Kind of weird running E6

[Ryon Hess]

Been driving this MH 613 E6 350 a couple weeks now and maybe I didn’t notice at first but lately after it warms up, or when it idles a while after driving, or after correcting itself then the air dryer purging causes engine to start a kind of rise/cycling down up sound that shows a slight drop in oil pressure than directly back up. fuel pump governor? Or maybe air dryer related? anybody encounter this or have any thoughts? They’d be appreciated. Y’all dudes been behind these Mack’s so long you’re a great resource for narrowing things down rather than a random shop 

[terry]

Maybe when the air compressor kicks in slows the engine slightly?  Terry

[Ryon Hess]

6 hours ago, terry said:

Maybe when the air compressor kicks in slows the engine slightly?  Terry

Yeah but it begins cycling after like down and up that shows from 33psi and at idle time down to 30 up to then down every few seconds then stopsq for minutes until compressor purges then it starts again. If i rev accelerator it goes away for a while sometimes or after driving gone for a while or when truck starts engine sounds great until air pressure builds and air tank releases air then it begins. 

Edited May 30, 2023 by Ryon Hess

[Ryon Hess]

Funny because like 4 noticeable days of this happening. Today it has sounded great near best ever for hours. 

[Joey Mack]

Do you have an air powered throttle?

[Ryon Hess]

11 hours ago, Joey Mack said:

Do you have an air powered throttle?

Had truck a couple weeks and actually not sure but it looks like air throttle was only factory installed in E9 and some CHs around year 2000

[Joey Mack]

🤔

[fjh]

So when the the compressor runs it puts some load on the engine! This helps hold the engine at a stable rpm! When the compressor unloads and the air drier purges operated by the governor on the compressor s the engine now has no work to do! So wear on governor parts linkages lets the rack float in the loose zone and varie rpm’s 50 or so rpm ! Just my thoughts on it!

simple wear and tare!

 

[mrsmackpaul]

Air throttle was fitted to some E6 macks in Australia 

800 and something the Australian Army had or still have

Hunting like this is pretty standard I feel when the compressor is pumping 

The oil pressure will be a bit unstable at low revs as the governor chases the engine up a down

Paul

[Joey Mack]

I swear I worked on some MR's and LE's  with an air throttle..  I just figured it was a cab over thing..  However,  I am away from those trucks for many years now...   

[Full Floater]

I notice this on all my Mack E6's.  The gov springs in general seem to be a weak link on these and can be very touchy.  I bet the slight load, or lack there of it when the compressor is off, throw the gov springs off slightly.  

I wouldn't worry about it much, although it can be a bit annoying.   

 

But hey, it's way better then a new truck with a check engine light

[Ryon Hess]

4 hours ago, Full Floater said:

I notice this on all my Mack E6's.  The gov springs in general seem to be a weak link on these and can be very touchy.  I bet the slight load, or lack there of it when the compressor is off, throw the gov springs off slightly.  

I wouldn't worry about it much, although it can be a bit annoying.   

 

But hey, it's way better then a new truck with a check engine light

Interesting, good info. Thanks, E6 is new to me.
Ohh yeah, definitely agree.. beats a check engine light 😂