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Old 07-19-2019, 04:44 PM   #1
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Smile Changing fuel water separator on ISB

Good day all, this is my story for better or worse about changing the fuel water separator on a Cummins ISB engine. I attempted to learn as much as I could from this forum an youtube but as you will see I didn't get it right. The search function and I don't seem to get along. The impression I got was that it was the same as changing a standard filter, screw off and on. My first mistake was trying to drain it before removing it. This didn't seem to work as diesel fuel just kept coming. Thinking the flow would stop when I removed it I did so. As I was removing it the flow didn't really slow as I expected and when I had removed it the flow continued and I made a quick decision to reinstall the filter. At this point I called the Frieghtliner help line and spoke to a gentleman who explained that the system I have will continue to drain diesel and that the mechanics have advised him that the way they do the change is to have the replacement ready and work as quickly as possible to remove the old one and install the new one. As I was planning to reuse the plastic bowl off the old one and didn't have a spare I made a trip to the local Frieghtliner shop and bought it. Found out that it doesn't come with the sensor, you buy that separately or simply move the old one onto the new one. I asked if I needed to prefill the new filter and he said no that the fuel which continues coming as you change the filters will fill it. Here I made another mistake by not realizing or taking into account the amount of fuel that had drained on my previous attempts. This lead to my not turning on the ignition enough times to get a good prime and my attempts to start the engine failed. Another call to the Frieghtliner help line and a young lady couldn't offer any real help except to say I may need to get some shop air into the fuel tank to help move fuel thru the system. She didn't know how much pressure to use but mentioned that some folks have taken a 2 litter bottle cut in half and used it to build pressure in the fuel tank. Not comfortable with this I called Cummins to see what they might be able to tell me. The fellow I spoke to was friendly but due to liability issues couldn't really tell me too much. He did suggest turning on the ignition for 30 seconds then off and repeating this 10 or 12 times. Five or six attempts failed. Next I found a youtube video about starting a diesel which had run out of fuel. He was demonstrating on a tractor so not an apples to apples comparison. He mentioned the importance of the fuel being higher than the fuel rail. Not something I can do much about on the coach, but while I had ¾ of a tank I added another 25 gallons to top it off hoping it would help. I also tried cracking open the injectors to bleed off some air, I didn't see or hear any air when I did. Returning to basics I removed the fuel filter and topped it off. Again trying the key on for 30 seconds 10 times I attempted to start the engine. To my surprise and great relief on the third attempt she fired up! So to sum up if changing the fuel water separately on a ISB Cummins engine consider the following:

Start with a full tank.
Have the new filter including the plastic bowl prepped and ready before starting.
After installing the new one remove and top off the fuel filter.
Turn the key on for 30 seconds then off about 10 or 12 times, very likely you can get away with far fewer as you won't have lost as much fuel as I did with my attempts.

My plan to use the old plastic bowl also failed as I still haven't been able to remove it from the filter element. Its the original when bought new, I'm at about 24000 miles, not sure if they used some type loctite or just lots of muscle but its not coming off easy if at all. Happy and safe travels everyone, hope this helps someone avoid my mistakes.
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Old 07-19-2019, 05:49 PM   #2
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Always a good idea to mention the year of your Cummins , when posting info .
ISBs used two different fuel systems over the years .
Attempting to bleed air from the system on your, 2016 HPCR, by cracking a connection at the injector tube to cylinder head connection; or anywhere past the injector pump; can be very dangerous. Fuel pressure there is high enough to penetrate your skin and put diesel fuel in your blood stream.
There is a bunch of different info out there on the electric lift pump cycle to prime the system , some say just to turn the key on, for 15 secs/off/on15 secs/off/etc , some say the starter has to be bumped to start the pump cycle.

If in doubt about your fuel system, lift pump cycle, then pre-fill the fuel filters .
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Old 07-19-2019, 05:53 PM   #3
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Road salt. The bowl will freeze to the filter from corrosion. First change on mine the Freightliner shop had a heck of a time separating it.

You’re on the right track. Change it with a full tank; have a complete spare bowl and filter to swap in; and a bucket for all the leakage. It’s a damn mess to tell the truth. Shame on FL for being to cheap to install a valve.
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Old 07-19-2019, 06:51 PM   #4
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My last coach was a 2015 and had an ISB. I changed both fuel filters annually. I always waited until the tank was below 1/4 then I blocked the front wheels and extended the rear jacks all the way, front jacks still up. I would then change the chassis filter first, prefill and install it. lower the jacks and then start the engine and let it run a few minutes. Never had fuel siphon out that way. Next I would change the 2 micron filter on the engine. Since I do my maintenance inside the garage, I do the extra steps to keep fuel off the floor.
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Old 07-19-2019, 07:07 PM   #5
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Thanks for the info and ideas, a mess to be sure. Glad I didnt have issues with high pressure, lucky again .
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Old 07-20-2019, 09:31 AM   #6
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I use fuel line clamps and have the extra bowl and sensor. On most of my equipment in the past a fuel shut off valve was standard equipment. It certainly would be a nice feature. Thanks for sharing your experience as it will help others down the road.
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Old 07-20-2019, 06:39 PM   #7
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I to do this on our new to us, Holiday Rambler. Someone please tell me I am wrong if my ideas are wrong as I am new to diesels. Would it not be a good idea to install a valve be fore the filter that could be shut off to prevent the spillage in future changes. I could use a line clamp to keep leakage to a minimum and install valve and then reconnect lines, shut the valve off and do the filter change with no leakage and not be in such a hurry and get something cross threaded or other problem. I realize valve would have to be of high quality and fuel safe. I am more used to building cars from ground up where you address these problem in the build and not a after thought.
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Old 07-20-2019, 10:13 PM   #8
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Howdy gmc70, I don’t think all diesels have this issue. The impression I got when talking to the Freightliner folks was my particular model was set up this way. Mine is a ISB15 Cummins engine. Hope yours has a better design. B safe
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Old 07-21-2019, 08:01 AM   #9
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Are you saying, that until you remove the filter you won't know if it is going to leak fuel? Or that some have a valve to shut the flow of fuel off.
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Old 07-21-2019, 08:26 AM   #10
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Originally Posted by gmc70 View Post
Are you saying, that until you remove the filter you won't know if it is going to leak fuel? Or that some have a valve to shut the flow of fuel off.
Based on the number of folks on other threads installing valves, I suspect most don't have

Mine doesn't and it is a 2016 ISL9
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