defective distributor cap - 4.3 Vortec

Saturday, my son's S-10 Blazer suddenly started running rough, would barely idle. Threw a check engine light. At home, we put the code reader on the computer, and picked up a P0302 code, which is a intermittant misfire, cylinder 2. We replaced plug, and bypassed plug wire with another. Replaced rotor. Still no help. By then it was showing P0300 - general misfire. Out of despiration, son pulled cap off my car - put it on his. Problem solved. Got out my digital test meter, attacked old cap. This is one of those "flat-top" covers where terminals are out the sides, rather than on top. They have cleverly routed the spark through a conductor through the cap to the sides. Somehow they cleverly managed to get cylinders 2,4,6 one one side, 1,3,5 on the other without crossing any conductors. Cylinders 1 and 2 run parallel across a portion of the cap however. All conductors tested good, and all but one showed no short between any other conductors, except one pair. Cylinder 1 and 2 showed a 24,000 ohm short between them. Most probably a burned brigde through the plastic insulator, and with the high voltage spark, it was enough to cause misfiring. A new $26 cap, and we're back in business. (Didn't buy the $56 - gold plated version!)

Another cause of phantom 4.3 snoretech missfire is the distributer will get out of time with the crank. Causing the rotor to be between terminals while a cylinder is firing.
The dist has to be pulled then a bit milled off the base to allow the dist to be rotated and timed.

Recently, our shop and two others I know of got some bad new caps for the 5.7 Vortecs that would cause a similar problem after only a few hours of use.

Of course, the parts store had "never heard of the problem before.

My first thought was a bad plug wire or two causing the caps to "burn", but on one of the jobs, for sure, a new set of wires was installed with the new cap and the cap still failed. Putting the old original cap (with lots of miles) back on would cure the mis 'til a new cap was obtained.

When it comes to that style distributor cap,I install nothing else but GM and never have any problems.Wasted too much time with the aftermarket crap.Seemed like EVERY time it rained or was damp out,the 4.3 and 5.7's misfire or back fire with an aftermarket cap & rotor.

yeeaapp!

The way I fixxed that problem, bought a DIESEL!

Tom

If you see white corrosion inside the cap remove the two screens in the bottom of the housing. You may have missed a recall.