Help me help a good friend - Bobcat 873 starting/running issues

[DigitalFusion]

Hey all, A very good friend of mine is helping me out big time by letting me use his 873 while I am building my new garage. It has a few issues, and I think fixing it for him would be the right thing to do. The machine will only start if you shoot a qwik shot of starting fluid on the air filter. It doesnt matter if its warm or cold, you have to do this every time to get it to start. Once its running it normally doesnt have any issues. The other day we were using it a lot, and it starting bogging down and dieing under only moderate loads such as pushing a dirt pile or lifting a stump... things this machine should handle no problem from my past experience with skidsteers. It also progressively needing more and more either to get it to start, sometimes starting up fine after a moderate shot, then idling down very low then killing out. The next day I fired it up after a heavy shot of either, and worked with it for at least an hour, maybe two and it had no running issues at all. So far he has replaced all the glow plugs, both fuel filters, and the rubber fuel feed lines. I did some browsing on this forum, and am thinking the next logical step is to disconnect the fuel line before the fuel filter and run a new line to a separate fuel supply to see if it is the fuel pickup being damaged? Can I just run this tube into a can of fuel or do I need to pump it somehow?

 

[DigitalFusion]

I cant edit the post? It ignored all my line breaks and made the post one big paragraph?

 

[thetool]

I cant edit the post? It ignored all my line breaks and made the post one big paragraph?

1. Make sure you have html on in your profile.
2. With the stuff already done to the machine, methinks it's time to do a compression test.
Good Luck

 

[DigitalFusion]

1. Make sure you have html on in your profile.
2. With the stuff already done to the machine, methinks it's time to do a compression test.
Good Luck

from what was reading on here via searches, its a very common thing for the fuel pickup to get brittle and break. The issues with this machine also seem to be more pronounced when the fuel level gets low... I am going to go out and flip the cab and check that sender really qwik.

 

[DigitalFusion]

from what was reading on here via searches, its a very common thing for the fuel pickup to get brittle and break. The issues with this machine also seem to be more pronounced when the fuel level gets low... I am going to go out and flip the cab and check that sender really qwik.

this forum doesnt work with firefox on html mode....

the 873 is much different from the others I guess... lifting hte cab and looking to the left doesnt apply to this machine. The pump is on the back of the block, and following the feedline back only goes so far. It looks like the feedline connects to the tank behind the block?

 

[Tazza]

this forum doesnt work with firefox on html mode....

the 873 is much different from the others I guess... lifting hte cab and looking to the left doesnt apply to this machine. The pump is on the back of the block, and following the feedline back only goes so far. It looks like the feedline connects to the tank behind the block?

It does sound like a fuel pump or pickup problem or low compression. But as it needs ether to start even when warm makes me think its fuel related. Even an engine with low compression when warm usually starts pretty easily.
Does it smoke when running? I'm just wondering if the injectors could be the problem too, but usually you get smoking.

 

[DigitalFusion]

It does sound like a fuel pump or pickup problem or low compression. But as it needs ether to start even when warm makes me think its fuel related. Even an engine with low compression when warm usually starts pretty easily.
Does it smoke when running? I'm just wondering if the injectors could be the problem too, but usually you get smoking.

honestly, I dont recall too much smoke when running... I know you get a puff when it first starts, but I never paid too much attention to the level of smoke while he or I is operating it. I was thinking of going and getting some fuel, and disconnecting the line from the tank to the pump, and placing that line in fuel can as that would let me know if it was the pickup or not.
I was reading some of the posts I found by searchign (the search feature here isnt the best, 32 pages of results no matter what search terms I use) that there is a screw on top of the pump somewhere that can let air into the system?

 

[DigitalFusion]

honestly, I dont recall too much smoke when running... I know you get a puff when it first starts, but I never paid too much attention to the level of smoke while he or I is operating it. I was thinking of going and getting some fuel, and disconnecting the line from the tank to the pump, and placing that line in fuel can as that would let me know if it was the pickup or not.
I was reading some of the posts I found by searchign (the search feature here isnt the best, 32 pages of results no matter what search terms I use) that there is a screw on top of the pump somewhere that can let air into the system?

we just checked the pickup, its fine, the screen is clear, and we can hear the check valve bb rattle if we shake it. What are these things? They seem to be leaking, seems like a good bet they are the cause?

 

[Tazza]

we just checked the pickup, its fine, the screen is clear, and we can hear the check valve bb rattle if we shake it. What are these things? They seem to be leaking, seems like a good bet they are the cause?

As far as i was aware those are the injector pumps, it seems like there is one per injector, not sure how they regulate how much fuel goes to each injector though.... The leaks, is it fuel? or simple engine oil?
It doesn't take much of a leak to look like its worse than it really is.
A small fuel leak i don't think would cause the problems you are having, a compression test would be a good idea, if its low you know why its hard to start, but if its good, it has to be the fuel injection system.

 

[DigitalFusion]

As far as i was aware those are the injector pumps, it seems like there is one per injector, not sure how they regulate how much fuel goes to each injector though.... The leaks, is it fuel? or simple engine oil?
It doesn't take much of a leak to look like its worse than it really is.
A small fuel leak i don't think would cause the problems you are having, a compression test would be a good idea, if its low you know why its hard to start, but if its good, it has to be the fuel injection system.

can I just use a standard compression tester? Those holes for the glow plugs look aweful small. What is the compression supposed to be at? How do I disable the fuel for the compression test? There does not appear to be any switch or lever near the pump to shut things down like some of the other 'cats have.

 

[Tazza]

can I just use a standard compression tester? Those holes for the glow plugs look aweful small. What is the compression supposed to be at? How do I disable the fuel for the compression test? There does not appear to be any switch or lever near the pump to shut things down like some of the other 'cats have.

I don't know how to turn the fuel off sorry, but the compression should be 400+ PSI at a guess. Is that an oil cooled Deutz engine there?

 

[DigitalFusion]

I don't know how to turn the fuel off sorry, but the compression should be 400+ PSI at a guess. Is that an oil cooled Deutz engine there?

im 99% sure its a kubota
(No, these use a Deutz engine Ken)

 

[DigitalFusion]

im 99% sure its a kubota
(No, these use a Deutz engine Ken)

lets play devils advocate and pretend the compression test comes back fine... what would be the next logical troubleshooting step? I need to use this thing, and I dont want to keep having to use ether on it everytime as its just asking for trouble.

btw - talked to my buddy today, he said he already replaced the fuel pump in addition to the items mentioned above (return lines, rubber feedlines, steel feed lines, both fuel filters (and we checked the pickup today))

 

[Tazza]

lets play devils advocate and pretend the compression test comes back fine... what would be the next logical troubleshooting step? I need to use this thing, and I dont want to keep having to use ether on it everytime as its just asking for trouble.

btw - talked to my buddy today, he said he already replaced the fuel pump in addition to the items mentioned above (return lines, rubber feedlines, steel feed lines, both fuel filters (and we checked the pickup today))

If the compression is good i would suspect the injection. Hopefully just the injectors. You should be able to pull them out and attach the tube lines so you can hang the injectors out the back of the machine. Crank it till fuel comes through. I think its in-direct injection so the spray should be a nice cone, direct injection makes like a star shape out the tip, out to the sides.
Its a bit crude but it works. I have done this many times on my machines.
The spray should be even, no droplets on the tip. This is just a go or no go test, it will not tell you what the cracking pressure is, an injector shop will need to test that. It will however show you the spray pattern which i hope is the problem as its cheap to fix.

 

[GhostOp]

If the compression is good i would suspect the injection. Hopefully just the injectors. You should be able to pull them out and attach the tube lines so you can hang the injectors out the back of the machine. Crank it till fuel comes through. I think its in-direct injection so the spray should be a nice cone, direct injection makes like a star shape out the tip, out to the sides.
Its a bit crude but it works. I have done this many times on my machines.
The spray should be even, no droplets on the tip. This is just a go or no go test, it will not tell you what the cracking pressure is, an injector shop will need to test that. It will however show you the spray pattern which i hope is the problem as its cheap to fix.

This might be a dumb question, since diesel engines are new to me, but is it possible that the fuel is leaking back when the engine is shut off? This would make it hard to start, wouldn't it. My 825 (Perkins engine,) has a little lever on the fuel pump, you break open a fitting and pump the pressure up until all the air is out. My machine wouldn't start if it sat for a week or so, without copious amounts of ether and/or priming. Since I changed out the fuel pump and filter, it always starts now without fluid. It now will sit for two weeks at a time and fire right up after a few seconds with the Thermo-Start manifold pre-heat turned on. I always use WD-40 instead of ether, it starts just as well, and I hope, although I have no empirical evidence to support this, that the WD-40 might offer a little better lubrication. As I said, diesels are new to me, so I've been following this thread and learning a little. Thanks, Jerry

 

[DigitalFusion]

This might be a dumb question, since diesel engines are new to me, but is it possible that the fuel is leaking back when the engine is shut off? This would make it hard to start, wouldn't it. My 825 (Perkins engine,) has a little lever on the fuel pump, you break open a fitting and pump the pressure up until all the air is out. My machine wouldn't start if it sat for a week or so, without copious amounts of ether and/or priming. Since I changed out the fuel pump and filter, it always starts now without fluid. It now will sit for two weeks at a time and fire right up after a few seconds with the Thermo-Start manifold pre-heat turned on. I always use WD-40 instead of ether, it starts just as well, and I hope, although I have no empirical evidence to support this, that the WD-40 might offer a little better lubrication. As I said, diesels are new to me, so I've been following this thread and learning a little. Thanks, Jerry

I havent had time to do a compression test or test the injectors. I went out just now to monkey with it, but since its cold and rainy I didnt want to open up the injectors. It started right up with just a tiny shot of ether and ran great. I paid attention to the smoke this time. There was a good puff of smoke when it fired up and then it ran clean. I picked up some brush and just did some light stuff and it still was running clean without smoke. I need to get some more fuel for it before I do anything else.

 

[Tazza]

I havent had time to do a compression test or test the injectors. I went out just now to monkey with it, but since its cold and rainy I didnt want to open up the injectors. It started right up with just a tiny shot of ether and ran great. I paid attention to the smoke this time. There was a good puff of smoke when it fired up and then it ran clean. I picked up some brush and just did some light stuff and it still was running clean without smoke. I need to get some more fuel for it before I do anything else.

If it uns clean it rally doesn't sound like injectors.... Fuel leaking back could indeed me an idea.
When you don't give it a snort of ether, what does it do? does it puff white smoke and refuse to start?

 

[DigitalFusion]

If it uns clean it rally doesn't sound like injectors.... Fuel leaking back could indeed me an idea.
When you don't give it a snort of ether, what does it do? does it puff white smoke and refuse to start?

if we don't give it a lil ether it just cranks, sounding like its right on the verge of starting. I didnt notice if it was smoking or not when we dont use ether.
how does the fuel leak back? what would be the right way to explore that option?
(edited Ken)

 

[DigitalFusion]

if we don't give it a lil ether it just cranks, sounding like its right on the verge of starting. I didnt notice if it was smoking or not when we dont use ether.
how does the fuel leak back? what would be the right way to explore that option?
(edited Ken)

fixed typo