Engine down. Bad fuel pump?

RollerCoastr

RollerCoastr

Well-Known Member
Nov 15, 2007
3,884
Cedar Point, OH / Miami, FL / MacRay Harbor, MI
Boat Info
1997 400DA
340HP 7.4 Mercruiser Bluewaters
Garmin 741, 742, 8212, 24HD, Intellian I2
Engines
1999 280BR
Twin 250HP Merc 350 Alpha Ones
454 Bluewater Mercs. These have an electric fuel pump mounted up high by the ECM, and the notorious mechanical pump that shares the water pump shaft.

I was just outside of my marina and ready to throttle up when port stalled. It would restart, but only run for ~5 seconds.

I returned to the dock in high winds on the stbd engine. (which includes a turn to stbd into the fairway and another into the slip!) It only took 2 shots of vodka to get my hands to stop shaking, but I got her into the slip on the first approach. With any luck I looked cool from a distance.

I took a lot of 5 footers to the beam on the last trip home, so while my tanks tend to stay clean, logic pointed to clogged filters.

I manually fill new filters in routine maintenance, but this time I spun them on dry and cycled the ignition a dozen times to see if the electric pumps would fill them. Not a drop, but I don't know if that's normal or not?

The engine continued to fire, then stall. After ~10 tries or so, it stopped firing, so I assume the filters are empty again.

I carry replacement upper-ends to for the mechanical pumps, so I'll start there, but I'm not convinced that's the issue. I bought those parts not because I've ever heard them failing to pump fuel, but because they tend to leak fuel into the lower housing and dilute the gear oil for the cam. Does the internal diaphragm fail?

The other suspect would be that electric pump... I cycled the stbd engine for comparison - they both make the same sounds. I meant to try the same dry filter experiment on the stbd engine, but I had company on the boat and never got around to it.

thoughts?
 
Sorry to hear you're down in July!

Side note....I thought the rig on top of our motors was a "Vapor Separator Tank" and not a pump?

Perhaps I have the wrong manual (very possible) but I have read that you could check the site tubes on both that tank (or is that a pump?) and the mechanical pump to see if the diaphragm has failed. Based on photos I have of my engines I'm assuming the site tube is the only vinyl tube coming off that rig. Allegedly if there is fuel in the tube, the diaphragm has failed and the unit must be replaced.

Sorry if this is one thousand percent wrong. Perhaps I should have merely offered my condolences and a beer.
 
Thanks for the condolences! Yes, what I'm calling a pump is a vapor separator. That would explain why cycling the ignition circuit didn't fill the filters. (the 280's pumps go crazy when I turn the key...)

I've never had gas in that tube before, but I didn't think to check it this week. Good place to start.
 
Are these fuel injected engines? If so, you need to put a scanner on it and check fuel psi. Typically when the mechanical pumps go bad they shoot sludge all over the place and make a mess. Also, they usually don’t just quit all of a sudden. They will pump enough at low rpm to run fine but the engine will fall on its face at higher rpm.
If your engines are carbed, turning the key won’t bring up any fuel. Spin off the filter and fill it with fuel and reinstall.
 
Air-locked!

I removed both filters. The bulkhead filter was bone dry. The engine-mounted one was down 1/3rd. (Opposite of what I’d expect?)

I refilled them both and started the engine. It went from no-start back to running for 5 seconds.

I topped off the filters again and now she’s running great.

This was the first time in 20 years that I’ve had a clogged filter. It was a learning experience, but not one I want to repeat. I might start seeking out rough weather now and then to stir up the tanks.

I’ve always used a coffee filter to strain fuel from used filters into my dinghy tank. The debris didn’t look very bad, but it slowed/stopped the flow through the paper - I had to keep repositioning it.

Stay tuned for my next post: “why won’t my dinghy engine run?” :D
 
RollerCoastr said:
Air-locked!

I removed both filters. The bulkhead filter was bone dry. The engine-mounted one was down 1/3rd. (Opposite of what I’d expect?)

I refilled them both and started the engine. It went from no-start back to running for 5 seconds.

I topped off the filters again and now she’s running great.

This was the first time in 20 years that I’ve had a clogged filter. It was a learning experience, but not one I want to repeat. I might start seeking out rough weather now and then to stir up the tanks.

I’ve always used a coffee filter to strain fuel from used filters into my dinghy tank. The debris didn’t look very bad, but it slowed/stopped the flow through the paper - I had to keep repositioning it.

Stay tuned for my next post: “why won’t my dinghy engine run?” :D
Click to expand...

Had the same thing happen recently doing a service on the genny. Swapped out the filter, fired it up, and then it shut down within 30 seconds. Checked the filter and it was dry. Filled up the filter with fuel and it fired right up and kept going.
 
I pre-fill filters during changes, but not all the way because it’s nearly impossible to avoid filling the inside/post element section. Seems like a design flaw?
 
I spoke too soon - I declared victory before a sea trial. I had been running her at the dock: extended idling, high idle, revving... At one point I had switched the port engine over to the starboard tank. Before heading out, I remembered that and switched it back. All good at the dock. Just as I was exiting the marina, I glanced down at my fuel meter display and noticed that port wasn't showing any flow. Right then, she stalled and I had to make my way back on the starboard engine again.

The vinyl tube was dry, but replacing the upper assembly of the mechanical fuel pump had been on my list anyway. (they leak gas into the cam chamber of the lower end and dilute the gear lube) This wkd I pulled the whole assembly, changed the impeller, dumped the contaminated lube and filled it with fresh, and swapped-out the upper pump with a replacement.

I re-primed both filters and fired her up. Suspect of the port tank, I ran her from the starboard tank. She ran for about 10 minutes and the fuel meter was showing flow. I was satisfied and shutdown. A few hours later I kicked her again. She fired and immediately stalled. The primary filter was down 1/3rd and the secondary was just slightly low.

Now I'm back to the condition where she'll basically run from the filters and stall. The fuel meter shows flow from whichever tank I have selected. When I re-prime the filters she'll start right up and do it again. At this point it's happened when drawing from either tank, but I can't rule out the possibility that there's a problem pulling from the port tank that only manifests after I switch over.

The fuel line runs from the port tank to the primary (bulkhead mounted) filter. From there the line runs to my GFS-10 fuel meter, and then up to the fuel selector manifold.

The electric pump isn't responsible for drawing from the tanks, right?

Could I still be fighting air in the lines somewhere? The tanks are both at half btw.

I guess I'm at the point of needing to measure pressure, but I'm not even sure where.
 
When you cycle the key, do you hear the fuel pump turning on? How about the good motor? Sounds like a fuel pump, relay, or fuse to me.
 
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