OK... with consistent boost (belt not slipping so much) and LTFT's dialed in adequately enough to zero out at WOT, there are still inconsistencies in optimizing the tune.

OK... so, the 55# injectors give me more fuel. But, they have been a bear to tune compared to the 42's.
(I'm not saying all the reasons I state below are related to the larger injectors)

Some of you tuning pros give me your thoughts on what I perceive frustrates my tuning:
(For this discussion, note that there is no audible detonation and KR is mostly zero or less than 3 degrees.)

Temperature change
Checking my EFILive logs and modifying the PE/RPM table, I'd get the perfect O2 readings (about .930 or so) only to find on a cool morning, I appear to be MUCH leaner, maybe .907 or even less. At the track, where the car is not running so cool (staging lanes, previous runs, etc), the O2's can show quite a bit richer... say .945 or .955 or more. Too rich kills power, too, right?

Octane change
If I up the Octane, it APPEARS the car runs a bit richer. Also, however, I usually up the octane when going to the track, so this may be intermingled with the temperature issue as well, but this seems to occur on even the cooler days at the track.

Street or Strip
With better hook-up and less spinning, the O2's show richer as well. I rarely try to tune fuel looking at 1st gear. Even on the street, I spin all the way thru 2nd and even into 3rd if I don't pet it. There are less data points to analyze in first for sure (on the street).

OK... I go to the dyno. The accepted norm is to target an A/F ratio of 1/2 point richer than what you want in the street, right? Isn't A/F going to fluctuate by temperature and the conditions I just related above, even then? Do I get my dyno tune, st it and forget it? IS the failing of the O2's to give true tuning data significant enough that I can put my blind faith in the dyno tune? Or do I temper it with continued monitoring of O2's.

It has been suggested I need Injector Offset Table values for the Siemen 55 Hi-Imp Injectors, but I can't find any such animal. I am loathe to experiment... even with known values from other brands. Such values could be totally bogus for the Siemens, right?

Opinions?

Thanks!

 

pe vs temp if you don't want it richening up when it warms up.


imo unless your tuning a race car and need every single horsepower possible to be able to put food on your table I would tune it to be optimal in optimal conditions. IE no belt slip, nice cool day, etc... Then on those warmer days or belt slip days yah I might be missing 10-20 hp due to running a bit rich but I won't be missing pieces of my pistons Especially at your powerlevels 10,20,30hp is nothing. Myself at least I would not sweat it and instead just go enjoy the car.

that's my $.02 anyway.

 

Well for starters do not pay attention to the stock O2s.

Only do your WOT tuning on a wideband dyno, stock O2 sensors are horribly inaccurate and very inconsistant. They are very dependent on temperature and only accurate within a small range of 14.7 A/F. This is very important in FI applications like yours, you must get a real reading from a wideband.

As long as you have your LTFTs slightly negative and staying away from anything in the positives you can hit up the wideband dyno and dial in your WOT A/F. This will get you as consistant and accurate as you can get.

You want it safe for pretty much all conditions tune for an 11.7 A/F down low and rise up to a 12.0 A/F up higher RPMs after peak torque on a dynojet and leave it be.

Remember, ignore the stock O2s, they will always change their voltage WOT even if you didn't make a change because they are inaccurate and inconsistant.

Injector offset will help out your idle issues if you have any, it really doesn't affect your WOT fueling.

 

I think htmm just got his car tuned at detroit speed works last week with his new 55's
might talk to him about it.

Im getting my 55's tuning pushed back to next month so ill have to run my 42's till then.

 

Get an in-car wideband no more guessing with stock o2s. My car would not even be driveable without it.

Gary

 

So, you are saying if I dial it in at the dyno, I am done, no matter WHAT the O2's say (and I don't change boost or fueling or something related)? I will be locked in (within a reasonable range of values) to my tuned A/F?

 

Yes, as long as you have your LTFTs staying slightly negative and always 0 when WOT, you are good to set your WOT A/F on a wideband and be good to go. Your stock O2s will read something different everytime because they are for 14.7 A/F closed loop only.

 

You can use your stock O2's as a safety device (e.g. if they start reading very low I would probably verify with a wideband, look for other problems) - they work very well for telling you that you are dangerously lean - but that's about it.

You should also check out the IAT timing table - with the stock settings you can see a 3-4 degree difference cold vs hot, which is a huge deal on a blower motor - and this timing difference could account for some/all of your a/f change

 

Thanks guys.