When I'm just driving around, the spark advance on the scanner reads between 30 and 33 degrees. When I floor it, it goes down to 10-12 degrees. I have my base timing set at around 7 degrees, and I followed the correct procedure with disconnecting the ECM and everything to set the timing. Why would it do this? I've noticed that sometimes it actually detects a knock and it retards the timing 2-3 degrees, but even when it doesn't, the advance still goes way down. Could this be something with the actual PROM, or what? I haven't tuned the PROM myself yet. ANY help would be greatly appreciated. Thanks in advance.

 

Interesting......

dug into your ignition system? Esc etc?

let me know what you find

how many knock counts per WOT run?

 

I'll speak about my car since it's a good example here.
A lean mixture, like in cruise takes a long time to burn, and the leaner the cruise the more timing you need to run. ie, in cruise at 16.5 AFR in my car I run 44d of timing. At WOT which is richer I run 17d of timing. granted being a turbo car I don't need much timing to make good HP at WOT.

 

Well just getting started in chip burning so I'm not positive if my analogy will be correct, but in general automotive theory you should have a bunch of advance in cruise mode. In a carbureted motor this is controled by the vacuum advance, cruise mode is a high vacuum situation. Then when you nail it the vacuum goes away so you lose the vacuum advance and as the rpm's climb you gain advance back as the mechanical advance kicks in. You weren't specific about rpms and such so I dunno if this fits. But if you are cruising along and nail it the advance should drop and if you keep it nailed as rpms climb the advance should as well, but if your getting some knock retard it may mess with that. Hope this helps or is even close
John

 

As mentioned above, YES, the eprom purposely will back off the spark advance when you place a load on it. All ignition systems do this, whether they are computerized or mechanical.

The reason as Bruce began to explain is that at part-throttle, you only have "partial filling of the cylinder". When you are cruising, you have a high vacuum. This is because you only part of the cylinder gets filled with the mixture. You may only get 1/3 of the cylinder filled with the mixture when cruising down the road. So your "dynamic" compression ratio is going to be significantly less than the "static" compression ratio.

This lower "dynamic" compression ratio during part throttle driving is a lot less volatile. To restore power and throttle response, we add more spark advance. Now, add a functioning EGR and a lean ratio (as with Highway Mode) and the mixture becomes even less volatile and you need to add even more spark advance. This is why cars with EGRs typically run around 38-40* of spark advance at "part-throttle" and if you invoke Highway Mode, you often have to advance your spark even further to reduce the "sponginess" of the throttle.

At high load situations, like climbing a hill or WOT, the vacuum of your engine is virtually nothing. This is because the cylinder is being filled as much as the heads, cam and intake can support. Now the cylinder is almost completely filled and your "dynamic" compression ratio has climbed to as much (or possibly more) than the "static" compression ratio - depending on your cam etc. The mixture is now very volatile and cannot toloerate too much spark advance without detonating. This is why we need to lower our spark advance when we place a load on the engine, or we will start to have detonation occurring.

This is something that engine builders noticed 100 years ago, and why all ignition systems (mechanical distributor, electronic or even Opti-spark) behave this way - high spark advance at low load/low spark advance at high load.