Okay, I've been trying to "dial in" a tune for my new 396 LT1 engine, and, of course, I have been doing a fair amount of datalogging on it using Scan 94/95. Recently I've been seeing erroneous readings from my datalogs.
For example, I'm doing 4th gear pulls from about 45 mph to 75 mph to try and load the engine, while keeping the rear end from "stepping out". (With both cooler weather and the street tires I'm running, I can't do pulls without "blowing off" the tires in any gear lower than 4th).

Now, when I chart speed (mph) as one of my inputs, the (auto (?)) scale for mph goes from 0 to 30 mph, even though the speedometer in the car is showing 45-75 mph. Anyone know what's happening here?

TIA for any replies.

 

Replied on ltxtech

 

Asked Gary to take a look.

 

Thanks (again) Fred!

And if you need any Scan 9495 data logs showing what's happening here, I have them, but .......... you may have to tell me how to send/post them.

 

Is this for the engine scan or the transmission scan?

Yes, post the log file here. It will be in the same folder as the scan9495.exe file and will have the date in the filename. The file extension will be ".csv".

 

Gary, it is definitely the "Engine" scan that I'm seeing the problem with. I have a manual transmission in my car and I have never used the transmission scan.
Now, I did find the log file with the ".csv" extension, but, when you say post it here ...... where is here? Can I "attach" the log file to this post on this website, or,
do you want it e-mailed to you???

If you want it posted on this site ...... please tell me HOW to do that, or ....... send me the e-mail address you want it sent to, okay.

Thanks sooooooo ..... much in helping to resolve this issue.

 

Attach the file to a post right here.

Hit the “Go Advanced” button at the bottom next to the “Post....” button. When that screen opens, at bottom left, immediately under the post text field, click on “Manage Attachments” button. When that opens, click on “Browse Your Device” (assuming the .csv file is saved somewhere on your computer). Find your .csv data log file in your directory and select it. That should put your file on the screen. Click “Upload” button. That should attach the file to the post. Click “Post....”.

Gary and I can then download it to our computers and look for any possible problems with the file,

Appears you want to son one axis of the plot. What do you want on the other axis?e MPH?

 

Okay, I'm giving this a "shot" per Fred's instructions. And ....... thanks to your great instructions Fred ..... it looks like this actually worked!

Attached are two (2) data logs which were scanned yesterday. In both of them the vehicle speed (MPH) data is corrupted. In one of these logs you will see a 4th gear "pull" (where the TPS% hits 100%), and the data shows an increase in vehicle speed from something like 9 to 15 mph, when in actuality the car is accelerating from like 40-45 mph to 75-80 mph. This discrepancy is what first caught my attention. The recorded engine rpm during this pull seems correct, but the mph is waaaaay off.

Please DO let me know what going on here, okay.

Thanks (again) for your help with this.

 

Fred, I honestly don't know what you're asking here? Any clarification would be very helpful.

Thanks

 

The subject of your post is a problem with the scaling of the MPH in a "chart". A "chart " (which could be called a "plot" or a "graph") typically has an "X" (horizontal) axis (base line) and a "Y" (vertical) axis (base line) axis. But let's answer the next question first, because the only thing in the data log that looks the least bit "off" is the MPH.

Is it possible you have a digital conversion box between the vehicle speed sensor (VSS) and the speedometer, or between the PCM and the speedometer? That device can be used to calibrate the speedometer for things like a change in rear axle ratio, or when using a PCM calibrated for an auto transmission (40 VSS pulses per revolution) with a manual transmission (17 VSS pulses/revolution). I do that with my TH400, using a Dakota Digital box, although I run it through the PCM in the normal routing, then to the speedometer, so the PCM and the speedo both show the correct speed..

The error in MPH with the wrong trans VSS reluctor would be 17/40 = 0.425 X actual speed. That seems pretty close to the numbers you are quoting.

Might want to adjust the closed throttle TPS voltage closer to 0.50 volts.

 

The mph data is a very simple calculation. It is a single integer having a value from 0 to 255. That number represents the vehicle speed in mph. The program is correctly reading the data coming from the pcm. It seems that there is something else going on to offset the data to the pcm. Fred's idea makes the most sense. To add to that anomaly, the speed goes often from 0 to 5 mph or back with no speeds in between at any time (no 1mph, 2mph...4mph). That indicates something going on with the signal to the pcm not being correct. The maximum speed shown in both files is 27 mph

 

Fred, first off, no there is no such device on my car, as you've asked about. And secondly, thanks for the tip about re-adjusting my TPS voltage closer to 0.50 volts, will do!

Did you also notice the split LT BLM's between bank 1 and bank 2? I intentionally raised the maximum BLM setting range to 180, in my last tune because, it did peg at 160 on bank 2 in the previous tune, and now ..... also pegs at 180 in the new tune. I'm going to switch my bank 1 and bank 2 O2 sensors, and see if the problem follows a (bad ?) sensor.

 

Gary, thank you for confirming that the program is correctly reading from the PCM. I'm guessing that this anomaly might be (?) something recent in the laptop computer I'm using??? Again, I've been using your Scan9495 program, and this laptop, to data log for several weeks now, and before these latest scans, the MPH was indeed reading correctly. If I attach an older scan where the MPH is reading correctly, can you compare the correct vs non correct scans and maybe better pinpoint where the current problem came from?

Also, in this sentence, "It seems that there is something else going on to offset the data to the pcm." .... did you mean to say ..... to offset the data ..... being displayed on the laptop?

And again, thanks for any "light" you can shed on this.

 

First of all, I know very little about the tuning parameters and procedures on this engine. I have only done one very minimal change to my test PCM just to see how it can be done long ago.

However, after viewing the parameters listed in the Tunerpro "EE" definition setup, it appears that there are multiple vehicle speed scalars to adjust. One of them is designated the one for a scan tool. I have some suspicion that the scalar for the gauge output has been changed from it's normal setting because of differences in the transmission, but the one for the scan tool has not been changed. The bottom line for this is that your pcm is outputting the wrong data for vehicle speed. At this point I have no other suggestion except to investigate those settings.
This problem has nothing to do with your pc.

 

First off .... Thanks Gary!

I have just checked the scalar settings you've referenced above between an older tune, and my most recent tune using the compare feature in the CATS tuner program that I'm using to write my tunes, and, unfortunately ..... there is no difference in those settings.

But ......... it is good to know that you don't think the problem lies with the PC I'm using! At least now I can focus trouble shooting this problem on the vehicle, and not worry about any PC issues.

Thanks ...... again for your input.