Oil & Fuel 1986 JD bogs down under load (help)

   / 1986 JD bogs down under load (help) #1  

lennypoulin

New member
Joined
Apr 19, 2017
Messages
13
Location
North Brookfield, MA
Tractor
JD 855
My 1986 old faithful JD bogs under load and I now I can’t do much with it. The problem evolved slowly over a couple of years and I compensated running at higher rpms, then running in low range, while looking to solve problem. I’ve done the following:
- checked all fuel lines, replacing as needed
- removed and cleaned the fuel tank
- changed the fuel filter a few times, replaced the air filter
- the electric fuel pumps seems to pump just fine
- removed the fuel injectors, completely disassembled, inspected, cleaned, reinstalled since all looked perfect to me. This did solve for the engine running a bit rough when cold

I don’t know anything about the fuel injector pump or how to test. When I had the lines off and engaged the starter motor, fuel would bobble out of the fuel injector pump consistently.
I am at a loss for what to do next. Suggestions?
 
   / 1986 JD bogs down under load (help) #2  
It will be a bit of work but you could run a compression check.
Also depending upon your dealer an hours dyno time and tune could be beneficial.
The last and most expensive way would be to replace the pump.
 
   / 1986 JD bogs down under load (help) #3  
Is there a company in your area that can test the injectors? If they are not spraying properly they could cause low power

another thing to check is valve lash. If this is happening as engine gets warm could be one of the valves is being held slightly open reducing compression
 
   / 1986 JD bogs down under load (help)
  • Thread Starter
#4  
It will be a bit of work but you could run a compression check.
Also depending upon your dealer an hours dyno time and tune could be beneficial.
The last and most expensive way would be to replace the pump.
Thanks for the idea, there are no nearby dealers in my area, and before I replace the fuel injector pump, I want to find out how to test it.
 
   / 1986 JD bogs down under load (help)
  • Thread Starter
#5  
Is there a company in your area that can test the injectors? If they are not spraying properly they could cause low power

another thing to check is valve lash. If this is happening as engine gets warm could be one of the valves is being held slightly open reducing compression
I couldn’t find a shop who could test the injectors. Today I read a post where the guy removed the injectors from the engine, then reattached the lines to let the tractor and the fuel injector pump do the “test” . If there’s a good spray, inject and pump should be good. I’m going to try that!
I’m handy but not a mechanic, how do you check valve lash?
Thx…
 
   / 1986 JD bogs down under load (help) #6  
I couldn’t find a shop who could test the injectors. Today I read a post where the guy removed the injectors from the engine, then reattached the lines to let the tractor and the fuel injector pump do the “test” . If there’s a good spray, inject and pump should be good. I’m going to try that!
I’m handy but not a mechanic, how do you check valve lash?
Thx…
You checked and replaced a lot of components but I would remove the supply line to the injection pump (IP) and check for fuel flow to the pump. It's possible that there is crud in the filter head, or in a fitting in the fuel delivery system that is restricting flow. You may have to crank the engine to make the lift pump work. Some lift pumps have screens on them and they can clog. Some IP's have a screen at the inlet. Before you start messing around with the IP make absolutely sure that the fuel delivery system is not restricted. You should see fuel pouring out of the fuel discharge line like a cow peein' on a flat rock!
 
   / 1986 JD bogs down under load (help) #7  
Injectors need to be tested to determine if the valve inside injector opens at correct PSI & that spray pattern is correct.

Have you checked to be sure fuel tank is venting allowing air to enter tank as fuel is leaving when engine is operating?
 
   / 1986 JD bogs down under load (help) #8  
I agree, make sure the fuel flow to the main injector pump is good.

I cringe when I hear people take injectors apart. If your engine is not a high pressure common rail, the injectors aren’t that delicate but it takes an expert with the right equipment to mess with injectors and test them.

There are so many things that could cause your problem, valve lash, injectors, a plugged fuel flow, main injector pump, low compression etc. it’s tough to diagnose. How many hours on the machine?
 
   / 1986 JD bogs down under load (help) #9  
Sounds like you have a clogged screen somewhere. Did you see one inside the tank? Just because an electric pump makes noise does not mean it is pumping. Went through same thing with my dad. I took them off and put in a pan of fuel and they made a pumping noise but no pumping action. There is a 68 model Deere here, man ran 1000 head cattle with it. Pump never been off of it. I have a 58, pump never been off. Sounds like restriction or supply problem. If your valve lash is off it gets more clearance, not less. It won't keep a valve open longer, but keep it closed longer. You check it with feeler gauges between the valve stem and rocker arm tip. Never hurts to run the rail and check valve clearances. Probably in your scheduled maintenance to do it ever so often. I'd still check for a suction screen or tank sock.
 
   / 1986 JD bogs down under load (help) #10  
Injectors spray a high pressure mist of fuel. In no way is that a safe task. Not to mention, subjective if you just viewing with the naked eye.

Before you do anything call D&W in Oxford. They may be able to test your injectors and pump for you.
 

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