Reduced max RPM in gear

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C36CC
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Reduced max RPM in gear

​​​Hi all.  I'm starting a new thread for my own similar situation rather than hijacking the recent similar threads originated by Cuba660 and brietz. I've been thru many of the steps on those threads to no avail.  

 

We have a 1993 Catalina 36 with Universal M35AC, 1760hrs, freshwater-only until we got her in 2020 after several years of light use by her one prior owner (seems well-maintained with no obvious neglect). She has a 3-blade MaxProp that was installed years ago by her PO.  We've put about 200hrs on her.  She's never been as fast as we expected and I just learned we've actually been cruising her at 2300rpm when we thought we were at 2700 due to an inaccurate cockpit tach (this season the cockpit tach decided to stop registering above 1900-rpm displayed, so I got just a handheld tach to troubleshoot). While the cockpit tach is on my list (I've checked alternator belt tension) the major issue now is that the engine currently revs to 3000+ in neutral but in gear it tops out at 1760rpm with an inch or so of throttle travel remaining...and there's no response when that added throttle is applied.  Because of our inexperience with her and the tach issues I can't say if the low-revs-in-gear has gotten gradually worse or suddenly happened. Actual idle in gear = 800, actual idle in neutral is 940rpm. I'd guess she was running up to at least 2300rpm earlier this season under load. One other possibly relevant detail is that with a 160F tstat we usually see temp gauge run at 180 under load, and often the gauge goes to 185-190 so we dial her back even though we were apparently already at low RPM (HX was cleaned last year, impeller changed this spring, bled coolant from t-stat housing, checked temp with handheld and gauge seems correct, have to fix this issue too).

 

Motormounts were loose when we got her last year, no obvious signs of binding or misalignment, re-tightened at the time. I've just now changed Racor and on-engine filters and checked the lift pump screen on the original lift pump (screen was very clean), bled fuel system - no improvement. Fuel pump did click away during bleeding. Based on another thread I changed the low oil pressure switch as that was on my list anyway - no improvement. Rotating the prop shaft by hand I can hear and feel the MaxProp change directions, so I doubt the prop is fouled but have asked our diver to check later this week. I removed the air cleaner - no improvement.  

 

At this point I believe I have a fuel problem. What next?

1. Test lift pump?

2. Just replace lift pump? (Don't have a spare aboard right now)

3. Loosen and 'test' injectors one at a time by listening for engine change?

4. Just remove and rebuild/replace injectors? (I have not done injector work before so am anxious about finding and having all necessary gaskets and seals on hand first)

5. Blow thru all the fuel lines?

6. Other?

 

All suggestions are welcomed and appreciated so we can safely transit NYC's East River enroute to her winter home as soon as Saturday. Thanks in advance!

 

-Keith

S/V Cool Change

1993 Catalina 36, WK TR, #1229

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

C36CC
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A few other things I plan to try based on more intermet searching:

1.  I ordered a new fuel lift pump so can change that and keep original for spare if appropriate.
2.  I'll drain and refill the Racor with injector cleaner.  I did not do this when I changed it; refilled with clean diesel instead.  
3. Use soapy water to look for injector area leaks.
4. Check shutoff cable and lever to be sure it's free (mine moves freely, but will look hard at the business end of it)
5. Local (NYC) diesel shop says 2-3 days to test injectors, $96/ea plus $75/core for rebuilt units, most costly approach is to have my injectors rebuilt (labor).  Found new Denso injectors online for $68/ea under the Kubota P/N 15271-53020.  Due to time pressure I'll likely order new ones and keep any good originals as spares.

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

C36CC
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Posts: 12

Shutoff lever is about 'halfway' engaged when at rest.  Checked shutoff lever impact under load...no improvement in RPM when lever is opened fully, rpm still tops out at 1760.

Cracked each injector line separately while in neutral at 1800rpm...upon cracking each of the four result in slight rpm drop.  As such, injectors *may* be ok.  

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

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Cuba660
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Posts: 22

Thanks for the update. Just a thought. Have you checked if your fuel tank is venting, not creating some pressure. I checked mine by running the motor with the fuel cap off. 

Cuba Gonzalez
S/V Joyita
Chesapeake Bay, Harrington Harbour South
1994 Catalina 36 MkII #1326
Universal M35A

C36CC
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I have not yet, and I will.  Thanks for suggestion!  Also going to see if any fuel lines got kinked somehow.  I have my doubts...but...strange things can happen aboard.

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

C36CC
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Question for those who fill their fuel filters with injector cleaner when reinstalling:

What injector cleaner do you use, and please confirm you use straight cleaner to refill - no diesel?  Thanks

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

C36CC
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Fuel pump changed...no improvement.

Ran with tank cap removed for venting...no improvement.

Diver found and removed quite a bit of growth since last cleaning 4-weeks ago.  No issues with prop.  She's going to be faster, but still only 1800rpm in gear at mooring.

This pic is rearmost (#4?) Injector.  Not sure what a 1760-hour diesel injector is supposed to look like.  Is this 'normal'?  

Have three new injectors and will install all of them plus best one of my existing injectors.  Fourth new injector is on order.

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

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C36CC
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And here to the left is the number two injector and on the right is the number one injector on the belt side of the engine. The corrosion around the base of the injector seems unusual and has me concerned. The number three injector not pictured has some oil around the base but the same pattern of late carbon deposit at the tip. So I am confused...

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

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C36CC
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Three new injectors later, using the 'best looking' original injector on Cylinder #1...the engine runs and boat speed is restored to 6.8-7.0-kt (speed seemingly from the bottom cleaning)...but...she still has a dead zone above 1850-rpm in gear, and she gets to 190F at that speed.  At this point I've exhausted everything fuel-related I can think of...so...my thoughts are turning (no pun intended) to the MaxProp installed by her PO and I am wondering if it was installed with the correct pitch.  We will at least be able to get her to her winter home and I'll investigate the prop settings when she is out.  

 

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

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Cuba660
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Posts: 22

Well that is not what we were hoping for. Like you, I can't think of anything else. My prop is fixed 3 blade and it's been on the boat since I bought it. Would the prop cause that dead zone in the throttle? I've driven governed cars, motorcycles, etc. past a certain point  you can mash the throttle and you get no response, that's how it feels with this issue we have. This motor has a governor and the troubleshooting portion of the manual states there's a spring on the governor that could cause low power. I may still change out injectors but now I don't have high hopes. Sorry to hear it didn't help the RPM related issue, frustrating. 

Cuba Gonzalez
S/V Joyita
Chesapeake Bay, Harrington Harbour South
1994 Catalina 36 MkII #1326
Universal M35A

C36CC
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Posts: 12

Cuba I feel you.  From what I've read today on over-propping, yes, it will cause the dead zone because via the excess pitch I'm also overloading the engine...so she has nothing left to give beyond 1850rpm.  Other over-propping symptoms can include overheating, moving fast even at idle speed, smoke/soot and eventually ring sticking.  I feel like I'm seeing many of those symptoms, ...and I've now replaced most of the fuel system... and then I found a margin note from the PO in the prop manual that suggests it was mounted with what I would term excessive pitch...so checking and correcting that is my next move.  We'll be out in three weeks.

Given you found an injector that had an effect on performance, swapping it might cure you.  The injectors were not hard to change, and Oregon Fuel Injection shipped overnight (I paid for it if cour$e).  Speaking for myself, I put the old injectors and lift pump in my spares kit and felt good for having serviced it all successfully - they should last us awhile... emphasis on 'should'.

-Keith 
S/V Cool Change, City Island NY

1993 Catalina 36 Mk1.5, #1229, TR, WK

Universal M-35A

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Cuba660
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Posts: 22

The over prop makes sense. I ordered an injector from Oregon Fuel Injecton, thanks for the link, and will replace that one I think is bad. Glad to hear it's a fairly easy job. I hate to think we may be starting next season with a power issue. Did you get your boat to its winter spot? I'll keep everyone posted on my issue. Thanks 

Cuba Gonzalez
S/V Joyita
Chesapeake Bay, Harrington Harbour South
1994 Catalina 36 MkII #1326
Universal M35A

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