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Thread Title:

C15 fuel aeration/injector problem?

Created On Wednesday September 08, 2010 21:14

burke41176

Posts: 13
Joined: Sep 2010

Wednesday September 08, 2010 21:14

C15, S/N 6NZ 475HP with 200K miles, 14K hours. We have tree identical trucks with similar hours, very close S/N's.Started running rough at start up about a year ago. Smooths out in 5-10 seconds, worse the longer it sits parked. Engine has had meticulous service since new, only cat filters and oil since day one at factory intervals with oil samples all the time. Overhead/injectors adjusted regularly. Engine is still all original. Transfer pump, filter check valves replaced during starting issues by others with no improvement.

Here is the symptom: Engine runs ok at low load cruising. You can accelerate hard a few times to max boost (25-28psi) then engine starts skipping bad with total loss of power. Keep max trottle and it will clear up a bit after a few seconds, then skip badly again. It is undriveable with a load. Acts like you use up what fuel is in the filters, then it runs low.

Work so far: check all fuel plumbing, tank vents, filters, No faults on E.T. Still original flash file. Injectors pass all cut out tests. Ran separate suction line direct from tank filler hole to transfer pump and sight glass on a long hose from filter base into truck cab and back into tank return so I could watch while driving, also watched fuel pressure at filter base and return line from head. Fuel pressure 75-90 PSI, some air in glass all the time, but when problem occurs glass goes to almost all air.

I swapped filter bases(new filters) and transfer pumps with another same S/N engine for kicks, no improvement. I even bypassed both filters with hoses for one test and still no improvement. I finally did a manual 5 cylinder cut-out at 1200 RPM with sight glass installed in return line and with only #3 injector powered the glass almost immediately fills with air and fuel rate on E.T is slightly higher than the other five cylinders. Other cylinders had air as well, but nothing like #3. I have been fooled with, for example a bad #2 cylinder showing up on #3 as it is downstream in the fuel flow through the head but this seems like a sure thing here.

I suspect combustion getting past an injector sleeve or a cracked injector tip. There is no fuel/coolant transfer and no fuel dilution in latest samples. Visual inspection of overhead, injector springs is good.

Any other thoughts out there as proceed. I will probably start pulling injectors Thursday looking for some evidence as it seems like I have eliminated everything else. Hope I can fix this without an entire set of injectors as engine really only has 3-4K hours left to in-frame overhaul in all reality.

Edited: Wednesday September 08, 2010 at 21:32 by burke41176

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JoeZ

Posts: 938
Joined: Dec 2008

Thursday September 09, 2010 03:54

Am I reading correctly.....200K miles and 14k hours? Those numbers don't seem right. Why would the engine be so high hours at those miles? 200k miles not even broke in yet.
Either way, you are definately in the right direction with injector replacement. That's where I would go.......

-------------------------
One of the last 2 Stroke mechanics left.
44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.

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burke41176

Posts: 13
Joined: Sep 2010

Thursday September 09, 2010 05:35
Miles, hours are correct, this is a dump truck that runs short locally. Driver is terrible about never shutting it off, lots of idle time. Will let you know what I find today and thanks for the time and input from all!!

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Mobiletech

Posts: 94
Joined: Jun 2010

Thursday September 09, 2010 06:05
I think you're going to find the injectors erroded where they seat in the head. you can probably get away with replacing the ones that look bad on the seat. These injectors seat in the head not the sleeve so if the seat area is bad you would have to replace the head. I would go with injector replacement first and try it.

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burke41176

Posts: 13
Joined: Sep 2010

Thursday September 09, 2010 12:38

Found #3 injector clamp bolt a bit loose. Carbon trail past injector in sleeve and sleeve area of injector black with no carbon dam at tip like other 5 holes. I do have the seating area a bit "eroded" on four injectors, and probably the head as well. #1,3,6 also had cracked lower fuel seal orings. Other two cylinders look ok and of course the sleeves are perfectly clean as well for those two. Glad to find my troubleshooting was right on.

Now, since this in an "in house" truck of our company, they want to repair it cheap as possible and hope she runs a few more thousand hours until in-frame time when everything would be changed. Do you think re-using the injectors will work short-term? I would say at this point I reseal cups/injectors and put her together and hope for the best while company budgets for the more expensive option.

Thanks.

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JoeZ

Posts: 938
Joined: Dec 2008

Thursday September 09, 2010 15:53

If you want to try just seals......mix the injectors by putting the best injector in the worst hole and so on. At this point, you don't have much to lose.
Not the route I would take, but you have to do whatever the big wheels want you to do.
If it were me at my shop.....I would replace the head and injectors now to get the engine back in shape and run it out the rest of the way. Then freshen up the head and injectors at overhaul......Difference is that I have to stand behind what goes out the door.....as a company mech.....you can always let it fall back on the big cheese.

-------------------------
One of the last 2 Stroke mechanics left.
44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.

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Ed1

Posts: 38
Joined: Sep 2010

Thursday September 09, 2010 17:08
dont forget to replace the injector hold down bolts when you put it back togethor

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burke41176

Posts: 13
Joined: Sep 2010

Thursday September 09, 2010 18:51

Got parts coming, thanks for reminder on clamp bolts. I found a letter on revised torque as well, up to 41 from 37. If I were to swap injectors around, would I need to adjust trim codes even though they are not new injectors? I have not even looked at numbers on injectors yet. Thank you all for the advice, I sure appreciate it. I now play the role of full time excavator operator and just do the cat repairs as needed since I used to work at a dealer some years ago so I'm a bit rusty on some of this..

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Ed1

Posts: 38
Joined: Sep 2010

Thursday September 09, 2010 19:18
If your trim codes are programed in your ecm the way they are supposed to be and you swap injectors around you should change your trims to match the cylinder the injector is in. But most of the time when i look at a 6nz some one has changed all the trim codes to 5232.

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desertstormboy

Posts: 372
Joined: May 2008

Saturday September 11, 2010 08:55
the reason for the trim codes to all be programmed to the 5232 is from pittsburg power setting. those 6nz put out the horses. ------------------------- IT WENT BING BANG BOOM!

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Ed1

Posts: 38
Joined: Sep 2010

Saturday September 11, 2010 09:14
yep trim codes and after market mods is probbaly the reason cat stared requireing a warranty report uploaded to them before they will pay a claim.

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burke41176

Posts: 13
Joined: Sep 2010

Sunday September 19, 2010 21:16

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burke41176

Posts: 13
Joined: Sep 2010

Sunday September 19, 2010 21:17

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burke41176

Posts: 13
Joined: Sep 2010

Sunday September 19, 2010 21:20
Engine all back together and running well. Took a chance on the injector/sleeve reseal, torqued hold downs to 41 lbs with new bolts and checked trim codes set properly. Hopefully it runs a while longer until in-frame time. Thanks to all for the advice and help, I appreciated it. Always good to bounce things off others!!

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