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MPI engine loses power

D

Don Truskauskas

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"I have a 2003 searay 5.0 mpi.

"I have a 2003 searay 5.0 mpi. It idles fine but has very little power when accelarting. The ecm has no codes. We just had the injectors cleaned and calibrated, this made a small improvement. The mechanic has checked fuel pressure and that is good. any ideas ???"
 
Has the condition and color of

Has the condition and color of the spark plugs been checked for a rich or lean burning condition?
Is this a condition that has just started or has it taken awhile to get to this point?
Was the fuel pressure checked at different rpm or just an idle?
Is it running at normal temp?
Will the engine turn full rpm at wide open(4200-4600)?
Has the timing been checked?
 
"It happened all at once. Ran

"It happened all at once. Ran fine, anchored for lunch then after lunch lost power. Engine Temp is fine. Will not rev fully under load. Didn't try with no load. I don't know about the timiming will chack. thanks"
 
"When you tried to rev it, did

"When you tried to rev it, did it run smoothly or was it kind of rough? Look at the IC (Ignition Control) module, too.

How old is the impeller in the raw water pump?"
 
Impeller is new replaced this

Impeller is new replaced this spring. Under load it's kinda rough. in neutral its smooth
 
If it happened all of a sudde

If it happened all of a sudden one of the sensors could have quit working. Depending on what sensor failed it may or may not set a trouble code in the ECU / ECM. If it was a temp sensor the ECU could think that the engine is cold and not advance the timing or reduce the amount of fuel.
 
"Don- which motor is this? Can

"Don- which motor is this? Can you post a couple of photos? Have you run it since the power loss after lunch? If not, it could have been a heat-soak situation and the ECM acted like the motor had overheated. If you're in a hot, dry area, this is definitely possible. Make sure the tech cleared the codes and checked for overheats. Overheats don't clear as easily as other codes. If it didn't go over 2000 RPM, I would almost bet that this is the case.

charli- the ECM will add fuel if it thinks it's cold or did you mean reduce the fuel from "cold start" to normal operating temperature?. The timing would be unaffected by a bad ECT unless the knock sensor sends a signal.

Don- speaking of knock sensors, look on the side of the motor with the starter for a blue wire with a black plug, dangling in the air. That needs to be plugged into the large, gold colored device mounted where a block plug would go (just above the oil pan). If it's shorted to ground, it'll also cause problems. This would show up as a 43 or 44 code.

If the motor is run out of the water, look for cooling water flow and make sure the exhaust isn't plugged. There may be a flapper in the exhaust and if this melts, it won't move out of the way when the motor runs and can cause problems.

Since it's kind of rough, it sounds more like a shorted ECT wire/bad sensor, causing the ECM to see an overheat and go into RPM reduction, but that should have thrown a code. At normal operating temperature, the coolant temperature sensor should measure about 1.5-2.0 Volts dc, and this translates to 332 Ohms @ 80°C/176°F and 667 Ohms @ 60°C/140°F. This is measured on the two wire sensor (yellow/black wires), located on the head between #3 and #5 cylinders (usually). I have seen it in the intake manifold, but its location depends on the motor."
 
have mercruiser 4.3 GM blown m

have mercruiser 4.3 GM blown motor is the motor block heads and intake the same as a pickup or car motor
TKS
 
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