We have a 1986 CAT D3B that has a 3204 engine. We can run the dozer anywhere from 2 to 5 hours with little to no problems. Engine hums along at full throttle with no issues. Then at random, the engine will start bogging down and sometime completely dies. It doesn't matter if it's under load or not. The only thing I have been able to do to effect the stall is throw it in neutral but it continues to stall but sometimes will clear up. If I continue under any load it will completely die. It will restart most of the time but it takes a lot of trying to get it to fire off again. I have checked all the fluids and everything is clean and full. I changed the fuel filter believing that it possibly could be junk from the tank clogging the filter. It didn't change the issue. I had a friend bring up that it might be getting vapor locked because the fuel tank vent might be clogged? Anyone had this happen? I'm wondering if anyone has had this issue or knows of a fix/what the problem might be. Any help would be much appreciated as I'm not a mechanic and I'm running out of ideas.
idk how your fuel tank is set up but it might be a cracked pick up tube..?? Have u tried adding fuel to the tank when this happens.?? Just something to think about.. The vent is a possibility too..but I would think that it wouldn’t take 2-5 hours for it to happen..??
Did you try draining the "junk" from the tank.? There is a drain valve for that very purpose. Do it after the tractor has been left sitting overnight on level ground. Have you checked the breather in the tank cap.? Next time it acts up try unscrewing the cap to see if it makes any difference.
I'd have to opine it's rubbish in the tank blocking a fuel line, after a period of operation. How long after you stop does it take for the engine to start and run again? And does it keep running for the same period as before? Trash builds up in fuel tanks from moisture in the air causing corrosion and then rust flakes. Fluff from rags finds its way in. Dust in small amounts builds up in tanks, and the dust takes corrosive chemicals with it in tiny amounts. Even little sticks and leaves can find their way into tanks. The end result after many years is a concotion of rust flakes, cotton fluff, dirt and water, that blocks tank outlets, and which will also block lines further away from the tank - especially at elbows. Drain the tank completely and flush it and check the inside with a borescope camera. If the problem persists, remove the lines and check them for cleanliness, along with the elbows. Steel fuel lines also have a habit of corroding at clamp points, where moisture and dirt gather to create pinholes in the steel fuel lines. Sometimes the pinholes are very hard to find. Cat hammered the old line for many years, "buy clean fuel and keep it clean", as Cat field servicemen constantly found dirty fuel was the cause of 90% of the reason for service calls.
If there are any rubber hoses or seals between the tank and the transfer pump, that's where I'd look. Water separators are good for leaking air like this. Try priming it before re starting, you don't want to turn a minor air leak or fuel blockage into a burned out starter.
This is the exact problem I had on a likely identical 86 931B kind of all of a sudden. There is a long hex fitting on the inlet to the the lift pump. Inside that hex fitting is a screen that will plug up. You can reach in with a hex wrench and remove it for cleaning. Shut the fuel off under the tank before taking the fitting off. If the engine still runs at idle you probably won't have to bleed the system once you put it back on. On mine the machine would die and start up again and run at idle. As soon as I put it in gear and gave it throttle to move it would die again. It was driving me nuts because I wasn't fully understanding exactly where it was. It's really unassuming inside what looks like a standard hex shape fitting. Check that first before going to extremes trying to find the problem. Of course it's good to drain the water and any accumulated crap from the fuel tank.
A friend of mine said it could be possibly vapor locking the tanks to crack the lid and see if I heard a hiss of air rushing in next time. Thanks for confirming that idea. Draining the tank is also on my list.
It doesn't have a separator on it. That was one thing I considered adding to help filter junk out from the tanks. Thanks.
CHECK the screen in the hex fitting on the lift pump inlet. I had the exact problem you're having. If you think it's the fuel cap not venting, it's simple to leave it off and see if the problem goes away. I would guess there's a 95%+ chance the screen in the hex fitting is plugged only letting enough fuel through that the engine may idle. If it takes longer to start after it dies points directly to that screen as well.
I actually found a video on a "banjo fitting" that was supposed to have a screen it in but this unit doesn't have that kind of lift pump. I've looked at the lines but haven't found any other screens. That's one reason I was considering adding a water separator before I hit the filter. Thanks for the advise. I'll go back and check it again and make sure I didn't miss a screen.
Was it on the inlet or outlet of the lift pump?
You won't see it. The screen is not a seperate recognizable part and if you didn't know it was in the longer hex fitting you'd never find it. The steel fuel line goes into it and it goes into the lift pump. You could have a thousand people try to find it and unless they knew it was their wouldn't find it. It's inside an inconspicuous looking hex fitting.
OK, now we're getting somewhere. If you look at the bottom fuel line with the metal tag on it there is a 90 deg. fitting. That 90 deg. fitting is going into the longer hex fitting I'm talking about. Clean off all around the lift pump. Shut the fuel off with the valve under the tank. Then carefully remove the line where it connects to the 90 deg. fitting. With the line moved out of the way you can take the hex fitting out with the 90 deg. fitting still attached. After you have the hex fitting out you can remove the 90 deg. fitting. Inside the hex fitting is the small removeable screen. You have to reach in the opposite end of the screen with an allen wrench and thread it out through the hex fitting. It's a good idea to clean it some so they screen will thread out. Then you can clean it with solvent and blow it out with an air nozzle. Mine looked like it had wood particles in it. Gave me fits because I couldn't understand where this little screen was located.
You don’t have to drain the tank completely, just run enough through the valve until clean fuel is flowing from it. If you’re unlucky you might need to drain up to a quart.
Number 11 in the parts diagram!!!!
Remove the arrowed fitting......
Wow.. that is “unassuming”.. Cummins started doing that, except it’s a check valve.. Same as Bosch on the Mack and IH..
I thought it was in the hex fitting the lower fuel line goes into because I remember having to take the 90 off to be able to get an allen wrench in to remove it. I think Old Magnets pic. shows the higher fuel line connection in the background but it's kind of fuzzy. The hex fitting shows up a lot better if you blow up the original pic. the OP posted. Regardless it looks like just a hex adapter. You'd never think there's a screen inside.
I did find the fitting you were referring to but it was on the discharge of the lift pump. Also, the screen was so full you couldn't see through the mesh at all until I blew it out with the air compressor. I'll find out tomorrow if this is the problem or not! Thanks for the help so far.
99.9% sure that was the problem. Was it the bottom line in your pic.?
Yes it was. I'll be pushing out some trails tomorrow so we will see if it fixes the issue.
Too bad you didn't take a pic. when you took it out. It's quite amazing how much crap gets in there that the engine still runs. It would be a really bad idea to run the machine without it.
I believe that screen is on the suction side of the lift pump, not discharge. Correct me if I'm wrong.
I'm not positive but it makes more sense to be on the intake just by the way it's fitted. The junk collects inside which would seem the same way the fuel flows. Otherwise I think the lift pump would have a short life span.
Have you checked the tank yet.? If you haven’t then the chances are that small screen will only plug up again.
Where was the contamination on the screen, the outside or the inside.? If it was on the outside then I would say that port is the outlet.
Contaminates were on the inside of the screen and the screen inserted into the fitting and stuck into the pump housing. So, now that I've thought about it, yes, it was the suction side of the pump. Dozer ran good today. I have not drained and flushed the tank yet. I was trying to beat some rainy weather we are supposed to have come in on Monday/Tuesday. If it acts up again, at least I know where to go clean the filter. On another not, I still ended up with the dozer down after about 3-4 hours. as the old saying goes, "If it's not one thing it's another." Parts ordered from McMaster-Carr and we will be back going once I get them in Tuesday. I don't know how this thing was in there but maybe I can epoxy it to do a little more work tomorrow.
I bet the end was knurled/rolled/peened over the ball portion. If there's enough metal left, peen it again. If there's not enough metal, countersink that ball a little and then peen the center. Nothing wrong with Jbweld either. Clean the whole thing with brake cleaner, then some oil on the ball before you use it. They make a jbquick that sets in 5 minutes, just work fast and look at the label before starting. Or just weld that ball to the stud, it never needs to come off again.