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P0279 cylinder 7 injector circuit low...bummer

36K views 13 replies 4 participants last post by  DeadaHead 
#1 ·
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.
 
#2 ·
Check your cables leading from your FICM to your injectors. One of them is shorting out.
 
#5 ·
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.:thumb:
 
#4 ·
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
 
#8 ·
Ah, good catch and you are correct. I apologize I didn't pay close enough attention. :doh: Keep us posted on the progress...
 
#9 ·
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!!!
 
#10 ·
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?
 
#13 ·
20 seconds is excessive. It should not drain your oil back down. Is your oil filter cap broken or have a crack? It could lead to excessive cranking.
 
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