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Hi Ron, No doubt you owned a bunch of 'em; but I was the feller working for GM who was repairing 'em out on the line. HEI stands for "High Energy Ignition" and was/is a pointless ignition system. That's all it was; a new distributor that replaced those problematic points, which had to be cleaned & reset or replaced every year, and this new system was packaged in a nifty new styled distributor with the coil in the cap. This is where we switched to the "fat" plug wires and the resistor type plugs too because now we are pumping 30K volts instead of the 15K volts used with the breaker type systems. Hotter spark, more of a chance to ignite, don't ya know. The system was so far advanced that it didn't even have to use an old-fashioned hall-effects switch. It used a pickup coil mounted under the vacuum advance plate instead. This new distributor started coming in between 1973-1976 depending upon model. If memory serves, it showed up first in the Vega as a precursor in 1972 while everything else was still using the points. This was the next system that was introduced for air pollution control following the PCV (Positive Crankcase Ventilation) system, which was introduced in the 1968 model year. The point-type systems tended to wear the point’s wear plate with time; this changed dwell, which in turn had a huge effect on ignition timing and therefore, it affected the pollutants at the tailpipe. A year or two later, here comes the EGR (Exhaust Gas Recirculation) systems and we all fought them till we were black in the face. Hmmm, no pun intended. :>) However, all this while, the HEI advance was still controlled by vacuum over mechanical on many configurations. And, it continued to be all the way up until the computer controlled units in cars and pickups started showing up in 1985, again, depending on the model, and this changeover was a slow gradual process. They were phased in (and out) this way because of the Federal Clean Air Act, and how it was written. The lighter vehicles (read: numbers of vehicles on the road) always got hit first. In the Suburban, because they were heavier, these old units weren't completely phased out until they were totally done away with in 1991. Ron, I think you are confusing the HEI with the CCF (Computer Controlled Fuel) systems that started showing up in cars and light trucks in 1985 at the same time the first ECM’s (Electronic Control Module) were introduced. This is where the computer first controlled the fuel at the carburetor; yes then later, the advance of the timing at the distributor. Remember all those old 305’s that always bogged at launch? The carburetor was squeezed down so tight on these things, that they begged for fuel and flat fell on their face unless a little “behind the scenes engineering” was done to the timing to let ‘em breathe under those lean-fueled carbs. All pickups had this system in 1985 then switched to TBI fuel injection in 1987 when the body style changed. But, not on the Suburban, ‘cause it was so darned heavy. It sneaked in under the wire on many of these Federal mandate issues until 1991. 1991 was also the year the Suburban started having its leaky intake manifold gaskets too. And yep you guess it, it was because of that darned new block and it’s different angle matching the TBI’s intake manifold. I left GM and went to Ford in 1999. Have a good one, Allan
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