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.
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.
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
-= =-
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...
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.
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.
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.
Last edited by shimniok; 08-28-2012 at 11:57 PM.
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.
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*
-Phil, in Charleston, SC
'89 S10 Blazer: SOA SAS: Dana 44s, 5.7L V8, 700R4; 35s, 4.10:1; TBI with 1227747 ECM
'94 Grand Cherokee: 4.0, 4" lift, 31s
'90 Jeep Cherokee: In progress: 5.7L V8,700R4,NP231C, D44s. TBI with 1227747 ECM
'87 Fiero GT: 3.8SC (initial research stage)
-Phil, in Charleston, SC
'89 S10 Blazer: SOA SAS: Dana 44s, 5.7L V8, 700R4; 35s, 4.10:1; TBI with 1227747 ECM
'94 Grand Cherokee: 4.0, 4" lift, 31s
'90 Jeep Cherokee: In progress: 5.7L V8,700R4,NP231C, D44s. TBI with 1227747 ECM
'87 Fiero GT: 3.8SC (initial research stage)
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.
87 4Runner, 15" spring lift, 3" body, chevy vortec 355, 5.29 gears, 38.5x15.5x15" Boggers, 280hr, 16168625 running $0D
93 S10, 36x12.5x15 TSL's, custom turbo headers, 266HR cam, p&p vortec heads, $0D Marine MPFI with 8psi boost.
05 Silverado, 2' lift, 4" exhaust, Bully Dog programmer,
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