Bret Posted May 25, 2023 Share Posted May 25, 2023 (edited) Hey all, really hoping someone can help me out here. I have a 2010 Mack Ganite with the MP8 engine and Allison transmission. I recently had my fuel injectors, cups, and cam shaft replaced. Everything was running fine except for the loss of prime and the increased cutting out at mid range rpm’s. When mechanic opened the valve cover, he found a roller bearing that had seized up, explaining the need for a new cam shaft. Anyhow, fast forward to this week. After replacing two of the six new, (remanufactured) injectors in the first week, it is finally running and starting smoothly like it should. However, at 1500 rpm’s and up, I’m getting a horrible knocking sound. Mechanic says he’s stumped, and doesn’t think it’s from the pistons or bearings because it only starts making the sound at higher rpm’s. My dump truck has basically now been parked for two months during the busiest time of the year. Any help, or suggestions would be very much appreciated. I can’t afford to have it down much longer…..TIA Edited May 25, 2023 by Bret Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/ Share on other sites More sharing options...
fjh Posted May 25, 2023 Share Posted May 25, 2023 Might help to know which engine you have MP8 Or 7 ! Also can you duplicate the sound stationary ! MP8 These have a history of the idler gear coming loose and can cause a rattling knocking sound at the rear of the engine! Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/#findComment-531919 Share on other sites More sharing options...
Bret Posted May 25, 2023 Author Share Posted May 25, 2023 Sorry, mp8 with Allison transmission. I can’t duplicate the sound while stationary possibly because It will only let the rpm’s rev up to around 1400 in neutral Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/#findComment-531924 Share on other sites More sharing options...
fjh Posted May 26, 2023 Share Posted May 26, 2023 23 hours ago, Bret said: Sorry, mp8 with Allison transmission. I can’t duplicate the sound while stationary possibly because It will only let the rpm’s rev up to around 1400 in neutral Any engine codes? Cam shaft replaced is it in time? Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/#findComment-531966 Share on other sites More sharing options...
Bret Posted May 26, 2023 Author Share Posted May 26, 2023 No codes, as far as I know the timing is right. It ran like a top for about a day, then one of the springs broke on the aftermarket rebuilt injector. Within a few minutes of replacing the injector the knocking started. After a test drive it stopped and ran good for a few hours then started again. Mechanic said he’s tested the injectors and that’s not the problem? He’s thinking possibly something with the engine brake but is at a loss. I hate to just start throwing at random things hoping to figure it out. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/#findComment-531981 Share on other sites More sharing options...
Joey Mack Posted May 27, 2023 Share Posted May 27, 2023 did he check the injectors with a laptop, or did he roll the cam over and check the injector preload? 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/#findComment-531994 Share on other sites More sharing options...
fjh Posted May 27, 2023 Share Posted May 27, 2023 17 hours ago, Bret said: No codes, as far as I know the timing is right. It ran like a top for about a day, then one of the springs broke on the aftermarket rebuilt injector. Within a few minutes of replacing the injector the knocking started. After a test drive it stopped and ran good for a few hours then started again. Mechanic said he’s tested the injectors and that’s not the problem? He’s thinking possibly something with the engine brake but is at a loss. I hate to just start throwing at random things hoping to figure it out. This here is a big red flag for me ! It ran like a top for about a day, then one of the springs broke on the aftermarket rebuilt injector. Within a few minutes of replacing the injector the knocking started.I agree parts cannon not the best! How ever if you can get it nailed down to a cyl Then swap injectors? Sounds like fuel knock to me but I'm not there !🙃 2 Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/#findComment-532001 Share on other sites More sharing options...
steeler Posted June 8, 2023 Share Posted June 8, 2023 I agree it sounds like could be fuel knock. Did you program the trim codes after new injectors? How about a learned data reset? 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/#findComment-532624 Share on other sites More sharing options...
Bret Posted June 22, 2023 Author Share Posted June 22, 2023 Update: found another broken injector. Got lucky, the Mack dealership had someone return a set of OEM injectors the same day I lost the third aftermarket injector. Pulled out the ones we installed, replaced with OEM. It’s started and ran smoothly, still had the knock. Mechanic had a lightbulb go off, took a close look at the exhaust manifold and it has a crack in it. He’s nearly certain that’s what’s causing the knocking sound. Going to weld a temporary band aid over the crack tomorrow and order a new manifold. Hopefully, the knocking will go away or at least change so I can confirm that’s what I’m hearing. I’ll post an update tomorrow thanks for everyone’s input, this has been a challenging year to say the least 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72887-knocking-after-new-injectors/#findComment-533417 Share on other sites More sharing options...
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