2005 SRX NorthStar 4.6 V8, 24,500 miles. Starts fine when cold. After driving, will start up right away after sitting for only a few minutes but if it sits 15 minutes to 2 or 3 hours, when you try to start, it cranks 5-10 seconds before starting. I replaced the fuel pump relay because I know if that fails, you need the oil pressure to build up in order for it to start. That didn’t help. I changed the oil and filter thinking of the possibility of a faulty anti-drain back valve. There are no trouble codes in the computer. What’s the next likely culprit, please?

 

check fuel pressure at the fuel rail.
I believe that you are looking for approximately 40 psi.



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Checking fuel pressures: With the key on - not running, I get 53 PSI. When running, I get 60/61 psi. With the key off PSI drop to almost zero in about 1/2 hour. Is this supposed to happen? Couls there be a leaky check ball at teh pump?

 

Your static pressure sound good at 53.

When the pump is turned off, the system should hold residual pressure for several minutes (look up the specs to see how much pressure drop is allowed over a given period of time for your model).

If pressure drops quickly, the vehicle may have a leaky fuel line, a leaky fuel pump check valve, a leaky fuel pressure regulator or one or more leaky fuel injectors.
Low residual fuel pressure can cause hard starting and vapor lock during hot weather or if its really hot in the engine compartment.

To keep the residual pressure up try turning the key on every 5 minutes, w/o cranking or starting the engine, see the effects of doing that.



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OK, I turned the key on every 5 minutes without starting and get 54 psi. Pressure drop when off is about 1 psi/min.

So if it starts ok when cold, we know we have good fuel rail pressure, could one of the other sensors give a false signal when hot such as the Intake Air Temperature (IAT), Mass Air Flow Sensor (MAF) or the Manifold Absolute Pressure sensor (MAP)?

 

what I meant is, does the engine still do that after keeping the pressure up every 5 minutes or so, or does it start fast ?



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After driving to warm up the car, let it sit for 10 min, then turned key on for 5 seconds, then turned off let it sit for 4-5 min, repeated 3 times. Got the same result, long crank time.

 

Same Result Long Crank Time.
After driving to warm up the car, I let it sit for 10 min, then turned key on for 5 seconds, then turned off let it sit for 4-5 min, repeated 3 times. Got the same result, long crank time.

 

that is not what I had hoped for.
I left a note for slowroll .. hopefully he has a solution.

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Do you have access to scanner? Car has low mileage what kind of driving - how is it normally driven? Frequent short trips can lead to carbon build up which can cause starting issues. Car is 4-5yrs old, what is condition of battery? Batteries can degrade after about 3 years, so have it tested to be sure it is up to par. What grade and brand of fuel do you use? Or is it the most inexpensive/1st station you come to when you need gas? Sorry more questions than answers. It is normal for engine to turn up to 2 1/2 times to sync fuel injection and ignition timing.