Uber-easy DIY USB ALDL Cable

[EagleMark]

In TunerPro RT, I had to set 4800 baud and uncheck RS232 echo and it started acquiring data, and revealed an issue to chase down.

My $42 ADX file is that way, not sure how yours was differant?

[shimniok]

Mine had 2400 baud (I think) and RS-232 echo checked. I forget where I downloaded it, possibly here. $42-1227747-V4.2.adx *shrug*

[EagleMark]

Hmmm? That's one I did, but never had a reason to change that and the latest version is set to 4800 baud no echo... I've got a truck here to tune and will test it to be sure. If it works OK I'll upload the newest version ADX and XDF for you.

[shimniok]

Thanks. Not sure what happened.

So with ftdi connected the ses light flickers really fast and sort of randomly. And data stream stops. Not sure what's up. Going to dig into that next. Hard to know why the truck won't idle if I can't log data :)

[phonedawgz]

If you shorted A- B, the ses light will blink out the SES codes
If you had the 10K resistor between A and B - then the flashing light will tell you if the ECM is in a rich or lean condition. Note the ECM is supposed to alternate between the rich/lean states

By shorting pin A to B the Diagnostic ALDL connector tells the computer that it should put the SES lamp into Road Test mode. You can monitor the richness of the input by looking at how fast the SES lamp flashes.

If you've got a harness from a car and somehow neglected to get the ALDL connector (it's a GM, not Howell connector) then you can still do the test, but it will be a little more involved.

Look at the connector on the ECM. Find pin A9. This is the pin on the connector that would go to terminal "B" on the ALDL.

Pin "A" on the ALDL is simply engine ground and this point on the ECM is pin A12.

So what you're doing is grounding Pin A9 to tell the computer to go into Road Test mode.

Now when the SES lamp is flashing at the rate of about 2.5 times a second, you're in Open Loop. You'll see this happen at idle, and even sometimes when you're crusin' down the street and the engine is not working very hard.

However, after the engin warms up, SES is Off all, or most of the time the engin is running lean.

If the SES is on most of the time... the engine's running rich.

See, it's pretty darned simple:

SES on most of the time = Rich
SES off most of the time = Lean

[EagleMark]

You should build cables and advertise here?

[shimniok]

Okey doke... I broke out my o-scope to look at waveforms, looked fine whether vehicle running or not so that wasn't the problem. I thought it'd be interesting to try and buffer the signal with a PNP and was able to look at waveforms in that case. There may be a ground issue at play but need to investigate further and eliminate loose wiring. :) I was able to collect data during idle for about 30 seconds before TunerPro reported a data error (loose wiring, probably).

EDIT: it was a ground issue. Fixed. Data logging works at idle and engine off. Was able to collect about 3 minutes so far. Will have to test long term once I get this thing on the road. Wouldn't be too hard or costly to build my own circuit board.

Once the truck warmed up it was idling all on its own (not well, but still...) Pretty happy about that! Clearly open loop is whacked out. But this means idle is approximately stable enough to permit me to check and adjust timing. Whew.

I'm relying on Scott for the Autoprom emulator/burner until I can scratch together enough money for one of my own. I want to look into what it'd take to make my own emulator (or more precisely, some device that would permit near real-time bin changes). But all that's off topic.

Scott pointed me to this as a start for a DIY cable: http://www.aldlcable.com/sc/details.asp?item=daewoo

Pretty cheap too, all things considered.