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Old 07-13-2017, 09:38 PM   #1
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Cummins 6BT rough run after injector pump overhaul

I had the injector pump (CAV DPA) overhauled and the injectors checked in MD. Shop I've used before. This in response to rough running, occasional hard re-start 45 min. after a long run at cruise.

The work seemed to help, smooth run for about 30 hrs. and the rough run returned. Pulled injectors & had a shop in NY check them, end result 5 were rebuilt, 80 hrs since pump work now. #5 was the worst. #5 didn't stumble as much on a crack test as the rest, and I could feel on the injector line that #5 seemed to pulse harder than the rest. Re-start issue gone.

All back in, better, seemed to run much smoother, decided to continue on trip. (Georgian Bay). After a day, still seems to be running rough, but not as bad as before. WOT is up where it should be, no smoke, a bit of sheen at idle. No blowby, soot near exh. at end of day's run, have to look for it- minimal. Had fuel analyzed by lab, no water, no bugs, but they did report that it's 4-5% bio-diesel, but should not create a problem. No water in bowls, polished for days through 10 mic filter, no water, filter barely discolored, no restriction indicated on filter gauge, <2" Hg.

I'm still getting a harder pulse on the injector line for #5, this by feel. I'm concerned about continuing to run- although the rough run is just enough to cause a vibration that can be felt-doesn't shake in the mounts, can hear the roughness in the exhaust, but it's random, not a rhythmic "miss". Haven't repeated the crack test since injectors were rebuilt.

The shop in MD is in touch with the NY shop, to their credit they are working with me. I'm suspect of the pump due to the correlation of the #5 injector issue with the pulsing I'm feeling. Pump overfeeding fuel to #5? I don't know enough about the internals of the pump to know if that's really logical.

Any suggestions on what I might be overlooking or what else I can do?
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Old 07-14-2017, 01:35 AM   #2
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Not an expert, but working hard at it. I'd want to rule out any possibility of an air leak in the fuel system. Both delivery and return. And restrictions in the return.
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Old 07-14-2017, 01:37 AM   #3
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Not an expert, but working hard at it. I'd want to rule out any possibility of an air leak in the fuel system. Both delivery and return. And restrictions in the return.
Whatever you do don't abandon Georgian Bay without seeing as much as you can of it. Best spot in the lakes, IMO. Good luck.
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Old 07-14-2017, 01:38 AM   #4
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Not an expert, but working hard at it. I'd want to rule out any possibility of an air leak in the fuel system. Both delivery and return. And restrictions in the return.


From my rather extensive and painful experience recently, I think that most mechanics would do a test to see if there is any air in the fuel at a pretty early stage in the process.
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Old 07-14-2017, 07:31 AM   #5
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You can't read much into how much of a shock you feel in each injector line. All six have different shapes and different supports and the Bourdon effect will be different on each and in different areas. The Bourdon effect is that when a curved tube has internal pressure, it tries to straighten itself.

Rough running engine can be injector or injector pump related, but can also be due to things like valve lash off, low idle, poor ring sealing in one hole, too thick injection seal washers (or two in the hole), worn cam, leaky valve, tranny damper plate, loose prop, etc, etc. Can't assume an injection problem unless troubleshooting is complete and methodical.
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Old 07-14-2017, 08:34 AM   #6
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Ski, as usual, gives an informed and experienced based response. Curious, do you have a Murphy gauge on your Racor vacuum gauge? The Murphy would pick up a potential fuel blockage issue.

I was encountering periodic engine stumbling that was finally chased back to a failing after cooler (bad acid circulation cleaning). Water ingestion was sporadic, challenging many WTF moments and guesses by the experts. Do you have an AC? If so, when last serviced?

To fill in a few blanks, how many hours, age, model on your engine? Happy cruising.
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Old 07-14-2017, 11:41 AM   #7
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Originally Posted by Ski in NC View Post
You can't read much into how much of a shock you feel in each injector line. All six have different shapes and different supports and the Bourdon effect will be different on each and in different areas. The Bourdon effect is that when a curved tube has internal pressure, it tries to straighten itself.

Rough running engine can be injector or injector pump related, but can also be due to things like valve lash off, low idle, poor ring sealing in one hole, too thick injection seal washers (or two in the hole), worn cam, leaky valve, tranny damper plate, loose prop, etc, etc. Can't assume an injection problem unless troubleshooting is complete and methodical.
Thanks for the replies!

Engine is CPL0742, 6360 hrs.
Double checked valve lash @6325 when injectors replaced, also made sure holes were clean, accounted for all seal washers. Trans damper replaced with new Centa heavy duty coupler, prop reinstalled and lapped, trans coupler re-machined & faced @6127. Idle is 725 in gear, roughness follows entire rpm spectrum. Seems to be getting more pronounced with more running. No blowby from breather tube. Some sheen at idle.

Concerned about continuing trip or stop & get this resolved. Not a lot of options for service up here on Trent-Severn.
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Old 07-14-2017, 11:57 AM   #8
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Good info. I think the risk of harming the engine is low.

There are things in the governor that can wear and cause erratic fueling. The pump was gone through by a tech, but that does not mean everything is perfect in the governor. But erratic fueling generally will not harm the engine.

Can you post a vid with audio of engine when it is doing it's thing? Do another with engine at dead idle with oil fill cap off.

Are you sure no air is entering pump? Done the clear line trick on supply line?
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Old 07-14-2017, 12:33 PM   #9
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Good info. I think the risk of harming the engine is low.

There are things in the governor that can wear and cause erratic fueling. The pump was gone through by a tech, but that does not mean everything is perfect in the governor. But erratic fueling generally will not harm the engine.

Can you post a vid with audio of engine when it is doing it's thing? Do another with engine at dead idle with oil fill cap off.

Are you sure no air is entering pump? Done the clear line trick on supply line?
Will do the vid, have not done the clear line. Best before or after the lift pump?

I'm pretty meticulous with the maintenance & care of the boat in general, this episode is causing lots of angst. So the help is a huge relief.
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Old 07-14-2017, 12:36 PM   #10
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If you can, do the clear line between lift and inj pump. I think those are hard tubes so that might not be easy to do. Best that way as the lift pump itself can be a source of air.
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Old 07-14-2017, 02:00 PM   #11
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Had trouble uploading vids to the forum, I was able to put them on my server, here

http://www.maerin.net/images/DSCN8677.MOV

and

http://www.maerin.net/images/DSCN8680.MOV
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Old 07-14-2017, 02:39 PM   #12
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I did not detect anything unusual in the two vids. Sometimes things are not captured in the vid, had that issue before.
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Old 07-14-2017, 02:54 PM   #13
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I became convinced of the value of a clear tube after reading Tony Athen's advice. See https://www.sbmar.com/product/smx-co...b-priming-kit/

Built my own version of their kit after a trip to the local hardware store. I now view it as an essential component for hands-on maintenance and diagnostics. Mine is installed before the lift pump but after all valves and filters. Put a long section of clear tube that allows me to use the squeeze bulb with my face close to the IP, and it's made priming and purging of air *much* easier. Normally the clear tube is bypassed, but by adjusting the valves you can route the fuel flow through under operation to verify that all is good. I found some leaks by watching for air accumulating in a high loop of clear tubing during low-moderate speed operation.

Agree that there are advantages to mounting downstream of lift pump, but it's trickier plumbing wise. And for priming there may be something to be said for pushing into the motor rather than pulling from the motor. Dunno. I took the easy route of inline insertion in the rubber fuel hose.

Not suggesting that this is going to solve your stated problems, but can help rule out some things now and will inevitably be useful in the future.

Having trouble posting a picture of my setup, but it's essentially a clone of the Seaboard kit.
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Old 07-14-2017, 02:56 PM   #14
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Guess I wasn't having trouble posting the picture :-). Still needs to be secured obviously but I'm still caught up in a new motor install.
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Old 07-14-2017, 09:35 PM   #15
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Not suggesting that this is going to solve your stated problems, but can help rule out some things now and will inevitably be useful in the future.
I'll be making up the tubing tomorrow, Jeff. As you point out, it may not solve the problem, but it's another piece in the puzzle. And if it does point to the problem as being air, I'll take that!
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Old 07-18-2017, 07:05 PM   #16
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Follow up-
Spoke to a diesel shop here in Peterborough, they were helpful, and despite being busy said they'd be happy to put my pump on the test stand. Also suggested I contact a local diesel guy and have a second set of eyes & ears before I expend the time & effort to pull the pump.

I contacted David Wells, who it turns out is retiring and sold his business to a young woman who actually does most of the work. They both came by, had a look, listen, and went for a short run where we were able to get a pretty good sampling of run conditions. Both agreed that the engine is doing what it's supposed to, and didn't observe anything that would make them want to dig into it further.

He did express concern over the number of fittings in the fuel manifold, but concurred that my clear tube is telling that those fittings aren't creating a problem. Also acknowledged that I live with the engine, and am probably hyper tuned to anything that's out of the ordinary, and there may in fact be something that could be improved upon, but didn't feel there was any reason to stop and pursue it now.

I was in the service business long enough to know that experience is something that can't be learned from any amount of research, so I'm taking his experienced advice and unless something changes, I will defer digging into the issue until I return to MD and can have the guy who rebuilt the pump look into it with me. I know it can do better, it did before.

It was worth it to have them on board, I'm more at ease, and my wife probably won't slit my throat as I (fitfully) sleep!

Thanks for all the replies.
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Old 07-18-2017, 09:45 PM   #17
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I was in the service business long enough to know that experience is something that can't be learned from any amount of research, so I'm taking his experienced advice and unless something changes, I will defer digging into the issue until I return to MD and can have the guy who rebuilt the pump look into it with me. I know it can do better, it did before.
Sounds sensible.

I have one more thought and a simple non-destructive test. I should make clear that while there are pros here like Ski, I am definitely not a pro. But I have become fairly intimate with the same pump/motor lately, and am right now remediating my own installation mistakes.

It seems to me that the symptoms you describe could be caused by a small timing outage. And the progression of the issue is interesting.

As I'm sure you know, the IP is held in place by three studs, and there is a small range of rotational adjustment available. If for some reason the nuts were not properly torqued when the pump was mounted or have backed off since it's possible your pump has gone slightly out of time during operation.

Simple test would be to eyeball/finger test the three nuts, and with both hands try to rotate the IP. If you can move it you've found the problem and the locals can provide an easy fix.
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Old 07-21-2017, 10:56 PM   #18
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Just a final follow up on this- I have had the clear tube installed for several days, running hours each day- and have learned that I do, in fact have some minor air leaks, the tube is showing the cumulative effect. As I eliminate them, the engine is running smoother.

I'm frankly embarrassed that I did not follow good troubleshooting procedures in eliminating them early on. I'm retired from the HVAC business where I enjoyed a reputation as a crack troubleshooter, often consulting for peers when they would run into problems. So I know better than to short circuit the method. I'd never do it for a client, but it's OK to be sloppy on my own stuff?? I also know the value an experienced professional brings to the table, and I'm glad I got good advice here, and from the pros I brought on board. Good learning experience, if humbling!
So thanks again to all who replied, especially Ski, from me - and my 6BT!
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Old 07-22-2017, 09:25 AM   #19
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Don't mean to derail the thread, but curious on minor air leaks - what are some of the things you can do to eliminate them?
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