After the 1993 model year, no Bonnevilles had the flash feature (paper clip trick). The feature isn't even programmed into the PCM, as the codes for the hybrid OBDII (94/95) are alphanumeric. Not strictly numeric like previous years.

All OBD1 scantools will work with the 94/95 as long as you buy/make the cable to adapt it. Some members here have these cables if any of you need the pinout.

When placing these LEDs, where exactly in the circuit did you connect them? i.e., for the DATA terminal to ground, did you connect it in parallel with Q1, or from the base of Q2 to ground? For the RxD terminal, I'm assuming you went from the collector of Q2 to ground. For the TxD terminal, did you go straight from TxD to ground or in parallel with D1?

The important concept here: are your LED placements in such a manner that the current through them is limited by one of the 10k resistors? For example, an LED in parallel with Q1 will have 12V across it when the data line is high, but LEDs are generally designed for about 2V forward voltage drop. That'* presenting almost a dead short to the data line -- the LED will draw a lot more current than it should, possibly destroying the LED and may do damage to the PCM too.

Same for the TxD terminal -- from TxD to ground, there'* 12V present when the computer'* serial output is high, so an LED between those terminals would have the same results as above.

If this is how you connected your LED, your results are exactly as expected; from DATA to ground, 12V across the diode = very bright. From TxD to ground, 12V across the diode = very bright. From RxD to ground, there'* a 10k resistor in series from the power source, so the LED would only get a small amount of current = dimly lit, if at all.

In response to your previous question, only AC signals interfere with each other when the wires are close. 12VDC in a twisted pair acts almost the same as a ground -- no interference. Plus, twisted pair eliminates most interference anyway -- it'* only at extremely high frequency or if the wires are laid side-by-side for long distances that crossover interference becomes a factor.

In response to your latest question re: upping the current limit, the serial port'* input impedance should be nearly infinite, like the inputs of an op-amp. The 10k resistors are called pull-up resistors; when, say, Q2 is off (DATA terminal low), no current flows, and the voltage drop across the resistor is zero, so the voltage at, the RxD terminal is high (12V) -- when the transistor is on (DATA terminal high), current flows through R1 and the base-emitter junction of Q2, allowing current to flow through the collector-emitter path of Q2; there'* probably about 2V dropped across the collector-emitter path, and the rest of the voltage is dropped across the pull-up resistor, so RxD would sit at about 2V, which the computer reads as low.

Similarly, when sending data from the computer to the PCM, a high signal at TxD turns on Q1, pulling the DATA line to ground, and a low signal at TxD turns off Q1, leaving DATA high.

So the resistors are really just there as current limiters. Transistor-to-transistor logic (TTL) only requires enough current to turn the transistors on and off, which is usually a few hundred microamps in the base and a few milliamps in the collectors (obviously varying depending on the transistor). More current won't give you anything other than increased heating -- at least, that'* my opinion. I could be wrong

-b

Okay, I'll take Will'* word as gospel. I must have been hallucinating. Sorry!

By "scantool" I assume you mean Tech I/II, Actron CP9110, Snap-On stuff, etc -- and *not* the deals they sell at Sears that plug into the DLC to flash codes. If it can't flash, it can't flash, whether it be with a paper clip or a $40 plug-in thingy. Right?

-b

enmityst,

Thanks for the reply. I did a little more research, and RS-232 is specified as
a "0" level between -3 and -25v, and a "1" level between +3 and +25V. On my
laptop, I was reading -9v on TX, I believe, so it sounds like it would expect a swing between +9 and -9v. This circuit will only swing between ~12v and around 1 or 2v positive. Maybe the probelm then is, my "0" level is not going low enough for the PC to recognize it. This might vary from PC to PC. Maybe yours works because the long cable is causing overshoot and undershoot, so the PC sees a negative value when it switches to "0". Just a thought. They make special chips (MAX232), that have a charge pump built in to supply a -10 and +10 supply, to allow for use with a single +5v supply.

I'm not an expert on RS-232, only relaying what I read about, but I am EE trained, so have some knowledge on basic theory, although I do mostly software work, so I'm a little rusty.

Yes, but I've read that apparently many serial UARTs can happily deal with serial signals that vary between high ( > 3V) and "idle" ( -3V <--> 3V ) -- perhaps you're correct, and yours cannot.

I've played with MAX232s in the past (they're the communications chip used in many SCADA controls), but I tried this circuit because it was much simpler, and I didn't have to wait for some company to ship me anything.

You might be able to rig up a phantom negative supply, since the circuit doesn't really use much current; hook two 9V batteries together in series and redefine ground as their common terminal; then you could redesign the circuit such that it pulls RxD to -9V with the DATA line high, and pulls RxD to +9V with DATA low. The rest of the circuit I think could remain the same, save some grounding issues you may have connecting that floating circuit ground to chassis ground and RS232 ground. Just a half-baked idea, though.

-b

Actually, that sounds like a great idea. I will try it with a battery. Now that I have a better understanding of it, I think this just might be the solution. As far as damaging the PCM with LED, I already did some experiments with it, so if it was damaged, it'* too late now , but my car still runs fine, no SES lights. I wonder if blowing up the data port would still allow the rest of the computer to operate normally. I will let you know if this works.

Well, after much pain and misery, I found the problem. One of the transistors in my circuit was bad. Once I replaced it, it worked. Still it acts kind of clunky. Sometimes I can get 10 good data retrievals in a row, and then it hangs until I turn off the key, or interrupt the signal.

In any case, I got alot of info back. The thing that really stood out the most was there were alot of misfires reported. Also using your m1m1 ald file, I had a fair number of
faults reported, too many to be real, I think, unless my car really does have a serious problem, even though it runs smooth. Maybe my PCM is flaky.

Anyway, thanks for providing the info to make this work. I'll have to play with it some more to try to make sense out of the data.

I figured out the flaky reading problem. I was trying to apply the M1M1 ald to M1M0 data. That explains that. This program is not as obvious as it may appear. You have to dig into the help files, only available on internet as I found out, but the ini file also holds alot of info missing from the ald files to get the most out of it. I finally figured out how to use the charts after studying the example, and it'* pretty cool. You can chart up to 24 parameters at a time.

I can't wait to get home tonight to try some more. I'll take it out on the road with my laptop and collect some real time data.

Congrats, glad to see someone else got it to work Also remember that my data definitions files are not exactly the same for you, since you have an SSEi; somewhere above I posted a link to a zip file that has 200+ ALDL definitions in it, if you haven't already seen that, so that you can customize my files for your car.

-b

Enmityst,

I already modified them. There'* not that much different between them, other than a couple not used becoming boost control and a couple factor values different. So far I'm liking it. I also figured out the macros. You can alternate between "hush chatter" and a normal command automatically. I will try that out tonight to see if it helps with stability.

Good luck on your intake repair.