Slow Crank, No Start When Warm

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T. Fritz

T. Fritz

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Hello all, I've recently finished a 340 build for my 70 Duster. It is bored .60 over with a 4" stroker crank in it with aluminum heads running about 10.7:1 CR. My issue is that it turns over and starts with minimal issues from cold but when my temp guage is reading anything over 180F and I try to start, the engine almost doesn't want to turn over at all. I've already checked for clearance issues, all clear, I've installed one of those starter insulator/blankets, next to no difference, alternator charges to 14 Volts when running, battery reads 12.6V when initially starting when warm, the battery is only a couple months old, I even went so far as to turn the thing over by hand when warm and all felt fine. Could this be a result of heat soak on the starter solenoid? If not what could it be.
 
Hopefully you are not still using the stock 340 starter?

It kills the restart by 2 fold. Old stock starters crank slow especially when they are hot.

Then the stock starter sucks all the good electricity out of the ignition system at the same time.

Add in higher compression and today's poorer quality fuels...well you know.

Need a new Mini Starter on there like came on the Dodge Dakotas.

Mini Starters have enough power to crank the Hemi and 440 performance engines.

And the Mini Starters don't have the excessive ignition draw to boot. Fast starts like the engine has fuel injection.

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Next question > What are you using for an ignition system?


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I have a high torque mini starter from Tuff Stuff already on and an MSD ignition box and distributor. Sorry, forgot to mention what starter I have. Plus something to factor in is that I have TTI full length headers installed as well.
 
Where is your battery installed? If in the trunk, make sure your ground cable is sized appropriately.

Does it help if you crack the throttle?
 
Battery is trunk mounted with 2 guage ground wires going from block to frame as well as alternator to frame. Opening the throttle any amount makes no difference.
 
I’d try increasing your ground size from battery to ground.

2 gauge is too small. I run 2/0 wires.

I originally ran a 2 gauge and on hot starts the wire would heat up.

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I would do the following

1...Install some sort of method to get an accurate voltmeter on the block and starter stud, so you can measure batt V while cranking. One way is to simply get a couple of no 14 or smaller wire size eyelets with 3/8 eyes, get some scrap wire any size, 18-14, and bring out some leads from those points so you can get a meter on them

If V during cranking and hot is down to 10.5, this could be wiring/ terminal / connection/ battery issues or high starter draw.

2...Take your battery somewhere and have it load tested. If the guy comes out with a small box in one hand, go somewhere else. You want a carbon pile load tester.

3...Specs on PM starters are fairly rare as to locked rotor amps, etc, but if the above two check OK, suspect the starter and try to get it tested, or sub another, even if you have to buy a junkyard PM starter off a late Dakota/ Ram 5.2/ 5.9 magnum
 
I would suspect the MSD ignition next, reliability is not their greatest.....

These Mopar HEI conversions with the proper full 12 volt powered E-Coil does the trick on restarts on a hot engine.

Just reach in through the window and hit the key and it is running, without even touching the gas pedal.

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Most have a hard time wrapping their head around these > how can something so simple work so well?


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Where is your initial timing set.

A lot of initial timing could exacerbate the problem

But my bet is on the trunk mounted battery wiring
 
Does not seem excessive. But for a test you could try reducing it to 5 or 10 just to see if it makes any difference.
 
Ign type does not cause slow cranking.

You need a high HP starter. The MSD Dyna Force is over 3 hp. Some companies make a range of starters, with some less than 2 hp.
 
On my 440 had a ***** of a time kicking back/ slow crank warm. Turned out the dist was advancing just enough when hot to cause this issue. Re did it to a mechanical dist isuue is gone! ***** to find the issue. Turn it to 10 BTDC and see if it persists. If gone you need to adjust the curve.
 
Last edited:
halifaxhops said:
On my 440 had a ***** of a time kicking back/ slow crank warm. Turned out the dist was advancing just enough when hot to cause this issue. Re did it to a mechanical dist isuue is gone! ***** to find the issue. Turn it to 10 BTDC and see if it persists. If gone you need to adjust the curve.
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I still have that issue. Good to know.
 
My race car is wired like that, the solenoid is jumped at the starter, and had a Ford style solenoid back near the battery. That way the battery cable to the starter is only hot when the engine is cranking. Depends on how the rest of the car is wired. Sometimes the factory starter relay is used for a voltage junction. I would increase the positive and negative cable sizes, and check for voltage drop. And possibly try another starter. And I also like to get the engine turning over before turning the ignition switch on, seems to help when hot
 
I would do a voltage drop test from bat+ to starter+ and from bat- to starter case when hot cranking. Will need a helper but will confirm or condemn wiring. Should be less than 0.5v. I have 30ft test leads. HF has them for around $20.
 
Tyler Fritz said:
Would a remote starter solenoid be a feasible option
Click to expand...
You mean your starter solenoid is in the trunk now?

If that's the case it might make a difference to move the inherit resistance of the solenoid closer to the starter.
 
Dana67Dart said:
You mean your starter solenoid is in the trunk now?

If that's the case it might make a difference to move the inherit resistance of the solenoid closer to the starter.
Click to expand...
No I haven't done anything yet. I was simply asking if installing a remote solenoid would be a decent option to see if it's heat soak
 
Just checked for voltage drop, 12.61v at battery, 12.61v at alternator, and 12.60v at starter. Can't test while cranking as I'm alone
 
That is voltage, but not voltage drop. Voltage drop will check for high resistance in cables and connections , causing the starter not to get enough voltage. Heat increases resistance
 
Won't work without being loaded. You will need a helper or a remote starter switch.
 
That is unfortunate. Either way I just ran the car, shut it down at varying temps and the only time it didn't want to start was when the coolant temp was reading around 210F, everything else below that temp the engine started though rather hesitantly. This was all after advancing my initial timing from 5 degrees BTDC to 10
 
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