Uber-easy DIY USB ALDL Cable

[RobertISaar]

depends on the application. most cars don't need it, the some that do tend to need a 10K resistor connected from the B pin to the A pin(or the ground on the converter) either temporarily or permanantly.

if you use a male OBD1 connector, then you could simply run a wire from the B pin to a rocker/toggle switch, then to a 10K resistor, then to the ground circuit. you can then hide all of it in a small project box from radioshack. i think i use the 3" X 2" X 1" versions.

Having the 10K resistor between pins A & B won't hurt however.

depends. some applications go into "ALDL mode" and will change the idle speed and add up to 10* of spark advance.

[belaw]

depends on the application. most cars don't need it, the some that do tend to need a 10K resistor connected from the B pin to the A pin(or the ground on the converter) either temporarily or permanantly.

if you use a male OBD1 connector, then you could simply run a wire from the B pin to a rocker/toggle switch, then to a 10K resistor, then to the ground circuit. you can then hide all of it in a small project box from radioshack. i think i use the 3" X 2" X 1" versions.



depends. some applications go into "ALDL mode" and will change the idle speed and add up to 10* of spark advance.

This is for a '7427 PCM and I will probably omit the ALDL connector for a permanent install. So can I just de-pin the white/black wire that terminates at pin B from the PCM and pitch it?

[RobertISaar]

IIRC, the only thing the 7427 uses the ALDL pin B is for blinking out codes if connected directly to ground.

i'm not a 7427 expert though.

[EagleMark]

This 10K needed for 160 Baud ECM is a horrible rumor created on internet that won't go away! Even the Moates website shows 10k resistor needed for all 160 Baud ECMs. 10K really messes up good data on 1227747 and other old 160 Baud ECMs by putting the ECM in ALDL mode, it increases idle and adds timing, not needed at all for data!

Other then checking codes by crossing A and B I've had no use for 10K, it is needed in $6E to start data flowing. I have no idea what else it is used for except to screw up data.

[shimniok]

Glad I found this thread. I'm trying to build an ALDL USB cable using a different TTL serial to USB converter.

WinALDL can't connect to it and neither can TunerPro RT. Only one of my terminal programs displays any data.

Do I *have* to tie the tx/rx lines together for a 160-baud 7747?

The usb/serial converter is on COM11. Maybe TunerPro and WinALDL can't access those ports? Or maybe some incompatibility with the driver for it.

Since we know the FTDI thing works... I may use one of my two FT232 breakout boards from Sparkfun as soon as I can find them :)

One is 3.3V -- what I usually do converting from 5V to 3.3V is to throw a resistor inline to limit current. For an automotive application at such slow rates I might just use a 10K instead of my regular 1k.

More later, hopefully...

[RobertISaar]

with a 7747, no, all you need is the receive part of the circuit, since it doesn't communicate in both directions.

COM11 is fine, i'm all the way up to COM15 at times(i've connected a lot of converters) and i'm still communicating normally.

leave it at 5V, 3.3 might work, but it might also cause more problems.

[phonedawgz]

If you are looking at a 160 baud - one directional cable, and you want to keep the 3.3v input - you should be able to do it with just two resistors to divide the voltage. A single resistor inline won't drop the voltage unless there is current flowing.

From the pin E - connect to resistor A - then tie to both the RX pin and resistor B - and then connect to ground.

Try using a 1K for resistor A, and a 2.2K for resistor B. Check the voltage on the RX pin since the unknown is the resistance of the USB rx input.

You do not have to have TX and RX tied together for 160 baud pin E applications.

TunerPro has no problem with the upper COM ports. I have been up in the 20s with no problem.

[shimniok]

Ok, I found the 5V FTDI breakout board and it worked, sort of.

I can see data coming in over one of the serial ports. I tied tx/rx together and TunerPro RT sees it when the ECM is off or disconnected. Neither it or WinALDL can talk to the thing on COM10, however.

I will have to go find out what to do with TunerPro RT to get it to work with this setup.

Sparkfun did a tutorial on interfacing different voltages some time ago in case anyone finds this useful: http://www.sparkfun.com/tutorials/65

The single resistor approach probably works best if there's a clamping diode on the 3.3V end. Hmm.

[shimniok]

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.

[89S10_Project]

This 10K needed for 160 Baud ECM is a horrible rumor created on internet that won't go away! Even the Moates website shows 10k resistor needed for all 160 Baud ECMs. 10K really messes up good data on 1227747 and other old 160 Baud ECMs by putting the ECM in ALDL mode, it increases idle and adds timing, not needed at all for data!

Other then checking codes by crossing A and B I've had no use for 10K, it is needed in $6E to start data flowing. I have no idea what else it is used for except to screw up data.

See, this is why I should have kept reading before posting that last ...

[belaw]

IIRC, the only thing the 7427 uses the ALDL pin B is for blinking out codes if connected directly to ground.

i'm not a 7427 expert though.

Does the 7427 reset/"zero" the IAC when pin B is grounded, or is that just the earlier ECM's?

[RobertISaar]

good question, one i can't answer though.

if someone had a bench setup, then it would be very easy to test, otherwise, you might need to monitor the IAC movement manually, preferably without the pintle shooting off.

[PJG1173]

neither my 8625 or 7427 zero out the IAC when jumpered. what I have done is to use jumper wires to the IAC to send the pintle to its seat. also setting the park position to 0 in the bin will put it to what it thinks is zero.

[phonedawgz]

You have to send a series of rotating/reversing electrical signals to move a stepper motor (IAC). You can't just jumper power to it.

http://www.youtube.com/watch?v=t-3Vn...eature=related