New to tuning PCM's and could use a little advice

[runamuk]

I had my car dyno tuned and know that my air fuel is mid 11's from 3000 rpm up but I wasn't happy with my spark advance, I knew my car had alot more power than what it was tuned for (the tuner had little or no experience tuning a LS-1 with a Magnuson s/c). The first thing I did was started to add timing and then I added more, I pretty much doubled alot of the cells and from 4000 rpm up thru 6500 rpm I went from 12 degrees to 19 degrees, this really woke the car up and now it's running like it should have been when I left the tuners shop, I still don't have any detonation and I may try to go from 19 to 20 or 21 degrees. Now I'm ready to adjust fuel, I know the car is running excessively rich because my exhaust tips turn black within a few miles after I clean them and they weren't like that with my last tune from a different shop (where the car actually ran great after being tuned). I hear alot of different terms, what is the definition of +ve and -ve? I know LTFT and STFT are long term fuel trim and short term fuel trim but what do they actually mean and how do you adjust them? Also, I hear of people resetting there fuel trims by pulling fuses, what does this do? I have 42# ford svo injectors on my car how do I set the IFR table or know what to set it at if I change injectors? Thanks in advance

[runamuk]

I hear alot of different terms, what is the definition of +ve and -ve?

I know LTFT and STFT are long term fuel trim and short term fuel trim but what do they actually mean and how do you adjust them?

Also, I hear of people resetting there fuel trims by pulling fuses, what does this do?

I have 42# ford svo injectors on my car how do I set the IFR table or know what to set it at if I change injectors?

Thanks in advance

Wow 49 views and no one else knows what some of these are either

[ArmyVette]

Robert, I've read the thread a couple of times but don't have enough experience and/or info to provide any input.

In tuning, bad advice is MUCH worse than getting no advice.

[runamuk]

In tuning, bad advice is MUCH worse than getting no advice.

How true that statement is and I appreciate it, I'd love to find a good book that explains it all but I think the major problem is lawsuits that would be filed by people blowing there cars up and then pointing fingers saying well this book or this person told me to do this or that

[gojo]

http://ls1edit.slowcar.net/tuning.html
Start here. You'll catch on and have more specific questions. http://www.installuniversity.com


[Modified by gojo, 1:56 PM 6/22/2004]

[Mike Mercury]

In tuning, bad advice is MUCH worse than getting no advice.

it's important to know your AF ratio - especially at WOT. Do you have Autotap or a wideband device to let you know where you stand on the mix?

[ToplessTexan]

TAKING bad advice is much worse than getting no advice.

That said...

I rather be on the rich side with not enough timing. Better than starting all over in my book.

People are talking about VE tuning these days after many moons of speculation. Theoretical volumetric efficiency is the ratio between say the total cylider volume and the volume of charge it's actually filled with. 1 would be perfect filling, never happens NA. FI as you might expect increases the number. Clearly this number is an indicator of the fuel required. The VE tables you can access don't strictly speaking represent this concept, but close enough. People are trying to estimate what these values should be for their particular setup using OBD-II data and some (sometimes questionable) math. It boils down to raise the number if you want more fuel, lower it if you need less (all other things being ideal.) This a feedforward component in the fueling system.

STFT and LTFT are fuel trims. STFT is driven indirectly by O2 sensor feedback and oscillates between control limits, LTFT is updated when those limits are reached and STFT returns to 0. This introduces some hysteresis so that LTFTs are somewhat stable. LTFT also has control limits but reaching these indicates a fault of some sort. These trim adjustments are used to increase or decrease injector on time, or pulse width, relative to a base pulse width which varies with operating conditions. These values cannot be adjusted per se, they are a feedback component of the fueling system.

Pulling fuses is an attempt to clear the NVRAM holding the LTFT values. Think reboot, sometimes it's nice to be heavy handed.

There are some spreadsheets running around that might be useful in determining appropriate injector flow rate values. I don't know enough about FI tuning to give much guidance on how that impacts the offset, my personal belief is that I want a shorter offset but what do I know.

Take a peek at Charles Probst's book on fuel injection systems if you haven't already. At a minimum it will help you communicate with your tuner more effectively.

I'm a pinhead and if you break your car because of anything I said or didn't say you're an idiot.

HTH



[Modified by ToplessTexan, 12:05 AM 6/23/2004]

['06 Quicksilver Z06]

.

In tuning, bad advice is MUCH worse than getting no advice.

Amen

[runamuk]

I'm a pinhead and if you break your car because of anything I said or didn't say you're an idiot.

Thanks for the info it is very helpful and are you sure you don't want to replace my motor if I blow it up

Gojo: thanks for the links I'll check those out

[ToplessTexan]

Thanks for the info it is very helpful and are you sure you don't want to replace my motor if I blow it up

Yeeeeeeahhhhh... Let me get back to you on that.