LTFT and the VEC2

[Steve 00RT/10]

I was wondering what experience anyone has who set their LTFT to close to zero.
On the first car I did last spring, zeroing out the adaptives required going from a 65% base set to 70% and some additional individual cylinder trim. Bank 2 requiring a little more offset than Bank 1 from the factory default settings. Last night I played with the new car and found the same thing. I went from 73% base set (40 pounders)to 78% and ended up plugging the same cylinder offset as the 00 car. I'm around +5% now. I used the EASE scan tool for this tuning.

Anybody have a similar experience or comments on this process?

thanks--Steve

 

[red98RT10]

 

[Shelby3]

Mods, please move this post to the theories of relativity forum.

 

[Mr Hemi Head]

Mods, please move this post to the theories of relativity forum.

This is a feature of the Scan tool or the EASE product that is available from Roe.
Apparently there are not many on the forum that are familiar with it.

 

[Joseph Dell]

Not much happened when i messed with it. car ran about the same.

JD

 

[Steve 00RT/10]

During conversations with Sean last winter prior to buying the Roe blower, it was suggested that Long Term Fuel Adaptives are best if close to zero. I think factory parameters may be allow up to +18%. That means that the computer is trying balance out the LTFT in closed loop to achieve around 14.7 AF ratio. After the install, my car set a lean code a couple thousand miles in. A scan tool, generously loaned from Mr. Hemi Head, showed my LTFT to be +32% on one side and about 28% on the other. That's what set the code. The computer couldn't feed enough fuel at the 65% injector setting. Instead of adding big amounts to each cylinder, I increased the base setting to 70% and then added a little more cylinder trim on bank 2. I then relogged all my cards for temp. variation.

I bought my own tool from Sean after getting this new car because I decided to set the LTFT before logging anything at all---unlike the first car.

I'm not sure a dyno with a WB stuck up the exhaust pipe is the best way to tune these. That's the way this new one was done 3 yrs. ago. Even though the dyno sheet for this car is strong, I think it's running fat. A fair amount of smoke at WOT is evident for a second or so. I had the VEC2 S105 updated to 106 last week and am just trying to get some of the parameters in place that I had some trouble with last time. I have the WB meter installed, output to the VEC2 in, and the WB sensor going in next week. Then I'll be able to see the AF all the way up. I totally agree with those that say a WB set up and logging is the only way to go.

I thought I remembered reading about someone here who had to increase their injector base set after updating to the S106 program. This is all brand new stuff to me, but I decided if I was going the blower way, I would install it myself and learn a little more about the AF end of it.

Steve

 

[Jack B]

A couple of suggestions on setting fuel trim - It is best done while viewing LTFT as the car is driven. You will see the trim move around, it is a moving target. Look more for the average than the trim at a given moment. In other words have the scan tool set up when you are driving, if the scan tool is capable of logging (just as the Ease)that is even better, just look fo the avertage and adjust accordingly.

I could be wrong, but, in the diagnostics manual I believe it says that a code will be if the LTFT runs over 44% for a period of time.

 

[Steve 00RT/10]

Thanks Jack,

You're right, the LTFT is a moving target, but according to Sean...the closer to zero the better.

I don't have the capabilities of adjusting on the fly with the laptop set up I have. The EASE tool functions through the laptop as does the card reader for the VEC2. I only have one 9 pin port to use for both.

I guess I can't be certain what was setting the lean code, but I do know I have not set one the last 6500 miles or so since adjusting the LTFT down to around +2% average. I set the new car by getting the initial correction from idling......then I went for a spirited spin and back to the garage...engine running all the time...adjusted again. Did this twice. It's much better than it was. I'm in the 0 to +5% range now.

Steve

 

[KenH]

You are probably referring to a post I made last year. When I upgraded to the S106 firmware, my car threw a lean code on both banks within 20 miles. I bought the EASE software and checked my adaptives and the PCM was adding a huge amount of fuel, running out of range and then setting the lean code.

With the larger 53lb injectors, the offsets are normally set for around 57%, but on my car with the S106 firmware update, I had to adjust them all the way up to 74%. I also had to run my passenger side cylinder bank richer than the driver side which is the opposite of most cars. After doing that, my SC setup ran right for the first time since the SC was installed about 6 months earlier. Sean did not have an explanation, but said that he had run into at least one other Viper that responded as mine did.

I adjusted my offset at idle per Sean's recommendation, so I think you are fine doing it that way, though there may be something to be learned by logging at other than idle as well. If you want to run both the EASE software and the VEC2 logging and your laptop has a USB port, you can buy a USB to RS232 adapter so that you can hook up both systems at the same time if you want. They are pretty cheap.

 

[ViperBing]

As was said before, make sure you look at the LTFT's in the entire rpm range, not just idle.

Here is a decent guide to LTFT tuning (ignore the MAF translator stuff):

http://www.c5forum.com/diy/ltft.php

 

[Steve 00RT/10]

Thanks Ken. Yup, you're the guy.

The VEC2, in my 2000 car with 50 pound injectors, came with a 65% base set. I'm pretty well zeroed out at 70% with some additional trim on the passenger side. I have the 96 PCM in this car.

The 2001 car has 40 pound injectors and came with a 73% base set. I'm now at 77% and in the +2% range. This car has the stock 2001 computer and front O2s in the 'cheater' position of the 3rd tube (Belanger headers). No lights being set, but I'm a little hesitant to do anything with much individual trim (except 9&10)as I am not sensing an average of 5 tubes---only the 3rd one on each side. The WB sensor will hopefully be in the collector area by week's end so I can do a little logging and see where it's at.

Here is a decent guide to LTFT tuning (ignore the MAF translator stuff):

Thanks---good read. I printed it.That's how I understand it to be as well. Unless I'm mistaken.....at 80% throttle to WOT, the VEC2 takes over in open loop and the O2s are not in the equation at all. When you say the entire RPM range, you must mean only in closed loop operation. I think setting the LTFT at idle, taking a few runs, and then resetting it... is probably close enough and much better than it was. I could be wrong, but I thought the factory parameters allowed an 18% LTFT variation to be within spec. Also, as Jack mentioned above, LTFT is kind of a moving target. I take that to mean it can vary under different operating conditions.

Steve