btr85vette

I'm finding that because my 85 is so modded now I can't set the idle in the traditional method. I bought a cable from ALDL Cable, and use WINALDL to scan real-time.

Here's the problem. When I go into ALDL mode, the ecu changes the idle to 1000, and some other things. From what I understand this is a limitation of the 6870, and there is no way (that I have found so far) to get a "normal" unmodified data stream from the ecu.

What I really want to do is to set my idle using the IAC counts. Because the idle is now at 1000, how do I accomplish this? I can set the IAC counts to 15 - 20 now, but my idle is very high.

Any thoughts?

powerpigz-51

What "traditional method" are you using?
I do not think you need to be scanning to set the idle. As you have learned, the 870 scans are pretty much useless. What mods are we talking about? Are you burning your own chips? If you want to change idle speed, it needs to be done at the prom level, and then you need to find out the procedure for resetting the IAC. I do not remember exactly what this procedure is, but it is easy. If you are so modded that this will not work, you may have to idle in open loop.

rodj

http://www.thirdgen.org/techboard/po...610-post2.html
http://www.corvetteactioncenter.com/...-corvette.html

rodj

Could try removing the resistor after the data stream is flowing
http://www.thirdgen.org/techboard/po...84-post16.html

Even modifying the tune apparently has no effect if the scanner is in ALDL ( resistor ) mode
http://www.thirdgen.org/techboard/po...71-post15.html
http://forums.corvetteforum.com/1569931621-post3.html

CF member Joby who wrote WinALDL had some tips for datalogging
http://forums.corvetteforum.com/c4-s...-85-870-a.html

btr85vette

Ok, some background is necessary. This is what I have:

• FIRST Fuel Injection manifold
• Long tube headers
• 1.6 RR's
• Bosch 3 FI's, from FIC

I used the procedure above to set the idle, but I can't get it to idle at 450. I get a really bad idle surge the lower I set the idle. And yes, I used a pro smoke machine to check for vacuum leaks. I figure with these mods it just isn't going to idle that low, hence the reason I wanted to set the idle with the IAC count.

vetteoz

Only way to change the idle setting is in the tune as previously noted.
If our new combo needs a different idle speed than the stock setting then the computer is constantly
fighting itself trying to a achieve a unachievable idle that you have set on the TB; surge

FWIW
If this is a keeper and given the lack of support for the '870 ECM's ( not to mention the expensive MAF burnoff module ) you would be well recommended to upgrade to the later (86 - 89) TPI ECM
http://www.eecis.udel.edu/~davis/z28/ecm_swap/

powerpigz-51

The idle in your stock bin file is 650. I doubt it could ever idle steady lower than that with the stock cam, even if you lowered it with a chip burn. I had an ADS Superchip that had the idle set at 750. I am assuming this was for a hotter but stockish cam. What cam are you running?

btr85vette

What I meant was, during the idle set procedure, with the IAC grounded, you set the idle down to 450. Then reconnect the IAC, and the IAC will now control the idle to around 650. With the IAC grounded, I can't get the idle down to 450 to do the initial set.

c4mo

I realize you probably want to make it work with what you have, but like said above switch to a better ECM. Dynamic Ebl would be the switch I would make. Just a few pin changes and a map sensor hooked to the maf pigtail and your ready to go. You spent a appreciable amount on your mods, why not use a modern ECM to get the most out of it. I have a 85 did the swap and never looked back.

btr85vette

Do you have a link where I can get some more info?

vetteoz

The 870 to 165 bible

http://www.eecis.udel.edu/~davis/z28/ecm_swap/

bjankuski

The 1985 ECU adds 8 degrees of timing in the ADL mode, you need to eliminate the timing adder in this mode by changing the ADL timing adder in the constants to zero. Once you set that to zero you can scan the car and hold the idle at the same RPM as the prescanned condition. You can then use the scanner to see what your IAC count is and adjust as needed.

FYI I have tuned many 1985 cars and they work well. In my opinion the 1985 computer get a bad rep.

vetteoz

Mainly because lack of tuning support ( a tuner who can do it)
IIRC Corky and Ski were running their big cube race engines on '870's

alanwheeler

How is this done: "you need to eliminate the timing adder in this mode by changing the ADL timing adder in the constants to zero"?

DanielRicany

I have wondered the same thing myself. He has said this a few times but I can't find anything in the tune that relates to that...

bjankuski

It is called "spark advance added in ALDL mode", set it to zero. It is located under constants.

DanielRicany

I'm only seeing Scalars, Flags, and Tables...

bjankuski

Look in scalers, I use tunercat, you are using tuner pro, maybe the definition file you are using does not that the ALDL mode as a choice. If it does not search the web for a definition file for tuner pro that allows you to adjust that item. As a side note you can use multiple definition files to adjust a bin file for your car. If you find a definition file that allows you to adjust the ALDL timing advance but is not the one you want to use for your tuning you can still change the bin with file close it and save and then open the bin with your favorite tuning file to complete the tune.

DanielRicany

Would you be able to send me the definition file for tuner cat?

MrWillys

Just go to the tunercat site and pay $20 for it.