Slow crank when starting engine warm

Hi everyone.

I have been struggling with an intermittent hot start issue with my 86 F250 carb 460ci for over a year now. So far this one has got me stumped. i have replaced nearly everything i can think could possibly cause this issue (Battery, new starter with heat wrap, new starter relay, new ignition switch, new oversized battery cables to relay and starter) and still does the same thing. Initial timing is set at 8 deg btdc. It starts fine every time when cold and even when warm if i shut it off and immediately start it back up it starts fine every time. The issue is if i let it sit for more than a min or two like run into the store or unload it at the dump it has a slow crank/dead battery condition. Like its fighting compression. Sometimes it will eventually wind thru it and start but it is putting an enormous load on the battery and starter. when i put a volt meter on the s terminal of the starter while its hard cranking the voltage will drop to around 6 volts but the battery doesn't drop nearly that low. If i jump the relay (battery lug to s terminal) it will wind fine and start. If i disconnect the coil to distributer wire it will wind just fine with the key. I love this truck but im getting really tired of it leaving me stranded. If i let it sit for 30min or more it will crank and fire up every time. any help is appreciated. Thanks

Bill - Glad you joined.  

But you may have missed the email you were sent that asked you to go to the New Member's Start Here folder, read the guidelines, and post an intro in that folder.  We ask that because we hold everyone to the guidelines and they are posted in that folder, so we want you to have every opportunity to read them.

Don't worry, it isn't unusual for people to miss the email, but please assure me that you've read the guidelines before we discuss your starting problem.

Bill - Thanks for the intro.

Several things come to mind on the starting issue, and I think you may have several problems that collectively are preventing it from starting when hot:

If you are seeing a significant voltage difference between the starter and the battery then you have a connection problem or a bad starter relay.  And by jumpering across the starter relay and getting it to start you are pretty much proving that either the battery cable or the starter relay is part of the problem.
 One way to test that is to put the positive lead of your DVM on the battery's positive post and the ground lead on the starter relay's input terminal and crank the engine.  You shouldn't see much voltage drop across the cable.  Then test across the starter relay, then the cable to the starter.

You said you replaced the starter, and even added a blanket to it.  But did you go with a permanent magnet gear reduction (PMGR) unit?  Ford changed to those starters in the 90's and they make a big difference in starting.  They pull less current and provide more torque to boot.

You said that when you pull the coil wire it cranks just fine when hot.  And that tells me that the engine is kicking back due to too much timing.  But you only have it set to 8 BTDC, which shouldn't be too much.  However, two thoughts come to mind.  First, it is possible that the harmonic balancer has slipped and your 8 degrees is 12 or more.  But when a balancer slips once it usually slips again, soon, so that would show up as the ignition timing appearing to change.  If it isn't then the next thought is the ignition module.  A good DS-II module has a retard feature built into it that comes into play when you are starting the engine.  And I can assure you that w/o that feature the 460 can be hard to start hot.  Been there, done that.

The way to find out if yours is working is to pull the little red/light blue wire off the starter relay when the truck is running and touch it to the positive post of the battery/battery cable.  If the retard feature is working then the engine will slow down a bit when you put 12V to that wire.  If it doesn't that feature isn't working and you should replace the module with one that has it built in, and not all do.  A good Motorcraft one should.

Bottom line is that I think you probably have some of all three of those issues biting you.  A non PMGR starter pulls a LOT of current and your cables and relay have to be in perfect condition to start a hot 460 using it.  And if the timing isn't retarding then it is almost impossible.  In fact, I had excellent cables and a good relay plus a PMGR starter and when the retard feature quit on Big Blue he was hard to start hot.

Also, have you checked your timing?

When I first bought my 86 I used to own, it was very slow to start after I stopped to get gas on the way home.

I thought the battery or cables were shot. After checking everything out I checked timing. I don’t remember exactly, but it was 25° to 30° advanced at idle. I set it around 12° and it started good after that.

Gary you were this     close
I thought you were going to say check for stuck advance weights.
When hot they can stick out advancing the timing.
Any rust under the dist. cap?
Dave ----

Ok guys. I have had some time to get out and do some testing on the pickup over the last few days and this is what i have discovered. Voltage drop tests show that there is no drop in voltage on the starter cables to the solenoid or the starter. When i pull the S wire off the solenoid and touch it to the battery with the engine running the timing does change and i even went and turned the key to start with it running (s wire still disconnected at the solenoid of course) the timing changed as well verifying that the timing retard is working. As far as the pmgr starter goes i pulled my new starter off and took it back to autozone as they said they would swap it out with a pmgr starter from the 90s years but the problem is my starter is a 9 tooth bendix and all of the pmgr starters they have are 10 tooth. They did give me a new factory year starter to go home with so if i cant find the right pmgr starter i will be putting that in this afternoon. If anyone has the part number for a 9 tooth pmgr starter for a manual 460 that would be greatly helpful. I left the key on yesterday and the battery sat dead overnight in -32 degree weather so i will be replacing that today. I just cant understand why im getting the huge pulldown when i use the key but if i touch the s terminal to the battery cable post on the solenoid it fires right up? Makes no sense unless it is in the wiring from the key to the solenoid but voltage drop is good there too. Thanks for the help guys!

-32°?!?!?  😳   Do you live on the north slope?

Tooth count shouldn't matter.
It's all down to the engagement depth and how the throwout is clocked relative to the two starter mounting bolts.

I agree, the tooth-count on the starter isn't an issue as the flywheel itself didn't change.  So I'd go with the PMGR starter as it really helps crank that big engine.