DF140 surging

[Crispin]

‘04 DF140 in the family since new. Engine starts and idles well. At full throttle, generally down on RPMs but running fairly smoothly. Tach has stopped working so can’t report revs. No codes. Occasionally will “come to” and increase RPMs and take off. Then back to somewhat less RPMs. Definitely a surging type symptom. Replaced fuel line and pump ball
Cleaned water separator and replaced filter
Replaced low psi fuel filter
Low psi fuel filter fills to about 90% full when under way.
I have read a lot about the VST housing, pump, float and drain. I haven’t attacked that yet but do know this boat has had water in the fuel tank several times. Tank is under the floor.
Question- Can water and junk in the VST cause a surging type symptom? Gets stirred up and clogs high pressure filter and then falls back down as the boat not used. Or somehow clears and we get that burst of full throttle that I remember and then clogs again. This has been going on for a couple years. I want to exhaust all the things I can do in the water first. I think the VST job is easier done out of the water and we’re in High Season
Thanks in advance for any help and I will update findings on this fairly common problem. C.

 

[99yam40]

I would think monitoring the rail pressure would tell you if the pumps and filters are OK.
rail needs to stay in spec

 

[Crispin]

Update- I made a slick little fuel psi tester from a 1/4” npt brass tee, two 5/16” barb fittings and some longer lengths of 5/16” fuel injection hose. I put a 0-60 gauge on it and it sat in the space at the top of the fuel rail where that little air box usually lives. I ran the boat and it reported 40 psi.
Moved on to the injectors… removed the rail and used some of that same hose to get more room. With spark plugs out, I held the whole rail in my hand, secured all four injectors and had my able bodied assistant (wife) crank it. All four had what I would describe as a fan pattern with two streams within the fan. I cleaned all four with degreaser (didn’t have any carb cleaner) and compressed air. I did not actuate them with battery power. I also changed the spark plugs.
New boat!!! Ran like it hasn’t run in a couple years. Double the power and RPMs.
I really think it was the injectors and not the plugs although I can’t be sure. I haven’t retested the spray pattern and I’m not planning on putting the old plugs back in to find out. I may test the fuel rail. The improvement was so drastic that I would like to know if it was that wonky spray pattern causing the problem.

 

[Crispin]

Trying to add some pics but server problem..

 

[Captain Caveman]

It sounds like a fuel issue than a spark issue, so I think that the injectors were the likely culprit. Great job chasing down the problem.

 

[cyclops222]

Remember the size difference between EFI hole size & the low pressure / vacuum size of a carburetor jets. Carbs run with no blockages. Compared to very tiny H P EFI holes for EACH cylinder.

 

[99yam40]

verifying the rail pressure before cleaning the injectors, would have been a better idea, but it sounds like you have it running a lot better now.
and it never hurts to verify the rail pressure is and staying in spec