I have owned both a few I6 300 CI carbed trucks and the 4.9L Fuel injected ones. I prefer the carbed versions, the FI ones have issues with selector valves and TFI ignition modules heating up and stopping spark. The carbed versions IMHO are the most reliable gasoline engines ever made, I never had it on a tow truck.
Indirect injected motors are just awesome for reliability. I had an 89 ford F250 7.3L IDI with a ZF5 I paid $600 for with a "junk" engine. It was never maintained, you could tell the previous owner ran tapwater because the impeller on the water pump was eaten off and the water necks were rotted out. To top it off the engine sat exposed, outside for a few years. The top half of the engine was disassembled and missing major parts, I went to the Junkyard, put an injection pump on it, intake, new return lines, a lift pump, starter, water pump and drove the piss out of it. She ate 1 quart of oil every 1000 miles and had massive blow by, however the old girl never let me down and unlike my LLY Duramax, it never cared of what it towed, always ran cool even when towing crazy loads, got great mileage and was snappy. Since it had dual tanks I experimented; the stanadyne DB2 injection pump is a beast. I ran that poor thing on everything, waste veggie oil, trans fluid to small amounts of gear oil mixed with gasoline and engine oil HAHA! I loved that engine. I have a 12valve 5.9L cummins 6BT, 8.3L 6CTA and 6.6L LLY and the IDI was by far the cheapest engine to maintain and always started/ran even when it had broken components (broken glow plugs, air in return lines, water in fuel). I regret selling that truck. Just run anti cav supplement with the coolant and they will go forever. Dont be scared of the abused ones, the main problems with them are difficulty starting and poor performance due to air getting introduced into the fuel return lines, its under a $100 fix, use the OEM FORD plastic return line collars and you are good.
