I've started to dig into my programming a little deeper. I've noticed that the High Octane timing table, the main PE table, and Base Timing in drive, and in park, all have a VERY pronounced dip in the ~1,200 to ~2,400 rpm range.

In timing tables, were're talking about g/cyl's only in the .36 to .52 range. to be completely honest - I have no idea what those values mean, or where those particular tables come into play.

Sooo....

1: Does anyone else have these dips? (is it an '04 thing?)

2: What's it for? Emissions? Keeping temps down? Fuel economy? (doubtfull)

3: Has anyone corrected these dips? Anyone have numbers or methods to share?

I smoothed out my HO timing table DRAMATICALY, but haven't run it yet. I don't quite have the guts to. I had to add about 4-5* of timing in places.

If I could be instructed how to post screen shots, I'd be glad to do it. (that whole print screen thing doesn't work for me).

 

Sounds like tqmgt...lol

Anyway, I'd say a lot has to do with EPA/CAFE regulations and GM's ability to meet those year after year. If they tweak the PCM every few years they can easily meet those requirements and whatnot.

Not only is my truck faster with a normal advnace curve, the fuel economy went up a lot too.

 

That's what I'm thinking too...

Here with HP Tuners, I can do a 2D line graph, of the tables/values of a certain parameter. (I'm sure Edit can do that too). These dips stand out "like a green hat with an orange bill".

It's weird that all values under .36 g/cyl flow nicely... and all values above .52 g/cyl flow nicely. It's that hole right in the middle of the timing graph. A picture really is worth a thousand words here.

I think you're right about the tail-pipe-sniffers... it has to be a rpm/load range that gets special attention paid to it during testing.

 

I know its two completly different vehicles, but I had those high octane timing dips also. it'll dip down to 22 degrees as the rpm's get higher at WOT. We changed that part of the table to +28, that way from 3000rpm on up at WOT it'll stay at 28 degrees. I also deleted TM so it won't drop timing to 0 or lower during shifts. I'm not exactly sure which tables I changed, i had a friend help. PCM tuning section should have some good info.

 

Ah-hah. Here's the HO timing table.

 

Here's the LO timing table, as a comparison.

 

Looking over my logs, those values look like part throttle acceleration. Like taking off from a light. I think they're too low g/cyl for wot.

I don't think smoothing those will help wot performance, but might make it a little peppier around town.

 

Have you ever logged g/cyl? If you go do that for a while It'll give you a good idea of where you really want to change your timing.

 

Cool, I think I got it figured out!

I just pulled up a few logs, and I HAVE logged g/cyl's in a background field. (duh, stupid me)

I just breezed through one log, and it appears that I'm in the .36-.52 range around 15-35% throttle, under 2000rpm or so.

I've occasionally noticed that the truck will sometimes feel real doggy under 2K locked up in OD. I swear, right at 1,900-2,000, the motor will feel like it "cleans out" or "liven's up" and it will pull more cleanly. It was quite apparent pulling 4,500lbs down the highway this past weekend. I felt like I had to have at least 2K on the tach in order to easily cruise up some hills. I just thought it was a characteristic of the engine.

I just dug a little deeper in the logs, and sure enough, RIGHT at 1900rpm, I see .56g/cyl's........ which is the next higher up "clean" timing curve in the graph.

I'll throw my modified timing curve in later today.

 

Biiiiiiiig difference. Wow.