# 6 cylinder running rough and hot on 3&4



## Jay Evans (May 28, 2018)

HI, I'm new here. I have green (3255) and yellow JD equipment and need some help on a backhoe as I'm out of ideas. 1998 JD 710D. Really nice backhoe, but suddenly it runs rough and smokes grey smoke and has no power. If I shut it off for a short time, it runs fine again, even though it is still hot, for 5 to 90 minutes. I've been through EVERYTHING. Rebuilt pump, new injectors, new lines, lift pump, everything. No air in lines, no clogged filters. Checked valve lash. No blowby, doesn't run hot.

I *did* note one interesting thing, perhaps it will shed some light to you guys.
The measured temps, from 1 to 6 on the exhaust manifold, are normally 190, 210, 230, 235, 210, 195.
BUT, when the roughness occurs, the temps are 190, 210, *310, 315*, 210 and 195! The center 3 and 4 exhaust goes up 80+ degrees!!! I did this several times and each time it registered 65-80 degrees hotter as soon as the missing started. Once time passed, usually while I was changing a line or something and I restarted, it was smooth until at some point, from 15 to 60 minutes later and always at a low RPM setting, the missing and roughness starts again.

Has anyone experienced this, what is causeing the heat and rough running?

Is there any scenario where the injector pump ( even off a fresh rebuild) might cause this? It still seems like a pump with something loose or floating around. I'm thinking excess unburned fuel is going into the manifold and igniting from heat.

Thank you, just starting to hay and don't need this headache too.


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## mlappin (Jun 25, 2009)

I've had supposedly rebuilt and bench tested injection pumps have to come right back out and go back. Usually it's on the 3208 Cats. Either they have absolutely no power and no smoke, or under the slightest load it looks like a stack of car tires on fire from all the black smoke rolling. Most of the time if the pumps are good on a NA 3208 you can bog em WAY down and barely if any black smoke.

It seems like it shouldn't be the pump if it was rebuilt and is the same issue unless the shop actually rebuilt the pump instead of exchanging it and they missed whatever was wrong on 3 and 4.


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## somedevildawg (Jun 20, 2011)

Have you checked the valves....
Oops, just re-read.....


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## SCtrailrider (May 1, 2016)

Sure sounds like a bad IP to me... new or rebuilt doesn't mean it's a good one.... where did you get or have the pump built and was it doing this before you replaced the pump...


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## slowzuki (Mar 8, 2011)

That injection pump needs to be flowed. I don’t know inline pumps well but I believe there is a flow adjustment per cylinder when they bench them. If that is fluctuating maybe a discharge valve on those cylinders was sticking or leaking when they set it up.


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## StxPecans (Mar 3, 2018)

When injectors were removed did you pressurize the cylinders? Not sure about that engine but have seen this one a few and 3208 cat comes to mind where fire ring is blown on headgasket letting pressure go from on cylinder to the other. Will nit cause blowby but will cause a miss on those two and will increase cylinder temps as it effects scavenging. Sometimes accompanied with popping sounds in exhuast or intake(with intake tubing off). By pressurizing cylinder i mean remove injector and put a rubberized air nozzle in hole with cylinder position in the begining of the power stroke. Should either push cylinder down or hold air pressure for a couple of seconds. You will know real fast if its leaking.

With engine misses I always check fuel pressure,then filters , then isolate the cylinder ( either by electrical means or temp or cracking a line) check valve lash and inspect cam lobes,then I remove injector and pressurize cylinder. If mechanicalinjection like yours I may also put a sightglass on return fuel line and check for combustion. Then after that I would take the injector to the test bench.

Grey funny smelling exhuast is normally incorrect fuel mixture/ Air supply issue to cylinder more so air delivery to cylinder like vavles or such. Black smoke along with a fuel knock would indicate too much or improperly atotomized fuel.


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## NebTrac (Aug 12, 2014)

Don't know if this applies to you or not, but it would be an easy check.

Had a mechanic/farmer buddy of mine read your post and he said he had a Massey Combine do that one time and it ended up being the fuel cap.

He said "The mechanical pump sucked so good it put the tank into a vacuum." Said they fought it for a long time before he figured it out.

Hope you get it fixed and I'd like to hear what the fix is.

Troy


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## slowzuki (Mar 8, 2011)

So its not an inline pump I see but a rotary. Have you rechecked the return line for clogs/free return to the tank? This pump likes to puke bits of a governor dampening ring into the return line and it really messes up operation.


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## Gearclash (Nov 25, 2010)

That disintegrating damper problem will affect all cylinders, not just a few. If this is a rotary pump chances are it’s not a pump problem.


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## Gearclash (Nov 25, 2010)

I’m going to guess the injectors are sticking open on those cylinders. Were these reman injectors or aftermarket new?


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## 8350HiTech (Jul 26, 2013)

Gearclash said:


> I'm going to guess the injectors are sticking open on those cylinders. Were these reman injectors or aftermarket new?


If that's the problem, it would be easy to switch them to different cylinders and see if the problem stays with them or stays in the 3 and 4 holes.


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## slowzuki (Mar 8, 2011)

True, I'm just not familiar with an injector problem that comes and goes on two injectors simultaneously.



Gearclash said:


> That disintegrating damper problem will affect all cylinders, not just a few. If this is a rotary pump chances are it's not a pump problem.


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## Gearclash (Nov 25, 2010)

I would try a lubricity improving fuel additive. Stanadyne markets one, plain ole 2 stroke oil might help too.


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## Jerry/MT (Dec 14, 2017)

The intermittency is what puzzles me.

Leaking injectors on affected cylinders? Fix 'em before they burn the piston crowns.


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## somedevildawg (Jun 20, 2011)

Welcome to haytalk Jerry in Montana.....


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## Jerry/MT (Dec 14, 2017)

Thanks for the welcome somedevildawg! Lots of knowledgeable folks on this site.


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## SCtrailrider (May 1, 2016)

Any updates here??? Did ya figure it out??


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