99 mustang gt hard start after sitting

May 16, 2018
14
0
1
19
South Carolina
#1
Hard to start if sitting about 30 mins or starting shutting off then immediately restarting it has trouble somtimes stalls then clears up and runs fine. Also fuel pressure is About 51 and idle but as soon as Key off drops to about 6 Ibs in a few seconds.
Thanks!
 
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wmburns

SN Certified Technician
Aug 14, 2009
4,717
311
154
Houston Texas
#2
The fuel pressure needs to remain up between starts. Fuel pressure dropping to 6 PSI in a few seconds after shut down indicates a leak somewhere in the system. The usual leak locations are:
  • fuel injectors not closing/sealing fully
  • fuel regulator or pressure sensor (FRPS). Check the intake vacuum reference line for raw gas.
  • fuel pump one way check valve.
  • leaking flexible fuel line between the fuel pump and gas tank hat.
If a fuel injector problem is suspected I have had great luck with an injector cleaning and flow test service such as InjectorRX.com. Once cleaned and tested they are as good as new but cheaper.

As a short term work around try cycling the key on/pause/off a couple of times to see if this improves starting.

Obviously many of the other items on the list will require for the fuel tank to be dropped.
 
Last edited:
May 16, 2018
14
0
1
19
South Carolina
#3
The fuel pressure needs to remain up between starts. Fuel pressure dropping to 6 PSI in a few seconds after shut down indicates a leak somewhere in the system. The usual leak locations are:
The fuel pressure needs to remain up between starts. Fuel pressure dropping to 6 PSI in a few seconds after shut down indicates a leak somewhere in the system. The usual leak locations are:
  • fuel injectors not closing/sealing fully
  • fuel regulator or pressure sensor (FRPS). Check the intake vacuum reference line for raw gas.
  • fuel pump one way check valve.
  • leaking flexible fuel line between the fuel pump and gas tank hat.
If a fuel injector problem is suspected I have had great luck with an injector cleaning and flow test service such as InjectorRX.com. Once cleaned and tested they are as good as new but cheaper.

As a short term work around try cycling the key on/pause/off a couple of times to see if this improves starting.
Thank you I have checked injectors for leaks but I think there ok
  • fuel injectors not closing/sealing fully
  • fuel regulator or pressure sensor (FRPS). Check the intake vacuum reference line for raw gas.
  • fuel pump one way check valve.
  • leaking flexible fuel line between the fuel pump and gas tank hat.
If a fuel injector problem is suspected I have had great luck with an injector cleaning and flow test service such as InjectorRX.com. Once cleaned and tested they are as good as new but cheaper.

As a short term
 

wmburns

SN Certified Technician
Aug 14, 2009
4,717
311
154
Houston Texas
#5
How did you check the injectors for leaks? By "looking" at them?

IF they are leaking the leak will be inside the intake manifold at the injector tip and therefore not visible unless removed.

What about the other leak points?

IMO it may be short sighted to rule out the injectors without testing. But for the home DIY'er testing fuel injectors is not easy. Which is why I just send my out to be "handled" by a pro. If this is a high mileage car the likelyhood of one or more injectors being partially clogged is high. One of the better parts about InjectorRX.com is you get a flow report before and after cleaning.

Tech tip. bag each injector with the Ford cylinder number it came from. Then if there are problem injectors this can be tied by to the original cylinder.
 
Last edited:
May 16, 2018
14
0
1
19
South Carolina
#6
Took them off but left they them on the rail and primed them and they were dry engine bay never smells of gas either if that matters
 
Last edited:

wmburns

SN Certified Technician
Aug 14, 2009
4,717
311
154
Houston Texas
#8
Took them off but left they them on the rail and primed them and they were dry engine bay never smells of gas either if that matters
Since it's a known fact that the fuel pressure does drop between key cycles there has to be a leak somewhere. IF you are certain it's not the fuel injectors then what has been done to rule out the other "possible" leak locations pointed out?
 
Last edited:
May 16, 2018
14
0
1
19
South Carolina
#9
Pretty confident it’s not the injectors not positive though just wanted someone’s input on if I should give the fuel pump a try or not
 

Neuron

Mustang Master
Nov 6, 2016
674
129
83
69
#10
OP was nice enough to take the time to try and help with this:
  • fuel injectors not closing/sealing fully
  • fuel regulator or pressure sensor (FRPS). Check the intake vacuum reference line for raw gas.
  • fuel pump one way check valve.
  • leaking flexible fuel line between the fuel pump and gas tank hat.
Why aren't you going down this list?
 
May 16, 2018
14
0
1
19
South Carolina
#11
OP was nice enough to take the time to try and help with this:
  • fuel injectors not closing/sealing fully
  • fuel regulator or pressure sensor (FRPS). Check the intake vacuum reference line for raw gas.
  • fuel pump one way check valve.
  • leaking flexible fuel line between the fuel pump and gas tank hat.
Why aren't you going down this list?
Because it was just posted a few hours ago and I’m not home yet
 

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