P0279 cylinder 7 injector circuit low...bummer - Ford Powerstroke Diesel Forum
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post #1 of 14 Old 03-15-2010, 06:49 PM Thread Starter
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P0279 cylinder 7 injector circuit low...bummer

Is this something i can fix myself? Truck wouldnt start couple weeks ago so i did the FICM re solder trick it worked awesome!!!

But now the injector problem. Im not sure what to test. Thanks for any help.
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post #2 of 14 Old 03-15-2010, 09:04 PM
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Check your cables leading from your FICM to your injectors. One of them is shorting out.

Shawn Carlson

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post #3 of 14 Old 03-15-2010, 09:07 PM Thread Starter
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ok ok cool deal!!! sorry if stupid question but the wire is shorting..? a loose connection would be different code or problem?
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post #4 of 14 Old 03-16-2010, 05:45 AM
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What a short is

Bear in mind there are different kinds/degrees of shorts.
The most familiar is the massive short that blows the fuze. You can have a small short,say just a few or 1 strand of wire touching ground or another wire. This situation will not cause the fuze to blow but will allow part of the voltage to be drawn away from the normal circuit path.

Now every sensor has a wire that carries a reference voltage, the computer knows which reference voltage is for each sensor. For example the reference voltage is 5v but part is being bled off to ground and only 3v is getting there, the computer reads this and throws a code relateing to voltage being low or out of range or some such.

Hope this clarifies some
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post #5 of 14 Old 03-16-2010, 06:37 AM
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Originally Posted by DeadaHead View Post
ok ok cool deal!!! sorry if stupid question but the wire is shorting..? a loose connection would be different code or problem?
Most common occurrence is the wiring has rubbed up against something and now instead of sending the firing voltage to your injector, it shorts out to the chassis. It could also be that your wiring has come loose, but that is a less likely scenario since it is only occurring on one injector. Keep looking because the chafed wiring is sometimes difficult to find. Follow your FICM connections all the way to #7 injector.

Shawn Carlson

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BulletProof All-Aluminum Radiator
BulletProof All-Aluminum Intercooler
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SCT w/ Custom Tunes (TSD, DJ's, Innovative, Gearhead, QuickTricks)

Exterior Mods:
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Icon Adjustable Trac Bar
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BDS Dual Steering Stabilizer
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post #6 of 14 Old 03-18-2010, 07:57 AM Thread Starter
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Some good info thanks guys!!! If i do find the wire will the check engine light go off or do i need to clear the code with a scan tool?
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post #7 of 14 Old 03-18-2010, 08:17 AM Thread Starter
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I think i have an open circuit not a short. REading a FICM guide and it says a short would produce a message that says "injector circuit HIGH" while and open circuit would say "injector circuit LOW"
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post #8 of 14 Old 03-18-2010, 12:20 PM
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Ah, good catch and you are correct. I apologize I didn't pay close enough attention. Keep us posted on the progress...

Shawn Carlson

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Engine Mods:
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CCV Reroute (Reinstated)
4" MBRP Exhaust
MTW Stage 1 Turbo
Bulletproof 53V FICM
BulletProof EGR Cooler
BulletProof Water Pump
Riff Raff Intercooler Boots
Gogo Diesel Direct Drive Solenoid
BulletProof All-Aluminum Radiator
BulletProof All-Aluminum Intercooler
BulletProof Oil Cooler System w/ Bypass Filter
SCT w/ Custom Tunes (TSD, DJ's, Innovative, Gearhead, QuickTricks)

Exterior Mods:
Bilstein 5100 Shocks
Icon Adjustable Trac Bar
Firestone RideRite Air Bags
BDS Dual Steering Stabilizer
Aluminum Finned Differential Cover
Reese 16k Manual Slider 5th Wheel Hitch
Icon 2.5" Leveling Kit w/ F-350 rear blocks
20" BMF Novakanes wrapped in 33" Nitto Terra Grapplers
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post #9 of 14 Old 03-23-2010, 09:47 AM Thread Starter
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Progress sucks!!!! Thought i found and fixed a loose connection where the wires meet the ficm. STarted truck and check engine light was off. So we used the truck to tow a trailer out to the desert this weekend....engine light came back on....truck overheats...hear that whistle that im hoping is the degas cap im reading about.

About to search but anyone have advice to expose the injectors and check for loose wires? Being told they are under the valve cover. I wrecked my dirt bike and effed my back up. Gonna try to wrench on the diesel today so any advice to make it easy will sure be appreciated thanks guys!!!
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post #10 of 14 Old 03-24-2010, 12:19 PM Thread Starter
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UPDATE: no bueno

Took valve cover and oil rail off. Did not find any loose wires on the #7 injector. Now truck wont start. When cranking over it shows no oil pressure..then after 3 seconds its shows pressure.

Do i need to bleed or prime the oil rail? Any ideas why that sucker wont start for me?
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