I have a 980G CAT loader. When I pulled the fuel cap off, there's suction/vacuum in the tank. Why? I have a brand new fuel cap and have the same issue.
A new fuel cap should have fixed that. Wrong fuel cap? Are you sure its not pressure in the tank? Is the machine running rough?
You said you have a brand new cap - a replacement cap I assume. Is it a genuine Cat cap or a "will fit"..? The Cat cap is vented and therefore should not produce the symptoms you are experiencing which is the reason for my question.
Thanks. Yes, it's a brand new genuine Cat cap, right from a Cat dealer. If I pull the cap off and then put it back on, the machine runs great for about 10 minutes, and then loses power. When I pull the cap back off, the suction/vacuum returns. I took an old cap, pulled the vent right out of it so that it could "breathe" freely. It runs better from full to half-tank, then it starts to lose power again. I can't figure this out. Thank you again.
Have you tried running it at around a half-tank with the cap off and with just something over the top of the fill hole to stop dirt getting in..? The other thought I have is that maybe you might have a crack in the suction standpipe inside the tank at somewhere around the half-tank level. If that was the case as soon as the air leak was exposed above the fuel the engine would start to lose power because it would be sucking air.
I did try running it with the cap off at half-tank and below, but the same thing happens. As for the crack, I'm not sure because even with a full tank with a brand new Cat fuel cap, I run it for 10 minutes where it runs well, then I pull over with the engine running, pull the cap off, and there's suction as I pull it off. I have even tried three different brand new caps off of 3 other machines and same thing. Driving me crazy because it makes no sense in my mind.
Working one step at a time when you run it for 10 minutes with a full tank and the cap on does it run OK, even though when you pull the cap off you can hear the air rush in..? Also have you tried running it, then leaving it overnight and pulling the cap off first thing in the morning. Is the vacuum still there..?
Yes, it runs OK for about 10 minutes or so, then it seems as though it's starving for fuel. When I pull the cap off, the vacuum is there. Yes, the vacuum is still there. This has been going on for months, and every morning the vacuum is still there.
You said it's a genuine Cat cap. What Part Number is it ..?
I'll get the part number this week...it's at the quarry. My next angle was the return line. Do you know if there are any check valves or anything that could potentially restrict the flow back to the tank? By this I mean as the engine is running full throttle, could it be drawing more fuel out of the tank than is returning back, therefore creating the vacuum in the tank? Thanks again for all your help.
You never said what S/N prefix your machine is, the original 3406C engine has an elbow with an orifice inside it installed in the rear end of the fuel pump. This elbow is connected to the return line as it leaves the pump on its way back to the tank. The orifice is designed to allow a constant regulated flow of fuel back to the tank. Also there is a spring-loaded valve in the transfer pump (on top of the secondary fuel filter) that controls the pressure in the fuel manifold. Have you tried removing the return line at the tank end to see if you have fuel coming out of it while the engine is running..? Another question - does the loader still have the original 3406C engine model installed, or has it been upgraded to either a 3406E engine or a C15 emissions-rated engine..? If it doesn't still have a 3406C installed we could be on totally the wrong track.
The only way to create a vacuum is to make the volume of fuel or air in the tank smaller, and the only way to do that is to either burn the fuel or leak it somewhere? Is the cap hard to pull off then?
It's a 980G series II, which came with a C12. The original G series One came with the 3406C. So to answer your question, it has the Cat C12. That's exactly my theory. The return line must be restricted and is burning more fuel volume. Yes, the cap is hard to pull off because there's suction. The longer I run the machine, the harder it is to pull off, even with a brand new Cat fuel cap.
Strange that ........... all the 980G Series II machines I can find are/were equipped with a 3406E engine. What's the S/N prefix..? You have 3 options, AWH, AYT, & AXG. No point in going any further until we establish exactly what machine you have.
Will get the info this week. Thanks for all your help. I really appreciate it.
Very sorry...my mistake. You are right. It is a 3406E and the serial number prefix is AWH.
I think you need to be checking your suction lines for a leak. You won't see fuel dripping out where the leak is. Does this machine have an electric priming pump on the primary filter. It should have. Take the line off after the primary filter and run a hose into a bottle. Run the electric pump with the key shutoff and see if you get clear fuel or some air when the fuel tank is below the half mark.
Okey dokey, that makes more sense. As it's a unit injector engine and considering the fact that fuel is used to cool the engine ECM there should be a pressure regulating valve somewhere just before the fuel return to tank hose leaves the engine. However I'm struggling to find the Part Number and the actual location of the valve. Also if you disconnect the fuel return line at the tank and run the engine there should be a significant fuel flow coming back to the tank even with the engine idling. Do that and let us know how you get on.
Nige, We had an AWH00798. been a awhile since I looked at it but there is a manifold right near the ECM with many lines hooked to it and some check valves in them. It is shown in the "201-7652 - LINES GP-FUEL " area "B"
I found those Ken but I was looking for a spring-loaded pressure regulating valve as shown in the schematic of the SysOp for the fuel system. See below, reference #5. The check valves are in the fuel pump Item #10, one is so that when you are hand priming the system you can drive fuel past the pump gears. One the larger engines the PRV is always located at the rear LH corner of the engine, not sure about this one though. The thing is being common rail it has to have a PRV or an orifice somewhere in order to generate fuel pressure in the rail.
Thank you very much, everyone, for all your help and for the warm welcome to this forum. With your suggestions and help, what I've found was the return line and fitting were restricted, so I replaced both. That seems to have solved the problem now. The power is back and there is no vacuum in the tank, and it was running great today. It should have been changed a long time ago because the machine has almost 30,000 hours on it. Again, thank you so much. Am very impressed with your wealth of knowledge and the time you spent on this.
Just for my info. What are the part numbers of these items? Was the fitting the one at the tank or on the engine?
Nige, Not sure what I'm doing wrong but I can't find the schematic like you posted. Was just wondering what item 8 and 9 were being called.
Ken, I went to the System Operation for the fuel system under AWH prefix and the first thing in the document RENR1363 is that schematic. 8 is listed as a Distribution Block, 9 is the fuel temp sensor. The thing is that that type of engine has to have some form of regulating the pressure in the fuel rail, be it an orifice or a PRV.
Not sure what I did wrong but when I went to Sys Op for fuel system it took me to the middle of the page, just needed to scroll up to top to see the drawing! What is being called "Distribution Block" in the schematic drawing appears to be what the parts breakdown is calling the 103-4656 Manifold-fuel. It has the fuel temp. sender in it and two different valves the part book is calling "Valve-Check". The one, #19 p/n 210-9528 appears to be in the back half of the manifold that is right in line with the #20 elbow that the hose from the rear of engine is connected which looks like where the PRV in the schematic is located. As I recall from working on our 980GII a couple years back this "Manifold-fuel" does not have any openings from the front side to the rear side, it's divided where the two mounting bolts #25 are located. I did try going to NPR with the 210-9528 valve part number and it appears there are some documents relating to it but my access wont let me view them. At least the OP seems to have found his problem so all is well in that regard!