Fuel Injector Diagnosis

Zachary Mobile Technician Austin, Texas Posted   Latest  
Case Study
Heavy Duty
2004 Ford F650 7.2L (C7)
Dead Misfire

Hello all. Just wanted to take the time share this as it's somewhat unfamiliar territory for me but I believe something others can benefit from as well. This truck belongs to one of my fleet customers and was purchased used about 4 months ago. 2004 seems to be a split year for the CAT engines in these because even though it's showing to be a C7, everything I've found points to it being a 3126. I know they're closely related but there are some differences nonetheless. Anyhow, the truck has had a dead misfire basically since they bought it. I was called out several months ago to fix a coolant leak and mentioned this to them at the time. Most of the work I do is on passenger cars and trucks so my resources for Medium/Heavy trucks are limited. I'm hoping to purchase an HD capable scan tool sooner than later, but for now it's just not in the budget. This customer has a Bosch HDS 250 for his trucks which at least allows for code retrieval and basic data pid analysis. Recently he had me come out to diagnose the issue. I retrieved a code 6-11 for cylinder #6 injector current fault. This code is very general from what I've read and can indicate either a high or low current condition. The CAT scan tool (and I imagine the higher end aftermarket units as well) have an injector electrical self test similar to the Ford/International tests to help you pin point the cause. Since I don't have that equipment, I decided to see what I could learn with the tools I do have. I'm not the hugest fan of ohmmeter tests but I wanted to collect any information I could. I took measurements at the injector harness connector just outside the valve cover for all 6 injectors. Cylinders #1-#5 all measured approximately 3.4 ohms. Cylinder #6 measured approximately 2.3 ohms. Not a huge difference but one just the same. There are no published specs for this that I can find. These injectors fire at around 105 volts from what I understand so when you take that into account, that's a significant increase in current flow. Next I fired up the scope and current ramped the injectors for cylinders #5 & #6. Apologies for the scaling here, my low current probe was not wanting to zero properly. The first 2 captures are for cylinder #5 which is our known good. I assume the ecm limits spikes and/or over current but I'm not certain of that. The last 2 captures are from cylinder #6. I honestly wasn't sure if the ecm would even be trying to fire this injector because the code pops up as soon as the engine is running. As you can see, the spikes are inconsistent and vary greatly v.s. the known good. The zoomed in last capture suggests shorted windings based on the steep rise and fall and the sharp point. The current is lower for this one versus the known good though which is why I wonder if the ecm is limiting things. In any case, I may have totally botched this but I believe I'm on the right track. Any input is always greatly appreciated. Thanks for making it all the way through this novel. 

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Rex Technical Support Specialist
Alliance, Ohio
Rex Default
 

3126 will be a square top injector. C7 will be round. youtu​.​be/pS0i3f5hYhk Check out the link. Ape is great. A lot of good info. Wish he did Cummins, especially ISB. Swap the injector?

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

Thank you Rex. That makes sense based on what I've found. Haven't pulled the valve cover yet but that'll tell the story. The 3126 injectors look very similar to the 7.3L/T444E near as I can tell. Yes I agree regarding Josh with Adept Ape. Been following his channel for a couple years and he's very sharp and knowledgeable. I assume you mean swap with another injector to see if if the problem…

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Rex Technical Support Specialist
Alliance, Ohio
Rex Default
 

Short version. Was looking at active codes on 2006 international today. Code said high to low open but the injector was firing. A close reading of the code description mentioned that it could also be set if current ramping rate was not correct. Ohm tested injector and it is out of spec. Similar but not identical systems so CAT may very well shut the injector off. Ran into that issue a while back…

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

That would make perfect sense... particularly based on scope capture I have. I was considering de-pinning the harness side connector at the valve cover base and switching the wires around with another cylinder to see if the code follows the injector. That's pretty crazy the oil pressure was that high. I've never had one of the H.E.U.I. engines do that but I can definitely see where it could…

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Angel Technician
Boston, Massachusetts
Angel Default
 

Great write up Zachary, I could be wrong but is it possible to get a voltage measurement on the injector as well? Just to make sure you have good power/ground then condemning the injector. After watching Adept Ape's video, also check for metal debris in the line coming from the high pressure pump. Hope this helps & thanks for sharing.

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

Thanks Angel. I appreciate the positive feedback. I considered taking a voltage measurement but thought it might be risky considering the high voltage component. I believe these fire around 105 or 110 volts. Good point on the metal debris. This one appears to have failed electrically but better safe than sorry.

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

UPDATE Well as it happens, my Snap On guy has a loaner Pro Link Ultra & he let me borrow it to see how it measures up in the medium heavy truck market. It has the ability to run the injector electrical self test on this truck and showed a shorted condition for the #6 injector solenoid which matched up with prior testing. When I unplugged the injector harness and reran the test, the results…

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

Excellent write up Zach. Perfect example of drilling down to the correct diagnosis quickly and efficiently and then further checking it for confirmation. Keep up the great work.

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

Thank you Chris. I always appreciate your case studies as well as your input on things. I had a thought today about electrical testing on these type of setups and wanted to see what everyone here thought. Since many of the electronic diesel engines fire the injectors at a high voltage, a lot of direct testing in regards to voltage is risky at best if not impossible. That said, I wondered about…

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

It absolutely is an excellent way to go about it zach. Steve Scott (simply diagnostics), Adam Critchley (AC Auto Tech), and a bunch more of our UK friends all use them regularly and swear by them. I would recommend reaching out to them for some more in-depth usages as I don't have my own megger tester yet. Shoot me a message sometime and I'll see if I can't make some introductions.

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

Ok cool. I figured I couldn't be the first to have thought that, but I hadn't seen anyone discussing their usage in that way. I also haven't purchased one yet but it is on my endless list of tools to buy. Yes that would be great Chris I would love to talk to them and explore this further.

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