Using Diacom to tune a '91 Y-body, I measure about 6.7 frames of info per sec (at idle speeds) at max Diacom record setting.

However at 5000-ish RPM I think I am getting a different number of frames/sec - has anyone else seen this? Is it a feature of
Diacom (or is my old laptop screwey)? Or has the UV eraser started to affect my mind as well as my proms?

What I'm trying to do is adjust WOT PE fuel for a new SR intake by comparing delta RPM/sec on back-to-back highway runs, but I think the frame/sec-time constant may be shifting at high RPM, and I'm trying to pin down whether what I'm seeing is a software phenomenon or something actually occuring in the engine. (Or a hallucination from breathing too much exhaust.)

TIA for any enlightenment. And yes, this question originates from me burning my own proms.

DrJ

 

The data is transmitted at 8192 baud so regardless of RPM you will get the same data per time.

 

hectorsn -

Thanks for the thought but no, I didn't mean that the data rate at the ALDL port was changing - I was wondering if Diacom samples the data at a constant or variable frequency with RPM, say in order to maintain some level of data resolution.

Or to put the question a different way - does the ALDL bus output data at an absolute maximum rate of 6.7 complete packages of information per second; or does it update it's data faster, and then Diacom (or other software) sample it at some lower rate consistent with data storage? And is that rate held constant with RPM?

I'm looking at some high-RPM fuel transients and trying to figure out what I'm recording. One element of that is knowing for sure if Diacom is on a constant time basis - I know it can be set to sample slower, I am just not sure about faster.

What I'm trying to do is not read more into my software graphs than is really there, so I thought I'd try and double check the software picture before I started tearing apart the hardware.

Anyway, I sent this question to Rinda but haven't gotten a response yet, wondered if anybody here had run into this before.

drj

 

Well that I can't answer since I am not familiar with that software.

Actually that was the question I answered the first time. The data is transmitted at 8192 bits per second. Depending on what is in the prom is how many bits will be transmitted in every frame and that will dictate how many frames per second. For simplicities sake lets say the data is 82 bits in size. That would equate to almost 100 frames per second. Now, what the scanner software can pick up varies from that number. I would guess the software, connection, and maybe RFI might affect it in some way.

 

On my Diacom for my 7730, the display rate (at it's fastest frequency) is anywhere from 395-405 frames a minute.

There does not seem to be any pattern to these variance of +/- 1%. Possibly it is a slight "timing" error in the communication. But it does seem to vary approximately 1% with the overall average maintaining 400 frames/second for the SD 7730. I suspect yours is similar except each frame has a slightly difference amount of data when compared to the 7730.

 

Everthing with in the C3-P4 series of ecms is Time based. Newer stuff has some event based code in it. So if there is anything screwy it's in the software, but that doesn't make any sense to me.

What can happen, is that you can get out of synch with the sampling rate, vs what the sensor is doing. On a v8 you can read the O2 sensor faster then it can react to AFR changes. On a lab grade WB you can see individual cylinders firing, but not on a NB.