1990 F150 pu Vapor locking

Last fall I bought a used 1990 F150. It ran fine all winter. Now we're getting warmer weather, and after I drive the truck for a half hour or so, it refuses to turn over, or turns over so slow it's
rediculous. Once the engine cools, it starts right up.
This is a fuel injection 5 liter engine with manual trans.
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On Sat, 10 May 2008 05:00:37 -0500, snipped-for-privacy@invalid.com wrote:

Vapor lock is not likely your problem since it has EFI that operates at pressures much higher than a carb system and constantly recirculates cool fuel from the tank thru the system.
If it is turning over slowly, that would likely be a starter problem. Check all connections to be sure they are tight and clean. IIRC, that model has two starter solenoids; one on the right inner fender and the other on the starter. The most likely candidate is the one on the fender which is easy to get at and replace. It is also cheap. The other solenoid on the starter has an ignition wire that frequently corrodes or becomes loose. It is a spade connector that is easy to get at from under the right side. Make sure that connection is clean and tight. Put some electrical grease or jell or whatever on the connection to prevent future corrosion.
Don't forget the starter may be due for replacement. If it turns the engine easily when cold, it should be OK but, that is no guarantee. Many auto service centers or parts stores offer a free evaluation of the starting and charging system to be sure the charging system is up to par, the battery is strong and the starter is not drawing too much current. Your problem should be an easy fix.
Lugnut
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starter. Make sure the starter isn't right next to a hot manifold, if it is there should be a heat shield.
Ted
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On Sat, 10 May 2008 10:19:11 -0700, "Ted Mittelstaedt"

Is the starter prone to turning slow when it gets hot? Why? Every electric motor I have ever known work at most any temperature, not considering the load on them, like air compressors often trip the breaker in very cold weather, but that's because the compressor oil is thick. My engine oil should be thinner whne the engine is hot, and thats when it wont start. The other day I pulled home a heavy load of hay and the engine was working hard. I parked the truck went into the barn to disconnect the electric fence, got back in the truck (one minute after shutting it off), and it would not crank over. Acted just like a dead battery, yet all indications showed the battery was ok (volt meter, radio, horn, lights all worked). I decided to go eat before screwing with it. An hour later the truck started just fine. I always starts immediately when cold, even when the temp was 20 below zero in winter. The minute it gets hot, it wont crank over. That's why I thought the cylinders were flooding with gas vapor.
This is the first fuel injected vehicle I have owned, I know carbs used to vapor lock and flood cylinders, I dont know much about fuel inj. I'll suspect the starter, but it dont make too much sense that the temp would affect an electric motor of any type....
Thanks
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this is a classic case of a bad starter. once the starter gets hot, it requires more power to turn than the battery can supply. then when the engine and starter cool off, it starts fine again. another thing to change while the starter is being replaced, is the battery cable from the solenoid to the starter. for the few bucks it costs, it is money well spent

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wrote:

Thanks
One question though. What part of the starter is affected by heat to need more power? Do the starter bearings get tight? Do the stator coils somehow expand, does the rotor enlarge, do the brushes lose contact, or what? I just can't picture how heat would affect any of that. I know when any of these parts of a starter go bad, the starter dies, but how can heat make it temporarily go bad? However, I am aware that metal expands when heated....... ????????

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i have never paid any attention as to what "goes wrong", just that when they go south, they will not operate when hot.

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Electric motors work fine up to around 300 F or so. Much beyond that and you start having problems with the lubrication in the bearings not working, unless the bearings were designed for high temperatures and are internally lubed with high temp lube or some such.
Exhaust manifolds close to the engine run at around 1200 F. (think, what is the temp of fire?) They put out a lot of infrared energy. If your starter is right next to one, and it is close to the exit point of the exhaust gasses in the engine, the radiant heat from the manifold is enough to heat the starter a lot past 300 F, to the point that the bearings lose lube. Once that happens too many times the bearing races start to fail. When things cool down the starter turns a bit easier.
Usually you see these problems when people put headers on a vehicle since the header pipes run a lot hotter further away from the engine, if they don't wrap the headers or put in a heat shield. But some vehicles also have the starter located close enough to where they need a heat shield and the factory puts one on.
It's not uncommon for amateurs changing out a starter to forget to put the heat shield back on, and since everything works fine for a while they figure the shield wasn't doing anything useful.
Ted
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On Sat, 10 May 2008 22:39:48 -0700, "Ted Mittelstaedt"

Guess I'll have to see if there is a heat shield. If all the starter needs is bearings, I'll probably just rebuild it. Starters are pretty easy to fix as long as the windings are still good.
Thanks
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Correct me if I'm wrong, but the "vapor" in "vapor lock" was in the fuel line from the tank to the engine. IIRC, it happened mostly on engines with a mechanical engine-mounted fuel the pulled the gas from the tank to supply the carb. The gas in the line would heat up and vaporize, causing the pump to try to pump the vapor (which they didn't do very well at all). I had a '64 Galaxy with a built 390 that was prone to it when I lived in southern AlaBAMa.
SC Tom
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That should be "engine-mounted fuel pump that pulled."
My fingers can't type as fast as I think I'm typing, if you know what I mean ;-)
SC Tom
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are you sure that is the problem, or are you just getting to be a senile old fart like the rest of us?? ;-)

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Well, I guess that COULD be it, but I hate to admit it (mostly to myself!!).
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We get vapor lock issues today, half my jobs fleet went down a few years ago when it got into the '80's on a March day in the northeast. Still were burning winter blend fuel and half the fleet of Econolines wouldn't hot restart or died on the road. Loosening the gas cap to let the pressure out and 15 min. cool down got them restarted and leaving the cap loose kept them going till the day cooled down.
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