Help! Gt Cranks But Only Starts Once In Awhile.

fatdaddylines

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Jun 9, 2017
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Ashland, WI
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Hey my friends! My daughter and I own a '99 Mustang GT 4.6 V8 with 104,000 miles. Its been a great machine. Last year the car started to develop a problem. It would crank over with no start. No Check Engine light. Come back and it would start and run fine for a few days. Last fall as we were putting her up for the winter months, it was running fine. we finished cleaning her up and when to put in machine shed and it would not start....4 days later it starts. Parked it.
Fast forward to April and we try to start it, battery weak so we jump it but it would not fire. Installed new battery, nothing. I start researching problems and asked questions. I bought scanner and it pulled a pending code PO 191 FRPS. We replaced it, cranked but no start. cranked again and it fired up!! Woohoo problem solved so I thought. The car ran for 6-7 minutes and just died. I was told fuel pump is problem. I listened and heard fuel pump kick on when key was turned on. So I did a test of spraying some start fluid in my intake and car fired till SF wore off. I do not have a fuel pressure test gauge, I did have pressure when I replaced the Fuel Rail Pressure Sensor so I think fuel pump is good? I have not replaced the fuel pump yet. I also noticed the Tach did not move during cranking over, but would work when car did start. Cam position sensor? I was also told to have Alt checked for proper Amps? Any truth to that? Please if you can shed some light on places to look our check, I would greatly appreciate it. Thank you so much my friends...
 
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wmburns

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Aug 14, 2009
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It's always a good idea to post the full DTC code. There are 1000's and they each have a story to tell.

IMO your problem is NOT a CKP sensor. Why? The motor would never run without a good CKP sensor signal. Nor is this a bad CMP sensor. Why? Because the 4.6 will run with the CMP sensor unplugged.

But in general for the 1999+ 4.6 the FRPS is a no start sensor. Which means expect a crank with no start if the PCM is not getting a good signal. But in this case the issue is to figure out if this is a FRPS problem or a fuel pump problem.

Sooooo if asking for someone to make an educated guess.... my volt is the fuel pump. Why? Because:
  • The FRPS has already been replaced
  • the motor starts and runs from starting fluid.
  • the age of the car and the fact that it is stored for long periods of time.
What further proof? For a low tech fuel pump test bang on the fuel tank with a rubber mallet. Does it run now? If so, diagnosis is confirmed.

Want more low tech tests? Try turning the key on/pause/off several times without cranking. Does it run now? If so, suspect a fuel pressure leak down issue.

Disclaimer. I generally recommend starting ALL trouble shooting sessions with a through review of the battery and charging system. In this case it's VITAL that the battery be fully charged and the terminals are clean and tight. Don't think for a moment that something as mundane as a bad battery or weak battery connection couldn't cause everyone of your problems.

Disclaimer #2. Water in the gas tank is also a possibility. It's possible to hot wire the fuel pump and use to drain the tank. This could come in handy if you decide to put in a new fuel pump.

Disclaimer #3. To be certain it's a fuel pump problem it's necessary to "know" what the fuel pressure actually is. As well as "know" what the PCM "thinks" the fuel pressure is. Otherwise replacing the fuel pump is an educated guess.

Want some "higher tech" tests to confirm a bad fuel pump? Get yourself an ODB2 scanner and use it to monitor fuel pressure from the PCM's point of view. Here's some information on an affordable ODB2 scanner.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

1996+ Crank with no start check list
http://www.allfordmustangs.com/forums/4-6l-tech/336452-1997-mustang-wont-ignite.html#2984838

1999-2004 BJB CJB fuse panel layout
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271

>>From the Ford service manual:
P0191 - Fuel Rail Pressure Sensor Circuit Performance (FRP)
  • High fuel pressure.
  • Low fuel pressure.
  • Damaged FRP sensor.
  • Excessive resistance in circuit.
  • Low or no fuel.
A FRP PID value during KOER of 138 kpa (20 psi) and 413 kpa (60 psi) for gasoline or 586 kpa (85 psi) and 725 kpa (105 psi) for natural gas vehicles (NG) is acceptable.
 
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fatdaddylines

Member
Jun 9, 2017
5
2
13
62
Ashland, WI
www.facebook.com
It's always a good idea to post the full DTC code. There are 1000's and they each have a story to tell.

IMO your problem is NOT a CKP sensor. Why? The motor would never run without a good CKP sensor signal. Nor is this a bad CMP sensor. Why? Because the 4.6 will run with the CMP sensor unplugged.

But in general for the 1999+ 4.6 the FRPS is a no start sensor. Which means expect a crank with no start if the PCM is not getting a good signal. But in this case the issue is to figure out if this is a FRPS problem or a fuel pump problem.

Sooooo if asking for someone to make an educated guess.... my volt is the fuel pump. Why? Because:
  • The FRPS has already been replaced
  • the motor starts and runs from starting fluid.
  • the age of the car and the fact that it is stored for long periods of time.
What further proof? For a low tech fuel pump test bang on the fuel tank with a rubber mallet. Does it run now? If so, diagnosis is confirmed.

Want more low tech tests? Try turning the key on/pause/off several times without cranking. Does it run now? If so, suspect a fuel pressure leak down issue.

Disclaimer. I generally recommend starting ALL trouble shooting sessions with a through review of the battery and charging system. In this case it's VITAL that the battery be fully charged and the terminals are clean and tight. Don't think for a moment that something as mundane as a bad battery or weak battery connection couldn't cause everyone of your problems.

Disclaimer #2. Water in the gas tank is also a possibility. It's possible to hot wire the fuel pump and use to drain the tank. This could come in handy if you decide to put in a new fuel pump.

Disclaimer #3. To be certain it's a fuel pump problem it's necessary to "know" what the fuel pressure actually is. As well as "know" what the PCM "thinks" the fuel pressure is. Otherwise replacing the fuel pump is an educated guess.

Want some "higher tech" tests to confirm a bad fuel pump? Get yourself an ODB2 scanner and use it to monitor fuel pressure from the PCM's point of view. Here's some information on an affordable ODB2 scanner.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

1996+ Crank with no start check list
http://www.allfordmustangs.com/forums/4-6l-tech/336452-1997-mustang-wont-ignite.html#2984838

1999-2004 BJB CJB fuse panel layout
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271

>>From the Ford service manual:
P0191 - Fuel Rail Pressure Sensor Circuit Performance (FRP)
  • High fuel pressure.
  • Low fuel pressure.
  • Damaged FRP sensor.
  • Excessive resistance in circuit.
  • Low or no fuel.
A FRP PID value during KOER of 138 kpa (20 psi) and 413 kpa (60 psi) for gasoline or 586 kpa (85 psi) and 725 kpa (105 psi) for natural gas vehicles (NG) is acceptable.
Thank you so very much my friend! I can't tell how much I appreciate the info. We will keep you informed!! Blessings!!