Intermittent rough running, coughs when starting

[BeezFun]

Two symptoms, not sure if they're related:

• 
  When cold starting, engine runs rough and sputters for a few seconds, kind of like a gas engine that has too much fuel. Requires glow plug even in hot weather. Sometimes takes several starting attempts. After a few seconds it runs smooth. Warm starts are fine.

• 
  Occasionally while running at operating speed, it will run rough like it's only running on 2 of the 3 cylinders, then it clears up in 5-10 seconds. No noticeable smoke and exhaust pipe has some soot in it, but no fuel smell, and no oil.

I cracked open each of the injector nuts while it was running, and the change in sound/speed on each cylinder was the same. I don't have a compression tester, but I would have thought if the compression was bad in one cylinder it would show up when I cracked the nut on that cylinder. Also adjusted the valves, which didn't really need adjusting.

Any thoughts on how to diagnose this? The engine is 3cyl Shibaura with 2500 hours in a New Holland, but this forum is much more active so I thought I'd have a better chance posting here. I did change the fuel filter on it when I bought it a few months ago, and it was totally packed with fine sediment and grass, surprised it ran at all. I flushed the fuel lines backwards, cleaned the tank, and replaced filter, but that doesn't seem to have any affect.
tnx

 

[Pepsiboy]

How many hours on tractor?? I had similar problem with my BX 2350. turned out primary fuel filter was plugged. Changed that and problem was gone for about 4 days. Turned out REAL problem was that electric fuel pump was going out. New was $250 from Kubota Found aftermarket one at Auto Zone for $50. It had higher flow rate and higher pressure than original. No more starting OR rough running problems.:thumbsup: Took me about 45 minutes to change pump, including draining fuel tank first.

Best luck with your problem. :2cents:
Dave

 

[Rocky Hoffler]

If it starts fine when hot and only gives problem when it has been sitting for a time you might have a fuel drain back issue could be a check valve in the return to tank line

 

[BeezFun]

How many hours on tractor??

2500

Turned out REAL problem was that electric fuel pump was going out.

My pump is mechanical, but I suppose it could still have a problem.
tnx

 

[BeezFun]

If it starts fine when hot and only gives problem when it has been sitting for a time you might have a fuel drain back issue could be a check valve in the return to tank line

Doesn't have a check valve in return line. But while checking the manual to find out, I discovered there's a troubleshooting table for the fuel system. One of the things that fits my symptoms is an air leak on the suction side of the system. Not sure how I check for an air leak, but I'll look into that.

 

[Rocky Hoffler]

There hard to find will suck air and not leak if its rubber line try looking for damp area or dirty area if you can bend hose look for cracks or just replace hose cheap and then you know that line is ok.
If possible clamp off line at tank and then put a small amount of pressure on line and look for leak Good Hunting

 

[Pepsiboy]

2500

My pump is mechanical, but I suppose it could still have a problem.
tnx

BeezFun,

Does your tractor have JUST the mechanical fuel pump to the injectors? Or is there another fuel pump between the fuel tank and the injector pump? Mine has an electric fuel pump between the fuel tank and the injector pump. That is what I was referring to. If that pump has failed or is starting to fail, it could cause your problem. With the high hours on your tractor, I would guess that the fuel line MIGHT by the problem, also. :2cents: As others have said, I would also check the fuel lines for leaks.

Good luck. Please let me know how you do with this problem of yours. Thanks.

Dave

 

[BeezFun]

I installed a piece of clear plastic tubing between the filter and fuel pump. That allowed me to see any air bubbles if it's sucking air. No bubbles, so there's no air being introduced prior to the fuel pump. I guess there could still be something wrong with either fuel pump or injector pump, not sure how to diagnose that without guages to measure pressure in the line. I think I'm going to check compression next, I must know someone with a guage and adapters I can borrow.

 

[Pepsiboy]

I installed a piece of clear plastic tubing between the filter and fuel pump. That allowed me to see any air bubbles if it's sucking air. No bubbles, so there's no air being introduced prior to the fuel pump. I guess there could still be something wrong with either fuel pump or injector pump, not sure how to diagnose that without guages to measure pressure in the line. I think I'm going to check compression next, I must know someone with a guage and adapters I can borrow.

You could try putting a small (Zero to 35 psi) pressure gauge on the line that goes into the injection pump, turn on the key so the electric pump runs, and see what pressure is there. If less than 5 psi, replace electric pump. If more than 5 psi, put line back on injection pump and try putting about 6 or 8 oz of fuel injector cleaner into fuel tank. Then run it hard for a while and see if that helps.:2cents:

Dave

 

[BeezFun]

..., turn on the key so the electric pump runs, and see what pressure is there...

Pump is mechanical, not electric. I disconnected line at injector pump and cranked engine, output from fuel pump was quite impressive, so I don't think there's a problem with fuel pump. I don't think a mechanical pump fails the same way an electric pump fails, it would either work or not work, but wouldn't exhibit intermittent problems.

 

[sandyc]

glow plugs?

 

[Rocky Hoffler]

A diesel eng needs certain things to run it was running before so we assume that it's in time. So you have to have fuel and air, compression makes it fire have you checked air filters to see if they are clean . secondary air if equipped will sometimes look clean but can be stopped up take filters out and if it still does not start get a can of silicon spray as this is less likely to damage eng as starting fluid spray in intake while cranking. If it trys to run or starts leads toward fuel delivery problem. Good Luck

 

[rbargeron]

"Coughs when starting"

• 
  When cold starting, engine runs rough and sputters for a few seconds, kind of like a gas engine that has too much fuel. Requires glow plug even in hot weather. Sometimes takes several starting attempts. After a few seconds it runs smooth. Warm starts are fine.............................../QUOTE]
  
  Does this mean when it sputters it is blowing back? Can you describe the coughing and sputtering a little more? Any mechanical "ticking" with it? Maybe a lazy intake valve?

 

[BeezFun]

glow plugs?

Forgot to mention, that was first thing I checked.

 

[BeezFun]

...have you checked air filters to see if they are clean . secondary air if equipped will sometimes look clean but can be stopped up take filters out and if it still does not start get a can of silicon spray as this is less likely to damage eng as starting fluid spray in intake while cranking. If it trys to run or starts leads toward fuel delivery problem. Good Luck

I put in a new air filter because the old one was a bit dirty, but didn't think to leave it out. There's no secondary filter on this engine. Never heard of spraying silicon spray, I guess a diesel can burn just about anything.

 

[BeezFun]

Does this mean when it sputters it is blowing back? Can you describe the coughing and sputtering a little more? Any mechanical "ticking" with it? Maybe a lazy intake valve?

I would not say it's blowing back. It reminds me of the old days when cars had manual chokes. If you choked it too much it would flood and when it finally started it kind of sputtered to burn the excess fuel in the cylinder. It does belch a good bit of black smoke when it starts, but not much different than most diesels and particularly one this old (made in '95) that doesn't have all the new air pollution crap on it. It doesn't smoke at all once it's running.
I don't hear any ticking and I adjusted the valves.

 

[doxford jim]

If you can get at them easily, I would be inclined to remove the fuel injectors for testing. That way you can rule out the injectors if they test good and don't leak at all.
Prior to that I would also run some fuel treatment through the engine with the idea of cleaning the injector tips of carbon. Maybe double the recommended dose and work the engine hard will help.
I once had the engine in my F250 emit grey smoke smelling strongly of diesel fuel when running. I put triple dose of fuel treatment in and ran the engine hard for a couple of hours and it cleared up the problem for me. I have not had any trouble since. I think the truck spent too much time without working the engine properly and allowed a varnish type coating to build up.
Anyhow, treating the fuel won't be expensive and I am sure you will notice an improvement of some sort, but whether it will be enough remains to be seen.

 

[BeezFun]

If you can get at them easily, I would be inclined to remove the fuel injectors for testing.

That's my next step, they're really easy to take out. I found Midwest Fuel Injection, they're all over the country and have a place pretty close to my house. If anyone in the Chicago metro area knows a good place that does injectors, please post.

 

[rbargeron]

My first thought was an obstructed injector - maybe get one new injector and try it in different cylinders to see if it helps. Sometimes doing a pattern test costs more than a new injector and then you have to buy one anyway.

 

[Bird]

My first thought was moisture, or just a little bit of water, in the fuel tank.