Tune questions: 2008 Jeep Rubicon

[MR.T]

First, let me say that I really like the ability to change the WOT fuel and spark timing -- This sure beats changing distributor advance springs, carb jets, etc. back in the "old days". And, the throttle behavior of the Crawl Tune is a nice improvement, even on the pavement.

It's a 2008 Jeep Wrangler Rubicon, 3.8L V6 engine, 6-speed manual trans. The cal ID is 05187288AF. It has a DB Corsa off-road muffler, and a dry AFE air filter in the stock housing. So the engine may flow a tiny bit more air than stock. Only 13K miles, almost new.

I've been using the Crawl Tune, and testing for knock on hills at WOT. Ambient temp was 50F. Right now the WOT settings are 8% rich on fuel and -6 deg retarded on spark timing, same setting across all RPM ranges. It runs smooth and pulls good through 5k rpm, zero short term knock retard at these settings. With the base Perf Crawl tune, there was some ping (audible and knock retard) at WOT -- It was barely noticeable at 2K, more at 3.5K and above. As to why +8% fuel and -6 deg spark, I started by retarding timing only. The LTFT's appeared to be running in the +1 to +5 range, and after retarding timing -6, adding WOT fuel seemed appropriate. Tried advancing the timing above -6 after adding fuel, but any more and the short term knock retard would occasionally happen.

The fuel is no-name brand ~10% ethanol, ~87 rated. Concerned about being able to run a variety of available fuels while traveling without knock, and this stuff is probably a good choice to tune with.

So here's the questions:
1. Compared to the stock tune, where is the base Perf Crawl WOT fuel and spark timing? I'm interested in knowing where I am relative to stock, which may convince me to further test with either more fuel and timing greater than -6, or vice-versa.

2. How about the 87 perf tune and the MPG tune, WOT fuel and spark, compared to stock? Since I know good WOT settings for Perf Crawl, it would save a lot of fuel and time to know the equivalent in these other tunes when trying them.

3. Does the ECM on these engines do a good job of compensating for higher ambient and ECT temps? I'm wondering about how much different these WOT settings to eliminate spark knock would be on a 110F day.

Thanks in advance, other input welcome.
Mr. T

[mikel]

1. There may be about 1* added to the crawl tune over stock at WOT.
2. Well, we're not looking to give away our tuning secrets, but you can log the 2 tunes and see the difference in commanded spark. Timing is very similar between crawl and 87 tunes, there are other differences that make up the difference between the tunes.
3. Yes, the pcm will pull spark for higher IATs and ECTs.

[MR.T]

Thanks -- Is WOT fuel in the Crawl Tune less then stock?

[mikel]

No, fueling is the same across all tunes...

[MR.T]

Thanks for the info. BTW-- Having some adjustment is a major reason why I bought a DiabloSport over the competition.

[MR.T]

Log files for 0 spark and -10 spark (all ranges, with WOT fuel at zero) attached. Looks about ~5 degrees difference in timing instead of 10. I don't think the actual spark timing retarded until the setting was below -5. This is probably normal, and the setting doesn't change the actual timing directly -- But I thought it best to ask Mike: Is that normal behavior for the spark setting? Any further info appreciated.

After running log files for stock, crawl, MPG tunes with various spark timing I can appreciate the subtle changes in the tunes. For now, I ended up leaving the spark setting at -9 (all ranges) and the fuel to 0 (all ranges). The knock retard actually stopped at -7 or -8, but this probably isn't the worst fuel I'll use. The actual timing change was about -4 degrees (spark at -9 all ranges) compared to the 0 degree spark log file.

If conditions were exactly the same for the attached log files, the more advanced spark with some knock was slightly faster, and the crawl tune was quicker than the stock tune. Comparing the crawl with 0 spark to crawl with -9 spark, about 0.2 seconds difference from 2500 to 5000 RPM. Can't have the cake, and eat it to.

The stock tune also had some mild spark knock on this fuel at WOT. From reading the Jeep JK forums, spark knock is a very common complaint. Carbon build-up can of course make it worse, but I'm confident this is just typical fuel that's not quite up to par, and the mild knock retard/ping was only at WOT.

A little less timing at WOT is a perfect solution for me. Consider adding another canned Jeep JK tune with crawl attributes at idle to 1500, MPG attributes at 1500 to 3000 non WOT, and best-power/no-knock at WOT using low-grade gasoline/E10. Also, add an idle speed adjustment for the low-range 4WD idle similar to the normal idle -- The low-range idle is separate and higher than the normal idle from the factory. I think most Jeep JK owners would really like this.