Lucas Campbell Posted March 8, 2018 Share Posted March 8, 2018 I have looked around a bit and not found anything about this, just picked up this truck at an auction, starts fine seems to run fine except when you let off the throttle quick like if you were going to shift gears the engine misses and sounds almost exactly like a Jake brake has engaged. Any ideas? I’m new to these Mack engines, I suspect a timing issue but before I dive down that rabbit hole thought maybe someone has seen this before? The truck has a ENDT 673 engine in it. Quote Link to comment https://www.bigmacktrucks.com/topic/52753-misfire-on-deceleration/ Share on other sites More sharing options...
Freightrain Posted March 8, 2018 Share Posted March 8, 2018 (edited) Welcome to the forums. They make Jakes for those old 673T's, so first thing is to see if it has spacers under the valve covers? Switch on the pump arm? If it has them, maybe the dash switch is broke/missing? Edited March 8, 2018 by Freightrain Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/52753-misfire-on-deceleration/#findComment-393700 Share on other sites More sharing options...
Rob Posted March 9, 2018 Share Posted March 9, 2018 (edited) Ensure the valve clearances are correct meaning run the overhead first to ensure it's accurate. Verify you do not have a "Dynatard" engine brake installed without the appropriate operating gear in the valvetrain. "Dynatard" has oil solenoids on the valvetrain and they do some funny things if not set up right. Edited March 9, 2018 by Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/52753-misfire-on-deceleration/#findComment-393730 Share on other sites More sharing options...
turckster Posted March 10, 2018 Share Posted March 10, 2018 A sticking dynatard valve or if no engine brake it could be a loose exh. valve seat(s). Seems to me back in the day when we still saw those engines and I heard the same noise, a co-worker told me it was a loose exh valve seat. Quote Link to comment https://www.bigmacktrucks.com/topic/52753-misfire-on-deceleration/#findComment-393814 Share on other sites More sharing options...
Rob Posted March 10, 2018 Share Posted March 10, 2018 You are correct but the loose exhaust valve seats did not hold up long before breaking and the engine most times had a definite miss during all rpm's. An overhead run and compression check is first order of business. It almost sounds as if the solenoids for the "Dynatard", (if equipped) are "hot" all the time rather than selectable via a toggle switch on the dash. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/52753-misfire-on-deceleration/#findComment-393815 Share on other sites More sharing options...
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