870 Spark Control

[Matt Sandine]

Engine is pretty much stock with the exception of a 214/224 cam and roller rockers. It had some mild flow improvement in the intake department and exhaust is cat free. The combo worked flawlessly when it was in my Chevelle with a 600 CFM carb.
A little more info on it. When I time it to 6 deg, it will like I said idle fine. As soon as I plug the connector back in however, the retard kicks way in. I figure with the connector connected, timing should be somewhere around the 6 degrees that I set + the amount the chip is set, so I figured it is around 18 degrees if everything was working correctly. When I turn the distributor so the timing mark goes from 18-24 degrees after top dead center to about 18 degrees before top dead center, she will rev up and drive around normally for the most part. The problem is, when I turn the car off, disconnect the timing connector, I can barely start it again and the timing is about 25 degrees advanced because of how much I had to turn it previously.
Here is the bin. It is the stock one (HLH 3200) with the pulsewidth trimmed down a bit and not much else done to it besides fans, etc. I tried to disable the Spark Control Diagnostic thinking that this was erroneously retarding 20 degrees for no reason, but it made no difference.
I don't have the EGR solenoid hooked up, nor do I have an EGR valve, air diverter solenoid, or the other emissions stuff. Could the fact that these are not hooked up (even though no codes are thrown) make the computer go into a full retard because if they are open, then they are not completing the 12 volt circuit and the computer thinks there is a problem?
One last question. My helms manual for the 85 Vette states on pin D10 the exact type: "POWER GROUND ?" It had the '?' there. I do not have a ground there, but who knows.
Thanks again, -Matt-
    -----Original Message-----
    From: Programmer <nwester at eidnet.org>
    To: gmecm at diy-efi.org <gmecm at diy-efi.org>
    Date: Friday, May 11, 2001 7:50 PM
    Subject: Re: 870 Spark Control
    
    
    Can you give me a little history here--is this a modded unit, or totally factory. Can you upload your bin to me ?
     
    Lyndon.
        ----- Original Message ----- 
        From: Matt Sandine 
        To: gmecm at diy-efi.org 
        Sent: Friday, May 11, 2001 1:46 PM
        Subject: Re: 870 Spark Control
        
        
        I am not kidding. It bucks and sputters all over the place, but that is what is really happening. You can tell the fuel is totally being ignited at the wrong time. I thought my timing light could be way outta wack. I used another with the same results. She purrs like a kitten when the timing connector is disconnected and it is at 6 deg, besides the fact that you can't rev it because the computer isn't adding the spark. Just in case the balancer was slipping, I marked the pulley. It is honestly retarding the spark at least 20 degrees from the 6.
        Does this make sense? The only way I have been able to figure out spark advance on the 85 (since it doesn't show it in scan tools) besides using a timing light is to use a scope on the pickup coil input and EST output at the computer harness. By tracking both of these waves at the same time, I was able to see the EST get tighter and tighter compared to the pickup coil pulse remaining constant. Only problem is, I need to try to figure out if the EST pulse is actually being retarded from the computer or if it is being retarded at the ESC module. Thanks for the interest Lyndon, -Matt-
            
             
            Matt,
             
            If this thing was going into 24 degrees retard from 6 BTDC, it'd stall. Are you 100% sure it's going 24 ATDC ?
             
            Lyndon.

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