WHAT IS THE DIFFERENCE BETWEEN SPARK ADVANCE IN DEGREES AND IGNITION TIMING?
1997 Lexus LS 400
July, 29, 2012 AT 4:01 AM
Been having some problems that I'm trying to nail down (car hesistates at idle only after engine has warmed up and sometimes will rarely shut off when put into gear. I will have to get back with you because first I want to troubleshoot a few items before throwing in the towel per se. I have an Innova scan tool which gives me a live data read. It shows what they call "spark advance" in degrees. Is this the same as ignition timing? If so, why do they call it spark advance rather than ignition timing and if its not the same what is spark advance and its relation to ignition timing if any? You guy do a great service for us diy's. I appreciate your input.
Spark advance is the computer advancing the timing or retarding of the timing. Verus the ignition timing which is the actual position of the distributor in the engine in relation of distrubutor to the rotor which you can advance the timing or retard the timing by turning the distrubutor. Setting the intail ignition timing you would set the number one cylinder on top dead center and have the rotor pointing at the number one post for the number one cylinder on the cap. When reinstalling the distrubutor just to give you a example of actual ignition timing. So at idle when warm it misses?
July, 29, 2012 AT 4:29 AM
They are referring to the same thing. The spark has to occur before the piston gets to top dead center because the gas and air do not explode; they burn rapidly, and it takes some time for that to occur. The spark has to occur at varying times before top dead center depending on engine speed, load, temperature, and other factors.
Since the Engine Computer can't get a timing pulse from a sensor, then fire the spark plugs a measured amount of time BEFORE that pulse arrived, there is quite a bit of initial timing advance built in to that signal, then the computer varies how long of a delay is needed before the spark should occur. For example, the pulse might be designed to arrive at 30 degrees before top dead center. If the calculated desired spark timing is 10 degrees before TDC, the computer waits 20 degrees after the signal arrives to fire the ignition coil. The spark advance in this example is the desired 10 degrees before TDC.
July, 29, 2012 AT 4:41 AM
But that is in refrence of the actual phsical intail timing of the distrubutor which I was talking about before.I belive thats what they were asking.
July, 29, 2012 AT 5:12 PM
So the advanced spark I'm reading on my obd2 tool is the same is ignition timing?
July, 29, 2012 AT 5:27 PM
That would be the actual timing and where the computer is adjusting it too.
July, 29, 2012 AT 6:23 PM
I tried multiple ways to say it but no matter how it came out it is a real simple answer that gets way too complicated by trying to explain it. Your scanner is displaying the number of degrees before top dead center that the spark is occurring, ("where the computer is adjusting it too"). The ignition timing, or "timing of the spark" is the same thing, just different terminology.
July, 29, 2012 AT 6:27 PM
Oops. Let me clarify; I don't mean I tried explaining to YOU multiple times and you didn't get it. I meant I typed a reply, proofread it, didn't like it, deleted it and started over, didn't like what I typed, started over again, and still found my reply to be confusing.
You might be over-thinking this too and are getting "wrapped around the axle" over a simple concept.