Hey all, I recently bought a 1990 F-450 service truck off Craigslist for $2500. It has either an early 7.3 idi or a 6.9 idi diesel swapped in from an 80's truck as the previous owner threw a rod out the side of the oil pan. I don't know which it is because I can't find a serial # and the previous owner also rattle canned the valve cover sticker with all the Navistar info. This is what I've done in my spare time in the last month: -new injectors, fuel return lines, changed the filter housing + fuel filter, changed the air filter, changed a few glow plugs -replaced the radiator, thermostat, and checked the water pump The truck starts up well when cold, but once it warms to operating temp it won't fire when you cut it off and try and crank it again. When you try and crank it when it has warmed up, it will crank slowly like the battery is on its last legs but it will just keep turning and turning while the ground cable on the main battery gets warmer and warmer. We've checked resistance through the grounds that we found and those wires seem alright. What could we be missing?
I would look at replacing the starter and checking all the cables too back in the day we would put a tractor starter in as the 6.9 stater turned the engines to slow to start there was a significant difference depending on which starter you used I'm thinking now days there are gear reduction units to accomplish the same thing
6.9 used a round cold start sender and the 7.3 used a square transformer both at back top of engine. And yes those starters were not all that great. One thing to check is the engine harness connector on the right side {square connector} those will burn inside {main terminals for glow plugs}. Plus you say battery, there should be two.
Is the truck charging when it's running? sounds stupid, but I have to ask.
I have not had a lot of trouble with those starters but after checking that the battery voltage is good, if it cranks OK when cold but slow when hot it likely has to be a starter motor. They like engine RPM to start, but normally they start very easy when hot.
We had a idi that would start great cold but would just crank and crank when hot. Injection pump was getting long in the tooth if you splashed some water on it the thing would come to life.
Stanadyne injection pump, were not a high hour pump in most cases. See how a 7.3 runs when the advance takes a dump.
I'll take a look at the starter, I've seen that as a common hard start problem for these engines.
I can almost guarantee that it's the original injection pump on there. I'm pretty hesitant to touch that unless that's the only way to get reliable starts outta this jewel.
Yeah, it seems to be charging when it runs. Although I haven't tested to be sure, I ran the truck for about a half hour a week ago and let it sit. A week later it cranks right up, until it ran for a bit and warmed up. I'll put a meter on it to be sure.
I'll check out that harness, and see what the cold start sender tells me. I've got two batteries in there, I re-read what I posted and realized that is an important detail.
Is it a manual trans, and can you park it on a slight hill sometime when it's been running, and see how it starts roll starting it? sure sounds like a bad starter, I think mine was worse hot when it failed, but that was a while ago.
Do a voltage drop at starter while cranking...