HenryJ wrote:Ditch the quad tip plugs. Too much flame shadow. Swap plugs to the Autolite irridium XP and check the coil for leakage. Try the hairspray trick on the wires, cap, and coil.
Even if the plugs are not the source of your current problem I also highly recommend the Autolite XP plugs. Almost all of the fancy 2, 3, and 4 electrode plugs out there cause problems in GM engines like loss of power, surging, reduced gas mileage, etc. Do not believe the advertising hype that these companies try to sell you. I have tried several designs over the past 25 years and have found that GM engines run best with believe it or not OEM plugs. AC Delco platinum, double platinum, and Rapid Fire are all very good plugs. The Autolite XP's have been my favorite plugs for a while now and work great in the 4.3L and many other GM engines. I run them in my 96SS, 88 S10 Blazer, and my 05 ZR2. I put these plugs in my 05 Z around the 25k mark and just checked them about 1k miles ago at 148k when I was going to replace them and they still looked great so I left them in. That's 125k miles of use and they still work just fine! I have also had an MSD street fire ignition firing those plugs for at least the past 100k and yet they have held up fine.
Back to your problem. Are you having a loss of power above a certain rpm or does your problem only happen when the engine is under a load? The reason I ask is because I've seen and heard of similar problems that actually turned out to be the transmission or TC starting to fail. When your TC clutches start to fail you will feel more slippage in the TC which can feel like a loss of power. Even worse is when the transmission clutches start failing which really feels like a loss of power especially when under a load which is when it will slip even more. Just thought I would throw that out there in case your problem has nothing to do with the engine. A stretched timing chain can cause a loss of power, but from my experience the engine will also run very rough and set codes. I'm right behind you with 150k miles and my 4.3 runs as strong as the day I bought it and it still has the original timing chain.
2005 ZR2 Blazer / Mods- Spectre CAI, Descreened MAF, Shaved Throttle Blade, 31" Goodyear Kevlar MT/R's, Black Rock Rims, MSD Street Fire CDI & Super Conductor Wires, Accel Cap, Rotor & Coil, Flowmaster 30 Series, Gibson Tailpipe, ES Bushings, Goodridge Brake Lines, Power Slot Rotors - 1996 Impala SS / Mods- Too Many To List - 1988 S10 Blazer / Mods- Too Many To List - 2001 S10 Crew Cab 4x4 / Mods- Too Many To List *Wrecked 12/06*