help please - Won't Warm Start

[leoj]

1999 mustang v6 car starts right up runs great no lights on shut the car off will not restart checked with my scanner when running 40 psi at fuel rail when it wont start 10 psi at fuel rail let the car sit for a couple of hours and will start and run fine until i shut it off and same problem again have spark no fuel no codes

 

[Noobz347]

Welcome to OEM fuel pumps. You probably need a new one. Unless you have a lot of upgrades or are planning upgrades, I would replace it with the high pressure version of the stock displacement pump. Meaning: If the stock pump is 88 liters per hour then get a high pressure 88 liter per hour pump made by "Walbro". BBK pumps and many others are re-branded Walbro pumps but you want to be sure to avoid the parts store Chinese knock-off.

If you cannot positively identify a Walbro pump then purchase a replacement from the dealership. I would hazard to guess that any of the Mustang parts stores on-line have these pumps (I'm sure of it). Check the vendor forum for discount codes.

 

[wmburns]

Try this. Cycle the key on/pause/off several times before cranking the motor. Does this improve starting? If so the likely problem is fuel pressure leak down. This would confirm your test results that the system is not maintaining pressure between starts.

Where are some of the places for fuel pressure leak down?

• Fuel pump check valve
• flexible fuel line inside the gas tank between the fuel pump and gas tank hat
• fuel injectors. Note, you will not see a leaking fuel injector as it leaks inside the intake manifold.
• fuel rail pressure sensor (FRPS)

If leaking fuel injectors are suspected consider an injector cleaning and flow test service such as InjectorRX.com. Once cleaned and tested they are as good as new but cheaper.

One quick test for the FRPS is to inspect the intake vacuum reference line for raw gas.

Problems with the fuel pump check valve will require the gas tank to be dropped in order to trouble shoot.