Got DIS (Trip Computer) working on the 94!

[GnatGoSplat]

Yep, spent all of last night and this morning trying to figure it out.

 

What's missing is the Injector Flow Rate (gal/hr) from the ALDL chatter.

I logged some ALDL chatter from the 94 and the 89, stared at it, studied the source code, programmed a new chip, and voila! Now it works! Its accuracy is yet to be determined, but making it more accurate will just involve tweaking the injector flow rate. Apparently the 94-96 GP DIC's have the injector flow rate hard-coded into them. Either that or they calculate mpg differently.

 

There 2 bytes in the ALDL on my 89 that kicks out injector flow rate (which is a fixed value). On the 94, they're both zeroes. In the MEMCAL code, I could see those zeroes were coming from memory location 0333 which is just a stack overflow test location and is always zeroes. So I looked for an unused space in the chip where I could stick an 02B0 (688) which is the injector flow rate constant from a 93 3.4 DOHC. I ended up putting them in location 9270 and 9271. Then I changed those bytes in the ALDL stream to look at my new memory locations 9270 and 9271.

 

That's all it took! Let me know if you want detailed step-by-step instructions, but you'll need an EPROM programmer to even attempt this.

 

I have a feeling I'll have to tweak it, because I doubt the 94-95 3.4 DOHC's have exactly the same injector flow rate as 91-93 3.4's. This trick only works on 94-95 3.4 DOHC... 3100's have a much more sophisticated PCM.

[1990lumina]

Holy shit you are smart man!!!

[5speedz34]

Damn nice job, I could only wish I was into electronics that much!

[cutty]

i wish i could get a dis working in my car!

[THe_DeTAiL3R]

Pfffft.. I could have figured THAT out..

 

[Grand Moff Joseph]

wow, excellent work!! :worship:

[Psych0matt]

I would want this information. I'd love to get it all to work right. My dad does hvac controls for all sorts of big companies and hospitals and stuff so Im pretty sure I could get a hold of an eprom programmer... This would be amazing to figure out!

[GP1138]

Awesome!

[Dirty Rockstar]

[pitzel]

Nuts gnatgosplat. Actually, how hard is it to pull the EPROM for programming Gnatgosplat? Because if it is not that hard, one could probably reprogram a H-body DIS (Eighty-Eight, Ninety Eight from the early 1990s) to work on a W-body.

 

Too bad though, by the time we finally have these cars truly figured out, they'll be rotting in the dump. lol

[GnatGoSplat]

Pulling the EPROM is not too difficult. There are snaps on the MEMCAL and it comes right apart. Then to pull the EPROM itself out, a small flathead jeweler's screwdriver to break the solder joints will get it right out. You could also build an adapter to read and program the EPROM in place. The only difficult part of not removing the EPROM is the entire MEMCAL won't fit into the average EPROM eraser.

 

In my case, I have an old ADS SuperChips MEMCAL adapter which has a socketed chip. The MEMCAL piggybacks onto it and I've plugged a 29C256 Flash EPROM into the socket since it erases in the blink of an eye and programs in less than 5-seconds.

 

DIS from an 89-90 Eighty Eight and Ninety Eight will already work. They are nearly identical in every way except internally. Cutlass DIS has a uPD78C10 MCU with separate EPROM while Eighty Eight and Ninety Eight DIS has a uPD78C14 MCU which has an onboard EPROM. I believe I have a Ninety Eight DIS in the 94.

[Psych0matt]

I believe I have a Ninety Eight DIS in the 94.

 

That you got to work with this method, or that works without reprogramming?

[GnatGoSplat]

I got it to work with this method. It expects the same inputs as the 89-91 trip computer.

[GnatGoSplat]

Just a quick update and some info on this project...

 

I've been keeping a spreadsheet the past month comparing actual fuel economy to the DIS. Using the injector flow rate of 0x2B0 (688), the DIS avg fuel economy was WAY off. When I go to Fuel, the number of gallons consumed was consistently 1.68x higher than actual number of gallons consumed. It was showing about 10mpg when actual is around 17.5mpg.

 

I've since changed the injector flow rate to 0x19A (410) which is approximately 688/1.68=410 (rounded up). Hopefully this will make it accurate.

 

Something else I've learned is it doesn't matter for what engine the DIS was originally for, as long as it came out of a 6-cylinder car. The fuel economy computation is based entirely on the injector flow rate sent to the DIS. If the injector flow rate is accurate to real life, then the DIS will be accurate.

[90TGP]

You sir, have too much time on your hands. Good job 8)

[NOHC_WBody]

Shawn, j00 is Electronik Supersonik. 8)