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2007 Mack Tandem Dump ASET Engine Skip & Tapping Under of Valve Cover


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Sounded like engine skipping through exhaust (appeared to be a dead cylinder).  Felt loss of power and as I throttled truck, sounded like spark knock (lightening bolt appeared on dash but before I could count blinks, it cleared).  What would I be looking for or checking into that may cause this? Sounds to me like an injector trying to work, but not working.  Does not sound like valve train - sounds like an individual tick.

Any leads on what to check on next?  

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Did you use a stethoscope to locate the sound? Do you have an infrared temp gun to check the exhaust. Manifold per each cylinder?

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4 hours ago, Joey Mack said:

Did you use a stethoscope to locate the sound? Do you have an infrared temp gun to check the exhaust. Manifold per each cylinder?

 stethoscope/ infrared temp gun??? what are these things you speak of ??? guess you forgot the yellow crayon method. .forgive me Sir , I had a  tooo!!!!🤣major long day out in the cold prepping for the north east Blissard which mistakenly I assumed those projects for me  were over 40-50 yrs ago, Jack Daniels hasn't kicked in yet, knees let me know == not going to fill gas cans. gotta get back on topic .my john deere fires on all cyl ok== both of them LOL

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Yes I did forget about the crayons,,  I didnt use them much..  as far as a stethoscope goes, Yes I have one, but I actually use a long peice of 3/8'' car brake line to listen to the engine and so-on.. The temp gun is pretty cool,   you can stand back and take temperature..  sorry Old Man :)  but there are some neat ways to diagnose,,, i mean trouble shoot, issues.... I always chuckle when you post..  Jojo

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Thanks.  I tried using stethoscope, but was too noisy for me to detect.
I used temp gun and attached are the temps at engine idle.  It's obvious the front cylinders are significantly lower.  I was initially thinking it could be an injector, but wondering if I should lift the front valve cover just for a visual inspection.   Just looking for some guidance. 
 

image.thumb.png.1cbbc3a06518cc4ef580245d7569699e.png

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it wouldnt hurt to check lash again,, have you ever run the rack on an ASET-I or C engine?  Just curious..   It is not the same as Earlier Macks, Cat or John Deere, for example..   Jojo

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No and probably won’t  attempt it . I am trying  to get a feel for what or how to diagnose the problem . I just hate taking it In with no clue ? Im sure it involves the two front cylinders , thinking it may be odd for 2 injectors to croak at the same time . Just don’t want to start experimenting without some knowledgeable advice . I know these engines are computer controlled , wasn’t sure about loosening injector lines or other manual testing methods  ! Thinking I will lift valve cover on front and take a look for loose rockers on the two cylinders that are in the 150 degree range. What’s your thoughts ?

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I'd pull valve cover. Never know what you'll see, broken rocker arm shafts, broken valve stem....

I'd also look into condition of the camshaft EUP's and H Clips, you could have broken bits there eating up the camshaft. If so, this would be a prime time to read the "old dog dead dog loggin dog" remediation thread to delete your ASET AI (guessing your truck is a granite) emissions system.

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yes, pull the valve covers, certainly wouldnt hurt to drop the oil pan.  if you have lifter issues there will likely be bits in the pan.  you describe the sound as a clicking.  so it is not popping back into the intake or ''poof poof poof'' out the exhaust? is the oil level raising up, and /or is the oil diluted with fuel.  you can do a simple 'halo' test on a piece of cardboard to see if the oil is diluted. 

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10 hours ago, Joey Mack said:

yes, pull the valve covers, certainly wouldnt hurt to drop the oil pan.  if you have lifter issues there will likely be bits in the pan.  you describe the sound as a clicking.  so it is not popping back into the intake or ''poof poof poof'' out the exhaust? is the oil level raising up, and /or is the oil diluted with fuel.  you can do a simple 'halo' test on a piece of cardboard to see if the oil is diluted. 

Joey your comment on the poof poof out the exhaust, I once had a DM with a 237, when ever you backed off it or coasted down a hill it would do that, had a loose exhaust seat, ran a long time that way. When I eventually pulled the head you could see where it was moving up and down in the carbon buildup.  Terry:MackLogo:

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thanks for all the input ! due to a surgery i had planned i will be down a couple weeks . as soon as i can pull the valve cover i will relay what i find with pictures . i will continue to monitor this topic.

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  • 2 months later...
13 hours ago, Granitecv713 said:

after recovery from surgery i was able to get on checking on my issue with my skip in my aset engine ! I will not take credit for the repair , but with your comments and my mobile mechanic  he set out to go through a valve train adjustment ! that all went well until we rotated the engine back through to double check everything .at this point he said the rear cylinder adj. was out of adj, bad . as he continued inspecting  , he found that someone had tighten up the rocker cradle with an impact gun ! Broken and loose bolts had caused my valve adj  on rear  cylinder to be my  issue ! Many thanks to all who contributed input on my issue ! I have had 100% success on every issue i have had using this site (BMT) and its helpful followers

Wouldn't hurt to have him replace all the rocker bolts! they are torque sensitive !

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