I have done some, mainly the tech article and this board, looking into burning chips for my car, see sig, and before I drop the loot to get the needed hardware to start burning I have a few Qs.

From my understanding, in order to take full advatage of burning your own chips you need to be able to monitor your cars ecm under normal driving conditions. For reasons other than burning my own chips I already own and use an Auto X-ray scanner. For a while I thought I had some serious problems with my car due to this scanner. It would show up to 18` of knock retard on a full throttle launch. After a summer of pulling out my hair trying to find out why this was happening I decided to take it to a reputable GM dealer in the area to have them check it out. To my suprise they reported that their multi-thousand dollar scanner showed no knock what so ever. Hmmmm... So, before I called auto x-ray to b!tch them out I decided to read over the manual again and see if I was just using it wrong. As some of you might already be thinking, yes I was using it wrong. According to the manual, if your idle raises above normal while the scanner is linking to your ecm, you can only scan the engine at idle. I have found out that this is because it puts the ecm into 'special' or 'ALDL' mode. According to my Motor's manual scanning in this mode alters the operating characteristics of the engine; 1000rpm idle, EST at full advance, and so on. So now I have an answer to why my scanner reports knock. My engine is knocking, but only because my scanner is making it.

How do I get around this 'special' mode of monitoring?

My Motor's manual also says that most scanners are programed to enter the special or ALDL mode automatically, and need to be switched manually to one of the other two scan modes, the normal or open mode and factory test or back-up mode. It also goes on to say that "not all engine/ecm families are able to transmit information on the serial data line with the scan tool in normal (open) mode."

Can I/ How do I switch between these modes?

Is it my ecm or my scanner that prevents me from monitoring in open mode?

Please help

 

Dustin,
I'm new at this too, but you don't seem to be getting overwhelmed with replies, so here goes :-)

I think your problem is that you're reading data with the 10k resistor telling the ECM to go into ALDL mode as you have seen. Check out JoBy's site to see how the ALDL cable can be configured to sort this out:
http://w1.601.telia.com/~u60113744/s.../aldlcable.htm

JoBy's note says, "When you build the cable first try without the R3 resistor. That works for most vehicles. Some vehicles need a 10k resistor to start transmitting data but the resistor will change the ECM's mode. It will have a high idle and spark knock retard will be disabled. That is the reson why you should not use the R3 resistor if it works without it. "

So get the R3 out and you'll drop out of ALDL mode. This may mean modifying your plug or cable (I don't know what's possible there), or making or buying a simple cable and using other software on a laptop. What I can't tell you is whether you'll still be able to read data.

For someone else to know that, they're probably going to need to confirm which ECM is in your '87 Z28.

John

 

Your ecm doesn't need to be in any mode to transmit data. So go behind the aldl terminal and unplug the wire so auto-xray can't put the ecm into ANY mode.

 

Thanks for the replies fellas.

Jprevost- Can you expand a little on your previous post.

Which wire, or for that matter terminal on the ALDL are you talking about (according to the diagram below)?

./f./e/d/c/b/a/
/g/0/0/0/0/m/

Will this be the only wire at this terminal?

How does this work?

My ecm is 7165 if it matters.

Thanks again!

:hail:

 

ftp://ftp.diy-efi.org/pub/gmecm/manu...165v8tpi-2.jpg
http://w1.601.telia.com/~u60113744/s.../aldlcable.htm
Collectively you want to remove the wire at B. A is just a ground, B goes to the ecm and depending on the resistance between A and B, the ecm decides which mode to go into. I only know of 5 modes not all ecm's support all 5 but there are normal, ALDL, backup, diagnostic, and limp home. All except for limp home are decided by the resistance. So obviously normal mode is where you want to be on a car with some mods done to it. I'm not sure exactly how to remove the pin behind the aldl connector but you could probably just cut it or pull the pin out at the ecm. I'm pretty sure with a safety pin you should be able to remove the pin from the aldl connector.

 

Thanks a bunch Jprevost!

Unfortunatly I won't be able to try this out for a while though. My car hides itself in my barn if there is snow on the ground. Man, I wish we'd get an early spring like last year.