JD 450 missing at idle

brainsboy · Jan 30, 2015

I bought a john deere 450 bulldozer 1970 model with a 4219 diesel engine. The dozer must of sat for a few years because all the steering clutches were stuck and had to be rebuilt. Originally the gas smelled like old fuel and the exhaust would burn your eyes, so I went though the dozer and replaced everything I could. All hoses, fluids, filters, gauges, wiring have been replaced. This includes draining old fuel. The dozer runs great except for when it idles, I can hear a miss. The miss isn't too bad, just sounds like when a gas motor has a bad wire. I wouldn't swear to it, but I believe it may be worse after its warms up. Any ideas where I should start checking for something like this?

thanks

Dieseltech · Jan 30, 2015

Would be a good idea to check the valve clearance. If that's ok you may have a pitted valve face and seat that's leaking compression, can usually hear that while cranking with the fuel off, a steady hiss at the exhaust. There may also be a worn pencil injector allowing too much return fuel caused by excessive needle piston clearance. If you pull the injectors for testing that would be a good time for a compression test too.

JDemaris · Jan 31, 2015

Quick guess would be an injector. When worn
they work worse at low speed then at high
speeds. With the engine idling, just crack one
injector line loose at a time and see if the
idle speed changes. Just like you'd pull one
plug wire off at a time on a gas engine to
diagnose. If you located the weak or dead
cylinder -try swapping in a new injector. I
suggest you get yourself a new $30 injector
before trying to remove an old one. They can
get awful stuck and you might ruin what you
have getting it out.
If valves are too tight - engine can run
smooth and fine at high speeds, but develop a
low speed miss and be very hard to start.
For the injection pump - since it is a rotary
distributor pump - it is just about impossible
to get a skip on one cylinder. That being said,
a scratch in the head/rotor or a chip on a cam-
ramp can do it. I've only seen it happen maybe
twice in my life.

brainsboy · Feb 7, 2015

I installed 4 new injectors, no change in idle miss. I checked all valves which were all loose to .014int and .018exh. I did however try adjusting the injection pump by turning it in either direction. one direction made no difference but if I turned it counter clock wise enough the miss changes from a high tinging miss now and then to a deeper tone which you almost cant hear. Not sure if this is fixing the problem or masking it. Im guessing at this point I need to take the head off. I noticed a lot of white oil on bottom of valve cover and the rocker arms are real rusty, also in the valleys on the head its full of white oil, looks like white lithium grease. The dip stick oil looks fine, and radiator level hasent gone down, but smells like someone added in about a crap load of liquid block seal. I don't think the water in oil and idle miss are related but I think Im going to have to do an in frame now.

Harveylogging · Apr 12, 2024

Ever figure it out??

JD 450 missing at idle

brainsboy

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Dieseltech

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JDemaris

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brainsboy

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Harveylogging

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