help for sick running Cummins B 3.9 ?

[Mike Van]

Last winter I thought I had icing problems with the fuel in my loader, I can pretty much bet thats not what it was as in July, I still have trouble. The picture shows what it is, hopefully, and what it's doing is running out of fuel. It'll suck the water sep. and the fuel filter half empty, run no higher than idle, sometimes stall altogether. Sometimes after it stalls, I can start to spin off the water sep can, and hear a hiss as it either sucks in air or lets it out. I've changed the water sep, the fuel filter, drained the tank & blown out the lines [FUEL & RETURN] The tank was clean, it has a standpipe up into the fuel. It may start right up and seem fine, but in two minutes it'll just go flat, only idle, sometimes pick up and go, most times not. I hope I'm missing something easy, never owned a diesel before. Sometimes as it's getting going again, I'll get smoke out the stack [usually theres none] Those 4 fittings on the lines I've cracked lose while it's idling, fuel will squirt out & the idle bog down until I tighten it again. ???? I'm lost.

 

[lantraxco]

If the fuel suction line from the separator to the tank, or any part of it, is rubber hose, pull it out and just replace it. Most likely thing is that the hose is either sucking flat or the inner rubber liner has separated and is collapsing when under suction. The thing that makes it hard to figure is that you can blow pressure through with no problem, but under suction they'll close up. Just a guess. Another quick and dirty test is to run a short piece of good hose off the inlet to the separator into a gallon can of clean diesel and see if the engine likes it.

 

[Mike Van]

The suction line is that hard black plastic, the return is softer type hose. I thought about just sticking a 5 gal can up on the back, see if it ran steadier, may have to yet.

 

[lantraxco]

Probably got a kink in it somewhere, or has been too close to a hot object, unless you've already examined every inch of it. I would have said it was sucking air somewhere except you described a hissing sound when you loosen the separator which leads me to believe it's a blockage in the suction someplace. I am assuming, because I can't remember, that the water separator is before the transfer pump, and the filter is after, correct?

 

[wornout wrench]

Make absoulutely sure that there is nothing in the tank. I have had that drive me crazy trying to figure out what the fuel starvation problem is. A piece of something floating around, gets pulled onto the suction line, engine dies then once the vacuum is gone, piece falls off to float around until next time.

I agree with Lantraxco, replace the rubber parts. Make sure you use proper hose rated for fuel.


If you go with trying the 5 gallon can, make sure that you run both the suction and return lines to the remote can.
What you are describing sound like a classic fuel starvation problem, if you set up a remote tank and it all runs well, you have found the problem, just make sure that when you try it, you use all new rubber hose.
Personally, myself, I would change the hose first and see what happens, they deteriorate over time.

So the 4 fittings that you are showing in your picture are the high pressure injector lines. The fuel pump makes the pressure and times it to the engine. When you crack the line you loose the high pressure to the injector and cause a misfire, hence the engine bogging down, just like taking the wire off a spark plug.

Hope this helps

 

[Mike Van]

I am assuming, because I can't remember, that the water separator is before the transfer pump, and the filter is after, correct?

I believe it is, the filter is behind the sep., on the same casting, can't see it in the one pic I have here. Theres a little plunger/pump, it brings very little fuel to the water sep. first, that fills, then the fuel filter, then the pump.

 

[Mike Van]

Make absoulutely sure that there is nothing in the tank. I have had that drive me crazy trying to figure out what the fuel starvation problem is. A piece of something floating around, gets pulled onto the suction line, engine dies then once the vacuum is gone, piece falls off to float around until next time.

Hope this helps

I wish I could see down into the tank, but it's got an offset in the filler neck.

 

[Andrew_D]

We have a 3.9L B series on our MacDon swather, but haven't had any troubles (knock on wood) with it.

I have had trouble with my N14 in my KW W900 though. On it, there is a check valve in the fuel line. For some reason, I keep getting bits of plastic stuck in the check valve. Symptoms are lots of coughing and sputtering, stalling, hard starting. First time it happened was winter and drove me nuts. Now I know to pull the filter off first. If it sucks air, the fuel just drained back into the tank and I know I've got another piece of plastic stuck in the check valve. Take it apart, clean the valve, put 'er back together. Is there a check valve anywhere in the fuel suction system on the 3.9L's?

Andrew

 

[Mike Van]

Right behind the big hose in the pic. is the hand pump/primer button Andrew, there's probably a check valve in it, just guessing. It's one of the few things I haven't had apart, so i'll check it. Since spring, the problem is getting worse, so maybe something is slowly plugging up -

 

[Cotterpin]

Also check to make sure the fuel tank is vented . Wasps and spiders like to plug small holes .

 

[icestationzebra]

if you suspect that air is getting in try a short lenght of clear line and look for bubbles. ISZ

 

[Mike Van]

I get to report a happy ending here - I took the plunger/primer unit off, not knowing it was also a mechanical fuel pump - Just inside is a 1" or so brass screen that was pretty much plugged with what I could best describe as wet pipe tobacco - The screen is the coarsest i've ever seen, not like the fine ones on a tractor, but it still caught all that junk, before the junk even gets to the water/sep & fuel filter. I ran it about 15 minutes moving some logs, and it never skipped a beat. Thanks all - Only bad news, I broke yet another drop light bulb.

 

[Andrew_D]

Congrats on getting it figured out!

Andrew