Ok so my 4.9 had a mild miss about a year ago and over the past year it has came and gone, and recently got so bad that it was almost undrivable.   If I matted the gas it would almost shut down, it was like flooding a carbed motor.   Sustained speeds at really low throttle it would miss and buck a bit, but drivable.  If I tried to run it down the highway it would buck once about min or 2.  Just driving from Surrey to Aldergrove on Trans Canada I was not sure if I was going to make it home.  

I replaced, cap and rotor, removed and replaced the MSD 6AL box, checked fuses, checked grounds around the engine, ran extra grounds, ran an extra wire direct from the alternator to the battery.    I replaced the ignition module with a known good one from Craker and was about to bite the bullet and replace the entire dist shaft and related parts.  There are a few people on this forum that have driven my car and know about this miss, it has been totally frustating.

Well today I was working on the car and fixed an engine mount issue. (seperate thread about that)  I took the car out for a drive and the engine was almost shutting down on me, it was like someone was darn near turning the key off for a split second.  It really was killing the fun of having a motor that did not move around.

I had the scan tool hooked up and noticed something odd, every time the engine would buck, the scanner would change from "Monitor Mode" to Static Numbers from last scan.  Which only happens when 1 of 2 things happens, you turn the ignition off or knock the plug out of the ALDL so the scanner looses its data stream.  I checked the plug and it was firmly in the port.  I had to re-start the monitor mode several times.  So I brought the car home and removed the center console.  I checked all the plugs going into the ECM. (3 large plugs)  I looked down at the big black and clear plugs that go from the ECM to the main harness. The top connector was fine, but the lower one, was 1/4" out.  What the heck, I was shaking my head, no way, not that simple.  It couldn't be that easy.  I pushed it in, grabbed the first zip tie I could find, tied it up and fired the motor up.  Smooth idle, I revved it and it revved clean.  I backed it out of the driveway, put it in 1st gear and romped it to the floor.  The tires lite up like a crazy man.  I grabbed 2nd gear and the car just kept pulling.    One stupid plug that was out just enough to cause an interment signal from the ECM was causing an entire year frustration. 

Here is a pic of the devil connector that caused me all the frustration.

The shinny in the back is the thermal insulation pad to keep the heat from the engine from transferring through the firewall into the cabin and the ECM. 

Dave you need more Red Zap Straps..... Purple is so last year!