If you have a diesel engine, which you do, it will have a fuel pump.
![790188]()
JD 790 with fuel problem
First post - So my Great Grandfather owns a jd 790, while driving in gear anything above 1st high the rpm randomly drops down to 750 ( Normally you run it at about 1500 rpm )and if you don't put it into neutral it stalls sometimes even in neutral we have narrowed in down to a fuel problem and past the fuel filter, this is a older year so it doesn't have a fuel pump, anyone have any idea what could be the problem?
1 - 7 of 7 Posts
At a guess, since it's an intermittent problem you might look at the fuel in the tank. I don't know if there is a strainer but those can get debris on them and plug up. When the engine shuts down the debris falls off until it gets sucked across the strainer again. We had that happen on a IH and it drove us nuts until we finally disconnected the fuel line and pulled the strainer.
Another possibility is a small pin hole in a fuel line that lets air get sucked in when the vacuum is high enough. Then of course, there is at least one pump- the injector pump and most likely a lift pump to supply the injector pump. I'd start at the tank and make sure everything is good at each step. My 790 has the tank on top and I'd probably empty it, take it off and make absolutely sure there was no debris in it. Then clean the strainger, disconnect the lines to the filter and blow compressed air through them. I might plug that line and pull a vacuum to see if it held. If not, there's a pinhole in the line. Follow a similar process from the tank to the injector pump to make sure it's all good to that pump. If that doesn't fix the issue you could have an injector pump issue at which point some specialized tools are required just to test it. Probably would mean a visit to the dealer. I doubt it's the injector pump and I think you can find the problem.
Treefarmer
Another possibility is a small pin hole in a fuel line that lets air get sucked in when the vacuum is high enough. Then of course, there is at least one pump- the injector pump and most likely a lift pump to supply the injector pump. I'd start at the tank and make sure everything is good at each step. My 790 has the tank on top and I'd probably empty it, take it off and make absolutely sure there was no debris in it. Then clean the strainger, disconnect the lines to the filter and blow compressed air through them. I might plug that line and pull a vacuum to see if it held. If not, there's a pinhole in the line. Follow a similar process from the tank to the injector pump to make sure it's all good to that pump. If that doesn't fix the issue you could have an injector pump issue at which point some specialized tools are required just to test it. Probably would mean a visit to the dealer. I doubt it's the injector pump and I think you can find the problem.
Treefarmer
Like the above mentioned. Check to see if there is any debris in the bottom of the fuel tank, that will restrict the flow. It's been a talked about issue on this forum, in the 70 and 90 series machines.
I will check this thanks for the ideasAt a guess, since it's an intermittent problem you might look at the fuel in the tank. I don't know if there is a strainer but those can get debris on them and plug up. When the engine shuts down the debris falls off until it gets sucked across the strainer again. We had that happen on a IH and it drove us nuts until we finally disconnected the fuel line and pulled the strainer.
Another possibility is a small pin hole in a fuel line that lets air get sucked in when the vacuum is high enough. Then of course, there is at least one pump- the injector pump and most likely a lift pump to supply the injector pump. I'd start at the tank and make sure everything is good at each step. My 790 has the tank on top and I'd probably empty it, take it off and make absolutely sure there was no debris in it. Then clean the strainger, disconnect the lines to the filter and blow compressed air through them. I might plug that line and pull a vacuum to see if it held. If not, there's a pinhole in the line. Follow a similar process from the tank to the injector pump to make sure it's all good to that pump. If that doesn't fix the issue you could have an injector pump issue at which point some specialized tools are required just to test it. Probably would mean a visit to the dealer. I doubt it's the injector pump and I think you can find the problem.
Treefarmer
1 - 7 of 7 Posts
- This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Green Tractor Talk
A forum community dedicated to John Deere tractor owners and enthusiasts. Come join the discussion about towing, PTO’s, reviews, attachments, modifications, troubleshooting, maintenance, and more!
Full Forum Listing
Recommended Communities
Join now to ask and comment!
