Unresolved problems with Cummins QSB 6.7 liter engine
- Thread starter Doug_Snider
- Start date
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If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
Fletcher500
Guru
QSB and time for a break from TF
Sun,
You appear to be wanting to stir things up throughout this entire thread.
The fuel supply issues are related to truck engines, not marine. My earlier post #66 covered this in detail, and these are not my personal opinions and are based on speaking wit two large scale marine Cummins dealers.
There are NO open campaigns (recall/warranty/concerns) regarding the fuel systems on the QSB 6.7.
I was not going to reply to you, but just trying to set the record straight for others who have QSB’s regarding the mis information you are posting.
That’s it for me on this thread - tapping out, but I am sure you will have more to offer.
I need a TF break so I am signing out for the rest of Summer. Happy boating everyone.
Sun,
You appear to be wanting to stir things up throughout this entire thread.
The fuel supply issues are related to truck engines, not marine. My earlier post #66 covered this in detail, and these are not my personal opinions and are based on speaking wit two large scale marine Cummins dealers.
There are NO open campaigns (recall/warranty/concerns) regarding the fuel systems on the QSB 6.7.
I was not going to reply to you, but just trying to set the record straight for others who have QSB’s regarding the mis information you are posting.
That’s it for me on this thread - tapping out, but I am sure you will have more to offer.
I need a TF break so I am signing out for the rest of Summer. Happy boating everyone.
CharlieO.
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How many are out there running now with perfectly happy customers and lots of trouble free hours?
I think most common rail engines have similar - or their own unique - problems. Overall, Cummins has a good reputation.
sunchaser
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CO
Yes there are many Cummins engines with excellent results. This thread points to a specific engine and injection pump that has proven problematic. So how and why does one order a boat engine with this specific problem area?
In over the road use hundreds of thousands of Cummins, Chevy and Ford diesels have been recalled over this pump issue. The paltry number of marine engines may not have a voice to-get attention until engine failure occurs.
So the builder rolls the dice with buyers unaware of the injection pump failure history. Thus the question- is a Cummins 6.7 with a CP 4 injection pump a wise choice for the builder to install without advising the new owner of potential failures while cruising?.
Yes there are many Cummins engines with excellent results. This thread points to a specific engine and injection pump that has proven problematic. So how and why does one order a boat engine with this specific problem area?
In over the road use hundreds of thousands of Cummins, Chevy and Ford diesels have been recalled over this pump issue. The paltry number of marine engines may not have a voice to-get attention until engine failure occurs.
So the builder rolls the dice with buyers unaware of the injection pump failure history. Thus the question- is a Cummins 6.7 with a CP 4 injection pump a wise choice for the builder to install without advising the new owner of potential failures while cruising?.
Seas_the_day
Newbie
I’m chiming in to provide everyone that's been following this situation clarity to the actions taken by Cummins during their last and final visit to resolve Doug’s engine issue.
The Cummins tech’s troubleshooting on a previous visit showed that the PSI at the high pressure on engine fuel filter was ~30 PSI. The normal operating pressure at this filter is 70 – 100 PSI. This was a clue to the problem. One possible cause was a restriction in the fuel supply, but we ruled that out by running the engine directly from a jerry can and observing continued problems (e.g., engine shut down at idle).
At this point Cummins was confident that the issue was related to the low-pressure fuel pump (also known as the gear pump). Cummins replaced the low-pressure fuel pump in conjunction with the lift pump, as it was convenient to switch the lift pump out at the same time. The on-engine high-pressure fuel filter, which is downstream of these pumps, was also replaced.
Immediate observations showed that the replacement was successful, as the PSI read at the high-pressure filter now read in the mid-70’s while alongside the pier, We encountered no issues during the subsequent sea trial at any RPM. Pressure monitored at the high-pressure rail was also higher following the low-pressure fuel pump replacement, and maximum observed PSI increased from 12,000 to 17,000.
It appears that the issue with the low-pressure fuel pump was not physical damage, rather it was out of tolerance, leading to slippage and reduced fuel pressure measured at the on-engine fuel filter. It sounds like the impeller essentially wasn’t fit tight enough to the pump housing. There is some commentary in this thread about the high-pressure fuel pump, but that was not an issue in this case.
Diagram attached for your understanding of the parts and their relative locations.
Hopefully this information can be helpful to cruisers the future!
Van Helker
Helmsman Trawlers
The Cummins tech’s troubleshooting on a previous visit showed that the PSI at the high pressure on engine fuel filter was ~30 PSI. The normal operating pressure at this filter is 70 – 100 PSI. This was a clue to the problem. One possible cause was a restriction in the fuel supply, but we ruled that out by running the engine directly from a jerry can and observing continued problems (e.g., engine shut down at idle).
At this point Cummins was confident that the issue was related to the low-pressure fuel pump (also known as the gear pump). Cummins replaced the low-pressure fuel pump in conjunction with the lift pump, as it was convenient to switch the lift pump out at the same time. The on-engine high-pressure fuel filter, which is downstream of these pumps, was also replaced.
Immediate observations showed that the replacement was successful, as the PSI read at the high-pressure filter now read in the mid-70’s while alongside the pier, We encountered no issues during the subsequent sea trial at any RPM. Pressure monitored at the high-pressure rail was also higher following the low-pressure fuel pump replacement, and maximum observed PSI increased from 12,000 to 17,000.
It appears that the issue with the low-pressure fuel pump was not physical damage, rather it was out of tolerance, leading to slippage and reduced fuel pressure measured at the on-engine fuel filter. It sounds like the impeller essentially wasn’t fit tight enough to the pump housing. There is some commentary in this thread about the high-pressure fuel pump, but that was not an issue in this case.
Diagram attached for your understanding of the parts and their relative locations.
Hopefully this information can be helpful to cruisers the future!
Van Helker
Helmsman Trawlers
Attachments
chanprr
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Thanks for the explanation, Van. Your assistance in trouble shooting the problem is much appreciated.
Robert
Robert
Nick14
Guru
Van, thank you for posting the details behind the issue. Facts are always infinitely more helpful than speculation.
It can be hard to get a realistic sense of the true extent of a problem from comments posted on a forum. In any situation, it's those who have problems that post about them. Seeing a half dozen negative posts can create the impression a problem is more common than it is. The thousands of people who do not experience any issues rarely post about those experiences.
Tom-Jill-Lilly
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Wot
Hi Van,
All, agree, its good to get the facts - speculation churns, but post-mortem and facts are worth more than words.
Van, Thanks for the report out. Very good to hear what was measured before and after. It’d be great to think Cummins would come back with final determination from bench testing the components, but since this is probably a one-off, I doubt theyd spend time on it.
I found an interesting article from Passage Maker, for running your engine at WOT (wide Open Throttle) to test and feel out any issues. I believe this was in-part troubleshooting Dougs issue or at least an indicator.
While this might be well known in the boating community, being somewhat new to marine diesel, I thought it’d be good to share for a decent read.
https://www.passagemaker.com/techni...reased drag, or an improperly sized propeller.
The claim is If your engine cannot reach the rated WOT, here are the most likely causes: restricted air supply, restricted fuel supply, increased drag, or an improperly sized propeller. It goes through each one. Its worth a cup of coffee for a morning read.
With a new vessel, my first step is to assume everything is working as it should run it at WOT and take reads on parameters said in the article. Then do that from time to time and see what changes. If I make a change, ie clean bottom, change props, then run it again..
If you have any further comments of what to look for, please add to..
Tom
Hi Van,
All, agree, its good to get the facts - speculation churns, but post-mortem and facts are worth more than words.
Van, Thanks for the report out. Very good to hear what was measured before and after. It’d be great to think Cummins would come back with final determination from bench testing the components, but since this is probably a one-off, I doubt theyd spend time on it.
I found an interesting article from Passage Maker, for running your engine at WOT (wide Open Throttle) to test and feel out any issues. I believe this was in-part troubleshooting Dougs issue or at least an indicator.
While this might be well known in the boating community, being somewhat new to marine diesel, I thought it’d be good to share for a decent read.
https://www.passagemaker.com/techni...reased drag, or an improperly sized propeller.
The claim is If your engine cannot reach the rated WOT, here are the most likely causes: restricted air supply, restricted fuel supply, increased drag, or an improperly sized propeller. It goes through each one. Its worth a cup of coffee for a morning read.
With a new vessel, my first step is to assume everything is working as it should run it at WOT and take reads on parameters said in the article. Then do that from time to time and see what changes. If I make a change, ie clean bottom, change props, then run it again..
If you have any further comments of what to look for, please add to..
Tom
