Deere 797 Vapor Lock?

[Dusty Road]

Well, I read some of the 12 pages of "Vapor Lock Revisited" thread but could maybe use some more info.

The machine is a 2004 JD 797 Z-turn with ~1500 hours. 29 HP Kawasaki liquid cooled DFI. It was pretty neglected when I got it a couple hundred hours ago but I've gone through it pretty well- filters, all fluids, belts, some hoses, etc. The thing runs great, cuts ok and the only real problem I have with it is it seems to vapor lock when hot. It runs fine while hot, but if I shut it down and let it heat soak, the engine won't restart. When I "prime" the fuel pump, the filter will fill with gas but gets drained when the engine tries to start. Spark is present, etc. It is definitely a fuel problem. If I let it cool, either by waiting or pouring a bucket of water on the pump, it'll start right up and run fine as usual. I'm pretty sure I've got the cause of the problem figured out but now I'm looking for a solution, so on to the questions...

1) Is this a sign that the $500 fuel pump is going bad?
2) If the fuel pump is fine, does any one have any solutions for this? I was thinking some sort of heat shied or sink but would like some input on that.
3) Is vapor lock indeed what is going on?
4) If the fuel pump is indeed going bad, are their any cheaper acceptable replacements out there?

Also, I'm in South Louisiana and it's been HOT; ambient temps in the mid 90s. The engine isn't overheating, at least according to the idiot light on the panel. I did flush and refill the radiator a couple of months ago.

I'd appreciate any input!

Mitch

 

[rayikeo2]

The first thing to check is the "gas cap". Next time you are running the mower and it shuts off with what you are calling a vapor lock, try to unscrew the gas cap. If it is very hard to loosen and you hear a vacuum release hiss as you take it off you probably have a plugged cap breather hole. If you do not replace the cap then the fuel pump will break the diaphram and self destruct. All this requires to fix is a new cap for about $13. This may not be your problem but it is the symptom I was having when mine went bad. To check, next time you think it's vapor locked take the cap off and see if it immediately starts as soon as it reprimes itself. If it starts and runs that was the problem. If there is no change keep looking for other problems. The reason its dies is not heat but the fact the fuel pump can not overcome the vacuum created in the gas tank caused by fuel leaving the tank and no air entering the tank to relieve the vacumm created. By waiting 30 min the vacuum slowly releases itself and the mower restarts. Or you could buy a new cap before running next time and see if the problem goes away.

 

[Dusty Road]

Thanks for the response but I'm pretty sure the gas cap is fine. It's only a year or so old and the first thing I did when it wouldn't (re)start is I unscrewed the cap and checked the fuel, which should have solved the problem right then if the cap were to blame. The mower doesn't 'stop' running either. It fails to start when hot- It has never shut down without me turning the key.

 

[Engine_Tech]

It's vapor lock. The EFI fuel return line is too close to the pump pick up line, preventing the fuel from cooling down before being put back into the system. It's basically recirculating the hot fuel. Move the return line to the other end of the tank to solve the problem. Keeping the tank as full as possible also helps it be a better "heat soak".