pcm talk

[BlackGT97]

I never messed around with the computer stuff in cars before. ive heard in a few threads about the pcm "pull timing"

what exactly happens when it pulls timing?
delayed valves or delayed fuel injection? idk. just woundering.

 

[blueguy]

It means it pulls ignition timing when your car knocks (KR)...when you don't have enough flow mods...meaning...your car is slow then.

 

[matt5112]

so basically your pulley should be sized based on how your motor responds to mods.

not the other way around.

 

[BlackGT97]

oh, so its kr related. gottcha, no further explantiaon required.
thanks.

and im n/a

 

[matt5112]

apparently: cam, flow more, set timing at 28, run 87 octane.

 

[BlackGT97]

wait, were not done lol. what does 28*of timing mean. sorry. and i did try and google it.

 

[BillBoost37]

Timing is at what point in the compression stroke the PCM tells the ICM to fire the coil for that cylinder. Which in turn fires the spark plug and detonates the compressed charge of air and fuel.

The higher the timing, the more compressed the charge is and the greater the explosion from the spark.

 

[matt5112]

The higher the timing, the more compressed the charge is and the greater the explosion from the spark.

The higher the timing, the sooner the fuel charge is set off.

It has to be set off at the correct time to ensure maximum transfer of energy of the fuel into downward motion of the piston.

 

[BillBoost37]

The higher the timing, the sooner the fuel charge is set off.

Er.. Don't you mean the higher the timing the more compressed the charge (aka further into the compression stroke and more powah)

The more compressed, the bigger the bang.

 

[darkhorizon]

timing advance turns the spark firing to SOONER, which gets the burn started sooner, which gives you more VE.

The problem with alot of timing, is it is obviously easy to go with too much timing.

 

[FoSHO99]

The lower the timing, the later the cylinder fires, less compression, less power.

Knock is detected by knock sensors, pcm has tables that tell it what to do for each degree of knock and when to react. It will lower your timing (retard) but if you are getting too much knock, it may be too little too late considering how fast the motor is spinning and how fast the pcm is processing all of this.

 

[matt5112]

why you say compression?

Compression is static.

The optimal time for pressure peak due to combustion is 20* ATDC.

Give or take a few... as it does very much vary based on application.

The issue is, fuel doesnt burn instantly. But thats a good thing.

Otherwise it'd be like setting off a bomb in your cylinder.

 

[FoSHO99]

why you say compression?

Compression is static.

The optimal time for pressure peak due to combustion is 20* ATDC.

Give or take a few... as it does very much vary based on application.

The issue is, fuel doesnt burn instantly. But thats a good thing.

Otherwise it'd be like setting off a bomb in your cylinder.

Because there is less compression at that moment in the stroke...

Here:
Trailer Park Boys :Rickyisms - YouTube

 

[matt5112]

Why isn't he holding a glass of rye....