new life for an aging '84 V6 2.8L engine?
I've recently done a lot of tune-up work on my engine over a period of several months. My engine's #3 (passenger side, rear) spark plug was recently found to have a coat of carbon on the interior insulator and electrodes, and the #6 (driver side, rear) spark plug was fouled with oil and carbon so that there was an oil/carbon bridge cross the gap. I suppose that by conventional wisdom a valve job or engine overhaul is indicated, depending on a supposedly needed compression test. But the passenger-side spark plugs are hard to reach, especially the #6 plug. So I'm wondering how much "magic" can be done without first doing a compression test. (Incidentally, an manifold vacuum test was "steady" at 17.5 inch Hg with a 1/4-inch Hg vibration and about 1/2-inch Hg wandering -- according to my gauge -- before I removed, inspected, cleaned, somewhat re-gapped, and re-installed the platinum plugs.) Gas mileage before cleaning the plugs was 9.5 mpg and 10.6 mpg afterwards.)
The engine starts right up cold and idles nicely and the Ranger steps right out and gets about beautifully, but by the time I've driven to an inclined freeway-onramp, the engine is warm and the Ranger seems a bit sluggish in trying to get above 25-35 mpg on that incline. And when reaching a slight incline on the freeway itself the Ranger's speed will drop from about 55-65 mph cruising down to about 45 mph. (The Ranger is carrying a slide-in camper, by the way.)
There's another symptom that seems very peculiar and probably should tell a lot, but I don't know how to figure it. Namely, the Ranger will sometimes seem to struggle in trying to accelerate for a few seconds, and then all of a sudden, the engine will seem to have new power as if "no problem" and the truck then continues to accelerate effortlessly.
I've heard that I ought to check or have checked the Ranger's EGR system, and I've heard suggestions that a spark boost system could improve things by providing a more timely and vigorous spark and ensure timely and better burning of the air/fuel mixture in the cylinders, including the cylinders that are tending to foul. In fact, I'm wondering if a spark boost system could help to prevent spark plug fouling. I've also heard that it might be a good idea to switch the fouling plugs to a hotter heat range. And I'm wondering if I should do that for all cylinders because there was found some carbon deposit around the inside of the metal threaded base of each of the "normal" plugs.
Can anyone provide some insight as to what are the best things to try first? Is it possible that I could get, say, 100,000 more miles of robust, fuel-efficient operation out of this engine without a valve job or overhaul? How much guess work is required and how much can I rely on for sure?