Ok, need some help here. My truck has let me down the last two times I've driven it and until I get this fixed I don't trust it to go anywhere I have to shut it off during the trip.
The truck fires right up as long as the engine is cold or has had time to cool significantly after being driven. The problem is when I try to restart it soon after shutting it off while the engine is still hot. I turn the key and it will turn over VERY slowly but not anywhere fast enough to get the engine to light off. Jumping it off really didn't seem to help it either during this time.
The battery is brand new (this week) and the starter is less than a year old as well.

Any ideas? Thanks in advance!

 

Bad starter, or loose battery connection.
Either way, the starter is pulling more than the battery/cables can deliver.

 

X2. I would definitely check the starter.

 

I hear you but can you explain why it works ok when Tue engine is cool? Not doubting you, just trying to understand and learn why. Thanks for the help. I had written off the starter because it has less than 1500 miles on it.

 

I had the same issue with mine years back. Turned out the exhaust manifold would heat up the starter and make it hard to start. I put a heat shield around the starter and had no more issues.

 

I'm guessing its the brushes in the starter. When they get hot they lose contact with the armature.

 

Ford DSII modules have a feature wherein the ignition timing gets retarded on startup (possibly all the time, possibly only when warm, I really don't know) to help keep this problem from occurring, replacement modules I understand lack that feature.

The other guys are also right in that they also list things that could cause this problem - high heat can cause a failing starter motor to not work real well, pieces expand & contract as they heat up/cool down which can cause attenuation of electrical connections, etc. etc.

 

I know this may be way off but when that happened to me it was because my timing was advanced to far.

 

That scenario is entirely possible also. If it's the timing, the engine will usually make a womp, womp, type of cranking, not a steady cranking speed. One way to test to see if it's the timing, is pump the gas pedal a couple of times to flood the engine. This will drown the plugs and they won't fire for a few revolutions, the engine will turn over normally for a little bit, and sometimes fire off after the plugs clear.

If it doesn't do any of that, it probably is the starter or a cable. Unless the starter was brand new(not rebuilt) I would not trust it.

 

This is most likely the common 'hot starter' or 'heat soak' issue that these trucks and many other makes & models are plagued with. Anytime the starter gets hotter than it should be, the resistance is increased, meaning it takes more juice to turn it over fast enough to start.

This could also be the starter solenoid, or the connections there, or the wires to/from it. If your solenoid is hot... this is a result of the built up resistance.

OHM's Law is basically ' Voltage equals current times resistance '

As copper heats up, its resistance goes up... it has a "positive temperature coefficient of resistance".
So, as the wires get hot, the resistance goes up and the current goes down.
Less current means less torque to turn the engine over fast enough to start.

When I bought my truck back from the guy I sold it to, I drove it about 15 miles to the gas station. After filling up, it didn't want to crank over very fast. I thought it was a battery issue since I put the battery in a few months before I sold it to him 3 years prior and it was the same Motorcraft battery. Jumper cables didn't seem to help, so I pushed it out of the way and went to the parts store with a friend to pick up a new starter solenoid, a battery, and some starting fluid. Got back to the truck and gave it one last try and it started right up. Go figure.

After I got home installed the new battery and new solenoid and it still wouldn't crank over fast enough to fire off after about 15 minutes of run time. So I wrapped the exhaust manifold & pipe with header wrap. I made a heat shield on the manifold/pipe hammered out of 16-gauge steel and put some leftover Dyna-Mat on both sides of the shield. I made a heat shield on the starter the same way as the other shield. I also rebuilt the starter with a kit I got from the local starter/alternator shop for like $15. While I was doing all of that I made new battery and ground cables. I made two ground cables to ensure that there was no grounding issue. After I did all of that it has never acted up once since. I'm not sure which one of the changes made everything work properly, or if it was the combination of everything I did, but it works. Maybe it's overkill, but I'd rather put some extra effort into a solid repair rather than sit on the side of the road. Another idea I was going to try was to make a fresh air duct to direct air over the starter, but since it's fixed I never got around to it.

Good luck.

 

Your issue sounds just like mine. Jumping it or another (stronger) battery still won't start it. Nothing helps until it cools off. I think I'm going to try the heat shield route.

Thanks to all of you who have helped me out. I'll check back and let you know if it works. I really think this is it though.

 

I would re-check the timing first. Doesn't cost anything but a lil time. I was always a firm believer in giving a little more advance in my timing when I first started running big blocks. They always run super good, but they would also gert hard to start after getting up to temp. Once my friends started refusing to push start my 390 when it wouldn't start, I fixed the timing. That fixed the starting problem. As for my friends,lol, oh well !!!

 

Thanks Bluesmanmike
I think the timing may be my problem. I have a 78 F250 4X4 Supercab. My now deceased insurance agent bought it new. I had it setting in my back yard for several years. Recently, a nephew put in an engine he got from a friend that needed some cash. It will start up great when cold. Run it just a few minutes or for several minutes. Then try to restart, won't turn over. Usually one womp, thats all I can get.

I would also like to know more about the DSII module mentioned. I guess that is the electronic module mounted on the left wheel well. Some of the hard clear goop has drained out of mine. Could that be problem instead of timing?

Thanks.

 

I had this same problem - TWICE. The first time, the rebuilt starter was less than a year old and it started getting hard to start when the engine was hot. I took the rebuilt starter to my local auto electric rebuild shop where they discovered the brushes were worn. So much for a "rebuilt" starter. I have come to the conclusion that the rebuild starters and alternators from the auto parts store houses are a crap shot at best.

The second time happened a year or two later. The problem turned out to be the ground from the negative battery cable to the engine block was heavily corroded. After this was fixed, my truck has started faster than any new vehicle I have ever owned!

 

AutoZone starter?