# CAV injection pump debacle ...



## chris scott (Sep 20, 2019)

Hi Folks, Chris Scott in Bowling Green KY here ... Just got an 87 3910 (diesel) and catching up on a bunch of deferred maintenance. It WAS running fine.

So, I'm noticing the oil level is very high and seems thin. Looks to me that the only way that can happen is the front seal on the CAV pump. So I get the kit and replace the seal. Easy.
I figure while I'm at it might as well replace the vanes and "O" ring on the other side of the pump. Easy.
Growing increasingly more confident, I decide to disassemble and clean the inlet valve / regulator ...
So I carefully record the pieces as I pull them out, clean and replace. Easy.
Except now it no longer works. I filled it with diesel into the side plate opening, then placed a temporary cover over the hole with rubber gasket. Then I started dribbling fuel into the intake as I turned the shaft clockwise (looking at it from the shaft side.) It sucks down the fuel, but I cannot make the 3 injector outlets squirt. If I open the bleed port on the pump body it does squirt.
So, digging further and checking my parts sequence against an online drawing, I see I don't have the piston at the bottom (#7 in the drawing.) Can anyone tell me where I can get one or at least the material and precise size so I can machine one?

Signed,

I really stepped in it this time.


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## chris scott (Sep 20, 2019)

As I last reported, I thought I lost the piston / plunger somewhere. So I emailed pumpguysc, and he asked the obvious: "It's not stuck in the sleeve is it?" I admitted that I did not fully understand how the regulator worked, and didn't know if the sleeve was supposed to be completely hollow. Apparently it is, and my piston was really stuck in the middle of it. Light tapping wouldn't budge it. I arbor pressed it out, and both the piston and the sleeve bore were really gummed up. I soaked them in Hoppe's #9 and cleaned them up, and now the piston slides freely in the bore. Now to reassemble and test!

Thanks pumpguysc!


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## chris scott (Sep 20, 2019)

Well, it pumps out the body bleed screw a bunch, but not a drop to the injector pipes. It's looking like I'm going to have to send it to Mike...


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## thepumpguysc (Jan 25, 2015)

Looking forward to it..


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## chris scott (Sep 20, 2019)

Well, it's on the way back from Mike - he found a huge amount of debris and gum inside.

Question: My 3910 fuel line plumbing (tank / filter / pump input) appears to be 5/16" steel tube with what looks like a slight flare and a brass flare nut sucking the joint together. BUT it has a thick rubber washer in the nut. Nobody locally has any clue what it is or where to get it - anybody know?


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## oldmanfarmer (Mar 24, 2016)

chris scott said:


> Well, it's on the way back from Mike - he found a huge amount of debris and gum inside.
> 
> Question: My 3910 fuel line plumbing (tank / filter / pump input) appears to be 5/16" steel tube with what looks like a slight flare and a brass flare nut sucking the joint together. BUT it has a thick rubber washer in the nut. Nobody locally has any clue what it is or where to get it - anybody know?



I replaced mine and got the part from "Derby State Equipment" in Richmond Ky. Also "Messicks" have it.

Good luck.


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## thepumpguysc (Jan 25, 2015)

New "olives" will come back w/ the pump..


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## chris scott (Sep 20, 2019)

So, what would I call these "Olive" connectors?


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## chris scott (Sep 20, 2019)

Got my pump back today!


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## thepumpguysc (Jan 25, 2015)

Don't forget.. MAKE SURE that side cover valve opens & closes{spring loaded}
& put it on before trying to start.. otherwise the fuel pressure will equalize inside the pump..
No fuel out, means no fuel in..


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## chris scott (Sep 20, 2019)

In an effort to follow up and let all know of my eventual outcome, Refurbed the tank, cleaned the fuel lines, new filter, thepumpguysc rebuilt injector pump, new injector lines and injectors. Today she started and seems to run well!


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## thepumpguysc (Jan 25, 2015)

That sounds like a winner.. Thanks for the update..
Glad I could help.. Happy Tractoring..


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## chris scott (Sep 20, 2019)

The idle sounds weird to me, like the governor is hunting. I momentarily loosened each of the injector feeds and all caused the same rough, so I know all cylinders are firing ... you can hear it and watch the exhaust closer here. Is this normal?


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## chris scott (Sep 20, 2019)

So, I've tried individually loosening injector feeds, and each produces the same rough effect. So it's not just running on 2 cylinders. I measured compression at 400-400-350. Is that compression discrepancy enough to cause the rough idle in a diesel?


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## chris scott (Sep 20, 2019)

Note to self: If you spray oil into the diesel cylinder to check for ring blow-by, when you crank it, it may ignite and blow out the check valved in the tester...

Results are inconclusive. Without check valve in tester gauge all cylinders seem to peak at 350.

Going to send injectors to thepumpguysc. It seems that you can't mix-n-match them.


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## FredM (Nov 18, 2015)

The engine sounds like it is idling too low, did you try increasing the idle a little to see if this made a difference ?, and did you increase the engine revs to high idle to see if it was still running rough?.


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## thepumpguysc (Jan 25, 2015)

Lol.. Fred.. EXACT SAME thing I said..!!{PM} He said it clears up around 1800.. THATS abit to hi..lol
Upon further emails back & forth, I found he bought injectors off the web & a single nozzle..
I'm gonna get the old & new injectors & nozzles & see if I can make a decent CORRECT set..
Stand-by & we'll see how this pans out..


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## FredM (Nov 18, 2015)

thepumpguysc said:


> Lol.. Fred.. EXACT SAME thing I said..!!{PM} He said it clears up around 1800.. THATS abit to hi..lol
> Upon further emails back & forth, I found he bought injectors off the web & a single nozzle..
> I'm gonna get the old & new injectors & nozzles & see if I can make a decent CORRECT set..
> Stand-by & we'll see how this pans out..


Good thing you are on this forum pump guy, will sit back and await your findings.


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## thepumpguysc (Jan 25, 2015)

I have all the injectors, I think.. I haven't opened the box yet..
I'll report my findings..


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## thepumpguysc (Jan 25, 2015)

Just an update.. I hope Chris doesn't mind.. & it'll help others that go down the same path..
He bought 3 complete injectors of the web.. THATS what we saw in the video..
The injectors have the wrong tips in them for a 3910 tractor.. & were set at the wrong pressure.. 1 was stuck, 1 opened at 5000psi & 1 opened at 4000psi..
Anybody wanna guess what the opening pressure IS SUPPOSED TO BE with the correct tip.?? 2683psi.!!{2650-2700}
Its no wonder he couldn't get the "studder" out of it.!!
My poor pump was pumping its azz off trying to open those injectors..Lol
I hope to get'm going soon..
So buyer beware when using the ol' interweb to get injectors..


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## chris scott (Sep 20, 2019)

Thanks thepumpguysc! Installed my freshly tuned injectors today and the engine runs smooth. Starts easy too.


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## thepumpguysc (Jan 25, 2015)

That's GREAT news.. AND u have 2 spares..


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