DF90 died while underway, starts but chokes out immediately

[jnewbs]

Howdy all - thanks for any advice you can offer!

I have a 2005 DF90 that died on me today. Idled for about 3 minutes at the ramp in neutral, then for a minute in gear to get away from the No-wake area. Throttled up and it started up on plane for about 15 seconds before losing power abruptly and choking out. Now it will start but cough out in 1-3 seconds. Guessing something to do with fuel or air movement, but would really appreciate a more seasoned opinion before I start taking things apart.

Thanks again!

[Moonlighter]

First thing is your water separating fuel filter. If you have one with the clear bowl check the bowl and look for water and debris, and change the element too.

If not, change the filter element anyway.

Clogged fuel filter is a probable cause. If it does then run Ok you will want to change the filter again after 10 hours or so because you must have picked up a load of dirty fuel and there will almost certainly be more contaminants in the tank.

[Murray]

Air movement, try running with the cowl off. Be careful moving parts

[Moonlighter]

What Murray is getting at is the “known issue” affecting the early DF90-140 engines up to 2008.

It was corrosion in a plug in the engine holder, when it breaks through, exhaust gasses are released under the cowl and will choke the engine (not enough oxygen) at higher rpm.

Take the cowl and side covers off, then look on the port side just below the fresh water flushing hose attachment point. You will see what looks like a welsh plug there, look for signs of corrosion. If you do find it, the plug can be removed and corrosion can be ground out and a patch welded over.

If you search this forum for “DF140 engine holder corrosion” you will find more posts and probably photos. The issue was most common in the 140’s, I suspect simply because there were more of them in service than the 90/115 models.

[jnewbs]

Thanks for the help! I replaced the fuel/water separator and am having the same issue still - motor starts then coughs and dies. I did discover that if I start it and quickly start pumping the ball by hand the motor will stay on. Does that suggest an issue with the fuel pump, or one of the other filters under the cowl by chance?

Also, in case it’s material, the only other issue I’ve had was this spring (20 hours or so of run time ago). When the engine was cold and I pushed up the throttle it would start strong for a few seconds and then lose about 1000 RPMs for a couple seconds before surging back to full strength. This would repeat a few cycles before stopping and operating at full strength the remainder of the trip. Happened for a couple trips out then never again.

[Moonlighter]

Did you see any evidence of contamination when you tipped the contents of the water separating filter out?

re pumping the bulb, was it flat when the engine stalled out?

There could be any number if issues at play here…. We do see quite a few things on the forum that have resulted in similar symptoms…..

Including:

- Small birds entered the cowl and built nests inside the air box, choking the engine or air. Yes seen this reported several times! So inspect for that.

- the anti-syphon valve on the fuel tank sticks, again starving the engine at low rpm. Bulb will then be sucked flat. Solution is simple, unscrew the AS valve from the boat’s fuel tank, take it to the workbench and punch out the internals, they are just a ball, spring and seat. Then reinstall it. This is a quite common issue on US built boats where tanks come standard with these valves that are unnecessary on outboard powered boats. Just remove the guts anyway to be safe.

- tye tank breather may be blocked. Mud wasps like to make nests in the breather vent. Check it to make sure its clear. Take the fuel tank filler cap off and see if you can blow air through the vent inti the tank. It should flow fairly easily.

- yes there could be engine filters blocked, so changing the engine mounted filters can be required, but the high pressure filter is quite expensive. Worth doing other checks first.

- the contamination may have gotten into the VST, there is a small screen in there than can be clogged by debris. Can be cleaned out and float level reset. You will likely need a service manual to guide you thru this.

- the low pressure fuel pump may be defective. A mechanic can check fuel pressure to determine if this is the problem.

- did you check for the corrosion in the engine holder??

There is no need at all to advance the throttle when starting these efi engines. Just turn the key to the run position, wait for the beep to finish, and then proceed to crank and start the engine. If you listen closely with the cowl off, you will hear the fuel pump pressure up for a few seconds when the key is turned on, before cranking.

[jnewbs]

Moonlighter Thank you so much for the suggestions! I think it’s something to do with air getting into the tank based on this troubleshooting. Took the gas cap off of the center console and tried to blow air in and it seemed to pressurize the tank as the air whooshed right back at me. Also the bulb was previously not getting filled to hard, just a small amount of gas was coming through in spurts. With the fuel tank cap off the bulb finally pumped to hard and the engine fired right up!

I replaced the cap to see if I could recreate the problem (some kind of vacuum) but I’ve been idling it for about 5 minutes now and burped it up to 1500rpm for about 10 seconds in the middle, seems like she’s purring along fine. I certainly hesitate to take it out on the water without truly “fixing” anything, though… does this tell you any part should be replaced or serviced? Tough to access the plastic tank under the center console but I’m sure I can get at whatever if needed.

[Moonlighter]

Sounds like the tank vent is restricted. If air cannot get into the the tank to replace the fuel that is bing used, that will cause starvation and the primer bulb will go soft/flat.

Need to test the tank vent system to see what the problem is. Could be a kinked or blocked vent line, a restriction in the breather fitting where it exits the hull. That sort of thing. You have some trouble shooting to find out what is causing the restriction.

[jnewbs]

Only tank vent I can find is this Perko vented fill cap. But I’m not sure how that’s supposed to work when the lid is screwed on… boat is a 2005 Sundance skiff, 20 footer (in case that helps the mind’s eye).

Below pictures are:

The tank hiding under the console (makes it hard to get at - guess I can unscrew it from the floor and remove it if necessary)

Perko cap on (no holes or anything, those dimples are for a wrench)

Perko cap interior (see the tiny back flow vent at the top, which connects to a 5/8” hose inside the console, no kinks or sharp bends I can see)

Hoses pipe clamped to the poly tank, bigger one gas comes in, smaller one air comes out

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