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MP8 injector trim percentages


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2015 MP8 injector trim correction number running consistently -35% on #2 cyl others are low/mid single digits +/-. Also how critical are injector trim codes?

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The injector trim codes is not life and death but very critical for precise adjustments. This will tell the engine ecu the operating characteristics of the injector. Each injector is manufactured to different tolerances. The engine ecu will use this trim code to calculate a more precise injection event. Also the engine ecu will be able to determine what is the injectors operating range. So when you are doing a injector contribution test, you are seeing how the engine ecu is making fueling changes. Now if you did not have the trim code installed in the engine ecu when replacing an injector, the ecu would not be able to properly make these adjustments because it thinks that the old injector is in place. As for your percentages, I would run a cylinder compression test and make sure that #2 is okay because #2 fuel injector is over fueling. Might want to pull that injector out and see if the cup has failed.

V

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Have several MP8's/D13 I see on regular basis and observe injector percentages+/- up to 20-25% variance at any given time although typical variance is 5-10%. This particular one has new injector cup and injector in #2 cylinder. Prior readings were very similar. Cylinder balance/contribution test is very close range (less than 5 rpm variance between cylinders). Can't remember dynamic compression results. Engine has good power and decent MPG. pulls 39' end dump most of the time. Scanner does not show trim codes as installed on any of these engines although other makes of engines I see are shown in data stream. Will post further comparisons and test results towards weekend or as obtained. Thanks for the help.

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If you get a chance, check the valve adjustment on these engines. I have found that the cylinder that requires less shims in a particular cylinder than the others is a cause for concern. Especially #5. The valve seat is being pounded into the head, the valve itself is beginning to stretch or the valve face is folder over.

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The engine brake plungers are known to unscrew themselves and cause issues as well . Mack sent out a bulletin and tools to dealers to tighten the plungers . Every time we had the rocker arm shaft of a MP engine we would check the plungers and see if they were backing out     https://static.nhtsa.gov/odi/tsbs/2017/SB-10090649-6903.pdf

Edited by Mackpro
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