LITTR Posted August 13, 2021 Share Posted August 13, 2021 Driver pulled in with a knocking sound coming from engine. Hard to tell if it was lower end or not. Pulled the pan and found metal fragments. Checked #1, #3, #5 rod bearings; all good. Checked main bearing; all good. Looked for any damage to cylinder walls; all good. Pulled P/S pump to check gears and found chipped tooth that matched some of the fragments in pan. Replaced fuel/P/S assembly. Also replaced oil pump while I was there. Moved to the top end and found damaged cam lobe on #3 injector. My question is: can this be the cause of the knock? It sounded to me like a wrist pin or fuel knock. Was wondering if anybody has gone through this before. Quote Link to comment https://www.bigmacktrucks.com/topic/67720-2012-gu713-worn-3-injector-cam-lobe/ Share on other sites More sharing options...
Vmac3 Posted August 14, 2021 Share Posted August 14, 2021 Sounds like it can cause a fuel knock. The engine ecu monitors crankshaft speed between each power stroke. If the speed of the crankshaft is not what the ecu expects then in this case it will lengthen the injectors pulse width. If you have a worn out injector lobe then not enough pressure will build in the injector, when it comes time to inject, instead the diesel fuel coming out as a fine mist, it just dribbles out. This can cause all kinds of problems, and a fuel knock is just a minor one. V 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/67720-2012-gu713-worn-3-injector-cam-lobe/#findComment-478388 Share on other sites More sharing options...
fjh Posted August 15, 2021 Share Posted August 15, 2021 (edited) If this is an mp8 I would seriously check into the rear idler gear on this ! These have a track record for the idler gear coming loose! The cam will be the least of your problems if that is the case just sayin Edited August 15, 2021 by fjh 1 Quote Link to comment https://www.bigmacktrucks.com/topic/67720-2012-gu713-worn-3-injector-cam-lobe/#findComment-478420 Share on other sites More sharing options...
LITTR Posted August 16, 2021 Author Share Posted August 16, 2021 Thanks for the input. I am very familiar with the idler issue on these. I have already had this motor apart and the idler gear has been redone. I am going to replace the cam and bearings. I will post how I make out. Quote Link to comment https://www.bigmacktrucks.com/topic/67720-2012-gu713-worn-3-injector-cam-lobe/#findComment-478471 Share on other sites More sharing options...
fjh Posted August 18, 2021 Share Posted August 18, 2021 On 8/16/2021 at 10:43 AM, LITTR said: Thanks for the input. I am very familiar with the idler issue on these. I have already had this motor apart and the idler gear has been redone. I am going to replace the cam and bearings. I will post how I make out. Pulled P/S pump to check gears and found chipped tooth that matched some of the fragments in pan This comment prompted my response! Vmac3 has posted good info could also be a cracked injector tip or injector not uncommon either! Quote Link to comment https://www.bigmacktrucks.com/topic/67720-2012-gu713-worn-3-injector-cam-lobe/#findComment-478548 Share on other sites More sharing options...
LITTR Posted August 24, 2021 Author Share Posted August 24, 2021 Update: I replaced the camshaft, bearings, and all hardware for bearing caps and rocker assembly. Noticed a big difference as soon as I started the engine. Just took the truck for a test drive and it is running excellent; no knock! So, the knock that I was hearing was a fuel knock from the #3 injector due to worn cam lobe. 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/67720-2012-gu713-worn-3-injector-cam-lobe/#findComment-478843 Share on other sites More sharing options...
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