Cummins QSB 5.9 diesel running badly.

[driver0606]

Hello,
I have a 2006 Azimut 43 with twin 425hp Cummins QSB 5.9 diesels. I had full power on both engines about one month ago and have been running at about 900 rev/min for 4 hours since. If I now try full power, one engine is OK but the other runs fine to about 1600 rev/min, the drops back to about 1250, running erratically, sort of surging. A notice comes up on the tachometer “check engine”. Reduce to about 900 rev/min, “check engine” disappears, all OK until I get to about 1600 rev/min and the same thing happens. All temperatures and pressures normal. Will run to maximum speed on no load. The fuel filters (one Racor and one “screw on” secondary) are due for a change, which I will of course do.

However, the sediment bowl in the Racor is perfectly clean and I had full power 4 hours ago, so a blocked filter seems unlikely. Any ideas, please?

Thank you for any advice,

John.

 

[kashurst]

sounds exactly like a blocked filter - probably need to change them all. It may be a partial blockage elsewhere in the fuel line. I once had a piece of metal swarf come up out of the tank and partially block the switch over valves. Symptoms were exactly as you describe.

 

[Divemaster1]

Echo fuel restriction to be the most likely problem ...

Keep things simple and check in order of simplicity;

Partially closed fuel supply valve, gauze in tank pickup blocked (reverse flow with air blown into tank through fuel supply line to dislodge blockage.... is a quick way to figure out if this is the issue... won't prevent it happening again though)... or filter blockage...

If you OP had air issues, black smoke would have been the tell-tale..

 

[npf1]

FWIW, I once had a similar issue. The engine mounted filter was the cause, even though the Racors looked squeaky clean.

 

[Latestarter1]

John,

You have signs of fuel priming pump problem.

Pump is not expensive and easy to change if slightly fiddly to get at, normally manifests itself on very high hour or engines ot those which have stood for long periods.

Key on engine exhibiting the problem, you should hear slight buzzing from the pump which then stops automatically. If you have a pump in trouble you will not hear pump buzzing and fuel system is 'seeing' a restriction from non functioning pump unit hence the 'check engine' light.

Can sometimes be fixed with a good clout if pump just sticky from standing.

PM me if you want part#

 

[driver0606]

Many thanks for all that, chaps. I will certainly follow up all those points before I get the "local" Cummins man with his computer down to me in Menton, South of France. I have a feeling that could cost an arm and a leg!

I will report on the results in due course. In the meantime, wishing everybody a good start to the boating season.

John.

 

[Latestarter1]

If you go though steps as quoted no computer required. Fault which was 'active' will become 'inactive'.

I had pump playing up four years ago, gave it the clout treatment, owner purchased new pump and it is still in the box, over 1,000 hours later.

 

[driver0606]

Hello again, everybody.
It was the filters, or possibly a blockage in the fuel line. Having dealt with both, she runs perfectly. Unfortunately it was not possible to do one thing at a time and follow each one up with a sea trial. Very interesting, everything looked as clean as a whistle, including fuel I drained from (almost) the bottom of the tank.
Many thanks for all your replies. Once again the Forum comes up trumps!

 

[kashurst]

magic - if it happens again you may still have something in a fuel pipe otherwise fingers crossed thats it.

 

[Andrew38]

No specialist knowledge but met another SCMer en route to airport last week who has Sealine F46 with twin Cummins/Zeus and he was telling me that he has been experiencing problems just like those described by OP. Apparently Cummins have been very forthcoming in trying to out it out.