I've had this problem ever since I first tried to reprogram my car. Instead of having to mail my PCM off to Ion at MadZ28 everytime I need something simple changed, I decided to get the e-mail package and invest in an ALDL cable. Another thing to note: I did the ODBII to OBDI conversion, so my car is like the 94 and 95s -- OBDII port with an OBDI PCM. And the saga begins...

Process
As the instructions suggest, before trying to write a tune, it is recommended to read your tune first to make sure it doesn't fail (and won't fail during the write process). This is where I'm stuck.

Hardware
I have a laptop and am using the Belkin USB to serial adapter (the common one everyone recommends). I'm running Windows XP and absolutely nothing is wrong with the PC. I actually used to be a PC tech and know all about COM ports, IRQ conflicts, etc.

Software
As for software, I've been using C.A.T.S. Winflash (tried 2.11 and 2.15) to try to read the PCM and also FreeScan to see if that works.

Problem
Everytime I try to read the tune, it will get anywhere (approximating) from 2% to 40% finished and error out with "Invalid Response from PCM."

Hardware Part II
Allowing chance for the problem to be a quirk with my laptop, I tried using my desktop. It did the exact same thing. I even hooked it in directly to the serial port. No go. I went as far as to use my parents computer trying both USB and serial. Same error.

Then a few days ago I read a document suggesting that Windows 98 SE would be optimal. Reluctant, I formatted and installed Windows 98 on my laptop (which sucked ***, by the way). So last night after getting that up and running, I took it and hooked it up to my car. Invalid Response from PCM.

Other Troubleshooting
When I first bought the cable and attempted to read my tune and had problems, I consulted the ALDL troubleshooting guide. It suggested using hyperterminal and shorting two of the pins. If you get characters on the screen, the cable is good. I got characters, so it rules out my cable being bad (I think).

Even though I couldn't read a tune, I tried using FreeScan. On Windows XP, from what I can tell the logs show a lot of irrelevant chatter coming from the PCM. The only way I can get it to work is to do a FORCE DATA command. It will then work anywhere from 10 seconds to a few minutes and then randomly stops with a similar message to the "Invalid response from PCM." I can't recall the exact message at this point, but it's something like "Could not read header."

Last night I tried using FreeScan again with Windows 98SE on my laptop. All it would do as soon as I clicked Start Scan is get a Fatal Exception and crash.

More Information
I spoke to Ion from MadZ28 about my issue when I needed a re-tune. He had me ship it off to him to make sure the PCM was good. The way he tunes PCMs, from what I understand, is using a harness that plugs directly into the PCM. He said he had no issues tuning it. So the PCM is fine as well (I think).

What Could It Be?!
So, it seems like I can rule out the following as issues:
1. Computer - tried 3 computers, USB and serial, Windows XP and Windows 98SE
2. Cable - connects fine and tests OK in hyperterminal
3. PCM - has no problems taking a tune from Ion at MadZ28

I'm no tuning expert by any means, but it seems as though the connection between my OBDII connector and PCM has to be the culprit. But if that's the case, why am I not having any other problems?

Please help!

Also, if there are any tuners in the northeast Oklahoma area, I would really appreciate it if I could bring my car to you and see what happens with your equipment. I'd really like to get this problem resolved. Even if I can't fix my issue, I'd be willing to pay to have my car re-tuned (just to change gear ratios) if I get a new rear end this summer.

 

Could be the ALDL recive and transmit pins are incorrectly placed.

 

I thought about that. But if that's the case, how would it even begin communication and get to a certain point when reading my tune? A few times before it has gotten close to half way.

 

Did you repin the ALDL and the PCM lines ?

 

No, I haven't. What exactly to you mean by repin? Sorry, kinda noob at this.

 

obd2 and obd1 ALDL connectors have different pin assignments for programming lines.

 

This is what I have:
http://www.aldlcable.com/sc/details.asp?item=aldlobd2

It's an OBDII connector for an OBDI PCM, which is what I'm running. I've looked at the diagrams and it appears the wires/pins are matched up to where they should be.

 

This cable will not work on 1996 and later OBD2 cars! Although the connector style is the same, 96 and later cars use the OBD2 communications protocol, and are not backward compatible to earlier year cars. The 94 and 95 cars that are equipped with the OBD2 style connector actually have OBD1 ECM/PCM systems behind them. If you have a 1996 or later obd-2 car, buy our OBD2 Allinone scan tool.

 

Um, I have an OBDI PCM in my car. I think I already said that?

 

What i keep telling you and your not listening is that the ALDL and the PCM have differing pin assignments for programming from 94/95 and 96/97 if you have acess to an Alldata of mitchell subscription you will find out exactly how to fix it.

 

You can't tell me which pins to switch?

Also, you made it sound like you thought I was running an OBDII PCM.

^ Is that not what mine has? You're saying an OBDI PCM will work in place of an OBDII but the wiring is different?

What if my 1996 or newer car has an OBDI PCM? Will it work?

 

PM me.

 

Check out the pic -- I really don't understand how it can get so far in reading a tune and then error out if it's something to do with the pins being in the wrong place.

This is the farthest it has ever gotten.

 

Answer these questions.

1. Did you do the OBD2>OBD1 conversion yourself?

2. If yes, did you do anything besides plug a OBD1 PCM into the OBD2 harness on the car?

3. Why are you not using the flash program built into the CATS editor?

 

1. No, I purchased a tuned OBDI PCM from MadZ28.com and installed it.

2. No, only the OBDI PCM is plugged in (with an LT4 knock module).

3. All I have is Winflash, not the editor. I get my tunes from Ion at MadZ28.com

 

Look at the two diagrams.
On the PCM D Connector (Blue), 96-97 PCMs use pin 7 for the data line. 94-95 PCMs use pin 30 for the data line.
On the ALDL connector. 96-97 OBD2 cars use pin 2 for the data line. 95 OBD1 cars with the OBD2 ALDL plug use pin 9 for the data line.

 

Awesome, so on my ALDL connector I need to take pin 9 and put it in pin 2's position? That's the only one I need to change, right?

Thank you SOOO much.

 

I just tried switching pins on my ALDL connector and it wouldn't even connect. Then I realized if I'm going to make this work I'll probably have to switch the 7 and 30 wires?

 

The data pin in the ALDL connector needs to match the data pin in your interface cable. Since it is a OBD1 cable, it is probably using pin 9. Tho data pin on the PCM D (blue) connector needs to match the year PCM you are using.