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Ever had this happen??

PostPosted: Sun Aug 04, 2019 9:29 pm
Front cover
Well here it is one week before the show, and ‘old Stick Mixer’has thrown my mind into a tail spin... and I am throwing this out there for discussion and advise .
So far , the usual suspects have been consulted, and I still can’t fully understand what happened.

The story begins like this....
I have a NTC 290 cummins in the truck, and have had very good luck with it since install.
Since install about 4 years ago I have only put 2000 miles or less on it.

I have put about 150 miles on it so far this season with no problems,
Last Friday I developed a fuel leak out of the throttle control arm shaft.
The cummins PT pump is a AFC type. I figure it is just a seal or oring and no big deal.

I got the seals and gaskets, removed the pump and cleaned it up.
To get the shaft out you need to remove the front cover where the drive coupling is mounted.

I split the pump at this point, about 2 pints of fuel comes out of this cavity that has the drive coupling to the gear pump and the governor flyweights.also the governor plunger.

I remove this carefully to not loose any parts.
I remove the eclip holding the throttle shaft and slide it out, and find debris under oring and shaft a bit scored , but usable.
Install the new oring , reinstall shaft, eclip and replace cover.

Reinstall pump, ( remove pipe plug in top of pump and add fuel), I say pipe plug because there is also a slotted screw thst is the cover for the wire screen, I did not fill through that.

Hook all lines and control linkage.

Start up, truck fires right up , let idle about 5 mins.
Notice idle is about 850/900 which is high .
I wrap the throttle a couple of times, throttle response is there but still 850/900.

Maybe my linkage is out of adjust ment ????

The truck is still running at this point ( idle)....
Then all hell broke loose the throttle went to full open and then some .. like a Detroit diesel runaway!!! ( was thinking the pistons are going to go through the block)
I had no response at linkage... so within second I got back to cab turned key off and it shut it down.

I took pump back off and apart and found governor plunger / flyweight drive laying in the bottom. And the plunger jammed stuck in the bore.

I never made any adjustment to any setting or screws on disassembly or assembly.
I never removed governor spring at the back of the pump.

Anybody ever had a Cummins way over rev like this.????

Hoping to get a pump this week... just hope it is the pump and not larger collateral damage!!!

Re: Ever had this happen??

PostPosted: Sun Aug 04, 2019 9:40 pm
Oh yeah... forgot to add...
Yes I know I could have misaligned the drive tab on the flyweight, but if it popped out I would assume ( I said assume) the other governor spring would have not let it come off idle...
Then I also said it jammed the governor plunger IN... which would have put the plunger lobe over the governed fuel port which should have limited how high the rpms went.

Or ... and this is why I am asking... do I have this all wrong.??

Live and learn... we all learn from our mistakes.

Thanks to anyone that can help clarify this for me.

Stretch 8)

Re: Ever had this happen??

PostPosted: Mon Aug 05, 2019 5:01 pm
Got a good lesson from a local pump shop.

The obvious cause was the governor flyweight to governor plunger shaft being misaligned.
Other than that...doing the shaft seal was a easy fix.

With the governor plunger stuck and no resistance to the governor and idle springs .. unlimited fuel is supplied to the pump...thus the over rev.

I plan to bring the pump to the show, so if anyone is interested I will certainly share my painful learning lesson.

Stretch 8)

Re: Ever had this happen??

PostPosted: Mon Aug 05, 2019 10:09 pm
by stubnosebrock
Ugh, what a pain. Glad you got it figured out

Re: Ever had this happen??

PostPosted: Tue Aug 06, 2019 6:08 am
by oldspwr
Good deal Stretch, looking forward to this weekend!!!

Re: Ever had this happen??

PostPosted: Wed Aug 07, 2019 8:46 pm
Further development..

Important must read:::
If you ever get a takeoff pump or one that has been sitting...
DO NOT just hook up and go.

To get my truck going we tried a takeoff pump from a similar hp engine.
Checked the tags... should be good to go.

Well...? Strike two...
I put the pump on, flushed with clean fuel and hooked up.
Same result... engine idled a second or two then full bore!!!

Any guesses :?: :?: :?

Yep stuck governor plunger... old fuel and time.. water
Governor plunger after removal

So cleaned this up, had to get a driver t for plunger.
Cleaned up

Just got it back together... maybe not perfect running
But still hope to be at the big show.


In closing... I have to give a big thanks to the guys who helped me with this.
Being a part of this Brockway group is a great thing and there are people out there that will help you!
We all learn together .! Thanks guys!!!

Stretch 8)

Re: Ever had this happen??

PostPosted: Thu Aug 08, 2019 8:59 am
by oldspwr
Hey Stretch...

Do you think you may have some air in the system? When I replaced the pump on the 270 in the 68 360 it took me a while to bleed all the air out of the system.