lighting of the air/fuel mixture without the spark plug firing), reading the plugs is the place to start.

Deposits in the chambers can glow red-hot and act like a spark plug (or glow plug). The plug itself can allow this to happen too (one reason I mentioned a colder plug - something I would do in a forced induction set-up anyhow).

Making sure the coolant temps are in check can help keep things from getting so hot. And this can all be kicked off by leanness, too much timing, too much compression for the forced induction, too low octane for the application, intake air that's too hot, etc. EGR is used at part throttle, so that can apply in that situation.

There are clearly numerous things that can cause the issue (many more than I listed - you can see how many are related) - and with little ancillary info known, it makes it hard to know what to suggest. Did your tuner run the car at all (or do any datalogging)?

My two cents. Good luck Ian.

 

[jrichker]

Some helpful theory...

Pinging or spark knock is not the same as detonation.

Pinging is preignition of the fuel air charge by some source of ignition other than the spark plug. The source of the ignition can be a hot spot in the combustion chamber such as carbon, a spark plug insulator, side electrode, or a sharp edge on a valve. It occurs before the spark plug can fire and while the piston is still on its upward movement towards TDC. That is the cause of the characteristic ping or ringing sound, much like shaking a coffee can full of BB’s.

Detonation is the uncontrolled explosion of the fuel air charge after the spark plug fires and starts to burn. In a properly running engine, the spark plug ignites the fuel air charge and it burns slowly and evenly across the combustion chamber, much like a fire as it burns its way across a grassy field. When detonation occurs, the ignited fuel air charge causes an increase in the combustion chamber pressure and temperature. The remaining fuel air charge that has not been burned self–ignites explosively causing tremendous heat and pressure. The source of secondary ignition can be the same as preignition, or can be simply due to the heat and pressure. Detonation is what damages engine parts because of the excessive heat and pressure.

Pinging can lead to detonation, and the results are the same: engine damage because of the excessive heat and pressure