[Gmecm] Re: Piggyback ignition modules

[Andrew Gibson]

I figured out what is going on. I accedentally wired the pickup backwards to the module for the ecm. I noticed it because the pickup scope pattern looked clean and even. When I scoped the coil negative wire from the module for the ecm the pattern was bouncing everywhere. I then went to my parts dist from a 4.3L and spun it by hand while checking the signal. It was inverted from what I had on the truck. Switched the wires and now it starts easily on both modules or I can hook up just the module for the ecm and get est. (All tables are at 0 so the mechanical advances are still running) It runs great! Lesson learned, PAY ATTENTION TO POLARITY ON THE PICKUP COIL AND CRANK SENSORS WHEN WIRING CUSTOM JOBS!
   
  Aphelon thank you. The info you gave me on the timing locations (I have a $48 mask) works in the math now. (Maybe I'm just crazy and missed something before) I will slowly start playing with the timing as time permits. Today I have planned to get my fuel tables set right.
   
  As for switching to a 7730 or 7749, on of the guys here tired that with a 1bbl tbi on a 2.5L a few months ago. He was having a dickens of a time getting his fuel tables right. Since I have a very slight change in displacement per cylinder I think I will stick with what I have got. I figured worst case the fuel tables were documented on the 7748 so I could get the truck running better than my previosly uncontrolled fuel leak was doing (aka bad carb). And since I've pulled off the entire conversion on a $200 budget I think I'll keep the 7748.
   
  While scoping things I noticed something of real value for the site. The module needs to time off the vertical slope of the pickup coil's pattern. If you wire the pickup backwards it times off the curved slope. RPM variations change the timing drastically as the pattern changes amplitude. Interestingly enough you get the same pattern whether the dist is rotating clockwise or counter clockwise. I know it's an odd idea but if you think about how a mag pulse generator works, it makes sense.
   
  "Your automotive scope is similar to one I have at 
home.  It's a good tool, but I'm sure you know that it's not really a 
true lab scope.  Automotive scopes need to be user friendly (read: 
simple to use) and very rugged.  My experience is that most auto techs 
couldn't figure out how to correctly use a "true" lab scope.  There's 
just too many features.  I suggested Ebay because you can buy some very 
nice, older lab scopes for an eighth of what you paid for yours.  
They're not automotive grade instruments, but they'll certainly help in 
checking timing signals.  Obviously, you've already got one."

  I agree with the user friendly part. I'm not your average scared of technology tech. So a more complex scope doesn't scare me. The ET2011 has a bunch of menus with preprogrammed setups for different sensors, actuators, etc. But it also has a manual mode with a full configuration menu just like a real benchtop labscope. I like it very much. And yes, ebay is a great place to get inexpensive tools. (Basic timing light $9.00, love that thing) I've tried the modis, but from my perspective I can't validate the price. I would rather spend the money elsewhere in tools. The only downside I have found to the et2011 is it doesn't come with a low current amp clamp. Although one of the Standard Plus tech trainers told me where I could get one for about $100. It's on the wish list. Maybe I'll get one for Christmas this year.
   
  I laid on the sarcasm as to the overly featured scope beacuse I have seen a lot of guys buy tools they never use. (They think the toolbox is the resume) I just don't buy what I won't use. The equipment salesmen hate me beacuse the boss sends then out to me to show off their products, and I give it to them straight. 99% of the time the product is not purchased beacuse what we have works fine. The 1% is stuff like the smoke machine we have been waiting for a reasonable deal on (and got last week), high quality floor jacks, a self contained internal recycling solvent tank, etc. You know, the good stuff. And then we take really good care of the equipment so it lasts a long time. Our Bear ingnition scope/charging system tester is going on 15 years even though updates and parts are no longer available. The solvent tank finally burned up a vacuum pump after 6 years. I installed the pump instead of paying the repair tech the disgusting price for the double service call to diagnose and
 repair it.
   
  I like good shop equipment, but I'm not willing to break what I have to get the newest, best and greatest stuff. I'd rather have a lot of useful tools than a few cool feature laden ones. Sorry if I went on about this. It's just how I feel.

		
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