I just spoke with Autotap customer service and their response was somewhat disturbing:

Basically they told me they have no idea what the percentages mean or how I would go about converting them to counts.

so I'm completly lost as to where my INT/BLM's are other than I know I'm running rich. INT's show 50% BLM's show 25%

 

Well I'm pretty sure the formula I mentioned above is correct. There couldn't be another way. So your integrators would be 144 and BLMs would be at 136.
Do you have a cam in your car?

 

that would make sense. I have the LT4 hotcam

 

That doesn't suprise me at all. I live literally 2 miles from B&B Electronics (the makers of Autotap) and their customer service was absolutely no help to me. And I even offered to bring the car to them to see why their software wasn't working.

 

I spoke to B & B (Autotap) both yesterday and today...very friendly but basically got the same response...they don't seem to know what we are talking about. I was told to call back on Friday to speak to a programming engineer to see if he could shed some light on this. I just can't understand why they did this and what thes numbers are a percentage of.

Madwolf: would you explain your formula once again??? Thanks!!!

 

Plus or minus 5% in autotap equals 1.6 counts over or under 128 in counts.
So if you have 10% over, you will have 124.8. If you have 20% under, you will have 134.4.

I made a mistake in the above post when I calculated 99vette's BLMs. If the computer is dumping extra fuel, the counts will be lower than 128, not higher.

So his integrators are 112 and BLM is 120, showing a slightly rich condition.

PS. That is just my theory based on BLM boundaries of 96 and 160.

 

Did you get to speak with the programming engineer?

 

I have a 96 and Autotap, but have a question about Madwolf's response above.

I thought that if the BLM was below 128, the PCM was pulling fuel because the car is running rich.

If that's true, then if Autotap shows -10% for the LTFT, the BLM would equate to 124.8

I believe the percentage is "+10% above base fueling" for example, or "-5% from base fueling". The reason I believe it to be this way. My car pulls fuel (reads -11%) at idle, so by reducing the MAF for the idle airflow range table a similar value, the LTFT at idle gets closer to 0%.

I have seen 4 LTFT (2 for each bank) adn 4 STFT (2 for each bank) entries in Autotap on a couple of occasions. This generally occurs when the config file gets messed up. Wiping out the config and having Autotap re-scan all the parameters generall fixes that problem for me. However when all the extra entries are there, none of them work quite right for me. So you might try starting with a new config file and letting Autotap scan the parameters again.

 

Nice people to talk to at B&B (Autotap), but knowone has been able to give me a definate answer to any of my questions. The Programming Engineer that I spoke to did say that 0% should equal 128 in regard to short & long term fuel trims (integrator & block learn). We became a little side tracked during our conversation as he was trying to find an older DOS version that he thought may have expressed the intergator and block learn functions as units instead of a %, but he was unable to locate it while we were on the phone. He did promise me he would find it and E-mail it to me...the bad news is that unless you have older Autotap hardware (pre July-2002), it won't be able to read any data using the DOS version he spoke about. So I suppose the few of us that use Autotap on '96-'97 LT-1 motors will have to learn to interpret the data a little differently. It appears that Autotap chooses to express some of their data differently than other scan/data logging programs. ie. Lwillmann has a good example, likewise I noticed that they express their timing advance values as negitive numbers...confusing at first, but makes more sense when you think about it. It's still hard to believe that someone else doesn't have data logging sortware for the '96-'97 lt-1 cars. If I receive a copy of the DOS software, I will update this post.

 

If the car is OBD-II then you should learn the new ways for the scanner is already doing the math for you and simply telling you if LTFT say 10 then the engine needs to add 10% more fuel in to make up being +10 lean.
Negative values means its taking fuel out since its too rich.

BLMs are not a EPA OBD-II parameter so all OBD-II scanners use the long and short term fuel trims values

 

I agree that we should be talking about it in the OBDII standard way, however many of the tuning gurus use the 128 based method for talking fuel trims, so we have to do the conversion to interpret for them basically.

I have noticed on my car that timing values show as negatives, but on another car I scanned, they showed as positives. I think that the way the timing values are displayed is dependant on the PCM you're talking to. Another example is my wife's V6 car. Although the individual cylinder misfire data is shown as available, they never appear to read anything. If they do it's for just an instant and it's cleared. The Misfire history per cylinder doesn't work for my car, but those parameters are available.

 

ok..lets see if I understand this correctly. My long terms read 25% which means the computer is adding 25% more fuel in order to compensate for a 25% lean condition in order to maintain 14.7%. My problem is its adding too much fuel. only thing I have found is that my MAF reading seem a little high with 12.5 gm/s @ 950 RPMS.

 

If your LTFTs are reading +25 then yes the PCM thinks its that lean and is attempting to add more fuel in to drive the value down to zero (128 BLM)

Problem is it may not be that lean but something is fooling the PCM such as unmetered airflow, exhaust leak, lazy O2 or even a bent exhaust valve.

Also depends on how car is tuned, it could be when lifting on gas pedal the PCM tries to save gas and shuts down fuel but the airflow path is still allowing lots of air in and PCM should have fuel learn OFF is not and those decel fuel trims are being added to the LTFT.
Check decel fuel trims, are they the only ones showing high lean values ?
Is the MAF sensor wires dirty or ported, has someone tuned the PCM and now fuel learn is on when it should be off ?

If your short term fuel trims are reporting all the time closer to around zero and are stable but LTFTs reporting +25 clearly something is not roght and PCM is being fooled into thinking its that lean and if it really was that lean overall then it would be tripping lean DTC error codes.

 

I believe that a fault MAF might also be able to cause that.

My car reads lean above idle (some times adding 20% fuel) and rich at idle (pulling 11-15%).

Good luck figuring it out!

 

Thanks for the info....I'm new to this computer tuning/diagnostics and still learning what these scanner readings mean. My car is a 96 LT4 Vette. The Engine was just rebuilt, displacement increased to 355,Hotcam,30# injectors,52MM TB, LTCC, Long tubes,ported heads,stock MAF,no cats and ED wright tune.
I also recently purchased the LT1 edit software in order to do my own tweeking however I discovered afterward that I can't read or edit ED's tune because he locks them out some kind of way.

My short terms read 50% and other problems include some knock retard at idle through the entire RPM band even with 100 race fuel. engine stumbles at WOT and when returning to idle.