low WOT

[Mohabba]

My engine will only rev to 4200 with only 2/3 of throttle. It appears to run smooth and strong from idle to 4000-4100. If i go just above 2/3 of throttle, the engine will surge and bog, when pushing further it will bog and i will drop it to about 3500 to clear up then only reach 3800 with surging/bogging. If i power down to neutral i can get it up to 4100 again but same problem above that.

During this i have:
-Changed fuel filters + fuel line.
-Bypassed with new outboard tank.
-Fuelpressure above 40 psi up to and above 2/3 throttle and when surging.
Gauge will read 80 psi if i prime the fuel a second time before engaging starter.
-Pins? in distributor cap were green of corrosion but they cleaned up nicely.
Checked both exhaust flapper are in place.
- Bottom and outdrive are clean and boat is not loaded at all.
-22 pitch prop.
Engine #0M616759

Im not sure where to look from here.
I will appreciate any advice

 

[Bondo]

Re: low WOT

My engine will only rev to 4200 with only 2/3 of throttle. It appears to run smooth and strong from idle to 4000-4100. If i go just above 2/3 of throttle, the engine will surge and bog, when pushing further it will bog and i will drop it to about 3500 to clear up then only reach 3800 with surging/bogging. If i power down to neutral i can get it up to 4100 again but same problem above that.

During this i have:
-Changed fuel filters + fuel line.
-Bypassed with new outboard tank.
-Fuelpressure above 40 psi up to and above 2/3 throttle and when surging.
Gauge will read 80 psi if i prime the fuel a second time before engaging starter.
-Pins? in distributor cap were green of corrosion but they cleaned up nicely.
Checked both exhaust flapper are in place.
- Bottom and outdrive are clean and boat is not loaded at all.
-22 pitch prop.
Engine #0M616759

Im not sure where to look from here.
I will appreciate any advice

Ayuh,... What motor,..?? What drive,..?? What induction system,..??

 

[Mohabba]

Re: low WOT

Ayuh,... What motor,..?? What drive,..?? What induction system,..??

Bond-o, im adding Bravo 3 to my signature....

 

[Mohabba]

Re: low WOT

Anyone?

 

[Mohabba]

Re: low WOT

On my last trip the engine started a knock or ping once in a while not constant.

Cruising about 22-24 kt, 4200 rpm on the sea. I noticed a loud knock and thought that something fell on the floor in the cabin or in the engine room. I let my wife take the wheel and i looked for the knock while cruising. The single knock could return with 10 or 20 seconds in between. I opened the engine hatch while cruising and realized that the knock came from the engine.
While looking at the engine it suddently made 3 or 4 knocks and we let of to idle.

My best description of the knock would be that it sounded like a blow with a hammer to the bottom of the hull.
I got no alarm of any kind.

I got the boat on plane again and if i kept the rpm on 4000 22 kt. instead of 4200 it would not make any issues and had about two hours home to dock.

We dont have any well experienced Mercruiser specialist here, the certified Mercruiser shop just change parts until a problem seems to go away so im on my own on this.

A local boat seller borrowed me his laptop with a Mercruiser scan program. It hooked right up but did not show any faults, we also tried the compression sequence with no faults.

We also checked compression manually on warm engine - compression on all cylinders.
- +40 psi on fuel rail, even when it will surge and bog + external tank with fresh fuel.
- drive, prop and bottom are clean.
- Standard merc 3 by 3 prop 22" for this boat.
- Boat is not loaded.

I dont know where to go from here.

 

[Eric 3.7LX Alpha 1]

Re: low WOT

See this from the "Adults Only Sticky" at the beginning of this forum, and check off the list as you go thru possible causes:

List of possible causes of low WOT (Wide Open Throttle) rpm.
http://forums.iboats.com/showthread.php?t=295070

(there's alot of other really good info in that sticky

 

[Bondo]

Re: low WOT

I dont know where to go from here.

Ayuh,.... Pull the Sparkplugs, 'n look for signs of Detonation...

It Sounds like yer runnin' Lean at top end, causin' a Lean condition, leadin' to Detonation....
or yer over-proped,...
or yer draggin' 'round too much sealife,...
or,.........

Hopefully, ya haven't burnt the top off a piston, Yet...

 

[Mohabba]

Re: low WOT

1. Fuel condition. Type and Octane possibly old fuel - fresh from external tank
2. Propeller pitch or diameter, damaged blades - clean and standard for this boat
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test - See #1
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse - Perhaps a tad under normal
5. Marine growth on hull and outdrive - clean anti foul paint
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor) Clean
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive - flappers visually inspected just after the problem.
9. Poor cylinder compression Compression Test - both scan and manually test good
10. Carburetor defective, or wrong type. ---
11. Fuel pump pressure and vacuum - +40 psi on rail constant
12. Boat overloaded, improperly loaded, or improperly trimmed. - full fuel, tabs up, well trimmed, min. load
13. Engine Overheating - Not according to gauge....
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully. ---

14. Engine timing and ignition system operation
Can someone guide me to how or where i can get info on the procedure for this?

What are the knock sensors doing if im getting a knock or ping?

Thanks.

 

[Bondo]

Re: low WOT

2. Propeller pitch or diameter, damaged blades - clean and standard for this boat

Ayuh,... There's really no such thing as "standard for this boat",... It's discussed All the time in the prop forum....

Has this motor/ drive Ever run at 4800 rpms,..?? pushin' the boat, under load,..??
What are the Numbers on the props,..?? what size are they,..??

I missed the part 'bout this bein' a 'puter motor,...
Donno the if's or why's with their sensors....

 

[Mohabba]

Re: low WOT

When i say "standard" i say it because its the same 22" Mercruiser duoprop (3 by 3), thats installed on all (thousands?) 285 Bayliners.
I believe the duoprop only come in different size not different pitch.

 

[Bondo]

Re: low WOT

When i say "standard" i say it because its the same 22" Mercruiser duoprop (3 by 3), thats installed on all (thousands?) 285 Bayliners.
I believe the duoprop only come in different size not different pitch.

Ayuh,... You still haven't answered the question,... Has it Ever ran 4800 rpms, pushin' the boat, under load,..??

 

[Mohabba]

Re: low WOT

on my first trip last year i pushed it above 4600 for about 10 seconds and thought it was good.
This was on my first trip so i didnt take the time to trim the boat

I only ran the boat at 4000 - 4200 because that seemed to be a good cruising speed for the boat.
2 months later after 5 trips i wanted to "blow out the cob webs" and it stalled at 4200.

 

[Scott Danforth]

Re: low WOT

your fuel pressure is low at only 40 psi. you should be minimum 45psi for a 3-bar fuel system. Low fuel pressure will often lead to a lean condition. so you will have to troubleshoot the fuel system from pickup to anti-siphon valve to plumbing to filter to pump to regulator to injectors.

what happens to fuel pressure above 2/3 throttle? if it drops you have a fuel flow issue.

I agree with Bond-o, no such things as standard for the boat.

besides the pitch question, you did not answer the fuel type and octane rating. you state that you have fuel from an external tank. did you plumb an external tank? are you referring to you obtained fuel from an external tank? if you just topped off the tank, and you had water in your fuel, you still have water in your fuel. please explain your "external tank" answer.

 

[Mohabba]

Re: low WOT

- Fuel pressure was above 40, between 43 to 45 psi but constant even when stalling at 2/3 throttle.
- Pickup tube with mesh is clean, anti siphon is shiny and moving and all fuel lines was changed.
- EU Oktan 95 is the only fuel in Greenland besides diesel.
- External tank hook up with fresh fuel.
- I dont think that theres different pitch on Mercruisers B3 duoprops. All Bayliner 285 comes with 22" B3 prop from factory.

Ill try to look into regulators and injectors.

Thank you for helping and walking me through.

 

[shrew]

Re: low WOT

A few things to reduce confusion. Your signature says 350 Mag MPI, but then you refer to Carb in at least two posts. MPI doesn't use a carb., however if you do have a carb, then clogged jets and a carb rebuild would be the first place I'd loook.

Another thought, can you Rev the engine above 4,200 RPM in neutral? How much weight is on the boat when you're testing? If the distributor and cap were green with corrosion, did you consider swapping out the cap itself rather than cleaning and reinstalling? Have you pulled the plugs to see whether you're running lean or rich? I'm going to assume lean.

BTW- There is no such thing as a FWC BIII drive. (as per your sig.)

 

[Mohabba]

Re: low WOT

Thanks Shrew
- I didnt mention carb?
- In neutral it will easily rev to 5000
- No weight, just fuel and some water, no fouled hull or prop.
- Of course theres FWC mercruiser engines with B3 drives. why not?

 

[achris]

Re: low WOT

...BTW- There is no such thing as a FWC BIII drive. (as per your sig.)

Yes, there is... It's was option, along with SS exhaust elbows (but no longer because they last too long and Merc don't make any money out of spares)....

Have you run the engine (under load and faltering) with a full diagnostics program running on a laptop?

 

[Mohabba]

Re: low WOT

Today i installed a new distributor and cap. The engine now runs great, WOT 4800 rpm and 33 knots.