4th Distributor Cap

My husband owns a 97-GMC, V6 Sierra Pkup. It that started missin’ a couple months ago. Took it to a mechanic and was told it needed a cadilaic converter(hum,no spell check), ok had it replaced. Problem still there. Went to a parts store rented a diagnostic tool and it indicated problem with distributor-sparkplug, etc. Checked all spark plugs, spark plugs wires, distributor cap, etc. Found hairline crack in distributor cap. Replaced it and no problem for about a week and same thing again. For the last couple weeks my husband has been replacing either the spark plugs, spark plugs wires or distributor cap(s)but not at the same time. I’m thinking - against my husband’s wishes. Take it apart, check coil, etc. and replace all parts again only at the time. Instead of 1 part this week and driving it and 1 part next week, etc. This is a really nice truck, it only has 58,000 miles on, we bought it brand new. Help

He’s doing something wrong. He keeps changing the same parts, so, it’s obvious that he’s going to continue to make the same mistakes. Take it to a mechanic to repair. You’ll save money, and headache, in the short run.

We don’t know where you are at, but in the US many parts stores will check the car’s computer for free. Autozone and Advanced Auto Parts are two that generally do it for free. Get the exact code (Like P0123) and not just the English translation of the code. That may help pin down the problem. Those codes don’t say replace this or that part, they say this or that measurement is not normal.

I really don’t think replacing the same parts is going to fix things.

Do not know exact code, but have exact words "radom misfires on all cylinders.

Random misfire on all cylinders might lead me to think the crankshaft position sensor is bad, but it would help to know the exact code(s).
Random misfire does not automatically mean the problem is related to the dist., dist. cap, and wires.

One unit that can cause a lot of problems with the high voltage system, especially with cracks in the distributor cap, is the ignitor. The ignition module not only shuts off the coil current to get the coil to fire but also limits the current through the coil so that heavy current and excessive high voltage is not produced in the secondary. I don’t know of any way to actually measure the coil current sans an oscilliscope so replacement may be the only trouble shooting method available.

Let us know if this helps