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Old 09-28-2022, 11:12 AM   #1
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6.7 Cummins hard start

We have a 2008 Cummins 6.7L Turbo in a Tiffin 35QBA. Runs really great, plenty of power and good mileage.

Usually it starts right up but lately it has taken longer and longer to fire up. At a rest stop outside of Santa Fe it took about 20 seconds (and two tries) to start.

Where should I start looking for issues?

It has new fuel filters and the problem doesn't go away when I put new fuel in.

EDIT: it's worth noting that this particular rig does not have a lift pump.

!!THANKS!!
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Old 09-28-2022, 04:19 PM   #2
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I gotta' ask: What is the OEM Cummins filter PN and are you using an OEM filter or aftermarket?
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Old 09-28-2022, 04:52 PM   #3
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https://www.irv2.com/forums/f26/atte...sb-468655.html

1st thought was , no lift pump?

Then I Google and found the above
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Old 09-28-2022, 06:34 PM   #4
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Quote:
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1st thought was , no lift pump?
I don't know if this is common to all 6.7L rigs or what, but on the Front-Engine Diesels there is no lift. And even if i did have one, I wouldn't suspect it right away because other than some starting issues, the rig runs fine.
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Old 09-28-2022, 06:44 PM   #5
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I gotta' ask: What is the OEM Cummins filter PN and are you using an OEM filter or aftermarket?
I don't suspect the filters because the problem didn't manifest with new filters (and they're the same ones I put on every year). I'm not saying it isn't the filters, but I'm not looking that way just yet because the problem appeared so suddenly. Ya never know, though. I have spares with me an I'm not above installing them just to see if the problem goes away.

In any event I did look at my code reader and see a 157 code, which is low fuel press. So that's something.
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Old 09-28-2022, 07:02 PM   #6
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put a heavy dose of power service white bottle for injection cleaning . The issue your having is the injectors are possible dripping fuel after it shut off. make sure you follow the injecter clean up dose , it may take 100 miles to take effect. If that isnt your issue I cant be much more help , this is common with Cummins with around 125,000 miles .
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Old 09-28-2022, 07:36 PM   #7
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I don't suspect the filters because the problem didn't manifest with new filters (and they're the same ones I put on every year). I'm not saying it isn't the filters, but I'm not looking that way just yet because the problem appeared so suddenly. Ya never know, though. I have spares with me an I'm not above installing them just to see if the problem goes away.

In any event I did look at my code reader and see a 157 code, which is low fuel press. So that's something.
I ask because I learned the hard way that my ISM filter needs a built in "standpipe". Aftermarket brands may not have it. Without it - hard starts.
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Old 09-29-2022, 07:23 AM   #8
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Quote:
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I don't know if this is common to all 6.7L rigs or what, but on the Front-Engine Diesels there is no lift. And even if i did have one, I wouldn't suspect it right away because other than some starting issues, the rig runs fine.
Regardless, the 6.7 and 5.9 even in the Ram trucks all have lift pumps. If you read the link you would find the statement that the CP3 injection pump has the capability to operate w/out a lift pump for emergency situations...however greatly reduce pump life. There was discussion on the 6.7 now requiring electric pump comming from the 5.9 that had mechanical pump. Freightliner did not add and Cummins did not supply.

I am not saying this is your issue. You very well could have a leak be it injector, pressure control regulator etc and your dry at start up until the Injection pump picks up.

You need a diag laptop and connect to do a leak down test on the fuel rail after shut down, if it's out of range then you would follow the diagnostic tree.

Even though your filters are the same, you don't suspect them so on and so forth that should always be the first suspect. What if an oring is leaking and you lose some prime?
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Old 09-29-2022, 06:48 PM   #9
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What if an oring is leaking and you lose some prime?
Very possible!!! Good point. Even a little thing like this could be a big thing.

I'll replace the filters later on this week and see where we are.
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