Base Fuel Calibration on VEC2

[Achilles99]

Question:

I have 63 pound injectors. According to the VEC2 instructions, I should set the base fuel calibration to 30(GenII)/63 = 47%. However, my car currently has 55% on it (from a previous tune done by a well-respected tuner who shall remain nameless for now). I am throwing a "Bank reports rich condition" engine code. That means that I have the base fuel calibration set too high, right? IE, in closed loop (throttle < 80%) the PCM is having a hard time with the fuel adaptives?

If I change it to something lower, will that throw off the open loop fuel and ignition maps entirely off? Right now, after installing a WBO sensor, I'm running pretty lean (12.5-13 at WOT). I'm afraid that if I change the base fuel calibration to something leaner to help prevent the check engine light (which I assume is triggered during closed loop mode), I'll be changing my open loop fuel and ignition maps. So, perhaps I should bump that up a notch as well all across the board? Let me know what you think, thanks!

 

[grcforce327]

Regardless of your second paragraph,You need to set the fuel adapts as close to zero using a data scan tool and the Vec for the greatest window,and then start the tune.

 

[Achilles99]

What do you mean by "the VEC for the greatest window"? Thanks!

 

[grcforce327]

Read your Vec instructions,it's all right there!

 

[KenH]

Your logic is sound. As noted above, you need to bring your adaptives closer to zero by changing the injector offset. You can do that at idle with a scan tool. When you make an adjustment, it takes a while for the adaptives to change, so be patient with waiting for the changes to take affect. You should also check your left and right banks as one will tend to run leaner than the other one and offset the two sides appropriately. In my case, I had to adjust the injector offset drastically different than the formula would have suggested to get the adaptives correct.

Once you bring your adaptives in line, your fuel calibration will be running leaner and you are already too lean as it is. If your A/F is fairly even now over the RPM range, you can just scale the whole range up by 20% or something that should be safe and then do a quick run-up and see what your A/F is looking like. Scale the range up or down to get close and then you can dial in specific spots over the RPM range to smooth it out. I don't know if it makes any difference whether you scale the load or RPM tables to offset the injector offset that you are introducing. I tend to use the RPM table myself. Just remember that it is safer to start out too rich and work from there than to chance starting out too lean.

 

[Achilles99]

Ken, thanks for the advice, especially richening up the entire curve before going any further. I believe I'm going to scale the load up a little bit first, since the RPM range already has a few places at 133% (out of a possible 200%). Last thing I want to happen is to run out of adjustment room.

Grc, I reread the instructions. I even did a text search for "window," and only came up with the Microsoft variety. The only thing I can think of is that you are talking about the 33% window that the PCM can handle. However, I heard that anything greater than 10% on the long term fuel adaptive is too much.

I have a Paxton, with belanger headers and some various motorwork done
by Woodhouse. My 63lb injectors would indicate a 47% base, but for
some reason it was at 55%. I dropped it down to 50% (and richened th load by 5% to compensate), and to correct
the fuel trim I have the left bank set at -0.26 (it was 0.0) and the
right bank at -0.46 (was -0.20). My long term fuel adaptives dropped
from -15% to around 0% +/- 2%. HUGE difference! Can't wait to go to
dyno tomorrow and tune.

I hope this information helps others trying to tune their VEC. DON'T TRUST YOUR DYNO WIDEBAND. Mine was tuned with it, and after installing my own WBO sensor I can see that I'm too lean. So, either the tuner didn't know what they were doing, or the dyno was off.

 

[KenH]

Dyno A/F tends to read richer than you see when tuning on the road. General rule of thumb is to adjust on the rich side when dyno-tuning as you will tend to lean out a bit on the road.

 

[Achilles99]

Just got back from the dyno, did 15 miles (yes, 15 miles) of dyno runs to get the fuel right. NO IDEA how it was this far off. Actually, I do. Terrible tuner. I'll bite my tongue.

The car, when it had a VEC1 and the stock tranny, did 825rwhp. Today, just working on fuel and not timing, I got close to 800rwhp. Not bad.

However I don't want to touch timing before installing some kind of knock sensor. Guess I have to do some research on that. Also, has anyone installed a "vacuum box" with individual lines running to each gauge/VEC/etc. so that boost readings aren't bouncing all over the place due to multiple taps into the same line?

 

[Joseph Dell]

Just got back from the dyno, did 15 miles (yes, 15 miles) of dyno runs to get the fuel right. NO IDEA how it was this far off. Actually, I do. Terrible tuner. I'll bite my tongue.

The car, when it had a VEC1 and the stock tranny, did 825rwhp. Today, just working on fuel and not timing, I got close to 800rwhp. Not bad.

However I don't want to touch timing before installing some kind of knock sensor. Guess I have to do some research on that. Also, has anyone installed a "vacuum box" with individual lines running to each gauge/VEC/etc. so that boost readings aren't bouncing all over the place due to multiple taps into the same line?

Most people tuning don't use a knock sensor b/c they aren't reliable and w/ soooo much noise in that V-10 motor as-is the sensors don't work that well.

take me along and i'll teach you to tune by ear!

PS - thanks for coming out to help w/ Chris's car yesterday! it was good to see you!!

JD

 

[Achilles99]

Tune by ear? That sounds too scary But, I'll try it if you promise to buy me a new engine if our ears are off!

 

[Joseph Dell]

I keep a spare block around just in case...

 

[Achilles99]

I would say haha, except that I've seen your garage enough to know you aren't kidding!