jewels Posted December 4, 2013 Share Posted December 4, 2013 having trob starting A Mack, 2011 mp8 engine, we blocked off all lines to tanks, fuel seperator, and installed 2 new filters, also made sure top and bottom chk valves were working. I only guessing its the primer pump... help Quote Link to comment https://www.bigmacktrucks.com/topic/33749-hard-start-poss-air-in-system/ Share on other sites More sharing options...
Mackpro Posted December 4, 2013 Share Posted December 4, 2013 Injector cups strike again. Thats what I would shoot for. Quote Link to comment https://www.bigmacktrucks.com/topic/33749-hard-start-poss-air-in-system/#findComment-219877 Share on other sites More sharing options...
Challenger Posted December 5, 2013 Share Posted December 5, 2013 Another vote for injector cups. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/33749-hard-start-poss-air-in-system/#findComment-219911 Share on other sites More sharing options...
staxx Posted December 5, 2013 Share Posted December 5, 2013 Injector cups. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/33749-hard-start-poss-air-in-system/#findComment-219921 Share on other sites More sharing options...
turckster Posted December 6, 2013 Share Posted December 6, 2013 Check to see if you have air in fuel return, usually you can see this through the tank fill or run the line into a bucket. If you have air in the fuel return with the engine off but the key on then it could be a problem with the "T" fitting on top of the 7th injector. Sometimes the check valves in the "T" fitting get stuck and allow air to return through the fuel system.Is there fuel around the hand primer pump on the filter stand? When you pump the primer pump, does fuel come out around the little plastic cap? If so, air is entering the fuel system through the little cap in front of the primer pump. Its hard to start because fuel is returning back to the tank because of that little cap. Only cure is to replace the filter stand.If everything looks ok and you only have air in the fuel return when the engine is running then I'd have to say the injectors are most likely the issue. Just because its hard to start I wouldn't just jump in there and pull the injectors. I have removed injectors only find nothing wrong, then to find that "T" fitting bad. Ouch. Do some diagnostics, do it once and do it right. Good luck Quote Link to comment https://www.bigmacktrucks.com/topic/33749-hard-start-poss-air-in-system/#findComment-220120 Share on other sites More sharing options...
boyd Posted December 19, 2013 Share Posted December 19, 2013 get you a see through union and put it inline to see if you have bubbles running through while it is doing this.. Quote Link to comment https://www.bigmacktrucks.com/topic/33749-hard-start-poss-air-in-system/#findComment-222173 Share on other sites More sharing options...
Mackpro Posted December 19, 2013 Share Posted December 19, 2013 As Turckster said above, it could be the filter housing/hand primer pump, Tee valve on top of 7th injector (if equipped) , injector cups or something else. Years ago when I was doing somethimes 3 sets of cups a week, we got in the routine of not checking anything and just pulling the injectors out and replacing the cups. Back then about 98% of the time we were right. However those 2% made us look bad. One time I replaced the injectors and cups only to later find that the plastic elbow fitting on the fuel tank was cracked and sucking air, lucky warranty was paying for anything related to the cup/injectors no questions asked.air in fuel.pdf Quote Link to comment https://www.bigmacktrucks.com/topic/33749-hard-start-poss-air-in-system/#findComment-222182 Share on other sites More sharing options...
boyd Posted December 20, 2013 Share Posted December 20, 2013 do you know if this has the newer updated conical injector/cup set or is it still the older version. the newer version of the injector cups are stainless steel. Quote Link to comment https://www.bigmacktrucks.com/topic/33749-hard-start-poss-air-in-system/#findComment-222278 Share on other sites More sharing options...
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