diagnose fuel pumps

[BobS2]

Fuel issues in my Yanmar 1GM10.

It began 'sagging' at cruising speeds several weeks ago. Throttle behavior is normal up to 2000 rpm. Above that it starves and loses power and rpms. It can rev higher, all the way to 3000 for a moment when the throttle is opened wide, but there's no power and it dies quickly.

To date I have replaced primary sand secondary filters, the lift pump and the injector. Bled and bled and bled.

When hand cranking with the compression released, I can hear the injection stroke. It used to be a short, defined pop sound. Now it's a longer squirting tone that rings in the delivery pipe.

Has my high pressure pump gone wimpy? Do we dare rebuild or just buy the unit? Could there be Governor issues? How bout a cheap little spring to replace?

Thanks.

[HPLou]

You should also check for water in the fuel. Another possibility could be the fuel pump, possibly a worn out diaphragm or worn lever.

[dabnis]

Perhaps a minor air leak some where in the system, which can be hard to find. after running a while is there any air space visible in the filter bowl? Did it happen suddenly or gradually? Perhaps a partially plugged pickup tube in the tank if it has a screen on it?
Check the tank to see if it is venting properly, if you can't get to the vent run with the filler cap open, weather allowing. Replacing the injector pump could be the last resort.
Here is a way to pressurize the system which should show where an air leak might be:

The Diesel Page, Electric Lift Pump and Racor Filter installation

Let us know what you find.

Dabnis

[sigmasailor]

Sounds like fuel starvation. First thing I thought of (filters) has been taken care of; as are other possible problems. Hmmm, before you change the (expensive) fuel pump make sure there is no blockage (or air leak) of your fuel supply lines. Did you check your fuel tank?

[JimsCAL]

Next thing I would check is the pickup tube in the tank. Could be a blockage there.

[BobS2]

Thanks for the ideas, all. I now have the off season to tackle this issue. She's on the hard now. I'll look into the air leak before buying more parts.

[LakeSuperiorGeezer]

Find a place that rebuilds fuel injection pumps. They have the equipment to check the pump you have to see if it is working correctly. It could be the injector has a poor pattern. Have them check the injector.

[centaursailor]

Have you checked the exhaust as a blockage/restriction can cause power loss at higher revs.
Safe sailing

[Leftbrainstuff]

Before spending a fortune there are some simple checks you can do to identify the root cause.

Firstly check the no load flow rate. This will allow you to see if you can flow enough fuel and indicates worn pump, constricted lines or blockages. Remember most pumps are much better ar pushing than sucking.

Then you can run both suction and pressure checks under load using appropriate inline gauges. Often issues will only become apparent under load.

I've assumed you've already checked the basics from rhe tank to rhe injectors. Next will be injection pump and injectors. This is where it gets expensive.

[BobS2]

I've got vacuum and compression gauges for air, but not liquid. And not in-line. Before I posted this question I had replaced the loft pump, pulled the old injector and connected the fuel line, cranked the engine to see the pattern. Inside the engine compartment is not the best place to see a spray but the shape was close to What's drawn in the manuals. It didn't seem as fine as I would have expected. I went ahead and put the new injector in at that time.

I had asked my local diesel truck shop about testing the injector a few weeks ago. They said they send them out to a specialty shop. I'll see about getting the pump tested.