2015 Cat 302.7D CR Bogging Issues - multiple mechanics can't fix.

I have a 2015 302.7D CR with 1100 hours that has a bogging issue. I will describe the onset of the symptoms followed by the extensive troubleshooting I have performed. This machine was purchased about 2 months ago and was estimated to be sitting outside in a rainy costal region for approximately a year. Pre purchase inspection passed with flying colors. I used it for 2 days without issue then on day 3 suddenly had engine bog down when traveling. I cleaned the main relief and found no evidence of contaminants or wear within the relief. After re-installing the relief, it worked fine for the rest of the day (has now been determined this was entirely coincidental) Initial symptoms were as follows: Engine bogging down to the point of stalling when travelling in high speed or when holding any functions on primary pump against a relief or loading them down while digging. Secondary pump functions did not stall or bog engine (blade and swing). If I release the control the engine recovers instantly. Little preliminary note (all fluids and filters have been changed) Following morning the problem was present right away and has since not recovered. My first instinct based on the feel and behavior of the machine was a hydraulic relief sticking or the pump not de-stroking. steps taken so far have been remove, disassemble and clean all hydraulic relief valves, change hydraulic fluid and filter, verify pressures and travel times were within spec, (swing boom was slightly out of spec on travel time and this function was the only one that bogged engine during travel without load applied). Disassemble and inspect hydraulic pump internals. All hydraulic components have been clean and show no signs of damage or excessive wear. Pressures and travel times are all within spec except travel time on swing boom was slightly slower than spec. I then proceeded to go through the entire LP fuel system, cleaned tank and put new diesel #2 in, replaced all fuel lines, cleaned prescreen filter and housing that had sediment, new fuel filter, verify lift pump flow and pressure, verify check valve on lift pump functioned, verify check valve on return line functioned, verified spring check ball on return banjo was clean and functioning, verified inlet banjo was clean, verified system held prime, verified fuel inlet to injection pump was free of air. Interestingly the inlet side of the injection pump was free of air, but the return side of the pump had air bubbles. Ran off a bucket directly at filter housing with no improvement, verified rack was free moving, removed injectors and turned engine over with injectors hanging off the side to verify visual spray pattern was uniform and correct visual pattern according to manual. Had a very interesting discovery. When turning the key on and priming the lift pump for more than a minute the machine worked perfect for a short while. This caused me to double down and go through fuel system again. At this point I broke down and took the machine to CAT. They went through the whole fuel system again as this weird pump priming thing led them to believe it was fuel related. They verified all the hydraulic pressures again as well and noted that backing out the main pump screw a few turns eliminated the issue but stated that it was a band aid and returned the screw back to spec. They said nothing indicated the hydraulic system was the issue. Finally, they put a compression tester on it and claimed that all 3 cylinders were low on compression at approx. 300 psi. Spec for the 3tnv80f is 495 with the lower limit being 400. I had never suspected the engine to be bad at 1100 hours. It fires right up cold with just a quick small puff of white smoke on first fire, clears up instantly, idles perfect, free revs perfect, sounds perfect etc.. I never considered compression testing it because of that. Their official diagnosis was engine is severely worn and needs relace. They had no answer for me on the fuel priming deal. Since I don't have a compression tester that goes that high I took their word for it (they have a good rep here so I didn't assume they were just trying to sell an engine), I verified valve lash was in spec and after confirming it was, I pulled the head to find very minimal carbon buildup, Cylinder walls have factory crosshatching and look immaculate, head passed a vac test and no signs of HG failure or damage to pistons/rings/valves/head etc. Starting to go back to a potential fuel issue or hydraulic pump deadheading or not de-stroking but can't find anything wrong with the thing. Ive also had a local hydraulic shop run some tests and they cannot find any hydraulic issues. My local machine shop is very knowledgeable on equipment, and they are leaning more towards hydraulics at this point but agree the fuel priming thing is odd. So, my first question is would air bubbles coming out of the return side of the pump be normal and if not, what could cause that? I had suspicion that the return banjo might not be sealing due the crush washer being reused but have since replaced it and CAT said leakage at the fitting would only cause fuel to leak out not air in as the lift pump should overcome it. They were also not concerned about air bubbles coming out of the return side of the pump. At this point I have racked up a significant diag bill and have multiple well-known mechanics in my area completely stumped including myself. Totally at a loss on where to go next.

Ironline said: Finally, they put a compression tester on it and claimed that all 3 cylinders were low on compression at approx. 300 psi. Spec for the 3tnv80f is 495 with the lower limit being 400. Click to expand... Where did they get that info from I wonder.? Cat generally doesn't use compression testing to assess engine condition and certainly AFAIK has no published compression specifications in their service information system.

Not sure on that one, unfortunately they have had my SIS application in a pending state for over a month so I have no direct access to their troubleshooting info yet. I was able to pull the compression specs straight from the Yanmar manual.

Ironline said: I was able to pull the compression specs straight from the Yanmar manual. Click to expand... So did you give the specs to the dealer.? It amazes me that they even had a compression tester.

Ironline said: unfortunately they have had my SIS application in a pending state for over a month so I have no direct access to their troubleshooting info yet. Click to expand... You really need SIS access. Without that you are flying totally blind. SysOp Test&Adjust, Specifications, etc.

No, they told me what spec should be and it aligned with the manual? Why would you be surprised? Maybe it’s not typical for CAT but they would be limited on diagnosing the engine since it’s all mechanical. Can’t plug in a scan tool and check values. I wasn’t really surprised by them testing it. Pretty standard accross the board to check compression when engine is in question. Regardless of all that I don’t believe there’s any wear or damage to the engine so I’m not going to get hung up on that too much.

Ironline said: No, they told me what spec should be and it aligned with the manual? Why would you be surprised? Click to expand... Surprised because it's not customary to test compression on Cat machine engines. However I need to eat a slice of humble pie because I just looked and a spec for compression is actually there for that engine. Maybe the smaller machines like this one it's a thing but it certainly isn't on larger engines. I should really learn to stay away from Lawns & Gardens stuff.

I think I would be looking for info on pump unloading I would think engine would not have enough hp to run pump at full volume and maximum pressure

I just re-read your OP. While you were working on the fuel system did you ever remove the head of the fuel filter & water separator, strip both of them down to the bare casting and blow through all the ports to check that the passages were clear.? There is also apparently an inline filter assembly #26 on the attachment. Was that cleaned and/or replaced.?

The circled "filter " is the tank breather. I'm all for the filter head restricted internally. I use a Napa "3972" on the inlet hose to prevent future issues.

Nige said: I just re-read your OP. While you were working on the fuel system did you ever remove the head of the fuel filter & water separator, strip both of them down to the bare casting and blow through all the ports to check that the passages were clear.? There is also apparently an inline filter assembly #26 on the attachment. Was that cleaned and/or replaced.? Click to expand... I have not done that yet, flow is visually ok at injection pump but certainly will not rule this out. The inline pre filter is more of a screen that did have some sediment inside and a glob of grease floating around that would have been restricting flow but has since been cleaned with no change.

Ironline said: I have not done that yet, Click to expand... I would suggest that should be your next move. Remove all plugs & fittings from each head (taking care to note where they all fit) then remove the heads so that you can visually inspect the passages inside them. Blow through every one multiple times with compressed air using a rag over the outlet(s) so that you can check what pops out.

From the information I have read, it seems and sounds exactly like a fuel problem. As it ran fine for 2 days and on the third, the crappy fuel finally plugged something up. Gotta find it.