Absolutely frustrated with this Mercruiser engine

scoflaw said:
Did this motor ever run right?
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When I was looking at it to purchase it gave the appearance of running right and even fooled the surveyor. When I took it out for its first run after purchasing it Murphy decided I needed a bludgeoning with his laws.
 
I had the same issue. Turned out it was the cam shaft positioning sensor. Its located in the distributor.
5 minute job to replace it.
 
Are you saying that that it would rpm before you bought it or it idled and reved up before you bought it. Would like to see you have fun with this boat
 
scoflaw said:
Did this motor ever run right?
Click to expand...

With 566 hours on the ECM clock I would presume it did at some point unless they did those hours at less than 2000 rpm. Short of a sea trial.....the engine probably started and idled perfectly.

By his own numbers the OP has dropped $1,500-2,000 in parts/services trying to find out what is wrong with this engine. I can't imagine how many labor hours he has in it.

I still believe the ECM has an issue and is dropping into RPM reduction mode. If you look at his various load runs......2004 rpm and 2037 rpm was as far as he got. Those numbers are suspiciously close together.
 
PlayDate said:
With 566 hours on the ECM clock I would presume it did at some point unless they did those hours at less than 2000 rpm. Short of a sea trial.....the engine probably started and idled perfectly.

By his own numbers the OP has dropped $1,500-2,000 in parts/services trying to find out what is wrong with this engine. I can't imagine how many labor hours he has in it.

I still believe the ECM has an issue and is dropping into RPM reduction mode. If you look at his various load runs......2004 rpm and 2037 rpm was as far as he got. Those numbers are suspiciously close together.
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There is only three ways an ECM can back RPM out of an engine - reduce injector duty cycle, taking spark away, or back out timing.
Backing timing out has limitations and is usually used for knock reduction. So this leaves reducing the injector duty cycle or taking spark away. Taking spark away will give the exhaust a distinct raw fuel smell and isn't typically used for OEM applications. This leaves changing the injector duty cycle. Short of trying a different ECM, at this point, I would put an O-Scope on one of the injector connectors and see if a change in injector pulse width is concurrent with the limitation in RPM... Out of the box thinking.
Regarding the cam position sensor. These are usually work or fail - however it's not out of the question if the hall effect coil in the sensor is failing or becoming saturated that it cannot send a good signal in the upper RPM ranges. I would think, however, that the engine would behave differently/erratically than hitting a 2000 RPM wall.
 
His motor doesn't have a cam sensor. Never heard of a mefi 1,2 or 3 going into limp mode. Not saying that info posted 100 posts ago is wrong but never heard of anyone having that problem.

If this was my problem I would make sure everything is mechanically sound before moving to electrical
 
I agree but we are nearing the end of probable causes. Effectively he has replaced/rebuilt everything from the short block up. The only thing we know for certain after 327 posts is that it starts up idles nicely and refuses to go over 2,000 rpm.

That is by definition one of strangest problems we have seen. @370Dancer's engine was another perplexing story. His turned out to be mechanical and I have never seen a crank journal create a problem like he was experiencing so there is a first time for everything.

The refusing to go over 2,000 rpm under load is the weird part. That issue just doesn't make sense. Even if it was mechanical.....I would expect fuel flow to be making a very rich condition that we haven't seen.

Maybe it is time to look at the plugs again.
 
“Refusing to go over 2000rpm” is very arbitrary. Does it not go over 2k? Does it run like sht over 2k?
I had a 454 in the 90s that “refused to go over 1800”. It would go over but run like sht. Idled the boat at 1500 rpm to a marine mechanic’s shop quite a ways, with a buddy and large cooler of beer one Saturday morning. Left at sunup arrived at noon. HaHa what a trip that was.
Bad carb, he put a rebuilt QJ on, problem went away.
Whats my point? There’s a hella lot that could be wrong.
 
Yeah you're not kidding
 
My son is a reallly good car mechanic. He tells me its like being a veterinarian. The patient cant tell you exactly what is wrong, but they hurting. The owners are hysterical so you need to calm them down then ignore anything they say.
He’s good. The skill is the diagnosis, anybody can replace parts.
Don’t believe that ODBC tells them exactly what wrong. Its a tool, not AI robot.
 
Pirate Lady said:
“Refusing to go over 2000rpm” is very arbitrary. Does it not go over 2k? Does it run like sht over 2k?
I had a 454 in the 90s that “refused to go over 1800”. It would go over but run like sht. Idled the boat at 1500 rpm to a marine mechanic’s shop quite a ways, with a buddy and large cooler of beer one Saturday morning. Left at sunup arrived at noon. HaHa what a trip that was.
Bad carb, he put a rebuilt QJ on, problem went away.
Whats my point? There’s a hella lot that could be wrong.
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Take a look at the Fox Marine data he posted #224. Throttle is wide open on both runs under load...it isn't blowing black smoke like a freight train. He has replaced or rebuilt everything above the short block......the list of things left is pretty damn short.

On the carb issue.....yup....far, far easier to work on and diagnose especially if you have two of them.
 
@Pirate Lady Basically it starts and idles perfectly then runs normally until about 2000 RPMs while in gear and pushing along at about 10 knots. Then I push the throttle more forward and nothing more happens it just refuses to accelerate or rev any further. The engine doesn’t stumble or backfire or anything. There is no smoke from the exhaust and the only smell is one that suggests the engine is running lean. In neutral the engine revs all the way up. Something is preventing sufficient amounts of fuel from being delivered to the engine. I simply have no idea what that is.

@Scott215 When I bought the boat I had just sold my Chaparral 234 Striker which was powered by a Mercruiser 5.0 with an alpha 1 drive. I did all the work on that boat myself and it was a great engine. I thought that would be the same story with this Sea Ray. I wanted to move up to something bigger and this seemed to fit the bill. I paid $1000ish dollars for a survey and the sea trial was only done in the no wake area by the marina. The engine didn’t give me any indication then of major issues. The first time it showed me a major issue was right after I finalized the sale and was taking it out the channel to sea and it broke down on me. That was two years ago and I still can’t get it to run right. I also can’t afford the obscene amount of money they want for a whole new engine for it at this time. Especially since I don’t think there is a mechanical problem with the block but rather an unknown electrical issue preventing it from running as it should somehow. BTW the quote I got to repower it here was $60,000 which is beyond the blue book value. If I were to do the work myself first I’d have to spend $15,000 for a cheap trailer then find someplace to rent a parking stall that would allow me to work on it plus have access to either a forklift, crane or an a frame. There isn’t such a place here. Then I’d have to take off from work to do all the labor. Either I fix it as it is or I’m simply screwed and get to pay slip fees for a boat I can’t use.
 
@808 I really hope you get this figured out I had problems that prevented me from boating for a few weeks because my neighbor took off my outdrive and couldn't get it back on. I had to take it to the dealer and pay $175 an hour to have it fixed and I know what it's like not having a boat not knowing why something doesn't work I really truly do hope you get this boat running right I would love to see you have fun out there I mean that. I think he caused a little bit of damaged pounding in the alignment tool with a sledgehammer and so I feel you I had to break out the boat bucks and it was not cheap I feel you
 
PlayDate said:
With 566 hours on the ECM clock I would presume it did at some point unless they did those hours at less than 2000 rpm. Short of a sea trial.....the engine probably started and idled perfectly.

By his own numbers the OP has dropped $1,500-2,000 in parts/services trying to find out what is wrong with this engine. I can't imagine how many labor hours he has in it.

I still believe the ECM has an issue and is dropping into RPM reduction mode. If you look at his various load runs......2004 rpm and 2037 rpm was as far as he got. Those numbers are suspiciously close together.
Click to expand...

Agreed. The 2004 and 2037 are way too close to be arbitrary.
OP stated that the sensors and such are OK BUT that does not eliminate the possibility that the ECM itself is at fault.

Do they go bad and do stupid things? YUP. Can any brand new electronic part be bad right out of the sealed OEM packaging? YUP
 
Ericinmich said:
OP, does the engine change it's sound as you slowly roll up the throttle and it hits 2k rpm? Also, does it always go to 2k plus/minus 50rpm or so?
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No change in sound to speak of and always right around 2K.

@Bill Curtis I've replaced every single sensor with either Sierra or Mercruiser brand parts. Both the Fox Marine tool and the mechanics fancy expensive computer showed they were all working within specifications. The ECM isn't showing any fault codes whatsoever and its self check also says all is well. This is according to both the Fox Marine unit and the mechanic I paid.

I've checked the ignition wires at least a dozen times now as well as the injector wires and a dozen other things and all seems to be plugged in or adjusted correctly. I just don't know and it seems neither do any of the professional mechanics I can get to come out that are competent.
 
Out of gear the engine will free rev smoothly to the limiter right?
That tells me the ECM will allow any RPM up to the rev limiter.
It's under load that the engine hits a wall at 2000 RPM if I understand correctly. And, it doesn't stumble, smoke, smell like raw fuel, or make unusual noises, right?

We know now that the mechanical end of things is solid, sensors are performing correctly, adjustments (TPS, base timing, etc) are correct, no faults showing, and most importantly the injectors are validated.
It's assumed that the engine wire harness has been gone over and is in good shape and all of the ground lugs are correctly and cleanly terminated. As a note the ECM will demand more and more electrical current as load increases because the injector pulse widths are increasing; this is not insignificant.

What we don't know -
The fuel pressure when under load and hitting that 2000 RPM wall.
Ignition timing under load when hitting that wall.
Injector duty cycle under load at that wall. Are they getting lazy because the ECM can't deliver enough current?

A couple of other no-brainer things to consider -
Is the exhaust path clear? All the correct exhaust system gaskets?
Is the intake air supply good and unrestricted including air supply from the hull?
 
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