237 bucking/ very sensitive throttle

[b61fred]

Hi,

 Have 237 in a B61 ever since I installed the 237 it has had a problem with the throttle bucking when you are lightly adding fuel. I removed the injection pump and had the governor repaired. It was better when I got it back but still not like it should be. The driveline has some slop but I don’t think that’s the problem, it didn’t do it with the 673 and everything is the same other than the engine. I’ve read about maybe a throttle lever issue with the spring being weak, I think that’s my next step. This makes the truck hard to drive and not much fun either. The linkage looks good and the cab is tight on the frame. If I give it full throttle it runs smooth. Any ideas?

very Respectfully,

Morgan

 

[doubleclutchinweasel]

In all gears, or just in low?

[b61fred]

It will do it in all gears. Light throttle what I would call “tip in” from a deceleration. 

[MACKS]

Sounds like u have the wrong springs on you linkage,is it worse when your on a bumpy road..

 

[fjh]

Throttle lever break over spring is  worn  replace the lever!

[b61fred]

That was my next move! I will look into that.

Thanks

 

[Freightrain]

On 5/18/2023 at 9:17 AM, fjh said:

Throttle lever break over spring is  worn  replace the lever!

I know the throttle is actually sprung wide open and the large return spring returns it back to idle.  I know this because the big spring broke one day and awwwwaay I went!!!  Until I pulled the shut down.

What exactly are you referring to?  The little box on the side that has the linkage arm sticking out?

[Mark T]

8 minutes ago, Freightrain said:

I know the throttle is actually sprung wide open and the large return spring returns it back to idle.  I know this because the big spring broke one day and awwwwaay I went!!!  Until I pulled the shut down.

What exactly are you referring to?  The little box on the side that has the linkage arm sticking out?

The throttle shaft where it comes out of the governor. There's a lever ( serrated to go on the shaft and often has a 1/4" pinch bolt )  it has a spring in it that is strong enough to move the throttle shaft, but when the shaft rotates it's full travel the lever " breaks " so you're not still twisting the shaft. It's made with a spring to buffer that point of full throttle and linkage travel. 

[b61fred]

Update:

    I removed the throttle arm on the outside of the pump. Inspected for an overly weak spring in the break over portion of the lever. Seems to me that it is very stiff, probably not the issue on this unit. I checked the linkage for any sign of binding and I changed the return spring to a lighter one and a heavier one and it seem to do slightly better with the heavier unit. I believe this could be that when the engine starts surging, it makes the whole truck surge including my foot on the accelerator. The heavy spring dampened that. The governor has new pins and bushings so that should not be a problem. This is an APE pump, is there a damper spring for the governor adjustment or any other ideas would be welcome. If any one would have and old injection pump that they would part with I’m in the market, my pump seems good it’s the governor portion I’m looking for.

[Mark T]

Is the puff limiter by any chance disconnected ?

[b61fred]

Yes, all the extras have been removed

[Mark T]

🤷‍♂️   might be the problem

[fjh]

1 hour ago, b61fred said:

Update:

    I removed the throttle arm on the outside of the pump. Inspected for an overly weak spring in the break over portion of the lever. Seems to me that it is very stiff, probably not the issue on this unit. I checked the linkage for any sign of binding and I changed the return spring to a lighter one and a heavier one and it seem to do slightly better with the heavier unit. I believe this could be that when the engine starts surging, it makes the whole truck surge including my foot on the accelerator. The heavy spring dampened that. The governor has new pins and bushings so that should not be a problem. This is an APE pump, is there a damper spring for the governor adjustment or any other ideas would be welcome. If any one would have and old injection pump that they would part with I’m in the market, my pump seems good it’s the governor portion I’m looking for.

Any gap or slight moment  on the beakover lever between the two pieces will cause a surge! Just saying! Also does the  idle vary with the  truck facing up hill or down if this is evident it could be general wear inside the pump! also there are two springs inside the governor that control speed a big and a small and if there is a small gap between them it can also surge! Those shims are behind the the round cap 4 bolts at the back of the pump! You say the pump pins ect were new was the pump rebuilt or just the governor part?

[Mark T]

Lever's not on backwards ?   Should be going to the spring part (break) at full throttle .

[b61fred]

The lever breaks over both ways. And no slop at all. 
 

  Can I take the top cover off the governor and run the engine or will oil go absolutely everywhere?

  The injection part of the pump checked out to be healthy all the work was in the governor. 
 

When the engine first starts it will surge for a little bit and then level out. If you pull the throttle knob out to raise the idle it is smooth. As it warms the idle will surge less.

Im starting to think there must me some slop somewhere!

[Mark T]

I'm grasp'n at straws here (lol)   Just sometimes easy stuff gets overlooked .  I've seen trucks with the puff limiter disconnected do this. Maybe it's because of some other underlying issue in the governor, but it'll do it. Then once it starts, and you get bounced around  because of it, it amplifies it all.  These things are old, who knows what could be worn by now, and guys familiar with them to make a repair are becoming a scarcity .

[b61fred]

I’m going to try some more tests this afternoon. Maybe I can find a smoking gun somewhere!

[mrsmackpaul]

How high is your idle set ??

If the idle is to low they sort of chase their tail trying to maintain low rpm at a constant 

I feel idle should be at a guess between 650 and 700, no doubt someone on here quote the correct figure 

And another thing I have found is if compression is down on a couple of cylinders and a valve job is needed, can make them hunt really bad especially if the the cylinders are following each other

 

Paul

 

[b61fred]

Paul,

base engine on this truck is in excellent shape. Got it from Rob several years ago. The story goes that it was rebuilt but the truck rusted down around it. I but it in old “aunt B” to see how well it would run. The engine would not hold valve adjustment. To find out it was eating the cam shaft. Pulled the engine and replaced the cam and lifters. Ron Bogan to the rescue there! Had the pump worked on at that point. Put it all together and it still did the jerking around thing but when I had it down and after it’s all back together I performed compression test and it was very even and don’t remember the spec now but at the time looked it up and it was in spec. It doesn’t use oil and there is no blow by so I think is good there. I could have the idle down too low  and I will buy that for the idle quality issue. I need to pinpoint the jerky light throttle issue. I have the manual for the pump, could the puff limiter on the end of the rack cause an issue? I think my old engine just had a short plug in there. I’m going to take the governor cover off and look for loose stuff…

[mrsmackpaul]

Dunno about the puff limiter causing issues as I keep everything set stock standard

All E6 Mack motors I have driven with low ratio diffs hunt quite a bit in first gear and deep reduction with the foot just on the throttle 

I dunno why, I have asked and been told it is very common as the governor try's to hold revs and over compensates and then over corrects

If I put the foot down a little further it helps and if I shift up a gear ot helps 

I'm not sure if this is the same issue you have or not even close 

 

 

Paul

 

[b61fred]

It is quite violent! 
 

it will do it at around 20mph.

 

[terry]

Not sucking a little air somewhere is it?    terry

[b61fred]

Took the cover on the governor off. Started the truck and ran pretty smoothly for a bit. Then the rack started to move a bit and then it got more and more. I grabbed the rack and physically held it in one position and the truck idled better than it has ever done. No wavering in the idle at all. Put it back together and I noticed that it has a wavering at 55 mph, I never thought too much about it but I can hear it in the exhaust. The linkage seem pretty floppy in there, I think that is where the gremlin is hiding. I don’t think it’s sucking air because the idle snaps down when I shift really quickly, every one that I worked on would have a slow return to idle. 

[h67st]

One thing I've heard said on here is to get the truck on a hill (up or down) and see if the idle surges; if it smooths out when on a slope then the problem is in your governor.

[Freightrain]

On 5/21/2023 at 5:23 PM, b61fred said:

It is quite violent! 
 

it will do it at around 20mph.

 

Lucky mine isn't violent.  Just feel and hear the exhaust note surging as I try to hold a steady speed with little throttle application.  Heavy load, no issue.