1994 F-150. 167K mi. 4.9L I-6 engine.
The problem: for a while now, the truck has been occasionally stumbling (misfiring), in an isolated fashion–once, then not again for several seconds or minutes. The problem seems to be worse on the highway, generally only happens once the truck has been running a few minutes, and is most likely when goosing the throttle from a cruise setting–like when adding throttle to maintain speed while climbing a hill. (WOT, however, is not any more likely to have this problem, and probably less likely.) If pressed, I’d say the problem is somewhat less severe on the front tank vs. rear–happens on both tanks, though, and fuel level seems to have no impact.
Upon initial troubleshooting, I observed distributor rotor and cap to be worn and carbon-ed up…so I replaced them, as well as the wires, to no effect. (Plugs have 12K mi on them and look good.) Next, I replaced the coil, which also had no positive or negative effect.
Now, I’m thinking it might be a fuel delivery issue…either the fuel pressure regulator or maybe two roughly equally-tired fuel pumps. How should I approach this? I can buy a fuel pressure gauge to connect…but I’d really like “real-time” data vs. hood-up-and-idling. Do they make something like this?
How would y’all approach this? I’m inclined to break down and buy a half-dozen copper-cores, on the premise of “plugs have no shelf life,” and keep them in storage if no effect. Beyond that, though, I’d actually pay a financial penalty for continuing the “shotgun” approach.