Repeat injector failures Maxxforce 7 aka 6.4L powerstroke

Rex Technical Support Specialist Ohio Posted   Latest  

This failed #2 injector in Aug 2021. Failed it This again in Dec. 2021. Failed a 3rd time last week. A competent shop much closer to the customer replaced the first two. When the third one failed it was brought to us. We load tested the wiring. With an ohm meter connected aggressively shook poked and prodded the wiring from the ECM to the connector at the injector. No indication of a short or open. Installed reman injector. Engine ran a few minutes and failed that injector. All three injectors are from NAV. These are piezoelectric 2 wire injectors. 

Thought about swapping #4 into the #2 hole. Expensive test if it gets killed also. Or can I substitute a 220K ohm ½ watt resistor for the piezo stack and run the engine? I am thinking about doing that for 2 and 4. If the resistor blows on 2 and not 4 I would lean toward an ECM problem. I know very little about this injector type. Don’t know the volta and amps it uses. Have not found that info in SI yet. 

Code is SPN 652 FMI 5 “Current below normal or open circuit” The failed injector in the engine when we got it is open, OL on ohms est. The current failed injector reading is 1.2M Ω. Ideas or suggestions? TIA

Just starting to use a pico. Not sure what to scope or how. 

NAV Inj part # 5010889R91

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Rudy Technician
Texas
Rudy
 

I've worked for Ford dealers for the past 30 years. I would recommend replacing the injector wiring under the valve cover and also checking the compression of that cyl and comparing it to other cyls. The pcm is able to compensate for a weaker cyl thus the injector may be over working due to a lower coppression cylinder.

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Andrew Mechanic
Michigan
Andrew
 

I have seen a poor connection at the injector cause issues. I plugged in the injector and ohm tested at the connector in the rocker housing, through the injector and back to the connector, then wiggled the plug on the injector, just a thought.

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Rudy Technician
Texas
Rudy
 

You can perform an resistance test thru the circuit but that doesn't really tell you how well the current is going thru. The resistance test can pass but fail a voltage drop test. I know the made an upgraded connector ends to injectors. The upgraded had a locking g tab. The originals did not.

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David Technician
Georgia
David
 

If you want to build a dummy load , you will need a cap , resistor , and maybe an inductor , you can google diesel piezo injector dummy load for the details …

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Paul Mechanic
Illinois
Paul
 

Not a diesel guy and have absolutely no experience with this system, but if you want to know what's going on electrically, a scope with a current probe will tell you everything when coupled with monitoring the voltage/ground feeding the circuit. Compare to a non-issued injector circuit/device for a comparison of known good. Also, just because it's new, doesn't mean it's good. They don't make 'em…

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David Owner/Technician
Virginia
David
 

Use a current prob and lab scope campare other injectors amperage and on time I have this problem on a 7.3 with a bad alternator over charging but on. Multi cylinders

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Rex Technical Support Specialist
Ohio
Rex
 

All 3 injectors are Navistar remans but I agree. isn't like it used to be.

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Jordan Technician
Kentucky
Jordan
 

I would back probe the injector connector and watch the voltage from the injector driver. If you have a multi-channel scope, monitor as many cylinders as you can for comparison. Obviously a dummy load would be better than sacrificing another injector, but do what you must. You might need attenuators if you're using Pico, not sure what that current inrush will be initially. Pretty sure those…

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Marvin Mechanic
Mississippi
Marvin
 

I checked ohn on reman on shelf 198000 ohm on 200k scale

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Rex Technical Support Specialist
Ohio
Rex Resolution
 

Rudy and Andrew were correct. Bad UVC harness. Found it with a breakout harness and an Ω meter but followed up with a scope. Could see it drop out while running on the scope. We should have caught this first time in but my guy wasn't aggresive enough with his wiggle test. When I got into it first thing was to check the “failed” injector. It was fine. Hmmm. Then started into the wiring trying to…

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Michael Diagnostician
Illinois
Michael
 

Rex I have some Powerstroke injector captures I think showing voltage and current. If you'd like too contact me through my website and I can give you a drop box link once you give me your email. Or I could just load it here on resources if everyone would like that. mjediagnostics​.​com

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Rex Technical Support Specialist
Ohio
Rex
 

Sent a reply thru your site. Thanks

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