2004 3.9 major issues

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fatal1tywulf

Member

Nov 4, 2018

22

2

13

putnam, ct

Nov 23, 2018

#1

• Nov 23, 2018

• #1

okay recently hit with minus degree weather and suddenly the horn is no longer working when you double click lock button, next gauges aren't reading correctly, speedo not working. rpm gauge not working. gauge needles jumping to max and then bottoming out. also doing same when brake peddle pushed. this also cuts out radio. now car is dead nothing turns on off.. assuming battery is dead and alt not working can a bad alternator cause these problems?

 

wmburns

SN Certified Technician

Aug 14, 2009

5,892

514

204

Houston Texas

Nov 23, 2018

#2

• Nov 23, 2018

• #2

fatal1tywulf said:

alt not working can a bad alternator cause these problems?

Click to expand...

Yes it could. But IMO your problem is more likely a loose/weak ground. In the interest of good trouble shooting all electrical trouble shooting should begin with a through review of the battery and charging system. Best not to cut any corners.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

Once it is known that the alternator and battery is in tip top shape move on the checking the grounds. Start with the grounds on the left and right radiator core supports. Make sure they are clean and tight with no signs of corrosion. Then perform the voltage drop measurements as pointed out in the voltage drop test URL.

 

F

fatal1tywulf

Member

Nov 4, 2018

22

2

13

putnam, ct

Dec 10, 2018

#3

• Dec 10, 2018

• #3

latest update. alt and battery checked out fine alt was putting out 14.6 and the culprit was a broken ground wire which was making a slight contact until the autozone guy totally snapped it in half... as he was testing battery. connection was at radiator support. so now it starts and all gauges working correctly. once more. thanks for the info.

 

wmburns

SN Certified Technician

Aug 14, 2009

5,892

514

204

Houston Texas

Dec 10, 2018

#4

• Dec 10, 2018

• #4

Sounds like all is well.

Would have like to say, "score one for the voltage drop method" but that doesn't seem to be true. But the fall back visual inspection with "wiggle test" seems to have saved the day......

 

C

Calvin R54

New Member

Apr 26, 2019

1

0

0

California

Apr 26, 2019

#5

• Apr 26, 2019

• #5

Hello All, New to forum. I have a 2004 3.9 Stang and I am trying to test the fuel pressure with a gauge and can not find the shrader value port to test it. Anyone? Thanks in Advance.

 

wmburns

SN Certified Technician

Aug 14, 2009

5,892

514

204

Houston Texas

Apr 26, 2019

#6

• Apr 26, 2019

• #6

Your model year Mustang does not have a fuel pressure Schrader valve. Ford does make a "special" tool that inserts between the quick disconnection fittings to add a test port.

If you want to know the fuel pressure why not just ask the PCM?

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