MOloghauler Posted November 4, 2018 Share Posted November 4, 2018 I’m running a ‘93 RD688s with an E7 350 mechanical motor. Engine runs great empty and has tons of power, but if I have it in a hard pull or a long run loaded it has a very uneven idle. revs up to almost 1,000 rpm then will bog down to around 400 and kind of “shutter” like it wants to die then pick back up and rev up high again. Even seems to be lacking on power at times when loaded especially in warmer weather. But again, it runs great when empty no matter how long or hard I run it. Not sure if that could possibly be a problem with the pump getting too hot, or sucking air in the fuel system somewhere? Any advice is greatly appreciated! Quote Link to comment https://www.bigmacktrucks.com/topic/54739-idle-problems/ Share on other sites More sharing options...
Mack Technician Posted November 4, 2018 Share Posted November 4, 2018 Good to run a temporary line and gauge break-in from the circuit leaving the fuel pump and monitor pressure during the event. An eye glass would also be helpful. Couple times have seen junk in tanks, even a Dixie cup and once a bread bag. Leaking suction line. Cracked tank stand-pipe, etc. Quick way to rule out a lot of issues is running a hose out of your tank fill to your first filter (temporarily). Quote Link to comment https://www.bigmacktrucks.com/topic/54739-idle-problems/#findComment-408880 Share on other sites More sharing options...
70mackMB Posted November 4, 2018 Share Posted November 4, 2018 l know of a fuel draw line that came apart on the inside. A small piece of rubber would drop down and act like a flapper valve. lt would do it every now and then, drove my friend nuts until he found it. .....Hippy Quote Link to comment https://www.bigmacktrucks.com/topic/54739-idle-problems/#findComment-408886 Share on other sites More sharing options...
terry Posted November 4, 2018 Share Posted November 4, 2018 The high and low idling used be in the governor on the mechanical engines. Would get so slow as to almost die . terry Quote Link to comment https://www.bigmacktrucks.com/topic/54739-idle-problems/#findComment-408889 Share on other sites More sharing options...
fjh Posted November 4, 2018 Share Posted November 4, 2018 Another easy check I recommend is the tank vent just crack the fuel fill loose for a while and see if the problem goes away if it does the vent is pluged! Quote Link to comment https://www.bigmacktrucks.com/topic/54739-idle-problems/#findComment-408901 Share on other sites More sharing options...
MOloghauler Posted November 4, 2018 Author Share Posted November 4, 2018 Thank you all! I kind of had the same thought as Terry with the governor just based on other older diesel equipment I’ve been around. But will definitely check everything else. One thing I forgot to mention, there is a crack on my turbo housing right where it bolts to the exhaust manifold. What kind of problems could that be causing, if any? I don’t have a boost gauge so I really have nothing to judge it by Quote Link to comment https://www.bigmacktrucks.com/topic/54739-idle-problems/#findComment-408903 Share on other sites More sharing options...
Mack Technician Posted November 4, 2018 Share Posted November 4, 2018 Age or overheated EGTemps. Quote Link to comment https://www.bigmacktrucks.com/topic/54739-idle-problems/#findComment-408905 Share on other sites More sharing options...
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