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nonamebrand 26-01-2014 12:27

Rough idle and cuts out when going into gear

I have a issue with my diesel, but have very limited skills! Was hoping for some comments or ideas from more experience peoples!

I recently had issues with my diesel running rough/low power. I changed out the engine filter which was very dirty, opened the tank which had some water and plenty of diesel bug in it. I drained this totally, dried and cleaned it and filled with clean fuel (50ppm). I also added a racor R12P water trap filter, so my setup now runs tank -> hose -> racor -> hose -> fuel pump -> hose -> engine (fine) filter -> engine

Bled the engine using the fuel pump and I started the engine and the idle was rough/low, but it run ok otherwise, going into gear and driving, etc.

Come holidays and a month later I finally get back down to the boat. Start it, very rough idle, with the clutch disengaged the engine revs up fine and sounds smooth. However, when I try to put the engine into gear it cuts out the instant I try to rev it up.

I have a Nanni 2.5 14HP, it was installed new by the previous owner, although it has spent the last couple of years mostly sitting, I go it at about 52 hours and it now has 71.

The engine is idling at 800rpm, which seems to low, and I can feel/hear the engine seems to be idling low rough. I have an engine workshop manual with the boat which makes it appear idle should be 900rpm, but the operators manual downloaded from Nanni website seems to indicate 1050rpm.

One thing I feel is I feel it I need to move the throttle quite a long way before it begins to drive, and previously (althoug it was running dirty fuel/filter) I would be running near 2000rpm only and throttle would be full open. That said, at about 1800-1900rpm would drive the boat at 4.5kts (28 foot fin keel cruiser), however the manuals give the indication I should get 3400rpm, so that all seems a bit off to me.

Does anybody have ideas as to where I might begin checking for issues?

Kind regards,

s/v 'Faith' 26-01-2014 12:33

Re: Rough idle and cuts out when going into gear
Sounds like it is not getting enough fuel. Is it possible that you have a bend in a hose, or a partially plugged pick up in the tank?

You might try using an outboard fuel tank running directly into the engine mounted fuel filter... That will eliminate any restriction or blockage in the tank or the new Racor you added....

nonamebrand 26-01-2014 12:42

Re: Rough idle and cuts out when going into gear
That's a really good idea, especially considering the clumps of muck that where in the tank, I'm going to give that a try tomorrow, thanks for the tip!

S/V Antares 26-01-2014 13:04

Re: Rough idle and cuts out when going into gear
Check to see if the shaft moves by hand easily in neutral.

HappyMdRSailor 26-01-2014 14:00

Re: Rough idle and cuts out when going into gear
Hi Mark,

I like SV faith's ideas, and that's going to tell us a lot... Restriction likely the key... If it doesn't eliminate the problem with the temporary fuel supply, other thoughts are...

I'm not familiar with your lift or injection pumps... It is highly possible the muck/water combo compromised the performance of your lift pump/I-pump, or injectors... Happy day would be that a restriction is the fault, followed by a lift pump...

I personally don't think 800 rpm is too low

Try the can test and report back! Good luck!:thumb:

Boracay 26-01-2014 16:32

Re: Rough idle and cuts out when going into gear
If the fuel was very dirty then the new filters may also be partly blocked.

Have you checked the fuel return?

This may be a good time to change the oil/oil filters, including gearbox, if you haven't done so for a while.

nonamebrand 28-01-2014 12:00

Re: Rough idle and cuts out when going into gear
Ok, I went down to the boat and did test, basically what I did was disconnect the pipe from the tank side of fuel pump and connected it to a pipe in a jerry can sitting in the cockpit above (higher) than the engine, so my setup went: jerry can - pipe - fuel pump - pipe - engine (pump/filter etc)

I bled the whole system using the fuel pump and started. Unfortunately my results where largely the same, idle was rough/800rpm, ran fine out of gear, but cut out as soon as I tried to put it into gear.

I couldn't try it with the fuel pump out the picture as it seems the hose going between the engine and the pump is a larger diameter than the rest, so I didn't have enough to get it into the can (also its quite hard to get apart!), maybe there is something blocking in the pump, I don't know.

I noticed today though the it doesn't actually cut out "instantly", I hear it engage and start to turn, then it cuts out, but its only like a second or so it turns. Might have done that before though, hard to say.

To address some of the responses above:

(a) I can turn the shaft freely by hand in neutral

(b) I replaced the fuel/cleaned tank before I ran the engine again after replacing filters, so new filters are clean

(c) I also took off the new filter and put it back again in case I didn't seal it properly last time

(d) I didn't have time to remove the return line today, I left the setup running can - engine - return - tank; in the time I was running the engine idle/neutral most of my 10 litres moved into the main tank (maybe about 8 in total), I was quite surprised how much had moved, can't say how long (time) it was though. The return line is a fair bit longer than it was before ( I had to cut it as I had originally installed the Racor on the return line! :whistling: ) when I connected it up I added some slack, I hate it when people install cables/pipes so tight the next guy can't maintain them.

Is it possible that is might be air flow related? I haven't ever cleaned this, wouldn't figure
it would be blocked after so few hours. We do have a huge problem with manganese ore dust blowing across out marina (our boats are always getting coated in black dust), but I don't run the engine when it comes across!

Also, could it be that there is still air getting in somehow? I don't know though, because it never cuts out at idle or in neutral, just runs rough at idle. What would be the best way to check, if I put the return line in say a clear container with fuel, would I see bubbles coming out?

Lastly, my idea/feeling that there has been some play/stretch in the control cables since it was installed (give it is still inside its first 100 hours) causing the gears/revs to engage out of sync (too low), is this unlikely/silly? Or is it something that happens with new installations?

Many thanks for all you assistance and patience, I didn't expect to get so many comments so fast!! :)

perchance 28-01-2014 12:36

Re: Rough idle and cuts out when going into gear
Try disconnecting the control cable from the pump an move the fuel rack manually to see if that makes a difference. Another thing to consider is the governor.

glenn.225 28-01-2014 12:38

Re: Rough idle and cuts out when going into gear
Not familiar with your engine but your last comment about play/stretch in cables cause me to think that the fuel cut off lever (if you have one) is not going fully to the run position. This can have low power effect on some motors.

Neptune's Gear 28-01-2014 12:41

Re: Rough idle and cuts out when going into gear
Does sound like a fuel restriction. From the tests you have done, It's the pump or Injectors. Next you have to remove the fuel pump outlet port (pressure side) and test the fuel pump. It will be hard to tell if it is OK, as obviously there is some fuel getting through. Is it a crimped together type or a serviceable type? If serviceable, strip it and examine for clogging. If Crimp type, get another one - should have a spare on board anyway. You may not be able "bypass" the fuel pump - the engine/injector side of the pump runs at high pressure on many diesels. Disassemble it, inspect all pipes, and injectors for clogging - it really does not take much to stop it! If you cannot find anything, take the injectors to a diesel shop and have them tested. Diesel bug can stuff them. Good luck, report back!

nonamebrand 06-07-2014 06:36

Re: Rough idle and cuts out when going into gear
Hi again, just wanted to post again here to close this issue.

What I thought would be a simple issue turned into a major overhaul. Based on the above and what I had tried I got out of my league, so hired a local boat fixer to help me.

To cut a long story short, we ended up pulling the engine as even after adjusting the idle govenors (they paint had been stripped off these and it seems a PO had fiddled with them), but still cut-out instantly in gear, so he feared seized transmission.

In the end the gearbox was fine, but long on oil, however we found the marinization of engine was overall very bad, lots of mixed metals, non-stainless bolts, corrosion etc.

A major problem was the interior of the heat exchanger was corroded to the point were it was literally paper thin, the next run or so would have burst it and water poured into the cylinders. Apparently a known problem with this engine, word of warning to anyone else with this engine never let it sit for any extended period without sealing the exhaust and doing a decent layup or it will rot very quickly (this was an issue with mine as the PO didn't use it much and it sat before I could launch it)

The exhaust elbow itself (on the heat exchanger) was also rotten (it was cast iron) and it just started to crumble as we cleaned it.

Also took of the head, had to do some major skimming of the valves, and one cylinder appeared to have had water in, but may be related to being unused without being laid up.

In the end we serviced probably just about every element on the engine short of taking cyclinders out.

Overall it seems actually this is a very poor model Nanni, or mine was, lots of small things make it very poor for marine use, for example, you can't take the starter motor out without taking the oil filter/pressure sender off, and lifting the engine up off its mounts, and the mounting bracket blocks the started; this engine has lots of little catchs like this.

But now it runs very well, at least in the workshop!, only just gone back into the boat so I haven't run it yet hooked to the prop, but no reason why this should now not work now. So seems it was rather a whoe batch of small issues that had built up rather than a single cause.

I assisted the mechanic throughout the job so its been at least a great experience for me, know alot more now then when I first posted!!

Thanks again to everybody for your help.

HappyMdRSailor 08-07-2014 08:39

Re: Rough idle and cuts out when going into gear
Thanks for the follow up! :thumb:

Sounds like you had quite the run of servicing! :rolleyes:

Let us know how she goes...

Badsanta 09-07-2014 07:20

Re: Rough idle and cuts out when going into gear
Maybe the zinc are missing?

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