763 Bobcat pours black smoke

[fwilson]

Hello everyone. I am having a problem with my 763 bobcat. It pours black smoke when it is running. I have had the injectors rebuilt [2300 hrs]and I have done a compression test which shows the cylinders are within range of each other[410,406,402,408]. The fuel and air filter have been changed just to be on the safe side. The smoke from the best that I can tell is fuel and not oil smoke. It does not use any oil. Any suggestions?

 

[Tazza]

The compression sounds good, and you did all the standard things, there really is nothing else i can think of..... I'm just wondering if its over fueling somehow. Its possible the pump may need checking too. if it somehow got out of adjustment and is pumping too much fuel in, even if its only to one cylinder it will smoke.
If it was blue, it would be burning engine oil....
I assume it doesn't have a turbo? but burning engine oil through the turbo should give blue/white smoke.
Anyone else got any ideas?

 

[skidsteer.ca]

The compression sounds good, and you did all the standard things, there really is nothing else i can think of..... I'm just wondering if its over fueling somehow. Its possible the pump may need checking too. if it somehow got out of adjustment and is pumping too much fuel in, even if its only to one cylinder it will smoke.
If it was blue, it would be burning engine oil....
I assume it doesn't have a turbo? but burning engine oil through the turbo should give blue/white smoke.
Anyone else got any ideas?

Hmm no, it basically runs ok?
No turbo on this one, same as 753
Ken

 

[Tazza]

Hmm no, it basically runs ok?
No turbo on this one, same as 753
Ken

Only thing i can think is load?
If its under constant load from say the aux being stuck on it will load the engine down and blow smoke, mainly at idle, but at say 1/3 or higher throttle the engine shouldn't even know its drawing power.
Black smoke is text book plugged air filter or bad injectors. I sure hope you figure it out.

 

[mrfixitpaul]

Only thing i can think is load?
If its under constant load from say the aux being stuck on it will load the engine down and blow smoke, mainly at idle, but at say 1/3 or higher throttle the engine shouldn't even know its drawing power.
Black smoke is text book plugged air filter or bad injectors. I sure hope you figure it out.

How good is your fuel? Maybe a bad batch....if the problem is just recent.

 

[rbryant]

I had a 751 do the same thing. I had the pump rebuilt and problem solved.

 

[soutthpaw]

I had a 751 do the same thing. I had the pump rebuilt and problem solved.

somehow your engine is overfueling period! (the only way to get constant black smoke) or almost completely obstructed air intake system.. Injector pump is a good place to start if the Injectors have been rebuilt...

 

[soutthpaw]

somehow your engine is overfueling period! (the only way to get constant black smoke) or almost completely obstructed air intake system.. Injector pump is a good place to start if the Injectors have been rebuilt...

I can't edit my previous post, however if you try disconnecting the injector lines at the injector one at a time and use a clear piece of hose to capture the fuel from that line you can test for bad injector/ pump. do one at a time and run the machine on 3 cylinders to see if the smoke goes away you can also compare the flow of fuel to each injector.... if this solves the smoke problem, switch the guilty injector to another cylinder and see if the smoke returns. if so you know the injector is bad. if it stays clear, reconnect the fuel line and see if smoke returns with the swapped injector... then you know it is the pump issue.

 

[Tazza]

I can't edit my previous post, however if you try disconnecting the injector lines at the injector one at a time and use a clear piece of hose to capture the fuel from that line you can test for bad injector/ pump. do one at a time and run the machine on 3 cylinders to see if the smoke goes away you can also compare the flow of fuel to each injector.... if this solves the smoke problem, switch the guilty injector to another cylinder and see if the smoke returns. if so you know the injector is bad. if it stays clear, reconnect the fuel line and see if smoke returns with the swapped injector... then you know it is the pump issue.

I have essentially done that before too. If it is indeed a pump/injector simply winding back the nut on the injector line at the injector say 1/2 a turn, this is enough for it to not build up pressure to open the injector. It will make a mess with fuel, but you can wash that off. The engine will run on only 3 cylinders too, as southpaw said. If you are lucky, its a bad injector nozzle that the shop that re-built them missed...

 

[skidsteer.ca]

I have essentially done that before too. If it is indeed a pump/injector simply winding back the nut on the injector line at the injector say 1/2 a turn, this is enough for it to not build up pressure to open the injector. It will make a mess with fuel, but you can wash that off. The engine will run on only 3 cylinders too, as southpaw said. If you are lucky, its a bad injector nozzle that the shop that re-built them missed...

Somehow I can see just one bad injector making it smoke black, maybe grey....
Not that the suggestions given are not worth trying. They wil help you isolate the trouble
Ken