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  •  » Crank No Start After Driving

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    3/05/2026 8:18 AM  #1

    TremendousWand
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    Crank No Start After Driving

    1966 Mustang Coupe, 5.0 HO Swap, EFI, Painless Harness, T5z, 4 Disc Brakes, 3.31 Gears

    Sunday was beautiful weather so I took the mustang out for a drive with my daughter.  We drive about 30 minutes and ended up at this ice cream place nearby. It was about 80 degrees.  We were driving around a nice neighborhood at low speeds and I heard fan come on but the car never got close to overheating.   We were in and out about 30 minutes and I went to start the car and it wouldn't turn over. 
    -Fuel pump was priming
    -Fuel pressure looks good
    -I tested the spark signal at the ignition coil and I had spark.
    -Battery tested fine
    -Starter / Crank sounded fine

    After about an hour I gave up and called a tow.  Next evening I went to try and diagnose the problem and it fired right up no problem BUT it had a real deep oscillation at idle.  Like a deep low wave almost like it was going to die and then back up to normal idle.  It was very consistent.  When I accelerated it sounded normal.  Cars don't fix themselves and I don't have a repair fairy in my garage so I don't think the issue was fixed.

    I scratching my head on what could have been the issue.  Any ideas?

    thank you

     

    3/05/2026 8:57 AM  #2

    BobE
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    From: White Plains, NY
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    Re: Crank No Start After Driving

    Just to clarify, when you say it wouldn’t ‘turn over’, does that mean the starter didn’t spin the engine?
    If yes, I’d check that the starter didn’t get overly hot causing it to expand and seize, until it cooled down. 
     
    If the starter did spin the engine, I’d check the timing, or something inside the distributor.
    How old is the battery? 

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    3/05/2026 12:39 PM  #3

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
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    Re: Crank No Start After Driving

    How much fuel pressure does it have when it “ looks good”

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    3/05/2026 3:04 PM  #4

    TKOPerformance
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    Re: Crank No Start After Driving

    IIRC fuel pressure for the 5.0 should be 39psi at idle with the vac hose disconnected from the FPR and the line plugged (to prevent a vac leak).  

    One possibility, assuming it would crank over but not fire would be the FPR has failed.  My Subaru did something like this once and it drove me nuts trying to figure it out.  It turned out that the FPR was failing to bypass when the car was driven, the engine got up to operating temperature, I would stop, and shut it off, and the car sat for a couple minutes.  This led to the fuel in the rails turning into vapor, and preventing fresh fuel from replacing it when I went to restart it (since it wouldn't bypass the vapor).  It acted like a carb car with vapor lock.  I initially thought the fuel pump had failed, and replaced the pump.  I finally diagnosed it by blasting the FPR with Dust Off or something else that got cold when it was sprayed.  The FPR would bypass and the car would start.  I replaced the FPR and have never had an issue since.  

    IIRC it left me stuck at the ice cream shop too.  

     

    3/05/2026 9:05 PM  #5

    rpm
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    Re: Crank No Start After Driving

    When my carbureted 393w had this issue it was a bad battery ground cable that looked pristine.

    Bob. 69 Mach 1, 393W, SMOD Toploader, Armstrong  steering, factory AC.
     

    3/06/2026 9:54 AM  #6

    Rudi
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    Re: Crank No Start After Driving

    A faulty bullet connector crimp on the ignition power feed once almost drove me to insanity.
    The problem was intermittent and would rear it’s ugly head at the most inoportune time, like at 70 mph going down a through way in rush hour.
    I was able to trace the bad cennector when out of sheer frustrtion I slammed the car door and the engine quit running.

    Last edited by Rudi (3/06/2026 10:11 AM)

    Good work ain't cheap, Cheap work ain't good!
     

    3/07/2026 4:50 PM  #7

    TremendousWand
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    Re: Crank No Start After Driving

    MS wrote:

    How much fuel pressure does it have when it “ looks good”

    Right at 40 psi while running.   Ran it today for 2 minutes.  It turned over no problem but sounds terrible.

    There is a rattling sound coming somewhere at or close to the alternator and a have this low pitch whistle sound.  That this popped up all of a sudden has me scratching my head.  It's wet and cold this weekend.  I'll get it on blocks next weekend and try and make a determination.  if I can find a way to up load a video I'll do it.

       •Thread Starter
     

    3/07/2026 9:53 PM  #8

    Alan
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    Re: Crank No Start After Driving

    Have you checked for vacuum leaks? Had a few of those cause trouble when I went to EFI.

    67 Coupe, 5.0 EEC IV Fuel injected. T5, 3:70 rear
     

    3/08/2026 6:37 AM  #9

    TKOPerformance
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    Re: Crank No Start After Driving

    I would probably pull the belt off of it and run it briefly to determine if the noise or noises were coming from the accessory drives.  

     

    3/08/2026 11:06 AM  #10

    Nos681
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    From: Atlantic Mine, Michigan
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    Re: Crank No Start After Driving

    Does the ECM have error codes?
    What are they?

     

    3/08/2026 3:03 PM  #11

    BobE
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    Re: Crank No Start After Driving

    Might be worth it to check any wiring harness connectors.  Could be a poor contact(s), corrosion, etc. within a connector. 

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    3/09/2026 7:37 AM  #12

    John Ha
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    Re: Crank No Start After Driving

    Surging is typically caused by a lean condition.  That can be caused by a vacuum leak somewhere and/or by inadequate fuel supply (faulty injectors, clogged fuel filter, etc.).  A fault in the idle air control system can also cause surging.

    Founding Member of the Perpetually Bewildered Society
     

    3/16/2026 7:41 AM  #13

    TremendousWand
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    Re: Crank No Start After Driving

    It was 75 and sunny so I decided it would be a good day to try and troubleshoot the Mustang.  Went to move it out of the garage and it was dead as a door nail.  No juice what so ever.  Keep in mind, last week it fired right up with an awful sound after the previous week exhibiting a crank no start that resulted in a tow.  Checked the battery and it had 4 volts.  Checked all my lights and nothing was left on.  I but the plug in charger to it for a few hours and got it up to 8 volts.  When I rechecked the reading aminute later and it was down to 5 volts and dropping. 

    I pulled the battery and took it to autozone.  After trying to recharge it they said it was bad and ordered a replacement under warranty.  This is a yellow top, D34 Battery.  These have never failed in my experience and my last one lasted over 5 years.

    1) I was still getting good juice and crank when the car wouldn't start 2 weeks ago. Battery tested good at the time.

    2) Not sure how this could be related to the odd sound coming from alternator Last week. Car fired right up at that time.

    3) I Will replace battery and re-evaluate

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    3/16/2026 12:56 PM  #14

    TKOPerformance
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    Re: Crank No Start After Driving

    Maybe the alternator cooked the battery.  If it wasn't regulating output properly this could happen.  I would thoroughly test the alternator before putting another battery in it and assuming all is well.  

     

    3/17/2026 6:09 AM  #15

    BobE
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    Re: Crank No Start After Driving

    I had an alternator that was putting out 16+ volts intermittently and I didn’t realize it at first (no gauge), replaced the internal regulator and all was fine … and I added a voltmeter.
     
    The battery being drained that much indicates a short somewhere draining the battery.  Or, a poor connection at the battery posts. 
    I understand that once an AGM battery is depleted, as low as you indicated, it may not be able to bring it back to life.
    When you check battery voltage, check it on both the battery post, and the post connector.  I’ve seen where post connections do not show any adverse signs, but are not making good contact.  This can be a intermittent issue that can drive one crazy to locate. 
     

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    3/18/2026 9:03 PM  #16

    TremendousWand
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    Re: Crank No Start After Driving

    Pulled the alternator.  It was definitely damaged.  Trying to spin it manually  and I could feel and here it bind up.  I don't have more than 5000 miles on it but the alternator was installed back in 2014. Ordering a new one.

       •Thread Starter
     

     

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