Just wondering if anyone has any ideas why the engine won't run as it should. Its a 1994 311 Cat with a Mitsubishi 79 hp. 4 cyl. it's got 6700 hrs on the machine. Engine starts and runs fine at idle but any throttle setting above that and it stumbles and runs pretty rough, seems to smooth out a bit when there's a load on it. I have tried everything I can think of but nothing has had any effect.
Well, what HAVE you thought of and tried? How about a picture of the injection pump?
Changed filter, blew out fuel lines with compressed air, I even geared up another fuel tank directly to the injection pump but it didn't seem to make any difference, the injection pump is a Zexel made bosch style inline pump.
Did you remove and clean the screen in the banjo bolt in the intake to the transfer pump that's mounted on the injection pump? Not likely, but it's easy. HeavyEquipmentForums The banjo bolt is on the bottom of the red circle in post #3, the screen is screwed inside of the banjo bolt. Part #13 in post #11 in that thread. What's the history of the machine? Is this a new problem? What does the exhaust look like? at idle, when misfiring the worst, under max load? Have you checked the air filter? No turbo? Any small "vacuum" lines running to the injection pump?
How about checking the air filter and maybe check the inlet side of the turbo charger. The engine is pre-EPA regs so there shouldn't be much to it. That amount of hours isn't much either. How often has it been serviced?
I have had the machine for the last 2 years, been fixing all the little things that got neglected over the years so I haven't worked it at all. I have tried running it without the air filter but it didn't make a difference, I think I did check the screen on the transfer pump but its been awhile so I can't remember for sure but I will check it again. I haven't pulled any of the hoses off either side of the turbo but I will do that shortly. I don't think there are any vacuum lines running to the pump but I will post a picture of it tomorrow to be sure. I have changed the muffler, since the old one had a hole in it when I got the machine but other than that the exhaust looks fine. I don't know any of the history of the machine but I would say the problem has been there for awhile, there's a steel pipe from the turbo to the base pan that was leaking oil when I got it when I took it off to fix it the leak was in an old weld where it had cracked before, I'm guessing from all the shaking. One other thing that I've found, there's a valve in the case of the injection pump where the fuel returns to the fuel tank, when I took it apart the spring was there but the ball was gone, looked to me like someone thought that doing that might fix the problem. I replaced the ball and spring but it didn't make a difference.
Take the intake hose off the turbo and feel the wheel for any play axially or radially, whether it rubs the housing, spins freely, is THERE. Wouldn't hurt to check the valve clearances. You could try to see if it's one or two cylinders in particular by loosening the injection lines at the injector one at a time and see which ones don't make it run rougher. I think I'd empty the old fuel and run it hard an hour before doing anything to injectors. If you do pull the injectors, keep track of which cylinder they came from, do a compression test, and get them pop tested, or replace. A video of it running might be helpful. The injection pump is simple as long as there's not a bunch of wires going to it, or air hoses.
I'll try to post a picture of the injection pump and a video of the engine running tomorrow. Thanks for the reply.
I have posted some pictures of the injection pump and a video of the engine running. Its a bit hard to see from the video how the engine is shaking but hopefully you'll get the idea.
Take a noncontact thermometer ,measure temp at exhaust manifold. Same place for each cylinder. Temp should be the same for each cylinder,if not there is a problem
Another thing to check if it has one is the coupler from crankshaft to hyd pump. Sometimes when they go bad it causes a vibration like an engine miss
Thanks for the info, I will check that.