Logo
FULL SITE MENU

Mercruiser MEFI3 57Litre TBI Loss of top end

bulit7

bulit7

Contributing Member
Hi everyone. I am trying to fi

Hi everyone. I am trying to figure out why this engine I'm working on has lost its top end. Max RPM I am getting is 2600rpm. Fuel flow is good.

This is in a 2001 SeaRay 26' MCM engine(Bravo Three).

Fuel pressure is around 20-30 psi acording to a sealed 0-160psi guage I tee'd into the line right before the throttle body. The engine has no codes. My timing is dead on 8 btdc.

This is a brand new long block and ran fine for an hour or so and now it has lost its top. Any help would be appreciated.

Lee
 
I think I would start with a c

I think I would start with a compression test. You may have wiped out a cam lobe or something.
 
"I agree with Dave n! Compress

"I agree with Dave n! Compression,Fuel and Ignition are all thats needed. Does it Idle cleanly? Accelerate quickly? More symptoms please. Al W."
 
"Yes, it starts right up. And

"Yes, it starts right up. And runs smooth.

Fuel pressure is 20 psi. It should be 30-40 psi.

Engine runs fine untill it hits 2500 rpm.

Could the fuel regulator/damper on the throttle body be bad?"
 
"By the way. This is a brand n

"By the way. This is a brand new Marine Power long block engine. It ran well for an hour and then when the owner took it out again, it had no top end."
 
Fuel Pressure is deficient? Re

Fuel Pressure is deficient? Replace the pump and Relay would be a good start. Please advise us of the outcome. Al W.
 
"Yeah, fuel pressure should be

"Yeah, fuel pressure should be 30 PSI, not 40. At this point you could just start replacing stuff as Al suggested, but I would get a factory service manual and go through the troubleshooting procedures. That's the fastest and least expensive way to do it."
 
"OK. I'll list all I did.

"OK. I'll list all I did.

1.Replace fuel filter and inspect contents. No water, some debris.
2.Remove anti siphon valve and replace with a straight thru fitting.
3.Check for fuel restriction in line to fuel filter by sucking on the line. Negligeable resistance.
Installed a fuel pressure guage at the throttle body fitting. (no easy task assembling a flared T adapter) Pressure id dead at 20 psi.
4.Replaced the fuel pump and fuel pressure regulator at the CoolFuel assembly. No change in pressure.

Scan tool shows no codes.

I will definately post results once I fix it."
 
RE: "2.Remove anti siphon

RE: "2.Remove anti siphon valve and replace with a straight thru fitting."

Antisiphon valves are a safety REQUIREMENT.
Any insurance claim in the future that could be traced to the absense of that valve will not be paid. There are a few scenarios where the lack of that valve could lead to serious injury and/or loss of life. Is your E+O Insurance all paid up??
 
"It really doesn't matter

"It really doesn't matter how old the engine is. Are you saying it has 20 PSI of fuel pressure at idle, at cruise, at WOT under load or what? Have you tried deadheading the pump?"
 
"[b]Antisiphon valves are a sa

"Antisiphon valves are a safety REQUIREMENT.

Thanks Robert, I will install a new one.}

It really doesn't matter how old the engine is. Are you saying it has 20 PSI of fuel pressure at idle, at cruise, at WOT under load or what? Have you tried deadheading the pump?


Dave, it has, according to my guage, 20-25 psi at all rpms.

What do you mean by dead heading?


."
 
"OK,

Took the boat out tod

"OK,

Took the boat out today armed with a squirt bottle full of fresh fuel. Once the boat was at WOT, and reached its 2500 rpm max, I injected some fuel into the TB. It caused the boat to hesitate(flooded a little).

That is telling me it is not a fuel issue.

I also replaced the distributor sensor and the coil since it felt a little hard to start and I had made a mental note to replace those items when I replaced the engine.

I also pulled the plugs and they seem to be burning fine. Will do a compression test tomorrow.

I will also perform the fuel and ignition system checks as per tables A4 and A7 in the Merc shop manual.
If anyone can think of anything else, please let me know. Thanks for all the help so far."
 
"Lee,
Deadheading means to bl

"Lee,
Deadheading means to block off the fuel return and see what the fuelpump pressure is when unregulated. i.e. if the return is blocked and the pump produces high pressure (60+PSI), the pump is not the problem. If the return is blocked but the pressure remains low, you have a bad pump. This is all covered in the Merc service manual.

I think you are making two basic mistakes in your diagnostic process. 1) You are assuming that if parts are new they are good, 2) you are making up your own tests and drawing conclusions based on the results. Stick to the exact diagnostic procedures outlined in the service manual and you will find the problem."
 
"Dave n, thanks for explaining

"Dave n, thanks for explaining that!

Today I did a compression check, 210-205 on all 8 cylinders. That was a relief.
I rechecked the timing with a light and it was dead on 8 BTDC.
I reseated all the grounds and reseated all the connectors including the ECM.
Sea trial produced normal RPMs. What caused the drop? Bad ground connections, maybe.
One of those problems that we will never know.

Thanks toeveryone that hepled me out!
thumbs_up.gif
"
 
Back
Top