I have an 08 f350 lariat with the 6.8 with 66000 miles. A month ago took it to the dealer with a plugged catilityc converter. All covered under warranty. Got the truck back, starts great when cold including 18 degrees the other morning. I drive 7 miles to work, shut it off and restart, it acts as if the starter is struggling to turn the engine over. Once it cools off, starts fine again. I took it back to dealer, they replaced the starter. No change. Took it back again, they replace battery. Cranks a little faster, but you can tell it's still struggling. Any ideas? It always starts, I'm just wondering how it will be when it's 80 out, and in pulling my 9000lb camper

 

Did they put a meter at the starter to determine how many volts you are getting in both conditions?

 

sounds like they are going right down the trouble shooting chart. problem is if it starts....you have not problem. when does the warranty run out?

 

Probably a better meter would be an Amp Meter.

I would also check the engine ground to the frame.

 

You do NOT need to use this tool. A digital multimeter will work fine.

This video should give you some direction to help narrow down the problem.

 

I'm not sure what they have tested. They did do an interference check, whatever that is. After that they replaced the starter. I just left the service manager at the dealership. He is saying it could be back pressure. Possibly a plugged muffler. So I got home and unhooked it at the y pipe. Still no difference.

 

warranty is good till 110,000 miles.

 

Hot start troubles are generally related to a weak battery, a weak starter, a weak solenoid, high resistance in the primary wires (the smaller control wires) or the secondary wires (the larger battery cables).
As mentioned in a negative ground system such as on our trucks; clean and tight grounds are you best friend. I always follow clean and tight grounds with clear ignition sealer. Keeps them good longer.
Battery terminals and battery post get the shiny treatment too as well as spray terminal protector and or the felt azz holes impregnated with protectant.
A cable or a connection can visually inspect OK. The true test is with an ohm meter or the above drop test.
A new battery can be bad out of the box, same for a starter. Load test the battery and bench draw test the starter.
The only other thing I could think of is advanced timing or other heat soak related troubles in an ignition system, but thats on spark ignited engines not Diesel.

 

this has the 6.8 v10. Sorry, forgot that was the year they came out with the 6.8 diesel

 

I just dropped it off at a my regular mechanic. I trust his opinion and diagnostic ability over the ford mechanics. He tested the battery and charging system when I was there and everything tested good. He also is thinking a bad cable or connection somewhere. He is going to get into it tomorrow, so fingers crossed.

 

I got my truck back from my mechanic the other day. He checked the battery, starter, and everything in between. Everything tests perfect. He thinks it's something internal in the engine, like too much compression when hot. Any ideas? I pulled my new camper home yesterday. About a 40 mile trip towing 7300lbs, and it cranked even harder, tried to fire and quit. The second try it did start.

 

Could have a crank sensor on its way out when its heat soaked? Something could be effecting timing when hot. Causing advanced timing due to component breakdown (high resistance) when hot?
Need to hook it into an analyzer and take its pulse when hot.
I have a 95 GC Jeep that does this. It cranks but doesn't quite catch the first time when hot. If I try to restart with out bringing the key completely to the off position on the second attempt it acts like the timing is advanced and kicks back on the starter. Whereas if I bring the key all the way back it resets and starts as normal. I believe its the crank position sensor loosing its mind?

 

I got my truck back yesterday. Ford replaced the muffler saying it was plugged as a result of the plugged cat. No difference. I asked them to test the crank sensor while they had it. They said it had no codes for the crank sensor. That tells me they didn't test it, just hooked up the computer, and no codes came up.

 

The mechanic needs to see it happen which as we all know somehow the truck knows when its in the doctors office and acts 100% normal, making you look like you need a doctor...lol

My money is still on a dirty ground or high resistance (bad) battery cable. Electrical resistance rises with temperature(resistance toelectron flow). Which is what your describing. When cold the resistance is close to the threshold so it cranks ok. Once its hot the resistance exceeds the normal system threshold inducing high(er) resistance causing the slower crank.
So there is two cases here which lead to the conclusions.
1. The problem arises only when hot.
2. You said it improved somewhat with a new starter and battery. The new starter reduced some of the over all resistance just because its new and the connection was disturbed which likely made it better. The battery being new has a little more oomph to overcome the high resistance and its connections at the post were likely cleaned upon installation.

We've eliminated the starter and battery as problems (for now). So next in line is to examine each of the battery cables and connections. Each of the battery cables needs to be closely inspected. The easiest way to find the bad one is to perform the voltage drop test shown in the above youtube.

 

I performed the voltage drop test tonight with my digital multimeter. I first did the test with the truck hot, and cranking hard. The negative cable maxed at .46, and the positive cable maxed at .74. I tried it again after the truck cooled and the results were the same. I inspected the cables, and the only thing I found was the ground was a little rusty at the block. I cleaned it and retested with little difference.