Have you run a scan to see if there are any codes? That's the first step.
Also check the oil age, condition, etc. Used-up oil can cause problems with the injectors. Possibly one or more are gunked up on the oil side and won't operate correctly until the oil warms up and thins out a bit. Run an injector buzz test when cold, listening for differences in the sound of each injector (weaker than the rest), and then run one again after the engine is warmed up and running well. The weak sounding injectors will be the suspects. The buzz test activates all 8 injectors, then each one individually in numerical sequence (not firing order).
If you narrow it down, pull that valve cover, and pull the solenoids off the suspect injector and measure the clearance under the plate that the solenoid pulls up with a feeler gauge. IIRC, anything under 0.001 means the injector is worn out. While you're in there, check the under valve cover harnesses as mentioned. But at 135k miles, I'd guess your injectors should be fine if maintenance (oil changes) has been kept up and good quality fuel has been used.
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First truck -- 1929 Model A Ford pickup, restored from ground up. Wish I still had it!
99.5 F250 PSD Supercab LB 4x4, ZF-6 w/SB Con OFE, 3.73LS, Boost & pyro gauges, Swamps S175/146 injectors, DP 80 HP Econo PCM (classic version
), AIS, coolant filter w/"hokum" bracket,
regulated return, heated mirror mod, lighted cupholder, Marinco heater plug-in.
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