Cat Diesel Guys

Having a perplexing problem on my 4-150 with the 3208. The thing is randomly getting air in the fuel supply line. May run for 2 hours and not do it, may run for 200 feet and do it 2 or 3 times in a row and it seems to do it worse as the weather gets warmer. Tractor will be running along fine then all of the sudden it will become gutless and I have to shut it down, bleed the fuel system out and it will take off and go again. All the fuel lines from the tank to the divider block on the back of the engine are brand new. The steel line from the divider block to the fuel filter was cleaned out and checked, fuel primer pump is brand new, fuel filter is brand new and the fuel tank is clear full. Im 99% positive that its not the injector pump because the thing runs to good and to strong. Now the motor does run on the really warm side. Im going to get a new thermostat for it tomorrow since the radiator and water pump are already brand new. Im thinking that it cant be a coincidence that the thing does it when the motor gets warmed up, and gets even worse when its 70+ degrees outside. I didnt think it was, but is it possible for a diesel to vapor lock because that sure is what it seems like its doing?

Had same problem in 1805 MF with 3208. Took 3 years to find the problem. Turned out to be a crack in the line at the injector pump, it was under the nut that attached the line from the filter to the pump. and was found quite by accident. Swede

Try changing the throttle shaft seal I have seen this happen it will suck air at the seal.

That's one problem with the cats. Can you pressurize the line and use soapy water? That still may not find the leak. Does it have a square stanadyne type glass fuel filter? Sometimes those don't seal and don't leak fuel, but will leak air in under suction. You have an air leak somewhere but it may be a pain to find.
Josh

What I would do first is eliminate all the fittings and flares downstream from the main filter and install a temporary hose to a 5 gal container hanging on the side of the tractor. This will eliminate the tank(s) and all the replaced lines and fittings. To get such a large load of air, this has to be your problem area. This is assuming that the fuel pump has been proven good.

The heat could swell a bad fitting to the point of inducing air and maybe a pressure test on the low side of the pump will be show leakage results? Hard to apply soap inside the tank though.

Sometimes a high frequency vibration induced on a hard fuel line will cause a fitting to fail at different intervals of heat and rpm. i.e. the clamps on your injector lines.

Good luck.

Had a guy tear apart an engine in a truck due to a cracked fuel filter base on a 3208. I assuming you are pulling fuel from the main tank only, so everything should be gravity fed to the fuel filter if you have a decent amount of fuel in the tank. If it was sucking air, you should have fuel leak also. I would plumb a piece of clear hose between the fuel filter base and the injection pump to see if you have any air to prove it is lack of fuel to the pump and not air elsewhere. Then run it and see if you have fuel yet when it acts up. You co have check valve issues in the top of the pump. The transfer pump is a gear pump in the front of the injection pump. So remember everything from the pump rearward is suction. I'm thinking you have a piece of debris plugging off the fuel outlet at in the tank. Throttle shaft seal would cause hard starting letting the fuel drain rearward. There are two seals in the front of the pump sealing the camshaft and the front of the transfer pump. They may be an issue.

By your description the throttle shaft can probably be ruled out. As long as its above freezing all you have to do is crack the throttle and bump the key and the thing is running. The only fuel leaks I have is 2 injectors that weep a little, nothing I can find in the fuel supply or return lines which is the most perplexing part. We have already had the fuel tank off to replace the fuel lines and fix a leak in the tank and we thought we had any floaties out of it before we put it back on. Guess we are going to have to drain the tank and start at the beginning all over again. Thanks.

Thanks, sounds like im gonna need it. haha

Its still got a spin on filter. Ive had it off twice to check the filler base for cracks and make sure I didnt have a seal from the old filter still stuck on there. No issues there that I could find.

Thanks Ill check them out.

You could take a long piece of copper tubing and put it down fill neck into the tank and then run a hose to the inlet of the filter and try that to see if it stays running. We had problems with debris in 90* fittings and shut off valves. I'd definitely put a piece of clear hose between the fuel filter and injection pump to make sure you're running out of fuel, instead of the pump not sucking.