jmahoneclipse Posted October 3, 2016 Share Posted October 3, 2016 (edited) i have a 08 Mack GU813 and it started missing on cyl 1,2, & 3 randomly. if you shut the truck of it may start running fine and then if you shut it off and re start it, it will start missing on all 3 CYL again. ive already removed the valve cover and checked all the plugs on the injectors and i found no damage at all. not sure where to go next with this. Edited October 3, 2016 by jmahoneclipse Quote Link to comment https://www.bigmacktrucks.com/topic/47133-mp7-missing-on-cyl-12-3/ Share on other sites More sharing options...
fjh Posted October 3, 2016 Share Posted October 3, 2016 1 hour ago, jmahoneclipse said: i have a 08 Mack GU813 and it started missing on cyl 1,2, & 3 randomly. if you shut the truck of it may start running fine and then if you shut it off and re start it, it will start missing on all 3 CYL again. ive already removed the valve cover and checked all the plugs on the injectors and i found no damage at all. not sure where to go next with this. Check @ your ECU plug for oil! Quote Link to comment https://www.bigmacktrucks.com/topic/47133-mp7-missing-on-cyl-12-3/#findComment-347703 Share on other sites More sharing options...
Mackpro Posted October 3, 2016 Share Posted October 3, 2016 I vote for engine harness. Most all older MP's around here have been replaced once if not twice. Watch your engine brake plungers in the engine brake roller rocker arm and make sure there not uncrewing themselves. Harness.pdf Quote Link to comment https://www.bigmacktrucks.com/topic/47133-mp7-missing-on-cyl-12-3/#findComment-347714 Share on other sites More sharing options...
steeler Posted October 4, 2016 Share Posted October 4, 2016 I vote harness as well, if the ecu plug is oil free. I've seen a bazillion harness issues for the same problem, especially where the harness runs over top of the air compressor. They love to rub there. Quote Link to comment https://www.bigmacktrucks.com/topic/47133-mp7-missing-on-cyl-12-3/#findComment-347733 Share on other sites More sharing options...
fjh Posted October 4, 2016 Share Posted October 4, 2016 Yup great design features! Quote Link to comment https://www.bigmacktrucks.com/topic/47133-mp7-missing-on-cyl-12-3/#findComment-347746 Share on other sites More sharing options...
jmahoneclipse Posted October 4, 2016 Author Share Posted October 4, 2016 Thanks guys, after i did some looking last night i decided to buy the high tension connectors for the injectors, so next step is to install them and and inspect all the wiring. does anyone have a diagram or picture of how the plug comes off of the back of the head. i can only fit my hands back there to fiddle with it but i cant get my eyes on it to see how it comes loose. Quote Link to comment https://www.bigmacktrucks.com/topic/47133-mp7-missing-on-cyl-12-3/#findComment-347755 Share on other sites More sharing options...
Mackpro Posted October 4, 2016 Share Posted October 4, 2016 The harness is all one piece! It pulls out of the head. If you bend any of the wires under the valve cover and the insulation comes off, replace the entire harness. It aint worth fixing. If the harness is not brittle and in good shape , I would replacejust the injector plug ends. Quote Link to comment https://www.bigmacktrucks.com/topic/47133-mp7-missing-on-cyl-12-3/#findComment-347775 Share on other sites More sharing options...
jmahoneclipse Posted October 4, 2016 Author Share Posted October 4, 2016 the harness is not brittle,and also i was unsure if i would loose any oil by running it with the valve cover off? it would definitely make it easier to find the problem if i could. also does anyone have the procedure for testing the injectors? Quote Link to comment https://www.bigmacktrucks.com/topic/47133-mp7-missing-on-cyl-12-3/#findComment-347780 Share on other sites More sharing options...
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