Hi all, I have an older Cat 312 that's bogging down under load. I'm hoping it's a fuel delivery problem. I changed the fuel filter and it was much better for a day or two but then after sitting for a couple weeks the power loss is back. I should mention that accompanying this loss there was difficulty starting the machine after it sat. To get it to start I needed to heavily prime the fuel system (200+ pumps of the manual primer). Once started, it idled just fine but under load it loses power. I can't imagine that the fuel filter is bad again after just two days of work so I'm now wanting to check the fuel inlet screen. The banjo bolt appears to be in a VERY awkward spot to reach (directly at the bottom of the manual fuel prime pump). I was able to get a socket down there without the wrench and a 7/8 socket seems to fit. This is bigger than I was expecting so I wanted to ask you all if that size sounds right (I don't want to remove the wrong bolt). And if it's the correct bolt can anyone offer any tips on how to remove it? Trying to remove it from atop the machine seems to be a big challenge. Maybe I can get to it from some bottom access panel? Thanks to anyone who can help.
Post a serial number for the machine if you can so we can access accurate information for your machine.
That all sounds correct. Don't lose the metal washer on the bolt, the one between the "banjo" and the body will stay in place, but make sure the lower one stays on the bolt and you don't lose it.
ahart: Serial number is 7DK05412 (which Nige told me corresponds to 6GK393-Up). It's a 1994 Cat 312. Delmer: do I need to attempt this from the top of the engine or is there easier access from somewhere below?
I don't know if you can access it from below. Every banjo bolt I've seen you can access it from on top, but it's not easy, all around miserable is more like it.
If u changed the filter and all symptoms disappeared and then reappeared after a day or 2, WHY wouldn’t u assume it’s dirty again.?? THATS the FIRST THING I would suspect.!! Not to mention the EASIEST THING to check/replace..
@thepumpguysc : true. For the same reason as you, I do have some suspicion it could be the filter, but if that's true, then I must have a bigger problem in my fuel tank because it must be awfully bad in there if it's fouling a filter in 2 days. But I also suspect that given the difficulty of cleaning the fuel screen, it's likely never been cleaned, and this is an old machine so it could be really gummed up. It's worth it to me to spend a few hours attempting to clean it.
It might be a crazy suggestion but have you tried opening the drain valve at the bottom of the tank and see what comes out.? P.S. You are supposed to do this on a frequent basis.
@Nige : thanks Nige, good suggestion. I opened it very briefly to check for signs of water, but I never really let it flow to check for particulates. I'll give that a try too.
Drain a couple of gallons into a bucket, let it settle, and see what it looks like.
I tried to make it a habit on any equipment that had a drain valve to open and drain off about a couple quarts at each oil change. Wee used waste oil to heat the shop so I figured I was helping keep the shop warm as well as cleaning the tank.
Well it took a couple hours to take out and put back in (what a pain!), but the fuel inlet screen is now clean. See attached pics of the screen's condition when I took it out . I haven't tightened the bolt fully yet (need to borrow a tool from my neighbor) so I can't report if it's helped, but I'll let you all know when I'm done.
Hi all, so I can't tell if cleaning the fuel screen has helped with the lack of power because I can't get the machine to start. See my initial post about having difficulty starting it after it sits for a while. I believe I'm either losing prime or I have an air leak in the fuel system. Question: I read somewhere that CAT fuel filters have a check valve in them to aid with keeping prime. Is this true? I ask because this issue with difficult starts only began happening recently. It's always started like a champ. I realized that it's only since I changed the fuel filter (because of the lack of power) that I now have trouble starting it. If I use the machine every day there's no problem, but if I let it sit for several days it won't start. The old filter was a Napa brand and I changed it to a new Napa Gold. Could the filter be causing it to lose prime? Should I try a CAT filter?
No check valve in filters. Have run many napa filter on Cat machines here. Never an issue. When operating the hand primer, you should hear bubbles in the tank, after you've closed the bleeder. Continue pumping until you longer hear bubbles.
@heymccall thanks, that's good to know. I don't hear bubbles when pumping the primer and never have. Also, my hand primer leaks fuel like crazy when I pump it and I wonder if that's contributing to my problem (more suspicion of an air leaks). Another question: when bleeding the primer pump should I be able to force fuel out of the bleeder by pumping the hand primer (similar to how this occurs when bleeding the fuel filter)? I can't get this to happen. And, when I close the bleeder on the primer pump but leave the hand primer "up" I believe it's supposed to be difficult to push the hand primer back in to screw it closed. I don't have any difficulty pushing it down.
@heymccall : sorry, I just realized what you meant about the bubbles. I've never tried doing this (I always bleed the fuel filter until I see a steady stream of fuel coming from the bleeder screw and then close the screw) but I suspect that I'd lose a lot of fuel from the leaky hand primer while trying to do this.
Sounds like like your leaking hand primer could be the problem.
X 2..^^
I just had a hunch that could be the problem.
x3...... Question: If fuel leaks out when you are operating the hand priming pump what 3-letter word starting with "a" do you think can leak in when the engine is stopped.? Er, hello........
Hi all, thanks for your input. I had a local tech come look at the machine and the no-start was very simple: my fuel-shutdown solenoid was sticking in the "off" position. Manually moving the solenoid back and forth "loosened" it up and now the machine starts like a champ. So it wasn't losing prime after all. But I decided to replace the manual primer pump anyway and it appears that I now have full power back again! I'll confirm the gain in power this coming week when I use the machine heavily, and will report back.
If the solenoid was sticking, it means some garbage made it thru to the inj pump.. THATS a good indicator that your not changing the filter fast enough. I tell all my people to change the filters 2x a year, weather they use it or not, to keep me outta their pocket..