Forum Discussion

subtroll's avatar
subtroll
Explorer
Sep 10, 2013

Diesel Air Lock?

After being parked six days,our DP Motor home refused to start this morning! More accurately…it started but killed when I put it in Drive. Tried multiple times with the same result… couldn’t get more than 1000 rpm and the engine stalled and stopped when I pressed the accelerator.

Drained a cup of fuel out of the fuel separator… not a drop of water. Checked air filter DP indicator, no problem indicated.

Called our Roadside Service (Coach Net) and spoke with an engine tech. With him on the phone I started it again and this time it came up normal. The Tech indicated it was probably a small air lock ???, or bubble in the fuel line?? We did have 96 F yesterday and the coach was in the sun for nearly a week. While it’s never happened before when we’ve been in even hotter weather, the coach ran perfectly all day.

Cat 3126, 112k miles, last serviced at Freightliner 10k miles ago. Has anyone else experienced a similar problem?
Class A
  • Born_To_Travel's avatar
    Born_To_Travel
    Explorer
    Sep 12, 2013
    I had a school bus that would start ok after sitting for a few hours, but leave it set overnite and you would have to prime the filters and pump the hand pump to build pressure back up and it would start.. After removing the check valves in the fuel line (It had three of them if I remember right) I found one had a small piece of rubber o-ring material holding it open.. Replaced check valve and all was fine...
  • subtroll's avatar
    subtroll
    Explorer
    Sep 12, 2013
    I'm going with the sticky check valve theory. Drove it another full day yesterday without any problems. I've had no engine check lights. Think the CoachNet's engine tech "Air bubble" was a shot in the dark.
  • Born_To_Travel's avatar
    Born_To_Travel
    Explorer
    Sep 11, 2013
    If I had to guess I would guess you had a check valve sticking.. Check valves are one way valves in the fuel system that keep the fuel from draining back into the fuel tank after you shut it down.. All it takes is a small piece of dirt or rust to cause the problem you describe.. After starting the engine the object may have been flushed away and everything could be fine...
  • gatorcq's avatar
    gatorcq
    Explorer
    Sep 11, 2013
    2004 coach, this is a C7 CAT. When was the last time you change the oil? Was it recently? Dirty oil will cause various problems with the actuator pressure sensor and/or valve.
  • wolfe10's avatar
    wolfe10
    Explorer
    Sep 11, 2013
    OK, let's start by finding out whether you do have an "air in fuel" issue. If you have a Caterpillar secondary fuel filter with manual fuel pump, that is VERY easy. Unscrew it (knob counter-clockwise). Pump it (in/out). If easy, you have air in the system. If it is very hard to pump-- no air. Be sure to relock the knob by turning it clockwise.

    Air can enter the fuel system from a leak on the suction side of the system (same as on any diesel). So, fuel lines, fuel filter(s) need to be inspected. Remember, since this is on the suction side, it is unlikely that fuel will leak OUT-- instead, air can leak IN.

    If you prove the fuel system OK, next thing I would do is go to a Caterpillar dealer and have them check for codes.
  • ArchHoagland's avatar
    ArchHoagland
    Explorer
    Sep 11, 2013
    We've been over a hundred degrees for the last 50 days here in central California.

    If the heat caused that problem sitting there this forum would be slammed with people having your problem.

    Let us know how you make out.
  • ScottG's avatar
    ScottG
    Nomad
    Sep 11, 2013
    Long shot but if you have electric steps, were they stuck in the out position?
    I've heard some have interlocks maybe?

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