Unusual Air/Fuel Starting Problem...stumped - Ford Mustang Forum
 
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post #1 of 5 (permalink) Old 07-19-2014 Thread Starter
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Unusual Air/Fuel Starting Problem...stumped

Hey guys long time lurker, been using these forums for help forever. Finally, needed to ask a question of my own.

1999 4.6L, 130k, auto, cold air, straight pipes

Problem: When starting, turn key, cranks cranks cranks, nothing...turn again, crank crank low idle start. When it starts, runs awesome, No problems at all.

This has been happening without fail for about 2-3 weeks.

Things done:

New fuel pump
New fuel filter
cleaned IAC
cleaned MAF
Checked inertia switch
Checked voltages, per this site, at fuel pump, at inertia switch, at fpdm, at ccrm, pcm
Noid light shows all injectors working
All electrical connections have been cleaned that have anything to do with air/fuel
new battery, voltage readings with car off/while cranking are ok

Things to Note:
I have ZERO fuel pressure when i turn the key to the ON position, and i hear the pump priming, and the pump has voltage.

The only time it started right up, ever, was after i disconnected the IAC and tried turning it over, which did not start, i reconnected and it started right up. Then i took it apart and cleaned etc..

the only thing i haven't done is try an injector cleaner, and mess with the TPS or FPS (no one seems to have a test for it).

So in all, why would the fuel rail have no pressure, but then start and run like a raped ape after multiple starting attempts (key cycling?)..

Any help is appreciated, Thanks in advance

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post #2 of 5 (permalink) Old 07-19-2014
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If you have "one way" fuel system, your fuel pump is bad, doesn't matter old or new.
If you have "two way (with return line)" system, you have bad fuel pressure regulator.
Fuel pump module has a release valve, it is not actually part of fuel pump.
I did:
I held pump under water and attached compressed air to fuel hose.
Lots of bubbles were coming from release valve.

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post #3 of 5 (permalink) Old 07-20-2014
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Possible Fuel pressure leak down sources

Quote:
Originally Posted by scum138 View Post
I have ZERO fuel pressure when i turn the key to the ON position, and i hear the pump priming, and the pump has voltage.
^^^This is your problem. The fuel system needs to hold pressure between starts.

For further proof try this. Cycle the key on/pause/off several times without cranking. Listen for the fuel pump to run each time. Does this improve starting? If so, the problem is likely fuel pressure leak down.

Possible sources of pressure leak down include:
  • Fuel pump check valve
  • Fuel injectors
  • Fuel rail pressure sensor (FRPS)
  • Fuel pressure regulator (return systems).
  • Flexible lines inside the tank.
For the FRPS inspect the intake vacuum reference line for raw gas.

If an injector(s) problem is suspected, consider an injector cleaning and flow test service such as InjectorRX.com. Once cleaned and tested the injectors will be as good as new. Cheaper than new. This is NOT the same as a chemical injector cleaning.

Troubleshooting problems inside the gas tank is often best done by dropping the tank.

2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.
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post #4 of 5 (permalink) Old 07-20-2014 Thread Starter
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Thanks for the quick reply guys..one more thing just to clarify..since this is a one way system, no regulator, is the check valve part of the pump. A seperate threadddescribed what I was told to be a pulse dampener, a small chrome diaphragm looking unit about four inches from the fuel rail, to be the one way check valve. There were discrepancies from posters following that comment.
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post #5 of 5 (permalink) Old 07-21-2014
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For the return-less system in the 1999+ model year the in line chrome device is a pulse damper. It is not a check valve. It's purpose is to even out the pressure spikes that happen when ever the fuel injectors open or close. This protects the fuel pump and allows the fuel pressure sensor to read a more stable value.

There is a check valve that's part of the fuel pump sub-assembly located inside the gas tank.

The fuel injectors still need to hold pressure when closed between starts.

2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.
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