Suburban driving me crazy!!!

[LVJJJ]

When I was having some performance problems with my 94 GMC k1500 that I couldn't solve, I took it to a good mechanic up in the foothills. He is a former GM mechanic at a GM truck factory. I had put quality non-GM wires, dist. cap, ignition module, etc. on it as the original owner had not tuned it up at all after 125,000 miles, was all original and basically ran just ok. However all the new parts I put on it didn't seem to help at all and maybe ran a little bit worse. He told me to ALWAYS use genuine GM tune up parts for the ignition system. So, did and it ran much better.

 

[Schurkey]

had 250k miles but was meticulously maintained.

EGR has been removed and a bypass plate was put over the hole... ...the evap system had been pretty much removed... ...he removed the charcoal canister and cut the lines under the hood

So...NOT "meticulously maintained". More "butchered" and "hacked".

Iridium plugs matter on wasted spark ignition systems.

As do "double" Platinum plugs instead of "single" Platinum.

Any of those "fine-wire" plugs are wonderful...and more expensive...and work very well on engines that have terrific control over fuel and spark. They're very long-lived as they don't wear quickly.

But that matters less and less as the fueling becomes less-precise. The plugs foul before they wear out.

Current is flowing electrode-to-ground on one plug, and ground-to-electrode on the other. The plug where the current flows electrode-to-ground loses material from the electrode. An iridium plug resists that material transfer and lasts longer in that application.

Point is, it doesn't matter which polarity the spark is-- center electrode to side electrode, or side electrode to center electrode. There's going to be material transfer especially if the electrodes are made of common materials rather than Platinum or Iridium. And in the case of waste-spark ignitions where half the plugs fire in reverse-polarity, you'd need Platinum or Iridium on one electrode for one polarity, and on the other electrode for the opposite polarity...leading to Double Platinum plugs that have the Platinum on both electrodes so it becomes insensitive to spark polarity.

Our trucks don't run wasted spark, so an iridium plug is wasted money.

My Trailblazer also doesn't run waste-spark ignition (six separate coil-on-plug ignition) but uses Iridium plugs because the fueling and spark are so precise that fouling is virtually eliminated...so actual plug wear is the limiting factor. I didn't replace the original spark plugs until just shy of 170K miles. I did pull 'em out at about 90K for inspection. They looked so good I screwed 'em right back in.

 

[Russ B]

When you say you replaced all sensors, did you use OEM GM or something else? If you watch the YouTube Videos, techs go crazy if you do not use OEM GM. We all like to save a buck, but sensor quality is questionable. That being said, do you have the old original sensors. If so try them again.