Low RPM under load at full throttle

[patrscoe]

I have been struggling to find a solution to my low RPM while under load at full throttle. I have working on this for about 1 1/2 yrs. Prior to this, 2 full seasons ago, I was able to get 2500 to 2700 RPM at full load. If I pushed it, I was not getting any more speed.
I can run 3/4 throttle at 1700 - 1800 rpm at about 4.5 to 4.9 knots. If I push the throttle to full, the extra throttle only gets me to 1900 to 2000 rpms and 5 knots. It's like the travel to the 3/4 throttle mark, I get a good progression of RPM and then after that point, it just does not find any more increase in the RPMs.
I tested the RPM with a hand held instrument and my RPM appears to be close to the instrument.

Fuel System: This past winter, I replaced ALL fuel hoses from the fuel thanks to the engine, new hose fuel clamps, replaced the entire older Racor fuel filter with a 500 series, re-routed the fuel lines for a better flow, all new fuel filters, polished the fuel tank and provided fresh new diesel and cleaned the fuel lift pump; so basically replaced everything from the tank to the fuel injector pump.

- I added a solnoid early last year, I hit the glow plugs for a few seconds and starts fine.
- Does not stall out at any time
- RPM at ldle is about 800 to 900.
- Forward and reverse is fine
- There is no black or other color smoke from the exhaust
- I check the throttle cable and it seems to be to the extended length. Could go a little bit more 1/4" or 3/8" if I readjust the cable but not a lot.
- I don't believe I have any air in the fuel system; the new system that I installed is very tight.

Thoughts;
- Partially clogged exhaust elbow; any way to check this without removing the elbow, as they are on quite tight
- Clogged or bad fuel injectors
- Bad fuel lift pump but this seems to be working fine and the screen was cleaned
- overtighten waxing box but I am getting a drip or two per minute or so while running
- I replaced the prop with a new prop and I saw some difference in power but not overall RPM and speed
- partially clogged pick up tube but it seems to be getting fuel through this and I cleaned / polished the tank and did not see anything at the bottom of the pick up tube
- My bottom and prop is a little dirty and it has reduced my RPM a bit from above but this is not the source of the problem as I tested everything upon launch this spring and the results was per above. Plus I regularly clean the bottom and prop.
- I have checked the decompression lever and it is in the correct position and is clicked in

Any help or thoughts or if you experience something similar?

 

[Christian Williams]

One check for this is to move the throttle by hand (not using the cable). Might have to remove the cable to be sure throttle is getting full deployment.

It would be nice if that were it...some restriction in the cable. That would also account for failure to achieve high rpm in neutral gear, which no doubt is a test you've already made.

 

[patrscoe]

Idle without being in gear, no issues, RPM can reach in the 2600 rpm or higher but I don't to do this too often without being in gear.
Does not feel right for the engine.

 

[Alan Gomes]

I'd check the elbow first, then the injector. Getting that elbow off would be a good idea regardless, since it's something that should be inspected periodically anyway.

 

[Loren Beach]

Data point: I have motored along beside an E-34-2 at about 7 Knots, for several hours. Neither boat was straining. The Ericson has the stock 23 hp Universal M25xp, IIRC. Same engine that our boat was built with. That was at approx 2600 rpm.

 

[Pete the Cat]

The 25 XP should be able to hit 3000 RPM without load (you will not hurt the engine for a short period of running like this). . If it can't do that, the problem is not in your transmission, shaft or prop (well, you may have a problem there, too-but it is not causing the symptoms you described if the unloaded engine cannot make full RPM). I agree with your idea about the exhaust elbow or even the exhaust manifold. You have been lugging that engine a lot at low RPM cruise (a 25XP should be running at 80% RPM at at least 80% of hull speed). You should be able to hit max RPM for your engine at the hull speed max of your boat. In other words, you engine should be doing 2400 RPM at 6+kts (with a clean bottom and accurate speed measurement. If the exhaust elbow is clogged for a time, the actual manifold will often start collecting carbon buildup too. The 25 XP is not a difficult engine to work on. Exhaust elbows are expendable items on a boat and need to be periodically inspected and replaced--especially if the engine has been lugged at low RPM or idled a lot.

 

[patrscoe]

I will plan on removing the exhaust elbow and inspect. If that looks clear, I will move to the fuel injectors.

When I purchased the sailboat, late fall 2018 and the engine was surveyed in excellent condition. It ran at the proper RPMs.
Maybe this is a coincidence or not, late 2019 I got caught in a nasty storm for most of the day and it really tossed me around, and within the last 1/2 mile to the marina, my engine died. I knew something was wrong because I was losing RPMs and power; I restarted the engine within 20 minutes, and later in the fall of 2019 and into 2020, I corrected the issue by chasing down air leaks into the fuel system and clogged filters.
I continued to struggle with the issue again 2020 as I found another leak in the older hose (that short hose between the filter to the bleed valve) and it started hard.
So this winter I replaced everything from the tank to the bleed valve, and also cleaned the tank and replace the fuel. During 2020, fighting my air problem, it never got to the proper RPMs. Although I am not getting RPMs at load, the engine does not act like when I had air and clogged filters, as it starts up fine and does not stall.
So I am wondering if my injectors are dirty from the above but I would think that I would notice the engine not running right at lower RPMs and not starting well.

 

[Alan Gomes]

I will plan on removing the exhaust elbow and inspect. If that looks clear, I will move to the fuel injectors.

When I purchased the sailboat, late fall 2018 and the engine was surveyed in excellent condition. It ran at the proper RPMs.
Maybe this is a coincidence or not, late 2019 I got caught in a nasty storm for most of the day and it really tossed me around, and within the last 1/2 mile to the marina, my engine died. I knew something was wrong because I was losing RPMs and power; I restarted the engine within 20 minutes, and later in the fall of 2019 and into 2020, I corrected the issue by chasing down air leaks into the fuel system and clogged filters.
I continued to struggle with the issue again 2020 as I found another leak in the older hose (that short hose between the filter to the bleed valve) and it started hard.
So this winter I replaced everything from the tank to the bleed valve, and also cleaned the tank and replace the fuel. During 2020, fighting my air problem, it never got to the proper RPMs. Although I am not getting RPMs at load, the engine does not act like when I had air and clogged filters, as it starts up fine and does not stall.
So I am wondering if my injectors are dirty from the above but I would think that I would notice the engine not running right at lower RPMs and not starting well.

I'm not sure if this has already been suggested (and I'm too lazy to go back and read the entire thread), but have you removed the pickup tube from your fuel tank and looked to see if there is a mesh screen affixed to the bottom of the tube? If so, that may be your problem. This would be a good thing to check in any case, and remove that screen if there is one. Those screens (assuming there is one) are a really bad idea. You want to let your filter catch all the crap and not a screen on the bottom of the pickup tube that is not readily inspected and changed.

 

[Pete the Cat]

I agree with Alan's idea that the screen on the pick up tube could be the problem--manufacturers have stopped putting them on and mechanics generally just knock them out with a rod because they cause more problems than the prevent.. Or a blocked tank vent line if the problem seems to be worse with time run. Or it still could be the manifold--I recently had a case where the elbow was fine but somehow the manifold was all full of carbon--same symptoms as yours and the engine ran great after cleaning--I have no idea how this happened to a fairly low time engine. I would leave the injectors to the last--they do not fail catastrophically as your situation seemed to indicate. After all of this, i would take the injector pump out and have it serviced if it has been a long time. But i would bet you will find the problem before this.

 

[Christian Williams]

Just to confirm, what is the highest rpm you can reach at the dock in neutral gear?

 

[patrscoe]

Maxiumum rpm I can reach in neutral gear is 2900 to 3000.
I can re-test this week.

I removed the fuel tank pick up screen in 2019 when I was resolving the air problem.
I can check the fuel tank vents but the RPMs does not get worse while motoring long durations.

 

[Loren Beach]

Just Curious: what is the size/pitch of the prop? Number of blades?
And, question #2: Was there a similar difficulty before the prop was changed to the new folding prop, and was there an observed change after the prop replacement?

 

[patrscoe]

Flexifold 2 blade 15x10
I purchased new 12/2021

 

[patrscoe]

It is a geared prop. Opens and closes with no issues.
I notice it has more bite than my fixed 2 blade.

 

[Kenneth K]

Does your engine have the fuel bleed "knob" on top of the injector pump? If so, make sure the knob is fully closed. If open, even partially, it allows some fuel to bypass the injector pump and routes it to the fuel tank return line. Open it enough with the engine running and you'll get a noticeable rpm reduction at higher power settings.

If you don't have the knob, you'll just have a bleed screw, but you'd already know if this was leaking because fuel would be spraying out if it.

 

[Pete the Cat]

Maxiumum rpm I can reach in neutral gear is 2900 to 3000.
I can re-test this week.

I removed the fuel tank pick up screen in 2019 when I was resolving the air problem.
I can check the fuel tank vents but the RPMs does not get worse while motoring long durations.

The 25XP should easily hit 3000+--given the tach is right (which they notoriously are not because it is measured from the alternator and pulley sizes matter)--I believe its max RPM of the 25XP is 3200. And you should be able to hit 3000 in flat water fulling engaged at hull speed as you probably know--that is how proper pitch of the prop is actually observed. Seems like your prop could be overpitched--is it adjustable?. Let us know about your examination of the exhaust elbow. While you have it off, you might remove the exhaust manifold and expansion tank--as you have already done the hard part.. You will lose your coolant, but it is a fairly straightforward job and you could clean your expansion tank and ensure that your whole exhaust and coolant system is is up to snuff. You seem to have covered all the other bases.

 

[Christian Williams]

Yes, prop could be issue if you get full rpm in neutral. For what it's worth, I looked at Peter Compton's, "Troubleshooting Marine Diesel Engines."

 

[Loren Beach]

It is a geared prop. Opens and closes with no issues.
I notice it has more bite than my fixed 2 blade.

The prop could be functioning as designed, but the pitch might be wrong.
It's difficult to remotely calculate the correct pitch for any boat. Even with those detailed forms we fill out from the the prop vendor.

Back when we installed a feathering prop it took a couple of short "lifts" at the yard (just enough to swing the stern over the dock to access the prop) to get the pitch right.
And our prop was a lot easier to adjust than the older design of the MaxProp. We had an AutoStream feathering prop with external locking screws for controlling forward and reverse blade pitch.

 

[patrscoe]

Geared FOF do not have a adjustable pitch like Max prop. You buy the hub and the pre-pitched blades. I thought of that, perhaps they are slightly over-pitch. The tech that sized them appeared to go through the entire engine and transmission spec, and sailboat.
I read up on these and one comment someone had was that they had a good bite and I notice that as soon as I motored out of the launch slip this spring. More bite might mean over-pitched. That's where I am now - guessing at possibilities. That would be a risk - having them repitch and finding out that is not the problem.

yes, I have a fuel bleed valve and when I went through my entire fuel system in the winter, I removed it, cleaned it and reinstalled so that the knob was tight. When I was chasing my air leak 2 yrs ago, I mistakenly had the knob out too far but it had a more dramatic effect. As soon as I got to 1500 rpm, it dogged. What I am experience is different.

I am hoping to get to the sailboat this weekend and remove the exhaust elbow. I am hoping it is filled with carbon / rust, etc... and is my smoking gun.

Where is the governor? I read a thread some where else and they had identical issue and they ended up adjusting the governor and they indicated it fixed the problem.

 

[Pete the Cat]

The governor is a set of spinning weights deep in the engine. You do not want to go there. I seriously doubt if this is the problem. I agree with you that you should hope that it is the exhaust elbow (or manifold). On my installation the Elbow is an Onan part you can find on EBay--and there are people who will fabricate something from SS that will be cheaper and better than the OEM, but yours might be different. They are sometimes impossible to clean and need replacement. For folks thinking about prop replacement: adjustable pitch is expensive but often cheaper in the long run than the alternative things you have to do to adjust pitch (haul boat, remove prop, repitch, relaunch, repeat). The fixed two blade that came with my Ericson is properly pitched (my experience is that production boats are often over pitched). I have an Autostream feathering prop on my Tartan that I have had for 20 years that is externally adjustable and has been a dream--a very good investment and I have been able to adjust it by free diving it.