Mercruiser low rev unsolved

EHS

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A while back I had a local mercruiser garage to take a diagnostics on my engine.

It's a 4.3L MPI 220 HK 2003 mod in a Bayliner capri.

I had a problem with the engine being difficult to start, the cranky was fine, but it would often stopp abruptly when it got ignition.
I had checked that gasoline pressure, nozzles and ignition were working.

I told you about checks I had done earlier, like disconnecting different sensors and that it didn't seem to matter on engine performance.
I was just told that I should leave it as it was originally and not think about it any more.

When I returned after making the diagnosis, the answer was that I needed a MAP sensor and a cooling water pressure sensor.
But from what I have read, an error on the coolant pressure sensor typically puts the engine in "Limp mode" and does not make it difficult to start.

When I returned to the boat to check the engine, several of the pistons were full of salt water.
So it was the condition that the engine was left in after 2.5 hours of diagnostics.
The conclusion from the diagnosis was that the engine starting problem would be solved by buying these two sensors.

I installed the two new sensors, but still the same problem.

I went to get to the problem, and long story short, it was a bad grounding to the MAP sensor that led to the ignition timing to be very "advanced" during the cranking which then caused the engine to start the opposite way and suck in water from exhaust.

So the 1200 dollars I paid for diagnostics and sensors resolved very little of the engine problem.
Instead, I risked sitting with a broken engine if I hadn't emptied the cylinders shortly after.


Now I'm back to a problem that had for the last 2 years before this event. The problem is that the engine stagnates at about 4000 RPM under WOT when driving (5000 RPM at WOT in free) with the MAP sensor plugged in, while the engine is running at 4500 RPM at WOT when MAP is disconnected.
The acceleration is bad without MAP but come still it reaches closer to the max speed it had previously.

By the sound, it sounds like it is the same rev limiting mechanism that holds it within 5000 rpm when free, as the one that holds it within 4000 rpm when in drive. I have tested different trim tilts and propellers, to the point where the propeller is almost free spinning. Still the rpm limit in drive is quite constant.

I would have liked someone to look at it, but have to say I'm a little lost to see who I can trust to solve this problem.

I hope this is something someone here may have the opportunity to find an answer to?

Current status is that I have now changed all the sensors, except the crank shaft sensor. I have checked this sensor with oscilloscope and it looks like the readings are fine.

plugs, cables, distributor cap are also changed.
 

alldodge

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4.3L MPI 220 HK 2003
several of the pistons were full of salt water.

Exhaust leaking or exhaust needs risers. Have you pressure tested or leak tested the exhaust?
What are you using to check for codes, and what codes are being seen?

bad grounding to the MAP sensor that led to the ignition timing to be very "advanced" during the cranking which then caused the engine to start the opposite way and suck in water from exhaust.

Don't see the MAP causing this issue. MAP with the PCM controls the amount of fuel used based on the Manifold Air Pressure in the intake manifold.

The problem is that the engine stagnates at about 4000 RPM under WOT when driving (5000 RPM at WOT in free) with the MAP sensor plugged in, while the engine is running at 4500 RPM at WOT when MAP is disconnected.

Don't understand stagnates at 4000 rpm.
Are you running the motor in neutral to achieve 5000?
 

Scott Danforth

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Agree with AD on the exhaust

running the motor in neutral to 5000 RPM proves nothing as the amount of fuel to get there is minuscule. it will get there in neutral with only one of the 6 injectors firing

under load is a whole new mater.

what codes are you seeing on the scan tool? what does Rinda tell you?

FYI for the diagnostic charge of $1200 you can buy the Rinda diacom software delux kit and connect to any electronic marine motor

http://www.rinda.com/acro/prodlist.pdf
 

QBhoy

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Sounds like it’s in one of the faults that only give you 90% power maybe. You need to get it plugged in.
 

EHS

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I have pressure/ leak tested the exhaust and did not fond any leak.

I don't want to seem as a smart ass, but checking map sensor on Wikipedia seem to indicate that input from map is used by the ecu to bothh calculate fuel amount and ignition advance.

But still maybe this ecu may not adjust the timing advance with input from map.

But after the poor grounding was fixed there has been no water in the pistons since. And no issue with cranking and starting. Previously I could physically see that the engine started the wrong way.

but I should mention that I bought the boat when 2/3 of the engine was sitting in water. And have probably done so for some months.

Sure, I bought the boat knowing there would be a risk of complications, and got a reduced price.
.
I have thought about getting the Rhinda diagnostic tool. If I knew the 1200 were a throw away I would for sure rather spend them on a diagnostic tool.

But as far as I know only designated mercruiser dealers get o acces to the full set of details.

But thinking if maybe the ecu have suffered some damage, or maybe is just of poor quality and not suited for the present environment. Then maybe I should rather go for a programmable ecu and have full control and access to all input variables. Instead of spending more money on a diagnostic tool that may still not resolve the problem.

I have checked fuel pressure during full load and idle and it looks to stay well to the spec.

But again thanks for giving me input on this
 

Scott Danforth

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wikipedia is not a substitute for a factory manual, a multi-meter, a fuel gauge and Rinda
 

alldodge

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wiki is nice but in most cases they are talking auto not marine. Not saying the info is bad, but it needs to be associated as such. The ECM controls everything based on the inputs it receives from each of the sensors. The MAP, TPS send signals to the ECM which determines what needs to be done.

Timing for a car is different then for boat, meaning all timing has been given around 3000 rpm, and a car would not see it all until around 4000. Still don't see water coming in from being advancing timing on a stock motor, but if timing is not set correctly then it will run poorly

Here is the manual for your motor
http://boatinfo.no/lib/mercruiser/manuals/mercruiser32.html#/0
 

scoflaw

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The 555 ecm is known to be a weak unit and failures are common. You can send it out and have it diagnosed for less than a $100, and repair is possible. You don't mention the TPS which works with the MAP to control fuel and timing.
 

EHS

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Thanks for the feedback.

So the 555 is a weak unit...
Makes sense for me.
As it Seem as almost every day at the water the engine behaves a bit different. Sometimes just stopping and starting changes the max rev with about 100 - 300 rpm.
But what kind if fix are we talking?
Like a solid fix that will sustain, or a fix that may last some months, maybe 2-3 years?


It did take me some time to get convinced about the reverse starting, map and timing.

But disconnecting the ground to map sensor still causes the engine to start reverse. Also this gives a big load on the starter motor, seem to be why l had to replace the old one.

Still I agree that a manual and proper tools are the best means to the job.
 

alldodge

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Have not heard where the 555 is a weak unit, there has been some issues with the early units being damaged if the IAC started drawing to much current and was not replaced.

engine to start reverse.

Only way a motor starts in reverse is if the timing is way out. Could also be spark is craoss tracking in the distributor. Caps are known to have issues
 

kenny nunez

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If I read your post #3 correctly you stated that the engine will rev to 5000 in free, does that mean in neutral? The shift switches are supposed to prevent the engine from going much above idle unless the drive is fully in gear. Also you said that the engine was submerged 2/3 for some period of time. It may be possible that the wire harness could be damaged internally which can really cause some problems especially if the battery was still connected at that time.
 

EHS

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I did take out the whole harness and checked it with a multimeter. That was when I found the poor grounding to the map sensor.

it goes to 5000 rpm when I push the button at the pivot point of the power lever. This button is to disengage shifting whilst allowing to open the throttle to wot.
 

kenny nunez

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It appears that the problem you are experiencing started a very long time ago with the previous owner and possibly since the engine was new. Try contacting the warranty dept. at Mercruiser with the serial # to check if there is any history on this engine. When you had the harness removed and the wires were tested was a good thing. I have heard of problems where a wire harness had an internal problem where 2 and sometimes more wires had the insulation damaged by being pinched together and were cross feeding. I realize this is a long shot but it has happened before. Removing the tape and inspecting may show something. Also after the wires are separated try pulling on each one to see if the wire can be stretched and the wires inside are weak.
Have you inspected the wires under the instrument panel and all the way to the engine for any damage where it may have been damaged from a drill bit?
 

Scott Danforth

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it goes to 5000 rpm when I push the button at the pivot point of the power lever. This button is to disengage shifting whilst allowing to open the throttle to wot.

this means nothing as the amount of fuel required to make a motor spin to 5000 RPM in neutral is litterally drops per hour compared to about 14 gallons per hour loaded
 

EHS

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Thanks Nunez,

I'm eager to try this with the switch.
But I was just signed up for an offshore job. So I won't be back to test it for a couple of weeks.
 
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