Fuel in Exhaust on cold start

[Jmreim]

Have a 2013 Cummins QSB 5.9 305hp with 1300 hrs. Engine surveyed Sept. 2022 and no issues found - I've owned the boat for almost a year and it's been trouble-free.

On cold startup last week, some diesel fuel appeared to be coming from the exhaust for about 1 minute. Engine then ran for several hrs. and no further fuel was seen in the exhaust. After warm engine shutdown, we waited about 45 mins. before restarting and no fuel was seen. Waited about 24 hrs. and once again some diesel fuel appeared in the exhaust for about a minute after a cold start.

While I haven't had the contaminant in the water analyzed, it surely smells like diesel and appears as a sheen on the water like diesel - I assume if it were engine or trans. oil, it wouldn't stink like diesel.

Mechanic has done a dropout test to the injectors but nothing was found. We're now told that the injectors should be removed/rebuilt/replaced but I'm concerned (perhaps hopeful) that it might be something far less involved and less expensive to repair. It would be terrible to do the injectors ($7K-$8K)and land with the same issue afterwards.

Any comments or recommendations would be most appreciated -
Jim

 

[Jeff F]

Does that engine have a fuel return cooler? I'd check that early on if there is one.

Sent from my moto g play (2021) using Trawler Forum mobile app

 

[KnotYet]

Before spending money on injector servicing I would want to check the 'easy' stuff
like any possible head gasket issue, compression and if there's any fuel in the oil.
Is your engine pre-common rail?

If you've been only running it slow it could be losing compression due to some
glazing that may be helped by a few hard runs. A compression test may reveal it.

 

[Jmreim]

it is common rail

 

[DavidM]

Your problem is probably injector related, but uncommon on common rail injected engines.

But before you do anything take the boat out and run it hard at 200-300 rpm off of top for several hours. That will often burn off the crap on the injectors and clear it up.

In any case, I wouldn’t spend thousands to fix it. Previous generations of mechanically injected engines did this all of the time.

David

 

[Jmreim]

Interesting point about running slow - we usually run about 1500 rpm but it was suggested that we try running WOT for a bit to see if the problem resolved. We ran WOT for 20 mins yesterday, then stepped down to 1750 for about an hour. Still saw fuel in the exhaust after a cold start this morning. Are you suggesting we run more consistently at higher rpm? Should we have a compression test done before trying that?

 

[Jmreim]

I have no idea if the following might be related here but just to complicate matters further, WOT yielded 2535 rpm and the engine is rated at 2650. We saw this same max rpm (2535) when the boat had an engine survey at purchase last Sept. Surveyor suggested we have the prop tuned, which we did last winter but from what we experienced yesterday, we still can't achieve 2650.

 

[KnotYet]

Interesting point about running slow - we usually run about 1500 rpm but it was suggested that we try running WOT for a bit to see if the problem resolved. We ran WOT for 20 mins yesterday, then stepped down to 1750 for about an hour. Still saw fuel in the exhaust after a cold start this morning. Are you suggesting we run more consistently at higher rpm? Should we have a compression test done before trying that?

I'm slightly surprised that your mechanic didn't suggest a compression test when he
had the injectors out (if they were removed).
It's pretty trivial to do it then, at least a cold engine test. The fuel is either not getting
burned because of too low compression at start-up or coming from a leaking, failing
or mis-timed injector. If this engine has glow plugs make sure they are functional.

Since it's a common rail the fueling may be diagnosed as OK and you'll be looking
for a mechanical cause, i.e. glazing, rings, valves, head gasket, etc.

Do that wide open run a few more times and look for any change or improvement.
A good diesel compression gauge is a couple hundred dollars. If you buy one,
avoid cheap Harbor Freight type ones. You need some accurate data to start with.

 

[Jmreim]

injectors haven't been removed yet - trying to avoid the injector removal/rebuild/replace unless/until we've run out of other (simpler) causes/remedies.

 

[KnotYet]

I have no idea if the following might be related here but just to complicate matters further, WOT yielded 2535 rpm and the engine is rated at 2650. We saw this same max rpm (2535) when the boat had an engine survey at purchase last Sept. Surveyor suggested we have the prop tuned, which we did last winter but from what we experienced yesterday, we still can't achieve 2650.

That RPM may be close enough, within the accuracy of the electronics, at 4.3% low.
Maybe have your mechanic or yourself verify it optically. There's an app for that.

Obviously the prop and bottom must be very clean for that test to give good data, too.
Loading the boat differently or heavier/lighter can even affect the maximum RPM.

 

[Comodave]

Get a photo tach to check WOT. They are cheap, under $50, and easy to use. Then you will know for sure what RPM you are getting. Dash tachs can be way off.

 

[Lepke]

Whenever you start a diesel there is a unnoticeable amount of fuel exhausted. If you have excessive cranking to start then unburned fuel is going to show in the wet exhaust. It's also caused by a buildup on the injector tips. The buildup disturbs the spray pattern creating large drops that don't fully burn. As the engine warms up, it burns better. Usually cleaning the tips solves the issue. Most injectors have replaceable tips that anybody should be able to change. Something that helps is use the glow plugs even in warmer temps.
Sea Foam liquid will also remove light buildups. After the engine is warm, empty the secondary filter and fill with Sea Foam. Bleed, start the engine and run under load at full power. Yes the engine will run on straight Sea Foam. I do this on my diesel PU about once a year. I don't do this on the boat because I have Detroits and they don't give me any trouble and I always add a fuel additive that increases the cetane rating. The PU doesn't run hard unless towing, the DDs run flat out when cruising.

 

[Jmreim]

Thx Lepke - we've been advised to run @ WOT for 15-20 mins repeatedly in hopes the issue may clear itself after 5-6 times. Is there a fuel additive that might aid in this process?