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Discussion Starter #1
Having a rough idle and a miss at moderate speed. Ran Autoenginuity and ran buzz test, All solenoids fired, but getting a code 1278 on cylinder *8 says high to low side open? I have checked the harness going to the valve cover but have yet to open valve cover. Am I looking at a loose connection or an injector solenoid issue. Thanks.
 

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If it buzzed good, it is not an electrical issue.
 

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Discussion Starter #4
Update. Still not passing buzz test. Still failing on injector #8 P1278 High to low side open. I took the valve cover off and checked connections. Nothing obvious. I hooked valve cover gasket up to injectors and tested ohms. 3.4 to 3.6 ohms on all four injector coils. tested at the pin outs at the connector. Still getting fail on buzz test, even though all eight injectors clatter during test, they all sound the same. What now??
 

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Headwind Magnet
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From ITP Diesel's website:


7.3L Injector "Buzz" Test

The Injector "Buzz" Test can be used to look for a faulty fuel injector. It is best to run this test on a totally cold engine, one that has sat overnight and has not been started.
Initiate the "Buzz" test and then listen carefully to the injectors as the test is completed. First, all 8 injectors will "Buzz" at the same time. Then, the IDM will "Buzz" the injectors in numerical order (1, 2, 3, 4, 5, 6, 7, 8). Remember that cylinders 1-3-5-7 are on the passenger side and 2-4-6-8 are on the drivers side, with cylinders 1 & 2 being at the front of the engine. You should hear a strong "Buzz" bouncing from side to side for all 8 injectors. If one of the injectors doesn't "Buzz", you've found a problem cylinder. It is important to note that when an injector fails to "Buzz" properly, you will still hear the other 7 injectors make a faint buzz...this is a designed function to protect the IDM.

Note: Because the IDM will "buzz" the other 7 injectors faintly during individual cylinder tests, it is possible for the "Buzz" test to report no problems detected. If the "Buzz" test reports no failures, but you don't hear a particular cylinder "Buzz"...more than likely there is a problem with that injector.

It should also be noted that an injector failing a "Buzz" test can have many causes. The injector can be in a failed state (loose armature plate screw, bad solenoid, etc.), the UCV (under valve cover) gasket or harness could be damaged or disconnected, the main engine harness could be damaged or the IDM could be damaged. Further inspection will be necessary to determine the actual problem...but at least you now have a place to start



Personally, the other 7 buzzing a bit while one cylinder is being tested confused me. I thought one buzzed fainter than the other seven but in retrospect I don't think it buzzed at all. If one sounds any different at all from the other seven, it's not working properely.

According to the library, p1278 indicates open circuit, open injector, failed IDM. You could swap two injectors and see if the problem follows. If it does, bad injector; if not its probably wiring or IDM.

Best,
Jim
 

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Discussion Starter #6
I also tested the wiring harness at idm back to motor followed the test procedure. I got 3.6 ohms on all eight injectors and had infinity on the other test points per procedure so that should eliminate wiring issue. Still get P1278. Could the idm be bad on just the one injector?
 

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It could. But like Jim said, I would swap injector and see if the problem follows. You don't have to pull the injector, just swap a couple of injector plugs on the harness around. If the same injector fails, you know you have an injector issue, if the problem moves to another injector, you know you have either a wiring issue or an IDM issue.
 

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Headwind Magnet
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It could. But like Jim said, I would swap injector and see if the problem follows. You don't have to pull the injector, just swap a couple of injector plugs on the harness around. If the same injector fails, you know you have an injector issue, if the problem moves to another injector, you know you have either a wiring issue or an IDM issue.
That's sweet Andy...never thought of that but it would work very nicely on a buzz test!
Best,
Jim
 

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Discussion Starter #10
Thanks for the input. Will switch the wiring around and see if the problem follows or stays with #8 injector.
 

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was the connector under the valve cover loose or open? I know on mine when i did the glow plugs i left injector #3 open (must of knocked it off partially) and my truck ran like and #### and was down on power. Did a scan and showed injector #3. Took off valve cover attached connector WALA!.
 

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Discussion Starter #12
Didn't find anything loose. Performed all the test on the wiring harness at idm. Could find anything wrong. The problem is intermitent sometimes it idles rough sometimes it doesn't. Gonna try another idm when I get my hands on one.
 

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Can you monitor ICP? Does it happen after coming back to idle. Mine will do that sometimes, usually after a medium to heavy throttle when coming back to idle pretty quick (stop and go in town driving). A little pressure on the brake and build a tad bit of boost and let out of it will usually fix it.

I will be monitoring my ICP and see it rocking around at idle between 400 and 600. After the little load and let it come back, it will be between 550 and 600.
 

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Just one of those things, happens occasionally after a med to heavy romp and getting out of it fast. Just starts.
 
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