code p1278, not the wiring, IDM or PCM - Ford Powerstroke Diesel Forum
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post #1 of 10 Old 07-20-2012, 02:57 PM Thread Starter
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code p1278, not the wiring, IDM or PCM

So I finally fixed all my codes except the p1316. I was able to get my hands on a good scanner and did a koeo test which popped a code P1278. I did some research and everything said injector wiring and to ohm everything and find the bad wire. The problem is everything test the same. All eight injectors test 3.3-3.4 ohms. I even pulled the fender and tested there and I get the same thing on all injector circuits. So the next things were the IDM so I changes that with one I know works from one of the trucks at my work. Same missfire. So I thought maybe the PCM or ECU and swapped that while leaving the known good IDM in. Still the engine misses and gives the same code. What am I missing here?
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post #2 of 10 Old 07-20-2012, 03:26 PM
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How did you test your injector harness exactly? P1278 is one of my codes. See post below yours
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post #3 of 10 Old 07-20-2012, 08:33 PM Thread Starter
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With an ohm meter. I tested at the valve cover, the junction between the engine harness and at the IDM.

An update. I replaced the engine harness and still has the miss. I didn't even bother checking for codes.
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post #4 of 10 Old 07-21-2012, 12:25 PM Thread Starter
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Am I posting in the wrong area? Langpie is the only person to have responded to both of my post asking for help.

Anyway I ordered the #8 injector(because it's different than the rest on my truck) and hope it will fix the problem. I will let you know.
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post #5 of 10 Old 07-22-2012, 06:42 PM
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Can you be a lil more specific on how to test the UVCH? Like what ohms am I suppose to have? And am I checking from the common pin to the injector pin? Pulling valve covers off tom..
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post #6 of 10 Old 07-22-2012, 07:27 PM Thread Starter
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Less than 5 ohms is what you want. I used a fluke tester(good brand) and mine where all 3.3-3.4ohm. You want to check from the common pin with one lead and use the other lead to check the two connections to the left and right of the connector. the last two on each end are the glow plugs.

If those test good then you need to check the ohms at the engine harness and then if that checks good you need to check the ohms at the IDM. Your dealership can get your diagrams of which pins to check or if nessary I can get you at least the one for the IDM.
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post #7 of 10 Old 07-22-2012, 07:36 PM
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Thank you! My IDM checks out good, per ford. My thread is below this. I'm pulling valve covers off tom, if above 5 ohms it would only be the harness? Like the injectors don't affect the resistance at all? (sorry for kinda jacking your thread)
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post #8 of 10 Old 07-22-2012, 07:47 PM Thread Starter
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If you check the OHMs at the valve cover harness and they are high then it is either the harness or the injectors. If they are high then you should pull the valve covers and check for harness problems. If there are any problems, or if they look original then you should replace the harness. You should also check the injector OHM to verify that it is just the harness and not the injector. If it is the injector then you must replace the injector.
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post #9 of 10 Old 07-31-2012, 07:49 PM Thread Starter
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Well it was the #8 injector. I hope this helps someone because I didn't get any.
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post #10 of 10 Old 08-15-2012, 08:53 AM
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FYI.....
there could be one strand of wire inside a circuit that is good which will provide good OHM readings. The proper way to test a circuit is with a load test and voltage drop. Use a suitable bulb, fused power, and a known good ground. If possible, manipulate the harness and monitor the bulb for any flickering or dimming. There should be no more than .3V lost across the circuit with the load applied.


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