Hi ,, I'm new to this site ,but have been reading some of the post here and have found very helpful information. I have a late 80s Cat 426 back hoe with a Perkins 4.236 . I have replaced the fuel filters and installed a new mechanical fuel pump. I have cleaned the fuel injectors and fuel lines. Bleed the air out and am able to start the machine. It runs good and will stay running for exactly 2 hours, ( I have time it the last six time I started it up) then it shuts off like it's out of fuel, and will not start back up until I bleed the air air from the system. Any help would be appreciated. Thanks
Is there a breather in the fuel cap that needs cleaning ?
Not sure if there's one in the cap. There is one on the tank that is cleared
Pull of the fuel line when it quits and blow back threw it with your mouth so you can tell if there's any restriction in the line. The fuel line may be deteriorating on the inside or you may be picking something up in the fuel tank. It has to be something simple with the fuel delivery from what you've described. Solving some of these hick-ups can be frustrating.
Other than what BILL suggested.. does the machine have any shut down solenoids?? water temp or oil?? Hell, it might even be a crappy shut off solenoid on the inj. pump?? I've seen them where they'll get hot internally & shut down.. To diagnose a pump sol. problem.. the older ones have removable guts.. take the plunger & spring out & see what happens.. Just KEEP A EYE on the engine temp & oil after 2-2.5 hrs of running.. if it doesn't shut down.. Cuz basically, you took out the "safety" mechanism.. if it has additional shut downs, oil or engine temp..
The injector solenoid has been taken apart, the temp gauge works but not sure if there is a shut off solenoid on the machine, would it be located on or next to the top radiator hose where it connects to the head of the motor ? And there is oil temp gauge that works, at what temperature should it shut down at, and what's normal operating temp ?
lazy cat syndrome? Are you refilling the tank everytime it dies? Is it a gravity feed arrangement? It starts and runs for 2 hours then dies. Then you can bleed the air and it will run for another two hours without adding fuel to the tank, venting the tank or letting the machine cool off? Seems to me that anything related to temperature would be more variable than exactly two hours every time. The thing should be heat soaked well before two hours of operation. Rate of fuel consumption would be more consistent, though.
I am not refilling the tank after it shuts down Sometimes I try to restart but with no luck. I let it sit for a while then I'll go ahead and bleed the air and restart the machine. I have not let it run for very long after I restart it. I will shut it off, then try to start it the next day. And have to go through the process again of bleeding the air. If I shut it down before the 2 hours it will usually start the next day
Do you get air bubbles when you bleed the air? Then go back to the tank, and remove screen, or the junk that's floating around. Or run it off a temporary tank to see if it will work for longer. Or put a pressure vacuum gauge in the cab so you can see what the fuel pressure is doing between the filter and injection pump.
Seems to me that if it quits running and you have to bleed air out of the system you have something leaking allowing that air to get into it. You could maybe apply a small amount (5 to 10 psi.) of air pressure at the the fuel tank filler. Then look for fuel leaking somewhere in the supply side of the ip.
Yup I get air bubbles when I bleed the lines. I did remove the tank and some what cleaned it out there was a lot of debris in it. There is only a screen where you fill the tank , no screen on the fuel pick up line inside the thank. I installed a small clear filter between the tank and the lift pump. This weekend I plan on changing all the rubber tubing on the fuel system.
This weekend I plan on changing all the rubber tubing on the fuel system. I also have a small leak around the seal on the second injector, where it's held down to the head. and also noticed that there are a couple of crush washer's missing on the injector rail, but there's no leaks where they are missing.
The pickup tube may have a crack in it.
All good suggestions. I'm not familiar with the older Cat backhoes so I'm curious if you are bleeding it before or after the fuel filter. If you're bleeding it after the filter is it possible the filter is loose or the gasket seal is damaged/folded over? Its rare but I have come across a filter base with a hairline crack before that would draw air into the system.
I replaced the rubber tubing and (filter before the lift pump ) and bleed the lines of air. The machine ran all day Saturday. Sunday it fired up and ran about 1 minute and died. Bleed out the lines again and restarted it ran about 45 minutes and died again.Thinking about draining the fuel out of the tank and some how replacing the pick up tube in the tank, not sure exactly how to go about it seeing that there is only the opening at the filler neck and fuel level sensor is mounted at the top of the tank.
Does your tank have a drain? open it and flush the tank with diesel. You can reuse the fuel that drained out, just let it settle in a bucket and siphon off the clean stuff on the top. Keep draining into a clean bucket and continue until it come out clean. No drain, make a "suck bucket". If the tank is full of "chicken skin", then you need to take it off, or pressure wash with abrasives inside.
I have drained the fuel from the tank and power washed the inside of it. I did get a lot of debris out of it. While the tank is off I removed the steel fuel lines and found a bad connection in the fittings at the inlet of the fuel pump. I went to different parts stores to find fittings but had no luck so I call Caterpillar they sent me a digram and what is on my machine does not match what's on the print, so I'm going to change all the lines back to OEM parts, I'll let you know how it runs after this change of parts, Thanks for all the help this is a great site !!
I have replaced the lines from the fuel tank to the lift pump inlet and from the lift pump outlet to the separtor inlet, bleed the fuel system and fired it up. It's been staying running and starting up with no problems for the last 5 days. Next issue is to get the brakes working
Sounds like you finally figured it out. Glad it is working now. Keep us posted on the brake repairs. Is it just adjustments needed or new brakes installed? I also have a 426. I have good brakes on one side and just barely have brakes on the other side. I've tried adjusting the bad side but have used all the available adjustment so will have to replace them soon. Not much of a problem on level ground but will throw you in a circle if you hit the brakes coming down a hill.