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DIC in Overhead Console + LS Swap: Need your input

2K views 6 replies 4 participants last post by  Iroc-10 
#1 ·
I'm trying to work something out regarding the overhead console with the Driver Information Center (Mode Button) and LS swaps.

My truck is a 97, my PCM is a 2001 silverado, no BCM (because it's a pre-98) and I have an overhead console out of a 99 blazer.


What I need from you guys is to know, what PCM you use (year and vehicle), what year vehicle you have the swap in, and what year your overhead console came out of. On top of that, I need to know if your average MPG and/or instantaneous MPG displays accurately.

My average MPG works but my instantaneous doesn't. I'm trying to figure out if my PCM isn't sending out the data needed over the class2 data bus, what that data is, and if the OHC's from factory 411 PCM equipped s10s are different.

I'm about to start building translation modules to fix and correct little issues like this.
 
#2 ·
Using whatever PCM came from the 2000 Silverado I got the original engine from.
Can't remember the number.

Also using a DIC from a 1999 or 2000 Bravada, My average works usually within .2 gallons but instant usually only reads like 2-10mpg
I "THINK" the instant is calculated off injector pulse, and the LS being a V8 is showing two extra pulses? I honestly have no clue.
 
#3 ·
Thanks for the input. That sounds about like mine.

I plan on fixing my instant MPG. And here's where I'm going with all of this.

I assumed the OHC, being on the class2 bus, was a transmitting and receiving node just like the PCM, BCM (98+), ABS, and IPC (98+). But, I've been monitoring the data bus on a few of my s-series and my buddies too. I see the PCM (Address 10), BCM (Address 40), IPC (Address 60), ABS (Address 29) all broadcasting an "I'm here" packet if you will. It's just a status 30 packet showing that they are alive and on the network. What I don't see, is the OHC sending out one of those. The other thing that I see is PCM and ABS sending out broadcast data to functional addresses on the data bus. I do not see the OHC making a request for anything.

One of the things that I've noticed in both my LS swapped truck and some stock S10's is that the PCM broadcasts some kind of fuel data at a very quick rate. I know that it's from the PCM as it's coming from address 10. I know it's fuel related because of the functional address. Those address ranges are specified in the SAE documents. Since what it is sending is proprietary, I can't tell exactly what the data is without some further diagnosis.

One of the fuel related data packets that I've seen appears to be the fuel level. I noticed this on my buddies blazer. The packet looks like this "A8 83 10 12 D9 33". A8 is the first header byte, 83 is the fuel related functional address (the destination), 10 is the PCM physical address (the sender), and the 33 on the end is the CRC checksum byte. Now the 12 and D9 are the data bytes of this packet. 12 never changes but D9 changes SLIGHTLY over time. So I figure 12 means fuel level status, and the D9 is the fuel level itself. Dealing with a scale of 0-255 (the maximum numeric value for an 8 bit byte), we know that D9 in hex is 217 in decimal. 217 is 84% of 255. And when we were data sniffing my buddies blazer, it had a little over 3/4 of a tank of gas. So, we can draw the assumption that this is how the fuel level is sent to the IPC (Instrument Panel Cluster) and the DIC (Driver Information Center). They don't request it, the PCM just sends it out on the bus and since the IPC and DIC both handle fuel related functions, they pick up the data since the packets are addressed to modules that handle fuel related data (byte 83).

Now, the other packet that is fuel related that I see, comes across the data but at a very high frequency. It's a lot longer and constantly increases. Heres an example of the packet: "C8 83 10 0A 1B 58 B7". Now, C8 is the first header byte, 83 again means fuel related functional address, 10 again is the PCM, and B7 is the CRC checksum byte. That leaves 0A, 1B, and 58 as the packet data. 0A never changes. The other two increase at a constant rate. So 58 becomes 62 the next time that it's sent out. Converting the byte to an integer tells us that the number increased by 10. Each time the second byte (58 in this case) rolls over FF, the first byte increases 1. So 1B becomes 1C.

I did some searching online and can't come up with what this number means but I did however run across a guy playing with this same data on his harley and in his case, he called it a ticker. and each tick equated to .00005liters of fuel. Odds are that GM is doing something either the same or similar. In that case, this would be the fuel consumption rate and this would also be the data that the DIC is looking for in order to calculate fuel consumption. That would explain why this number increases. Because if it were injector pulse rate, it would go up and down and not just increase.

I need to do more logging on my LS swapped truck to see what that broadcast packet looks like on it but my guess is that the data is either formatted differently, or the functional address changed. But either way, I'm 90% sure at this point that is the packet that effects instant MPG calculations.

What I don't know right now is how this packet is used for the average MPG and accurate but way off in the instant calculation. It could have to do with a marginal error rate causing a much larger effect on the formulas used for instant MPG. OR it could be some other packet that is missing.

If I can determine how the silverado PCM differs from the blazer PCM, I can then write some code for my translation module to read the packet from the PCM then translate and output the one needed by the DIC.

These modules will be for sale once I get this figured out and a couple of prototypes out of the way.
 
#4 ·
Well I still haven't gotten range to respond to my arduino commands but I did manage to make the instantaneous MPG do something.

I mentioned the 2 fuel related packets in my previous post. The counter looking packet is required to make the Instant MPG function. As it turns out, if the fuel level sending unit is not connected to the PCM, the PCM doesn't sent out either of those fuel related packets. My fuel level sending unit isn't connected to my PCM because I have a 97 that uses the buffer module.

I programmed an arduino to send out that counter packet at a set interval and low and behold, the instant MPG started showing something on my truck when I was moving. The faster I went, the higher the MPG was. The counter always increases by decimal 10 so I know that how much it increases doesn't effect it so that only leaves the rate at which the data is being sent. So the faster those packets are sent, the more fuel is being consumed. I've got some new theories so I will do some more testing and see what I come up with.
 
#5 ·
This thread is relative to my interests. I've done a little messing around with Arduino and am pretty impressed with the things people can make them do.

Out of curiosity, had you tried using a tablet or phone running Torque or some other app, to see if the app can decode the info on the databus?

I'm putting a 2003 LQ4 6.0 in my '89 and essentially hope to have the truck just think it's a 2003 Silverado. When I get to building the interior, I may use a tablet for my cluster.

Jay
 
#6 ·
yea the torque app can decode all of the SAE specified parameters. Any scan tool can/should be able to. What I'm messing with is more on the side of the manufacturer specific commands and data. The stuff that is not SAE documented because it's left open to the manufacturers to implement how they see fit since it's not regulated by the EPA.

I know a lot of people who use tablets for their dash. I'm working the other way and making stock gauges work with basically any combination of engine.
 
#7 ·
I am with you Brandon, I like stock gauges, and stock looking stuff. In the right application, I may like a tablet with gauges, but for the most part, I like stock looking.

I like the project your working on for sure! I am not a fan of wiring, but can certainly appreciate what your doing!
 
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