1gm rpm after fuel filter changes

[frankfurder]

On my 25d I changed the fram filter and the primary? Filter on the engine. Took a long time to bleed the air, now the engine runs but only at 2000 rpm under load? I get 3000 rpm in neutral, but not under load.

Question- do I still have air in one of the filters. When I open the bleed screws on the engine filter I get some fuel flow but not much, no bubbles. Manual says 3600 rpm for the 1gm, never got that but 2000 rpm under load is kind of lame, should get at least 2500.

[Frenchy]

The low fuel flow from the filter bleed screw seems to indicate a restriction somewhere. If the engine ran fine before
the filter change, check the filters for proper assembly. Check fuel petcocks to ensure they're fully open. If the engine
rpms were always a bit off, you could check the tank's air vent at the stern and the exhaust elbow for blockages. That
exhaust elbow, if it's a Yanmar part, is plain steel and rusts from the inside. There are stainless substitutes that are better.
Also, after bleeding at the engine fuel filter, I would also bleed the high pressure system, either at the injection pump or
the injector itself.
If none of this helps, try rigging a temporary fuel line directly from the engine fuel filter to an open container of
clean diesel. At least if this works, you know that there is a restriction somewhere between the tank and the engine.
Good luck - hopefully someone else may offer other suggestions. - Jean

[John Stone]

The low fuel flow from the filter bleed screw seems to indicate a restriction somewhere. If the engine ran fine before
the filter change, check the filters for proper assembly. Check fuel petcocks to ensure they're fully open. If the engine
rpms were always a bit off, you could check the tank's air vent at the stern and the exhaust elbow for blockages. That
exhaust elbow, if it's a Yanmar part, is plain steel and rusts from the inside. There are stainless substitutes that are better.
Also, after bleeding at the engine fuel filter, I would also bleed the high pressure system, either at the injection pump or
the injector itself.
If none of this helps, try rigging a temporary fuel line directly from the engine fuel filter to an open container of
clean diesel. At least if this works, you know that there is a restriction somewhere between the tank and the engine.
Good luck - hopefully someone else may offer other suggestions. - Jean

Jean, is this a situation where a racor fuel filter vacuum gauge is useful? You may recall I did not install one on the FR so I am just curious about it. Thanks.

[Frenchy]

John, I think it is. Just as a thought on filter changes, Racor recommends a filter change every 500 hours or 10,000 miles.
This, I think, is mainly targeted for those semi trucks with larger diesels. Imagine how much fuel a 500 hp truck engine
pulls through a Racor filter in an hour - many times our tiny engines. On that basis, I change filters every 3 years and even
then it is probably too often.
I have one of those vacuum gages and it is always just a smidgeon above 0 at the filter change. It's useful because if
there's contaminated fuel, it will alert you. - Jean

[frankfurder]

Thanks for the replies to my 1gm RPM after filter change request. The local rigger/mechanic bled the high pressure pump this week and really didn’t improve the 2200 rpm under load at 4 knots.

For some reason rpm in reverse is closer to what I expect under load at 2500 rpm?

For now engine is running fine and while I would like to get higher revs I am satisfied with the results.

[mgphl52]

For some reason rpm in reverse is closer to what I expect under load at 2500 rpm?

Frequently the transmission has lower gearing for reverse.

[Frenchy]

I recently stumbled across this- maybe it's relevant. The Racor 500 also has a check valve. I don't know about Fram. - Jean




https://c34.org/bbs/index.php/topic,10681.0.html

[s2sailorlis]

Do you have factory service manual…?

[frankfurder]

I was looking at the yanmar manual yesterday but didn’t find much reference to low rpm under load. I’m stuck at 2200 in forward and 2400 in reverse.

Haven’t touched the throttle linkage, governor, or anything but the fuel filters. Began wondering if the fuel pump diaphragm on 1gm is wearing out,,as lines have been bled and engine runs fine, other than rpm?

[s2sailorlis]

Ah ok… I have a pdf of the factory manual, but sounds like you’re set with that…

I was looking at the yanmar manual yesterday but didn’t find much reference to low rpm under load. I’m stuck at 2200 in forward and 2400 in reverse.

Haven’t touched the throttle linkage, governor, or anything but the fuel filters. Began wondering if the fuel pump diaphragm on 1gm is wearing out,,as lines have been bled and engine runs fine, other than rpm?