MEP-003A: Irregular Misfire

[RichardR]

Looking for some help from all the smart diesel engine folks on this forum ...

I have a recently rebuilt MEP-003A with about 10 hours on the clock that runs very well except that the engine seems to miss a beat about every 10 to 20 seconds It misfires just enough to cause a slight dip on the Hz meter and a brief compensating throttle jog up from the governor. Then after the very brief interruption (which I suppose may be only a single cylinder misfire) everything returns to normal until the next unpredictable event. There is no exhaust smoke or other external evidence to help track down what or where is the source of this problem.

I bought this unit from a Federal agency that was trying to use it to run video equipment out in the boondocks, but they couldn't get the video equipment to work with the power frequency glitches so they gave up on it. It was a fresh rebuild when they acquired it, so I suppose it has exhibited this behavior ever since it was rebuilt.

I first suspected that air bubbles were getting into the fuel supply to the Injector Pump, but I have now thoroughly checked out the fuel supply at the IP input and am quite sure that is not the problem. There is lots of fuel flow and no bubbles into the IP. I also flow-tested the IP timing and found it to be very close (as close as I would be able to get it if I were to do it from scratch) so I don't think IP timing is the problem.

There is still a long list of things I can think of to do, including:

1. change the fuel to a fresh supply.

2. look for a sticking valve by removing the valve covers to assure adequate lubrication in that area, taking off the rocker arms and valve springs, and seeing that the valves slide properly in their guides.

3. I am thinking that the valves seat properly and the rings are good since this is a recent rebuild, but I could check cylinder compression.

4. change the IP to a known good unit, but that will require me getting a proper button unless I get lucky and happen to have the right button.

5. run the snot out of it under heavy load in the hope that it will fix itself.

6. etc., etc.

But life is too short and there must be at least someone on this forum who can point me in the right direction. HELP, please. Has anyone ever seen a problem like this?

Thanks for reading this long-winded post and thanks for any wisdom you can provide,
Richard

 

[Robbied46]

This really sounds like a fuel problem to me. I've seen this happen where the fuel pump did not push enough fuel and it would start emptying the filters. As the engine slows, there is less demand for fuel and the filters are refilled. This type situation will not cause air to enter the system. All appears normal until the engine begins to starve for fuel. I would recommend a test of the fuel pump. A partially clogged filter will sometimes result in the same problem. Sometimes you can hold onto the injection lines and feel them pulse. Any change in "feel" could help determine if this is the cause. I would think that an injection problem would tend to cause a little smoke. Adding about a pint of automatic transmission fluid to a full tank of fuel will clean the injectors if you think that could be a problem.

 

[RichardR]

Robbied46,

Thank you for two good suggestions. A weak fuel pump and/or clogged filters, as you suggest, was my first suspicion also. However, there seems to be plenty of fuel pressure at the input to the IP, although I haven't measured it with a gauge. I estimate 10 psi fuel pressure when the input line is disconnected from the IP and covered by my "calibrated" finger. And the free flow volume when the input line is disconnected from the IP will fill a 2-liter soda bottle in less than a minute so there is plenty of volume. And I don't see any air bubbles in the fuel flowing into the soda bottle. So I have pretty much dismissed fuel supply as being my problem. Besides, each "miss" event lasts only a fraction of a second, which seems to me to be too quick for a fuel supply problem to recover by itself.

Feeling the pulses on the injection lines is something I have not tried to correlate with the events, although I have noticed that the lines have a very noticeable pulsing. The first thing on my list is to see if the feel of the pulses changes on one or more cylinders when an event occurs. I suppose that would point to either the injection pump or, less likely, an injector.

Speaking of the Injection Pump, I had it off the engine when I was looking for a timing problem. But I didn't disassemble the pump because I didn't suspect an internal pump problem, and I know from experience that it's a PITA to take one of these apart without the proper tools (which I don't have). Not disassembling the pump when the opportunity presented itself was, I believe in retrospect, a big mistake. I did notice a very slight stiff spot when rotating the face gear, which I have never before noticed on one of these pumps. If I had taken it apart I might have discovered what was causing the stiff spot in rotation and, most likely, discovered my real problem. That's the next thing I have on the list.

Thanks for your suggestions, and I'll let you know what I find,
Richard

 

[storeman]

You mentioned it had old fuel in it. Have you changed the fuel filters and cleaned out the fuel pumps?
Jerry

 

[RichardR]

Jerry,

The Feds I got this genny from pointedly mentioned that they had put good diesel fuel in it, and that couldn't have been more than a couple of months before I bought it. So I am thinking that the fuel in there now couldn't be more than, say, 6 months old. It smells OK although it has a more yellowish color than I am used to. The color may have something to do with it being a summer blend and the hot desert climate they were trying to use it in. In any case, I am going to change it and see if that makes any difference.

Thanks,
Richard

 

[Robbied46]

It sounds like you have eliminated a fuel supply problem. The thing that doesnt make sense is that it clears itself so rapidly. A tight spot in the injection pump doesn't really add up in my mind as the problem because it would go thru quite a few revolutions between events. Have you paid close attention to the governor linkage or the shut down solonoid to see if the linkages are moving during these events? I guess it is possible to have some sort of problem with the governor or a weak coil in the solonoid that would allow it to partially close.

 

[storeman]

"The Feds I got this genny from pointedly mentioned that they had put good diesel fuel in it, and that couldn't have been more than a couple of months before I bought it. So I am thinking that the fuel in there now couldn't be more than, say, 6 months old."

The fuel may not be that old, but I was going by what you indicated were your options (ie, change to fresh fuel).

It is the filters I'd focus on. You don't know if they (federal agency) changed them after they got the unit. Initial testing fuel residue from rebuild has sat in the filters (perhaps for years before the agency got the unit) and you obviously haven't changed the filters or cleaned the fuel pump filters.....Easy small steps that might solve your problem...and SOP for most of the SS members on any new acquisition.
Jerry

 

[RichardR]

Robbied46,

Yes, I agree with you that the quickness of the problem from start to finish is a real puzzle. The duration of an event must be less than half a second. During that brief time, the Hz meter swings down about 2 Hz and the governor arm raises the IP throttle perhaps 0.1 inches in an attempt to compensate. Then everything quickly returns to normal operation. The shut down solenoid does not move and remains clear of the IP throttle arm.

Of course, the actual speed of the engine may briefly deviate from normal (1800 rpm) much more than the Hz meter indicates since the Hz meter cannot capture fast transients. Same for the governor response.

It may be that something is catching or jamming briefly in the IP to quickly slow the engine, then it releases and everything returns to normal. However, I cannot imagine that would happen very often before something went to pieces. And there is no obvious noise during one of these events. It sounds like a simple misfire and only the exhaust note changes momentarily, but no smoke. I have heard of an IP jamming in one of these engines and breaking the camshaft, but I've never heard of one fixing itself and returning to normal operation.

What do you think about the possibility that a valve could occasionally stick open? It would be closed by the rising piston on the next stroke, probably with no damage. I think the only symptom would be a miss on that cycle. However, I would expect the problem to fix itself fairly quickly or to become worse fairly quickly, neither of which is happening here.

At this point I have several good suggestions to work on:

1. change the fuel.

2. feel the pulses in the injector lines.

3. remove the IP and take it apart.

4. take the valve covers off and see how everything looks in there.

Thanks for commiserating with me about this. I'll let you know if/when I find something. First I'll need some warmer weather. It's supposed to actually FREEZE here tonight!

Thanks again,
Richard

 

[storeman]

Whatever.
Jerry

 

[rosco]

Change the filters and fuel!

 

[RichardR]

Thanks! That's still the first thing on my list. Hope it warms up a little so I get to do that soon.
Richard

 

[steelypip]

If the filters and fuel don't fix it then you're down to a relatively small list of possible causes:

1. weak lift (electric) pump - unlikely or it would get worse instead of clearing itself up. That's also why i don't anticipate success from cleaning filters as long as there's no water in the system.
2. something goofy with the injection pump. This sounds like it could be a sticky outlet check valve or something similar
3. something wrong with an injector. If one pop-tests weak that could certainly cause some operational oddities. I'd look for one cylinder slower to light than the others during startup.

After a thorough scrubbing of the fuel system (including tank) and another test run, if the problem recurred, I would put the thing under whatever load maximizes the sputter and then go after the engine with an infrared thermometer. See if one cylinder is colder than the other three.

 

[storeman]

I agree with Steelypip. Injector would be the next most likely culprit. I've seen several units where of the 4 injectors, 3 test about 1750 psi and one will be down around 1300 or 1400 psi, so it fires early and fuel is not combusted. Also seen injectors from contract rebuilt engines where 2 or 3 were OK, but other one was frozen. I guess the latter would be from fuel gumming the injector, the former from installing an improperly adjusted injector in a rebuild project. Once I adjust them to 1750 +,- 50, they seem to function as expected.
Jerry

 

[RichardR]

I finally got back to the irregularly misfiring MEP-003A and went down the list of suggestions for fixing it. By far the most frequent recommendation was to put in fresh fuel and clean out the fuel system, so that was the first thing on my list. I drained the old fuel and changed the filters, etc. I really didn't think that would have any effect because there was no water in the fuel, no rust or gunk anywhere in the filters or fuel tank, and the fuel itself looked and smelled like ordinary diesel fuel to me. Nevertheless, changing the fuel fixed it.

I filled it with fresh pump diesel and gave it a go. It started with only a few seconds of cranking, ran a little rough at first but quickly settled down and never missed a beat after that.

There is apparently something about the old diesel fuel that doesn't work as well as the new stuff, but I'm not completely convinced that it is just age. The folks I bought this unit from made it a point to tell me that they had put good fuel in it just a few months ago, and they must have run it more than 5 hours on their fuel before they gave up and surplussed the unit. The only difference I can tell between the old and new fuel is that the old fuel has a slightly darker yellow color than what I am now feeding it.

I now have a total of about 10 gallons of the old fuel. I'll bet the deuce will suck it up without complaining.

Thanks for all the good suggestions, even the ones that I didn't get a chance to try,
Richard

 

[NJ_Toolnut]

Hi Richard,

I find it very interesting that fuel was the culprit. I'm surprised your 003a is this sensitive to fuel, and I wonder what there was about this particular fuel your 003a did not like. Perhaps, with it having been used during summer in the desert, the fuel's more volatile components had evaporated by the time you received it. My 003a runs fine on home heating oil, and I like using it since it is cheaper and has better lubricity than the ultra low sulfur road use stuff. I also burn it in my Ford tractor with no issues. At my use rate, it is frequently six months old before I obtain a new batch. I always add Howe's to it to prevent any potential gelling at low temperatures, and keep the ready tank full to avoid condensation.

Best regards,

Stan

 

[storeman]

Good points Stan.
Jerry

 

[glcaines]

I'm glad you got your 003A running OK. Over the years, I've purchased a lot of old equipment, MV and otherwise, that has had old diesel fuel in the tank. I've also noticed that often, the old fuel has a yellowish or orangish tint to it. Sometimes it smells bad, othertimes not. I wonder if the fresh diesel the original owner put in it came directly from the station and was really fresh, or came from a storage tank that had old diesel fuel in it. No matter, cleaning the fuel system and filters is good PM in any event.

 

[RichardR]

Thanks again to everyone for the recommendations. And I agree that starting with fresh fuel and filters is always the best thing to do, but it's a little expensive these days and I thought I could skip that step in this particular situation. Guess I was wrong, again!

Stan, I certainly agree that the MEP-003A shouldn't be especially sensitive to fuel quality. After all, it runs on military grade diesel all the time, and we see lots of water and other crud in the tanks by the time we get them so I would expect some of that to be present in the military fuel supply chain. And I know that the deuce trucks will run on almost anything that will burn, although the deuce multifuel engine is a different design. The lesson I have learned here is that the MEP-003 engine is definitely not the same as a deuce! I still have the old fuel and one of these days when I have time, I will try it again in the MEP-003 to see if the symptoms return. Will report the results.

Thanks again,
Richard

 

[NJ_Toolnut]

Thanks, Richard!

There are several good reasons to not expect the 003A to be sensitive to fuel quality, but we have proof yours did not like the diesel the Federal Agency with the video cameras had been feeding it. However, we really don't know anything about whatever fuel they were using, so we perhaps should not leap to any conclusions regarding genset sensitivity. If I were you, I think I'd just feed the old fuel to the deuce and avoid buying trouble, since the symptoms could be worse if you try it again. In addition, even if the same symptoms return it will only prove the 003A does not like this particular diesel, whatever it is--the experiment will not allow any generalizations to be made.

Best!

Stan