Lombardini rough idle

[daveNZ]

I have a Lombardini 1404M, (4cyl, 1400cc) 550 hours, 10 yrs old. Runs well 'except' at 900rpm or lower it runs on 3 cylinders. Compression is ok, glow plugs ok, isolating the 'unit' injectors one at a time improves things, as does crimping the fuel return line as it exits the rocker cover/fuel gallery. Fuel supply pressure (after last filter, and as it enters fuel gallery) is 5-7psi which is slightly slower than workshop manual (7.9 to 9.4psi). The fuel pump diaphragm appears ok. The non-return valves above the injectors pass a simple blow/suck test.
Is the pump still the problem? If so how do you fix a self-regulating pump?
Or is it an injector? Any comment on these unique injectors would be very welcome.
Thanks.

[gjordan]

If you know which cylinder runs rough at low RPM, swap the injectors and see if roughness follows the injector or stays at the same cylinder. You have already done a compression test, did you have the injectors tested while they were out? If the problem stays with the cylinder, you may have a pump problem. You might want to disconnect all of the lines to the injectors and place clean cardboard at their outlet, and turn the engine over with the starter. Be very careful of your eyes, hands etc, since fuel will come out at very high pressure. If your pump is faulty you should be able to see a difference in how the fuel hits, or cuts the cardboard on the bad cylinder. It is a cheap and easy test. ______Grant.

[daveNZ]

thanks for that reply. The compression test was done via the glowplug hole so injectors didn't need to come out; and have not been tested. The FOCS series Lombardini has a can-driven pump and injector unit for each cylinder, and fuel is supplied at a moderate pressure from a single external diaphragm pump. Therefore I'm not sure I can do a test similar to what you have suggested.
When we did pull an injector-pump away from the cam, it seemed to run more smoothly, but this happened isolating any of the pumps??? Therefore we haven't yet had a reason to suspect one pump/injector.
Maybe replacing an injector/pump, OR removing and testing each one, might be the only option.

[d design]

You have a bad fuel injector or injector pump. Pull the injectors to see how they spray. Be very carefull, injectors can squirt fuel over 1000 psi and that could drill a hole straight through your hand.

[daveNZ]

Will have to live with it for a while and try swapping in a good pump/injector to test.

[Pegleg Sands]

Your line pressure is LOW.It sounds like a bad injector,worn cam lobe etc,but your high pressure is below the factory minimum and that will make a difference.Look for a collapsed filter,line,pickup tube,strainer.I would crack your injector lines one at a time,looking for air.Does your oil smell like fuel?You can put a 12V. in-line lift pump,or transfer pump in line to raise your fuel pressure for about 40 bucks.Since it gets better when you unbolt your pump it may be a bad diaphragm or spring.

[daveNZ]

Thanks again, I can add more info...fuel into the rail line above the pumps/injectors has some pressure but a cheap general purpose gauge fluctuates so much it is hard to read. Pressure on the return line from tappet cover to filter is about 10psi, (the gauge is much steadier) and has NO air bubbles in it a all. The fuel pre-filter diaphragm pump looks ok, diaphragm appears good. At 950 rpm and above engine is absolutely fine, runs very well reaches max rpm a 3600. The only issues it at 900 or below, it deteriorates into a lumpy idle, we assume it is running on 3 cylinders???

[gjordan]

Harbor Freight sells small infared thermometers that you can just aim at something and get a reading. Warm the engine up and take readings as near as you can get to each injector (same relative spot on each one) and if a cylinder is faulty for almost any reason it will show a different temp. There will be some variation, but if one is considerably different, then it is suspect. Do it at high and low rpm, giving it time to stabilize before testing. It may not tell you what the problem is, but it may help to locate it. Good Luck. _____Grant. PS, I am baffled by it getting smoother when you run it on one less cylinder.

[Pegleg Sands]

Originally Posted by daveNZ

Thanks again, I can add more info...fuel into the rail line above the pumps/injectors has some pressure but a cheap general purpose gauge fluctuates so much it is hard to read. Pressure on the return line from tappet cover to filter is about 10psi, (the gauge is much steadier) and has NO air bubbles in it a all. The fuel pre-filter diaphragm pump looks ok, diaphragm appears good. At 950 rpm and above engine is absolutely fine, runs very well reaches max rpm a 3600. The only issues it at 900 or below, it deteriorates into a lumpy idle, we assume it is running on 3 cylinders???

Does it do the same thing when under a load?Forward or reverse engaged?Thanks

[boden36]

Are you really idling at 900 rpm? If for some reason your tacho is misreading, you may just be idling a little slower than you think and therefore rough.
You can get a tacho that you just point at a crankshaft pulley ( you put a reflective sticker on first) which will give you rpm.

Regards,
Richard.

[daveNZ]

Hello, Xmas here so no engine time. Thanks for time and comments people.
The rough idle occurs weather in gear or not.
The suggestions re cracking the fuel line: we can't do that as the pump and injector are one unit.
Re temp. gun: we did look for a temp. difference by taking off the exhaust manifold, placing a big fan to suck out the exhaust through a hatch, and running the engine to look and feel for a temp difference, and wet exhaust from unburnt fuel. This didn't point clearly to one cylinder!!
I am beginning to suspect that the technique of pulling each pump/injector away from its cam lobe, may have given a slight improvement due to more pre-pump/injector fuel pressure being available to all 3 remaining pumps. Also the idle actually seems to deteriorate, rather than go bad immediately. So... I'm wondering if the pre-primary-filter pump diaphragm has a pinhole, even though it looks ok. Easy to test a new one I guess. Against this diaphragm theory is another boat with the same engine had a faulty diaphragm and the symptom was lack of mid to high end power; whereas my engine is fine at all revs above 950.
I have checked the engine label tacho with a laser tacho and it is accurate.

There are other boats with same engine so I'm going to have a very close listen to theirs!!
Cheers, happy new year.

[daveNZ]

Hello again and I appreciate the comments and questions posted so far.
As compression was ok and there were no other sign of leaking valves, I decided I would probably not cause further damage by using the engine and we have been on some trips over the summer. About another 40 hours, including some of 6 hours or so. We added some injector cleaner, not the 5 x dose for problems, as recommended, but the standard 1 x dose for maintenance (5ml per 20litres of diesel, from memory). At 3 litres/hour, that is about 120 or so litres of diesel through the engine and 40 hours running. To my surprise the engine occasionally idles much better, not all the time but sometimes it will even idle at 600 rpm!!! It is not the smoothest idle but a massive improvement on the extremely lumpy experience. In every other respect the engine seems to be ok.
So, I am assuming the problem is with the injectors, and will hopefully continue to improve. I used Fuel Set as the injector cleaner.

Any opinions as to whether I should use 5 x the standard dose (as suggested on the product) to help the injector cleaning along?

Many thanks.

[Pegleg Sands]

I use Power Service fuel add. at the normal recc. dose.Some fuel pumps are lubricated by fuel only,not engine oil.You have to be careful how toxic you make the fuel supply.Whenever I change my filters I fill them with ATF,regular trans fluid when I put em back on.