Cummins misfiring and exhaust "pop"

[Extreme-Duty]

Sorry, it's me again. Our Cummins 4BT 3.9 (VE pump) started doing this a few months ago, but stopped doing it temporarily. We cannot go beyond 1500 - 1600 rpm without getting misfiring and exhaust "popping". By popping I mean "pressure waves" of some kind. When it does this, there is NO visible smoke. At low RPM, everything seems normal, other than a little white smoke, the B7 might be a contributor here.

- The fuel filters are about 250 hrs. old and fuel can easily be pumped through them.

- The fuel pin and the AFC cone move easily and have been lubricated, while the diaphragm was replaced yesterday.

- Today, I replaced the lift pump, but the result is disappointing.

What I am thinking of now is:

1. The air filter
2. The injectors (The engine starts excellent 365 days/year, but you can never know with the Lucas, it's not THE PODs though).
3. A flat camshaft/other valve train issues??
4. A burnt or stuck valve??
5. A burnt piston (no excessive blow-by or oil consumption though).

No matter if the engine is gonna die, it's gonna kill me on its way.

 

[slickrocko1]

I would wonder about water in the fuel. As you may know, "biodiesel collects water, as it is more hydrophilic.
Even b4 is worse about collecting water from condensation in tanks, also, have you been buying your fuel from a commercial vendor? Sometimes small vendors have fuel in their tanks longer, which can add to the water in suspension problem. I would definately change those water separation filters!!

True, My Cummins is a 6 cyl, but have had the water problem from a small fuel station that did not sell much diesel compared to the big rig station I normally use.

Steve, in Kalifornia

 

[BobFout]

Might try some LiquiMoly / LubroMoly diesel additive?

 

[Chris142]

Flat cam or valve adjustment.Have the valves ever been adjusted?

 

[Cause4Alarm]

check the pump and injectors

 

[Extreme-Duty]

Wow, thanks for this variety of replies. A few more details:

We buy the diesel from one of the larger distributors in the area. The other tractors using it don't have similar issues.

Currently, the engine has a FS1280 fuel/water seperator. When I replaced the lift pump, I drained a cup of diesel from the filter and about a quart from the tank, no visible signs of water so far.

In July, we started using a multi functional fuel additive, which is supposed to add 750 PPM 2-Ethylhexyl-nitrate cetan improver.

A cam issue is not really inline with the fact that the misfiring went away for some time, but it's certainly due for a valve adjustment. I did one at approx 3.300 hrs, now it got 11.81x hrs. By the end of December, the filters were changed, and it was like all problems were gone, but the filters do not feel restrictive by now. The stuff I drained from the tank "looked good", and the storage tank is equipped with a filter.

Personally, I hope it's bad injectors, because the pump is unlikely to be a do-it-myself job.

In case something is wrong with the VE pump, what do you think it is, timing regulation?

 

[onion]

Without being able to listen to and lay my healing hands upon that engine, I can only venture a guess. But from what you're describing, I would probably start with a valve adjustment. Sounds like it's LONG over-due.

It would also be a good idea to check the fuel pressure, and check for aireated fuel. To check fuel pressure, the easiest way is to buy another banjo fitting to install at the OUTLET of the fuel filter. Drill and tap that banjo fitting so that you can plumb a gauge into it. It's been 11 years since I quit working at a Cummins shop, but I THINK the fuel supply pressure on that engine should be in the neighborhood of 3-5 psi, but you'll want to confirm that. The easiest way to check for aireated fuel is the run the return line into a bucket and watch for bubbles- particularly at high RPM. If you see bubbles, the fuel system is sucking air somewhere. Likely from the fuel supply line from the tank to the transfer pump, but possibly from the pump itself or the stand pipe.

If the valves are adjusted properly, the fuel pressure is ok, and there are no bubbles (or very few) in the fuel. then I would probably blame the injection pump.

 

[mechtech2]

Could be a weak valve spring, or faulty valve.

Lack of fuel for a variety of reasons would also fit the symptoms perfectly.

 

[Extreme-Duty]

Thanks for laying your healing hands upon your keyboard, Onion. A valve adjustment is to be done soon. To get the fuel pressure, I would have to buy a gauge, so that is nothing I can do today.

What I did is to disconnect the return line, and while it was misfing and popping, I got a steady stream of fuel and no visible air bubbles.

In 2008, I replaced these hard-to-reach hoses behind the fuel tank and last summer, they were retightened. Still, there might be a leak on the suction line inside the tank, who knows. Time to fuel her up.

Edit: Also changed the air filter today.

 

[Extreme-Duty]

Injectors would be cheaper to start with than valves, what am I gonna do?

 

[onion]

Injectors cheaper than a valve adjustment? That seems unlikely.

Will you be doing the valve adjustment yourself, or paying somebody to do it? A valve adjustment on that machine should require some valve cover gaskets and an hour or two of labor. It's not a difficult procedure. I could walk you through it if you want to do it yourself.

I suppose injectors are a possibility, but they wouldn't be high on my list. Usually a bad injector will cause a consistent miss and/or smoke. A set or worn-out injector nozzles will cause smoke and hard-starting when cold... not unlike low compression, really.

 

[Extreme-Duty]

Oh yeah, I made it sound weird. It was in reply to Mechtech's suggestion on a bad valve or spring. The less expensive valve cover seals from the Cummins dealer, are likely to arrive tomorrow.

Bad injectors are wishful thinking in this situation, I guess.

What symptoms can be seen with defective delivery valves as such?

Scheduled for tomorrow, btw: Putting a new seal kit in the Eaton steering valve/handpump. Any hints, Onion?

 

[onion]

I've re-sealed a couple of those, but it's been a long, LONG time (over a decade ago). As I recall, that steering pump is a pretty intricate mechanism, and you're better off not taking it completely apart. Once you remove the pump, you can unbolt the top plate, and remove that leaving the rest of the pump intact. You can replace the shaft seal in that top plate without much trouble- nothing unusual there. If you have the type of steering pump that I'm thinking of, there will be a long, thin, cylindrical perimeter seal- looks almost like a very thin piece of hose. You can carefully pull out the old one with needle-noze pliers and carefully slide the new one in without disassembling anything but the top plate.

If this doesn't describe what you have, then I can't help you. These rarely gave trouble during my brief time at the Case dealership, and we rarely worked on them.

As for a bad delivery valve in the injection pump, I can't give you much useful info on that. I've never worked in a pump shop. In most of the shops where I've worked, we would pretty much eliminate everything but the injection pump for troubleshooting purposes... then if we thought the pump was the problem, we'd either send it out to be rebuilt, or install a reman pump.

If you do end up removing that injection pump, here's a tip that can save you a headache: As I recall, this tapered pump shaft is keyed (I know the VP44 is, and I THINK the VE is too). So first make sure that the engine is at #1 TDC before you remove the pump- this ensures that the key is on the 'top' side of the shaft. Then once you break the taper loose and are ready to remove the pump, pull it out slowly and carefully, making sure not to drop the key. 'Cause it CAN fall out of the keyway and into the gearcase... in which case you've got a real mess on your hands.

 

[Extreme-Duty]

Thanks again Onion, the shaft seal is about as you describe, maybe a bit shorter. I think it is just "a ring" with a teflon lining. That's how it is supposed to be in the "Low input torque" version. The regular pumps use an x-ring from what I understand.

Even though the Eaton manual says it is a good practice to replace ALL seal, I might just follow your advice to stay out of trouble.

What I plan to do on the engine is to adjust the valves, and to try to determine whether there is an ultimately flat cam somewhere. If not, I would say the engine deserves some reman injectors after +11.819 hrs. Needles to say, we have to be prepared for a new pump also, but we will see.