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Old 05-01-2012, 02:02 PM   #1
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Fuel leak on 8.3

I have an odd problem with a fuel leak on my 8.3 350hp cummins. When it sits for a couple of days and I start it it will drip fuel down from somewhere around the injector pump. When I shut it down and restart it it won't leak. I have looked at it from the top and bottom and can't see a leak anywhere on the pump. The pump is not very visible due to the air filter and piping. I may have to pull all that off to get down there to see. I was just wondering if anyone else has had this problem. Thanks. It is an HR Imperial.
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Old 05-01-2012, 04:12 PM   #2
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Sounds like a leaking boost pump.
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Old 05-01-2012, 06:14 PM   #3
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Make sure it is not the lift pump.
The lift pump is located curb side of the engine transmission side just above the starter.
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Old 05-01-2012, 11:19 PM   #4
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Quote:
Originally Posted by dons2346 View Post
Sounds like a leaking boost pump.
Aw, shoot. Don't even know what to call the lift pump anymore

Yep, lift pump.
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Old 05-01-2012, 11:36 PM   #5
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Agreed....most likely lift pump. Leaking Cummins lift pumps of that era are common, per our local Cummins techs. Like mine, yours is probably victim of the new ultra low sulfer fuel which can dry out the internal seals. I don't believe a seal replacement kit is available any longer from Cummins. Pump runs about $300, and labor is about 1 1/2 - 2 hours.

Please let us know what you find out....thanks!
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Old 05-02-2012, 12:05 PM   #6
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Thanks for the replies, but it is not the lift pump. I can see all around the lift pump and everything is dry there. I can't see in around the injector pump very well. I did replace a cracked line on the back of the pump that goes to the top of the pump, its a return line and not high pressure but that and all the injector lines look ok from what I can see. The main fuel line to the pump also looks ok. It seems to be coming from somewhere on the back of the pump or the under side . I can't really see it because of the compressor and hydraulic pump from the under side. The air duct and filter makes it impossible to see from the front top. Before I pull the filter and ducting I was wondering if there is any famous place that the injector pump will leak from. It seems really odd that it will leak a bit after starting and then stop leaking. The coach has sat for about 7 months so is something dried up? I also traced the fuel lines and they seem to be ok as well. Thanks again.
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Old 05-02-2012, 05:21 PM   #7
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Just trying to help. Remember that the Cummins lift pump only operates for about 30 seconds....and shuts off. As you know, it is designed to ensure that fuel is "lifted" from the tank up to the CAPS fuel pump and only operates at about 5-7 lbs. pressure (if my memory serves me!). My lift pump did the same thing yours is doing. The leak would stop after the lift pump ceased to operate....and the fuel from the leak would dissapate from normal evaporation and engine heat. And the older Cummins lift pumps are prone to leak.

The other item that comes to mind is #5 fuel injection line at the pump....but that is not a leak that would probably stop after a short period. Per the Cummins techs, the fittings on those high presssure lines will "set" a wear pattern (due to vibration)over time/miles and can develop leaks. Tightening these lines to stop the leak is very hit & miss because of the wear pattern and the extremely high pressures present at the connections. For some reason, #5 seems to be the most likely to leak...probably due to mounting or excessive vibration issues. And that's the one that is usually out of stock when you need it....true. That should tell you someting about #5.

Hope this helps. PLEASE let us know what you find out....thanks!!
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Old 05-02-2012, 11:09 PM   #8
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Thanks, H B Engin, I will have to pull the air intake and filter off to get a better look in there. I will have a good look at #5. Thanks again.
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Old 05-04-2012, 10:15 PM   #9
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slickest1....you're welcome. Sure hope you find it without too much trouble. It's not easy "gettin' around" back there, for sure! If you do have a leak, I do kinda' hope it is the lift pump after all. MUCH easier and cheaper than getting involved with those injector lines.

The problem is that getting at #5 line (if that is the one leaking) requires taking off the rest of the lines at the fuel pump. And when you do that, you run the risk of disturbing the individual wear patterns (as I mentioned previously) on each of the connectors on each line at the pump. An experienced, savvy Cummins tech will tell you that there is always such a risk when loosening those connections. When our #5 line started leaking, I had the tech replace all of the rest of the lines when he stated that he could not guarantee that the other connections would not subsequently leak at some point following the repair. Since all of the lines were disconnected at that point anyhow, the additional labor was not significant....just didn't need the hassle of another fuel leak down the road somewhere. If you do have a leaking line, hopefully it will be one that does not require distubing any of the others. Even more hopefully, your leak will be something else, like a loose clamp, and all of this will be moot!! One can hope!!

Again, please let us know what you find out....thanks!
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Old 05-05-2012, 12:51 PM   #10
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Thanks again Engin, I will let you know what I find. I can't get to it till next week some time. I did replace the one line on the Caps pump as it was cracked . It was a low pressure return line that runs off of the top of the pump to the back of the pump. From what I read there was a recall on some of these lines years ago and I checked and my ser.# didn't fall in that category. I can see in there pretty good and all looks dry there. I will have to dig deeper.
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Old 05-05-2012, 02:24 PM   #11
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I had a fuel leak under the Fuel Pump (Not the Lift Pump) it was a sensor had worked loose, the dealer took it out and checked the O-Ring & the threads, put new O-Ring back on and Reinstalled the sensor. Did not charge for the O-Ring, Labor 1/2 hr. & back on the Road again (Happy) Jim Jessup
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Old 05-05-2012, 09:14 PM   #12
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Thanks Jim, that sounds like what mine is doing. I will check that out. I have good access to everything around the engine on my coach but can't see under there. Did they have to remove the pump or were they able to fix it on the engine.
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Old 05-06-2012, 07:40 PM   #13
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Hi, They did not have to remove the pump, they got under the pump some way I could not see it. Jim
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Old 05-07-2012, 10:19 PM   #14
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Thanks Jim, I will keep an eye on it. I started it up and took it for a drive today and no leak at all. I have to go 50 miles into the city tomorrow for windshield replacement so will see if it will leak or not. I just hate when something leaks or acts up and the stops and you can't find it. It's always in the back of your mind wondering when it will bite you. Thanks again everyone for the replies. I will update if anything changes.
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