Mercury 250-HP EFI Runs Poorly; How to Test Stator

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Author Topic:   Mercury 250-HP EFI Runs Poorly; How to Test Stator

brybasack posted 06-25-2011 02:10 PM ET (US)
I have twin [Mercury] 250 [EFI outboard motors]. My starboard motor has had poor acceleration past 2,500-RPM for a few weeks. I had changed all filters, changed separators, changed spark plugs, cleaned final filter, ran alternate fuel tank, and still no solution. [The Mercury 250-HP EFI outboard motor] seems to kick in and run well for a few seconds, then drop back down in [engine speed]. [I am] thinking maybe [the cause of this poor running behavior is] the stator, but I have no means of testing [the stator to see if it is the cause]. [The author is seeking] any ideas [on how to test the stator of the Mercury 250-HP EFI outboard engine or perhaps on what the cause of this poor running characteristic might be]. Thanks. Brian
Tom W Clark posted 06-25-2011 02:16 PM ET (US)
A defective Switch Box is my first suspicion.
Each motor has two of these. Try swapping one from one motor to the other. If the trouble switches sides with the switch box, that is your problem.
This is a very common failure.
captbone posted 06-25-2011 03:15 PM ET (US)
The 250 EFI 3.0 liter does not have switch boxes as they are CDM ignition. Your engine (depending on year) with either have a single PCM or two ECMs (one for fuel and one for ignition).
I suspect dirty injectors. I would buy a simple inline spark tester ($8 from any autoparts store) and test each hole for spark to eliminate all of other possibilies. If you find a dead hole, swap the coils over to the other engine (all of them). If you have fire for each hole then I would have the injectors cleaned.
Here is the best marine injector cleaner
(919) 718-0249
Tony Brucato
4743 Christian Chapel Church Road
New Hill, N.C. 27562
Just my opinion.
69wailer posted 06-28-2011 12:35 PM ET (US)
I had a really similar problem with my Merc 250 EFI. There are drain hoses on each side of the bottom of the block in the bottom of the cowl, make sure they are there and not worn out or broken off, what was happening to me is water was coming up threw the holes from the bottom of the cowl and would short out the bottom 2 cylinders, When you dropped speed the water would not come up and the plugs would dry and fire again. If you look at a diagram you will see these short little drain hoses that I'm talking about.
Owtrayj25 posted 06-28-2011 03:13 PM ET (US)
When you say "poor acceleration past 2,500 RPM's", do you mean that the engine acceleration rate is reduced, but still reached an recommended WOT RPM level, or that the engine accelerates poorly, and does not reach recommended WOT RPM?
jimh posted 06-28-2011 07:38 PM ET (US)
A "stator" consists of an assembly of coil windings arranged in a permanent magnet alternator. You can generally make a static test of a coil winding by checking its resistance, and checking any resistance from the coil to the chassis in which the coil is mounted. Most coils are made to be completely insulated from the chassis in which they are installed.
You can make a dynamic test of a stator coil in a permanent magnet alternator by measuring the alternating-current voltage that is produced by the coil when the permanent magnet alternator is rotated. Usually there is a load associated with the test, and you may have to fabricate an appropriate load.
Of course, to measure the resistance of the coil and the voltage produced by the coil in the stator when the permanent magnet alternator is rotating and compare it in a test you will need some standard resistance and voltage measurements. You will have to seek information from Mercury or another reliable source to determine what the normal resistance or voltage should be so that you have some basis to make a comparison in your test.
jimh posted 06-28-2011 07:43 PM ET (US)
I am curious to know why you think the poor running of the Mercury Marine outboard motor model 250-HP EFI is due to a stator malfunction. This is the second recent article in which an owner of a Mercury outboard motor with a running problem that has an onset at an engine speed range of above 1,500-RPM has speculated that the cause is a malfunction of the stator. What is the basis for suspecting the stator? The stator is a relatively simple component, just a coil of wire.
captbone posted 06-29-2011 03:01 PM ET (US)
The stator is often replaced for no reason and is not a common reason (anymore) for engine issues. The bad rap came from the inline 6 engines and still sticks around today.
This engine uses a crank position sensor and CDM coils which most people overlook.
Its not your dads engine anymore.
Plotman posted 06-30-2011 09:16 AM ET (US)
I had a 150 EFI that had problems as described - would rev in neutral, but would bog down under load above 1800 RPM. Turned out that there is a small, in line fuel filter UNDER THE COWLING that was clogged. Cleaned out the screen with a toothbrush and all was well.
brybasack posted 07-01-2011 11:49 AM ET (US)
After using techron and adding Stargell to gas it ran well in the bay. Haven't tried in the ocean with any swell. The engine work not go over 2200 rpms in the ocean last week. Would often kick in to match it's twin but then would come back down. When we got back in the bay it ran well. Baffling?? Thanks Brian
jimh posted 07-01-2011 04:17 PM ET (US)
Glad you didn't replace the stator. Thanks for captb' for the clarification that Mercury stators are not the first item to be replaced anymore.
brybasack posted 07-03-2011 11:39 AM ET (US)
Ran it yesterday under a heavy load. Ran real well. I'm hoping we cured the [problem with the Mercury Marine 250-HP EFI running poorly by adding fuel system cleaner TECHRON and an unknown product called STARGELL to the boat's gasoline fuel tank]. [I] will run [the Mercury 250-HP EFI] in the ocean on Tuesday. Oil [alarm warning] lights came on. The [oil] tanks are not filling properly. I'm gonna check the lines later. Thanks for all your help and happy 4th. Brian
jimh posted 07-03-2011 07:49 PM ET (US)
What is STARGELL? I have never heard of STARGELL. Who recommended STARGELL to you?
captbone posted 07-04-2011 12:07 PM ET (US)
I would still suggest pulling your injectors and having them cleaned. I would also change all of your fuel filters. EFI engines are very reliable but fuel starvation is a leading cause of failures.
Your oil injection system is easy to fix. The transfer system from Mercury is the best on the market due to its simplicity.
On the starboard side of your engine is a fitting with one of the oil hoses connected. This fitting is a one way check valve. Air generated by the pistons motion flows throug this line. This line goes to your remote oil tank and pressurizes the tank. You need to ensure you are getting air to the tank and that the tank is not leaking air. The other line flows oil to the engine mounted tank via pressure from the crank. The tank pressurizes and pushes the oil to the small engine mounted tank. If your engine mounted tank is not filling then the tank is leaking air or the oil line is clogged, or the check valve is stuck.
Pull the cap off your engine mounted tank and start the engine. The engine mounted tank should fill. It needs to have the cap off the first time as an air pocket will form and prevent the oil from following.
Just my 2 cents.

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Author	Topic: Mercury 250-HP EFI Runs Poorly; How to Test Stator
brybasack	posted 06-25-2011 02:10 PM ET (US) I have twin [Mercury] 250 [EFI outboard motors]. My starboard motor has had poor acceleration past 2,500-RPM for a few weeks. I had changed all filters, changed separators, changed spark plugs, cleaned final filter, ran alternate fuel tank, and still no solution. [The Mercury 250-HP EFI outboard motor] seems to kick in and run well for a few seconds, then drop back down in [engine speed]. [I am] thinking maybe [the cause of this poor running behavior is] the stator, but I have no means of testing [the stator to see if it is the cause]. [The author is seeking] any ideas [on how to test the stator of the Mercury 250-HP EFI outboard engine or perhaps on what the cause of this poor running characteristic might be]. Thanks. Brian
Tom W Clark	posted 06-25-2011 02:16 PM ET (US) A defective Switch Box is my first suspicion. Each motor has two of these. Try swapping one from one motor to the other. If the trouble switches sides with the switch box, that is your problem. This is a very common failure.
captbone	posted 06-25-2011 03:15 PM ET (US) The 250 EFI 3.0 liter does not have switch boxes as they are CDM ignition. Your engine (depending on year) with either have a single PCM or two ECMs (one for fuel and one for ignition). I suspect dirty injectors. I would buy a simple inline spark tester ($8 from any autoparts store) and test each hole for spark to eliminate all of other possibilies. If you find a dead hole, swap the coils over to the other engine (all of them). If you have fire for each hole then I would have the injectors cleaned. Here is the best marine injector cleaner (919) 718-0249 Tony Brucato 4743 Christian Chapel Church Road New Hill, N.C. 27562 Just my opinion.
69wailer	posted 06-28-2011 12:35 PM ET (US) I had a really similar problem with my Merc 250 EFI. There are drain hoses on each side of the bottom of the block in the bottom of the cowl, make sure they are there and not worn out or broken off, what was happening to me is water was coming up threw the holes from the bottom of the cowl and would short out the bottom 2 cylinders, When you dropped speed the water would not come up and the plugs would dry and fire again. If you look at a diagram you will see these short little drain hoses that I'm talking about.
Owtrayj25	posted 06-28-2011 03:13 PM ET (US) When you say "poor acceleration past 2,500 RPM's", do you mean that the engine acceleration rate is reduced, but still reached an recommended WOT RPM level, or that the engine accelerates poorly, and does not reach recommended WOT RPM?
jimh	posted 06-28-2011 07:38 PM ET (US) A "stator" consists of an assembly of coil windings arranged in a permanent magnet alternator. You can generally make a static test of a coil winding by checking its resistance, and checking any resistance from the coil to the chassis in which the coil is mounted. Most coils are made to be completely insulated from the chassis in which they are installed. You can make a dynamic test of a stator coil in a permanent magnet alternator by measuring the alternating-current voltage that is produced by the coil when the permanent magnet alternator is rotated. Usually there is a load associated with the test, and you may have to fabricate an appropriate load. Of course, to measure the resistance of the coil and the voltage produced by the coil in the stator when the permanent magnet alternator is rotating and compare it in a test you will need some standard resistance and voltage measurements. You will have to seek information from Mercury or another reliable source to determine what the normal resistance or voltage should be so that you have some basis to make a comparison in your test.
jimh	posted 06-28-2011 07:43 PM ET (US) I am curious to know why you think the poor running of the Mercury Marine outboard motor model 250-HP EFI is due to a stator malfunction. This is the second recent article in which an owner of a Mercury outboard motor with a running problem that has an onset at an engine speed range of above 1,500-RPM has speculated that the cause is a malfunction of the stator. What is the basis for suspecting the stator? The stator is a relatively simple component, just a coil of wire.
captbone	posted 06-29-2011 03:01 PM ET (US) The stator is often replaced for no reason and is not a common reason (anymore) for engine issues. The bad rap came from the inline 6 engines and still sticks around today. This engine uses a crank position sensor and CDM coils which most people overlook. Its not your dads engine anymore.
Plotman	posted 06-30-2011 09:16 AM ET (US) I had a 150 EFI that had problems as described - would rev in neutral, but would bog down under load above 1800 RPM. Turned out that there is a small, in line fuel filter UNDER THE COWLING that was clogged. Cleaned out the screen with a toothbrush and all was well.
brybasack	posted 07-01-2011 11:49 AM ET (US) After using techron and adding Stargell to gas it ran well in the bay. Haven't tried in the ocean with any swell. The engine work not go over 2200 rpms in the ocean last week. Would often kick in to match it's twin but then would come back down. When we got back in the bay it ran well. Baffling?? Thanks Brian
jimh	posted 07-01-2011 04:17 PM ET (US) Glad you didn't replace the stator. Thanks for captb' for the clarification that Mercury stators are not the first item to be replaced anymore.
brybasack	posted 07-03-2011 11:39 AM ET (US) Ran it yesterday under a heavy load. Ran real well. I'm hoping we cured the [problem with the Mercury Marine 250-HP EFI running poorly by adding fuel system cleaner TECHRON and an unknown product called STARGELL to the boat's gasoline fuel tank]. [I] will run [the Mercury 250-HP EFI] in the ocean on Tuesday. Oil [alarm warning] lights came on. The [oil] tanks are not filling properly. I'm gonna check the lines later. Thanks for all your help and happy 4th. Brian
jimh	posted 07-03-2011 07:49 PM ET (US) What is STARGELL? I have never heard of STARGELL. Who recommended STARGELL to you?
captbone	posted 07-04-2011 12:07 PM ET (US) I would still suggest pulling your injectors and having them cleaned. I would also change all of your fuel filters. EFI engines are very reliable but fuel starvation is a leading cause of failures. Your oil injection system is easy to fix. The transfer system from Mercury is the best on the market due to its simplicity. On the starboard side of your engine is a fitting with one of the oil hoses connected. This fitting is a one way check valve. Air generated by the pistons motion flows throug this line. This line goes to your remote oil tank and pressurizes the tank. You need to ensure you are getting air to the tank and that the tank is not leaking air. The other line flows oil to the engine mounted tank via pressure from the crank. The tank pressurizes and pushes the oil to the small engine mounted tank. If your engine mounted tank is not filling then the tank is leaking air or the oil line is clogged, or the check valve is stuck. Pull the cap off your engine mounted tank and start the engine. The engine mounted tank should fill. It needs to have the cap off the first time as an air pocket will form and prevent the oil from following. Just my 2 cents.