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Robbie_Welch's avatar
Robbie_Welch
Explorer
Aug 14, 2016

8.3 Cummins engine miss

I have a 1999 Monaco Windsor with a 8.3 Cummins 330 HP ISC. I've had a problem where about once a year it would stumble under load I'd change the filters and it would be good again. Well it happened a couple weeks ago and changing filters didn't help. I did the e-net research and though it was a lift pump. $550 later I found out It wasn't that. Long story shorter after checking for air in the fuel line's I hooked a vacuum gauge to the lift pump, it was reading 5 inch's with just the lift PP and about the same with the engine running. Test running the coach on the road up to the miss and it read 14 inch's. The problem ended up being the suction line check valve at the primary fuel filter inlet. It was full of rubber from the fuel lines. Cleaned it out and it runs great, I'd never heard of a check valve in the line but they're in there. Hope this helps someone else.
Class A

7 Replies

  • Robbie_Welch's avatar
    Robbie_Welch
    Explorer
    Aug 23, 2016
    The Primary filter is before the lift Pump. After the black stuff dried out I don't think it's rubber. It had the consistency of dried out plumbers putty?
  • Airstreamer67's avatar
    Airstreamer67
    Explorer
    Aug 20, 2016
    Robbie, I assume you changed out the deteriorating rubber fuel lines?

    Have you considered installing a filter on the suction side to catch trash in the fuel and/or fuel tank before it reaches the lift pump?
  • oldmattb's avatar
    oldmattb
    Explorer
    Aug 15, 2016
    Robbie Welch wrote:
    Hard to say where it came from. I believe the lines are fiber wrapped rubber. The check valve is attached to the inlet of the Primary (water separator) filter. Bio fuel? Its what ever the truck stops sell. I'm only posting this to try and help others going through the same problem. Its not always the lift pump and I've never seen a reference to a check valve in the fuel line. (and it's all factory equipment). Hope this helps


    Good information. I have a similar coach and have made note of the problem you had.

    Matt B
  • BigRabbitMan's avatar
    BigRabbitMan
    Explorer
    Aug 15, 2016
    Decomposition of the insides of rubber lines of various types is not uncommon. It also happens to brake lines and causes dragging/sticking hydraulic brakes.
  • Robbie_Welch's avatar
    Robbie_Welch
    Explorer
    Aug 15, 2016
    Hard to say where it came from. I believe the lines are fiber wrapped rubber. The check valve is attached to the inlet of the Primary (water separator) filter. Bio fuel? Its what ever the truck stops sell. I'm only posting this to try and help others going through the same problem. Its not always the lift pump and I've never seen a reference to a check valve in the fuel line. (and it's all factory equipment). Hope this helps
  • oldmattb's avatar
    oldmattb
    Explorer
    Aug 14, 2016
    Rubber from the fuel lines?

    Do you think the lines are decomposing inside? Maybe just random trash from 15 years of fuel stops?

    Is the check valve inside one of the fittings that attaches to the filter base?

    Matt B

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