'99 F250 5.4 missing, follow up

Mike(NEOhio) · Nov 25, 2018

Nice day for a change so I got into it. It didn't want to start Friday and I ran the battery down. Hour and a half with the charger and she lit right up. Seemed smooth at first but the miss started as it warmed up but this time accompanied by what sounded like an exhaust leak. Tried disconnecting one coil at a time but that was inconclusive. A little cold to really get into it outside so I pulled the first plug on the left side. Looked OK so I took the first on the right. AHA, the boot came out wet with what smelled like antifreeze filling the well almost to the tip of the plug. That plug looked darker and wet, most likely the missing one. Dried it out and put it back in with no change. Looks like I've got a project on my hands. I replaced the manifold gaskets 5-6 years ago for a leak at the coolant crossover passage. Are those heads prone to leaking of cracks? I'm going to keep an eye on it now that I know.

robgIN · Nov 25, 2018

it's not the head, it's the intake that fails, I replaced several of them during my Ford days, where the aluminum crossover bolts to the plastic intake, the plastic usually cracks. You get a coolant leak that runs along side the intake and starts filling up spark plug wells, then you get a miss.

4play · Nov 25, 2018

I don't think the 99's had the plastic intake but if yours does I bet it needs to be replaced. A lot of times its the coolant going bad that eats the plastic off the gasket. When I say coolant going bad, it gets acidic with age, nobody tests for this. If the intake is aluminum then pay attention to pitting on the intake and cyl heads around the coolant passage. You might consider replacing the heater hoses if you have the intake off, and flush the cooling system.

One more possibility but this usually affects the back or back two cylinders on the RH side (#3 & #4). The heater hose connection above cyl #4, if it leaks it will drip coolant onto the coils, if you find this then replace the clamp (don't tighten it more) you don't even have to remove the hose, unless its bad.

Mike(NEOhio) · Nov 25, 2018

Thank you both for the insight. It has the aluminum upper manifold. The lower part is plastic. The leak it had was on the right side crossover toward the center. The soft rubber around the coolant port failed. This time it looks like it's on the outer side of the manifold, toward the valve cover. The area of the manifold above the coil and injector looks wet.

'99 F250 5.4 missing, follow up

Mike(NEOhio)

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robgIN

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4play

Well-known Member

Mike(NEOhio)

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