33ss 8.1 crusader engines fluctuating rpms HELP

[tomschauer]

The screens are on the ends of the pick up tubes in the tank.
If it is indeed crud in the tank, getting to them won't help.
You need to get the fuel polished again.
If the cleaning was done the first time with low tank levels, its possible that when you filled up more crud was cleaned from the sides of the tank.
It is also possible the new fuel you got is bad.
It happens a lot.

[Viper]

Certainly check what the guys mentioned above. You may also want to check fuel filters you may not be aware of. There are a couple of different kinds you may have in addition to either a spin on or the Racor element depending on the engine model. You may have an Oberg which is a black pancake/puck like looking assembly down low on the engine usually on the right side toward the back when facing the front of the engine. The assembly/puck splits in half and there's a screen mesh inside. This usually gets clogged with debris that gets picked up from the tank/s and is often the cause of some of the symptoms you're experiencing.

If you don't have the Oberg filter, you likely have an in-line filter assembly mounted directly to the low pressure fuel pump by the Racor filter assembly. This assembly has a filter element inside and is rarely serviced.

If you have a fuel control cell which is a long canister with hoses and wiring usually at the front of the engine, there is a filter element in it that again is usually overlooked.

Hope you solve the issue. Keep us posted.

[bud37]

Just a comment on this considering the last post from the OP. Seems to me it cleared up on the other tank, so I think filters are out, once they are plugged they don't generally clear. So bad gas is looking more and more plausible or perhaps a component temp issue.....or there is a fuel feed issue with one tank.

Two big block engines running will change the air in the engine compartment quite efficiently. You will really have to go thru that compartment and cross things off the list one at a time going thru the fuel feed system first one component at a time.

[Viper]

Definitely could be anything previously mentioned but I wouldn't rule out the filters I mentioned. We don't know the exact conditions when they act up and may not have all the facts. The filters may be allowing just enough fuel to run properly until some external conditions contribute to exacerbate a hidden deficiency. They're easy checks and would eliminate them as a possibility, especially when these filters are usually overlooked.

[buster53]

Ok, I have Crusader 8.1’s as well. Each has 2 fuel filters. A spin on Racor 10 micron mounted on the bulkhead between the tank and engine and a small, engine mounted 2 micron Racor, model 110A filter assy. Replacement filter is R11S. You might want to replace those as well.

[bud37]

Qr Bbpost Replacement filter is R11S

Buster, are you sure that is enough fuel flow for higher throttle settings.....seems a bit low unless I am missing something.

[buster53]

Qr Bbpost Replacement filter is R11S

Buster, are you sure that is enough fuel flow for higher throttle settings.....seems a bit low unless I am missing something.

It’s not unusual to have a 10 micron filter as primary and a 2 micron as secondary. That’s what was on the engine when I bought the boat. I have no problems getting up to WOT and usually cruise at 3100.

[bud37]

FYI...the R11-S is 2 micron max flow 15 gph diesel filter element...R11-T is the 10 micron 35 gph element for gas in the same filter housing....that is why I was puzzled. Restricted fuel flow equals less available HP.

Sorry for the hi jack.

[km1125]

There's probably a good study out there with some real data, but I'd bet it would be better to put two 2 micron filters in parallel than to put a larger filter in series with the smaller filter. In the second scenario (series), one or the other IS going to get blocked and strangle the engine. Unless you have gauges on them you'll have to replace them both anyways. In the parallel scenario you have twice the surface area to tolerate debris..so if they get clogged then they both need to be replaced.

[buster53]

FYI...the R11-S is 2 micron max flow 15 gph diesel filter element...R11-T is the 10 micron 35 gph element for gas in the same filter housing....that is why I was puzzled. Restricted fuel flow equals less available HP.

Not saying you are wrong…the S is what was mounted on my motors when I bought the boat. I bought new ones to replace them and my mechanic didn’t suggest otherwise.

Of course, I rarely run the boat at a speed that would exceed 15 gph.