jayrod2

OK I did a short test datalog on my 95 383 LT1 using SCAN 94/95. First thing, one line showed a timing advance of 170!! That's super high, but it was only one line. Max advance is set at 46. But why did this happen??

Its an open loop tune, and I saw on 2 different lines the BLM went to 190. Max BLM in my tune is set at 160 so how does this even happen!??

I noticed at idle a DTC code will pop up for one line, but it will not tell me what it is not even on the line looking at the datalog. Thoughts??

Maybe these are glitches in the program, esp the 170 advance and 190 BLM. Thanks!

Injuneer

The all sound like data errors. This is not unusual, and is not generally a program problem. Could be a poor connection, or may be interference on the data line. I see these all the time. One thing DataMaster does is flag errors like this, with a window that turns red. There is a writeup in the DataMaster instructions regarding data errors, but I just checked and there is something wrong with the link on the TTS website..

I'll flag this post for GaryDoug. Maybe he can shed more light on the problem.

jayrod2

Thanks. Yeah I was pretty sure the first things were errors, but I'd really like to know what the DTC is. Or maybe its just an error too.

GaryDoug

It's not unusual to see readings that are out of bounds occasionally. The program verifies that the checksum at the end of a data line matches the data checksum calculation. If it does not match, the line is not used and a "reset" sequence occurs. You would see a delay of a few seconds and a message like "1:13:51 PM - Data timeout - signal missing (Engine)" in the Data Errors window and three messages of "Shutup request..." in the comms data window. Otherwise the data is verified to be "correct" as far as the communications are concerned. I don't know why or under what conditions that happens, but the pcm is responsible for it.

If the DTC is only showing for one or two lines, it probably hasn't been set and will not appear on the DTC tab. You can look up the explanation for the code, but I wouldn't trust it as valid.

Datamaster does use lines with errors and those lines can be seen in the datalog. One problem I noticed after adding the code to read a "uni" file was that the checksum did not match occasionally and I could trace it to a bad reading. I chose to add an option to ignore errors in the "uni" files if the user prefers, otherwise the line was being skipped. So Datamaster sees the same errors but, in general ignores it, and sets an indicator as a warning.

jayrod2

How would I look this up?

GaryDoug

I don't know if this site has a reference section but you can use this one. Fred (Injuneer) contributed to it:
OBD1 DTC Codes & Troubleshooting - LS1TECH

jayrod2

Oh I misunderstood you. Yeah I know the codes, but what I was saying is that it isn't even giving me a number as to what DTC it is. It only shows that "1" DTC popped up on the line.

GaryDoug

oh I see what you are saying, the number is reported as 1 but there is nothing in the column next to it? I don't know how that would happen. The only way to know for sure is to have generated a comms log file so I could see the original data. But that does slow down the scan a bit. It is possible that the pcm reported a DTC number that doesn't exist in the malf.csv file I suppose. I will double-check the completeness of that file.

GaryDoug

I found a possible omission in the malf-csv file. DTC35 is listed as "not used" in the definition file I used and it does not appear in the 94 service manual in the LT1 section. But it does exist in other cars. It is possible there was an omission in the manual and the definition file, since DTC35 is for the IAC valve and there are no codes for that shown in the manual. To be safe, I have added it to the malf.csv file so it will appear if indicated in the datastream. There are also several others that I find no reference to anywhere, but since they may be reported I also included those. The file has been updated on the file storage location and is in the zip file with the rest. The zip file revision remains at version 1.0.8. All you have to do to update yours is to download the zip file again and replace the malf.csv file with the newer one. Thanks for the "heads-up" ;-)

jayrod2

Hey thanks so much for this program. Its amazing. IAC does make sense, because for one I only see at idle, and 2nd my idle is wandering/surging a little. Thanks a lot!!

Edit - what is the definition of DTC 35?

Injuneer

Interesting. In the 15+ years Ive been running codes I've never seen 35 used with reference to the 94/95 LT1. It's not listed in the factory manuals for both the F-Body and Y-Body. Even TTS Datamaster shows it as "n/a".

On the other hand, I've seen Datamaster set DTC 52 for the engine oil temp low, and 62 for oil temp high. Those are valid codes for the Y-Body LT1, but not for the F-Body. But they show up as a valid code in both versions of Datamaster, and will sometimes appear in F-Body scans.

GaryDoug

52 and 62 were already present in the file. But I did add the following, all without any description: 30, 39, 40, 49, 56, 57, and 60. Those will now show up in the DTC screen and on the log file but will have no details.

Injuneer

Be good to see what pops up.