773 bobcat power problems

New to the forum and I have a 773 bobcat and it seems to have a power problem. Say if u were going to take a scoop into a pile it will bog the motor down some. Doing that it won't tip the back of the machine up. And if u go to spin it in a circle with empty bucket it pulls the motor down to the point where it almost kills it. I originally started out thinking it was a fuel problem. I did find water in the fuel so I drained the tank and changed fuel filter. This did not fix it so I looked for pinched or cracked fuel lines and didn't find any. Replaced the lift pump. Still didn't fix it. Thinking it still might be getting air I disconnected the return line and put it in a pail of fuel and watched for air bubbles. Now appeared. When doin this I noticed no fuel came out of the return line at low or high idle. This seemed odd. I replaced both air filters. The engine compartment is covered in soot coming from the back end of the muffler near the air box. Thinkin that may be plugged I straight piped it but still no difference. Any thoughts. I originally thought fuel but could it be more hydraulic? I'm at a lose here and it's drivin me nuts. I appreciate any ideas. Thanks Jared

Welcome to HEF Jaredj. :drinkup

You to run it really hard under a hard load and make the engine stall. At the very instant it stalls out, immediately open the rear door and check the primer bulb in the fuel supply line. Check to see if it's sucked flat as a pancake.

Ok I'll give that a look in the mornin

Ok I pushed the machine till she bogged down and died. Ran around to look at the primer bulb and it was not sucked down flat. Did notice it wasn't hard as a rock and could squeeze it to prime it.

Well, if you've replaced the fuel filter and the fuel lift pump, I'm not certain what's going on with your machine if that primer bulb is hard. You should be able to open that bleeder on the injection pump return line and pump that bulb, although it will be a little stiff.

Does it have the external shut down solenoid on the injection pump? If so, are you certain it pulls the fuel lever fully into the run position?

Check your air filter, also, you didn't state whether your machine has the turbo engine or not. What is the condition of your tires? If they are oversized or flat, they'll suck a lot of horsepower. Check your drive belt tension, also.

Ok my machine is not turbo. Tires are stock size with proper pressure. Belt tension appears adequate. I believe if the belt was just slipping then it would lack hydraulic power only and not big the motor done. Right? Air filters are new. Fuel shut off solenoid opens fully and did it manually and wired it open. Still acted the same.

I'm running out of ideas Jaredj.

To clarify for everybody the work done so far; fuel lines checked, lift pump replaced, fuel filter replaced, air filters replaced, verified fuel solenoid lever fully engaged, non-turbo engine.

The only thing I can thing to try, just to verify fuel supply, would be disconnect the fuel line from the primer bulb and drop that fuel line into a clean fuel can, see if it responds differently. Aside from that, and I hesitate to go there just on internet diagnosis, but maybe time to pull injection pump section and have it checked, that is if you have an injection shop nearby. :beatsme

What brand and number of fuel filter are you using?

Not sure it's farm fuel though.

When i was at the rental company we had a dynapac roller that kept losing power. Change fuel filter it would run good until put under hard up hill pull. Changed many filters cleaned tank replaced fuel lines replaced fuel filter base and even sent injector pump off. Finally as a shot in the dark i went to parts house and bought a different filter.( a bet with shop forman if it didnt fix it the company didnt have to pay me for filter) well it fixed it. Im glad he was the one that pulled the injector pump off and not me. We had all our filters of that number sent off and tested. Everyone failed.

I'll be damned. I'm usin bobcat brand filters.

Well you should be good there

How many hours are on your machine? If your pump or injectors are weak, that'd cause some power issues, does it look as if they've been meddled with? Paint chipped? Nut smeared?

Not having a turbo automatically means that when you put a big load on the engine, it is much slower to regain its composure. If your engine isn't reaching rated high idle, again, you'll notice a lag in performance.

quick test
start the machine, and run at full throttle
engage the aux

if the engine still bogs down hard, and wants to stall
1 check the primer bulb
2 pump the primer see if it changes the engine rpm

report back

:drinkup

what about the fuel pickup tube, some times they break off near the top so if you simply add fuel the symptoms will go away until you get down to where the break is. When the tube first cracks, it pulls air and not enough fuel and gives the illusion that something is wrong with the engine, when if finally breaks off then it will quit all together. I had to hang a 5 gallon diesel can off the back door to get it back the shop for repair. Don't blow air backwards to the fuel tank, there is a check valve on the end of the pickup tube and you will blow it off. If you haven't already replaced the fuel pick tube the originals will rot off anytime after about 10 years. Mine fell off with only 471 hours on it.