2008 V6 Mustang - Cranking but no start on occasion - When engine is warm???

TitansFan

New Member
Sep 26, 2019
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Middle Tennessee
Purchased a 2008 V6 Mustang in December of 2018 for our son to drive to college. Clean Carfax. Around 70k miles. Car ran great at first with no issues. Here's a list of what has happened since then:

- Car became difficult to start after he drove it a couple of months. Would crank, but it wouldn't fire up.
- When it did run, very poor acceleration.
- Local mechanic ran a fuel pressure test. Low pressure was discovered. Determined it was the fuel pump.
- Replaced fuel pump and fuel rail pressure sensor.
- Car ran better than ever after fuel pump replacement.
- Recently became difficult to start again.
- Difficulty starting seems to coincide with short trips (i.e. go to store, run in, come back out and won't start)
- If car sits for 30 minutes or so after difficulty starting, it will fire right up
- Does not do this every time

Not sure what's going on or how best to diagnose. Any help is appreciated.

Thanks!
 
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TitansFan

New Member
Sep 26, 2019
3
0
1
52
Middle Tennessee
Didn't want our son to drive the car so it has been sitting for several days. Tried to start it last night and now it won't even start up. Cranks just fine, but will not fire up. Showing a code now of P0690 ECM/PCM Power Relay Sense - Circuit High. Any suggestions what to look for? Thanks
 

TitansFan

New Member
Sep 26, 2019
3
0
1
52
Middle Tennessee
Tried to start it a couple of days later and it fired right up so I took it immediately to the local Ford dealer. They kept it a few days and tried to duplicate the problem. Ran various diagnostic tests, but couldn't find anything wrong (I was afraid this would happen). Will pick it up and wait for it to happen again...sigh...
 
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