I have recently purchased a mid 80s JD 750. A little history is that I bought it off of a friend and the fuel filters have probably never been changed and theres a leak in the gas cap that has allowed water to enter tank for who knows how long. Runs great for 20 minutes and then has misfire and power loss with light blue smoke. Tractor is not running hot or using coolant so Ive ruled out head gasket for now. Drained tank, cleaned, fresh diesel , and fuel treatment. Took injectors out, cleaned and put back in. I noticed that there is no fuel recirculating from the injectors to the tank. My thought is that everything is good until the injectors get too hot due to no fuel circulating to keep them cool, hence causing fuel starvation and poor running. My thought is the injector pump is weak due to poor previous maintenance not producing enough pressure to recirculate fuel. Any thoughts before I try replacing the injector pump?
- Thread starter RichSiri
- Start date
wore out
Well-known Member
Even when all is working properly VERY little fuel is returned from the injectors in this engine, certainly not enough to "cool" them.
I would GUESS you have some sort of fuel supply restriction, is the fill cap properly vented?
There may be an issue with a rubber fuel hose or with the little fuel filter unit they used.
Whoa!
IMHO replacing an injector pump should be last resort.
This tractor should have a thermostart valve and tank in the return lines between the injectors and the fuel tank. Possible problem with this valve?? See if fuel is returning to the thermostart tank. Possibly valve is stuck open, dumping return into manifold??, thus none getting back to fuel tank??
Dieseltech
Well-known Member
- Location
- Akron, Indiana
As already mentioned, CORRECTLY working injectors pass very little return fuel..
I agree with jimtrs. My first guess was the thermostart is stuck open. There's a test for this on page 30-10-20 of the manual. But if the return/leak-off lines are not returning any fuel, then I would think nozzles are not working right/leaking? There's not a lot of flow in these return lines, but it should not be zero.
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