Merc 2.4 V6 lost wot power

[oldseaox]

Engine is mixed years, ran great on Monday and lost 1000 rpm Tuesday from start up. Mechanic found nothing definite, small blip with stator. Since then have tried Stator, Flywheel, Trigger, Fuel pump, Carbs, Switch boxes, reeds. Mech has not charged for trying parts and still has found nothing. Compression is within 5% at 120 on all cyl. Also tried portable fuel tank. Still 1ooo Rmp down at wot.

 

[Faztbullet]

Re: Merc 2.4 V6 lost wot power

What year 2.4? Chrome bore or steel sleeve?

 

[oldseaox]

Re: Merc 2.4 V6 lost wot power

Block looks '89

 

[j_martin]

Re: Merc 2.4 V6 lost wot power

Somebody stole your prop and put a steeper one on.

Or your tachometer took a 17% crap.

 

[oldseaox]

Re: Merc 2.4 V6 lost wot power

Did I mention its also 8kts slower by the gps?

 

[j_martin]

Re: Merc 2.4 V6 lost wot power

Did I mention its also 8kts slower by the gps?

That eliminates the tachometer. Check the prop.

 

[oldseaox]

Re: Merc 2.4 V6 lost wot power

When problem started was running a 14x15p=4400rpm trimed out, had a couple of heavy buddies in the boat so tried a 16x13p=4800 rpm. Before problem- 14x15=5200 rpm and 16x13= carefull with the throttle. Have taken all gear except for CG required off the boat and running alone it dosen't vary more than 150-200 rpm. Mech has looked for internal problems and found nothing, no rattles, knocks or pings. Bearings seem ok (dowell in the plug hole method). All plugs appear to be firing.
Even checked foot oil.

 

[CharlieB]

Re: Merc 2.4 V6 lost wot power

When you tried another fuel tank did you also try another fuel line/primer bulb?

Have you checked fuel pressure at the carbs, idle vs WOT to see if there is still any restriction in the lines/system?

 

[oldseaox]

Re: Merc 2.4 V6 lost wot power

Supposed to be clear weather tomorrow so I plan to replace all the fuel lines including the bulb, have already disconnected the lines and done the "blow thru" test which was OK but may as well replace. I rairly have fuel problems because I am on the water twice a week all year, the boat is never in storeage over 2 or 3 days. I don't go far but I go often.

 

[oldseaox]

Re: Merc 2.4 V6 lost wot power

Replaced ALL fuel lines including blub, no joy. Same problem, starting to think maybe heat related coil problem. noticed #1 sparkplug very clean. Have to idle engine 1/3 mile to reach ICW before I can open up, gives engine time to reach full temp. ALL ramps this area have long idle zones because of the manatees so no choice.

Ideas???

 

[Faztbullet]

Re: Merc 2.4 V6 lost wot power

How does it idle? Is is nice and smooth or lopey like its rich? The only thing I can think of that would/could suddenly happen is: (A) weak spark on a cylinder due to bad switchbox (B) a crankshaft seal ring breaking and that would cause low crankcase presssure on a cylinder/s

 

[j_martin]

Re: Merc 2.4 V6 lost wot power

Replaced ALL fuel lines including blub, no joy. Same problem, starting to think maybe heat related coil problem. noticed #1 sparkplug very clean. Have to idle engine 1/3 mile to reach ICW before I can open up, gives engine time to reach full temp. ALL ramps this area have long idle zones because of the manatees so no choice.

Ideas???

Super clean plug and piston top indicates water intrusion. Do a compression test. Look for a crack in the exhaust divider if that's good. (spits water back into the cylinder through the exhaust port.)

A mechanic worth his salt would not have missed this.

hope it helps
John

 

[oldseaox]

Re: Merc 2.4 V6 lost wot power

Agreed but the compression is spot on, 115-120 range with less than 5% difference. Eyeball through the sparkplug hole shows normal looking piston top.
I am starting to suspect a heat related ignition failure, would any one know of a test for coils that doesn't require special equipment. I have a super hot blow dryer type gizmo and a volt ohm meter but nothing to measure output of a coil, could it be checked on the input side.

Ideas???

 

[j_martin]

Re: Merc 2.4 V6 lost wot power

Agreed but the compression is spot on, 115-120 range with less than 5% difference. Eyeball through the sparkplug hole shows normal looking piston top.
I am starting to suspect a heat related ignition failure, would any one know of a test for coils that doesn't require special equipment. I have a super hot blow dryer type gizmo and a volt ohm meter but nothing to measure output of a coil, could it be checked on the input side.

Ideas???

If the plug isn't firing, it'd be pretty oily and wet with fuel.

Run an induction timing light from that plug while underway. If the coil fails to fire the plug, the light will also fail to fire.

You could also watch the primary side with a portable oscilloscope.

If it fails, then start playing musical coils till you isolate whether it's the coil or the switchbox.

1 plug fail, coil or switchbox
2 plugs fail, opposite in timing, like 1-4, trigger
3 in a bank fail, switchbox or stator
other combinations----crap shoot.

hope it helps
john

 

[CharlieB]

Re: Merc 2.4 V6 lost wot power

You have pretty much replaced most of the ignition system with no improvement.

Already cleaned carbs and checked the fuel system.

How about a stretched throttle cable, that will limit WOT opening, or a sticking trigger plate/timing arm, not allowing full advance at WOT, either will cause a limit to WOT RPM.

 

[j_martin]

Re: Merc 2.4 V6 lost wot power

You have pretty much replaced most of the ignition system with no improvement.

Already cleaned carbs and checked the fuel system.

How about a stretched throttle cable, that will limit WOT opening, or a sticking trigger plate/timing arm, not allowing full advance at WOT, either will cause a limit to WOT RPM.

Is there a chance that when the stator was replaced one of the screws is too long, interfering with the trigger.

Don't ask me what made me think of that.

 

[oldseaox]

Re: Merc 2.4 V6 lost wot power

Gentlemen, As my knowledge base grows I have decided to start over on my own. I have a manual and good advice, there is the possibility (probability) something was missed. I am starting with resistance and voltage readings per the manual, I re-tested the compression and all is well.
I will also check the mounting screws.

I will repost Wednesday with results, Thanks folks!!!!!!

 

[oldseaox]

Re: Merc 2.4 V6 lost wot power

There has not been an opportunity to run test (duties with the CGAUX, chasing poles on the ICW) but have found the engine is now noticeably skipping at lower RPMs. Below 3000 it can be felt and below 2000 it can be seen, however it will idle at 750 for miles. I am going to do a test on the ign switch boxes to try and find a cause but if not I am going to change them out. A local parts dealer has offered a super price, he is also in the CGAUX.