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Merc 200hp EFI 1996

T

The Duke

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Hi all, I am having problems with throttle control when engine running cold. When first starting I always warm engine (on the trailer) to where thermostat has opened and water is flowing through the head. Then there is always a bit of low revs motoring to get the boat out from the ramp etc. When I try to get the boat on a plane there is a distinct lag in throttle response. The boat revs increase only slightly but it takes 5-10 seconds to come up to required revs. This only happens when first started and the engine has been running for at least 5-10 minutes although the temp guage doesn't register very much heat. Any ideas? Thanks
 
Dirty injectors? Dump the fuel/water separator and fill it w/Seafoam. Run the engine at idle for 3-4 minutes and shut it off. Wait an hour and run it at 3-4,000 RPMs on the water. Note: Seafoam will make it smoke like it's a smoke screen maker. That is normal and will quit.
 
Hi thanks for the replies. I am running the fuel through a separate water separator and have replace the fuel filter. No water in either. The motor doesn't do it when it warms up so a little bit confused. I have put an injector cleaner additive through but nout seem to help? Cheers
 
The first steps:compression and spark???
Then the fuel system:Test the fuel pump pressure on the rail.Should be about34- 36#(if my memory is right).
Sometimes too much pressure can cause this.
Do a stator test too.J

Sent you a PM.
 
If it runs great after it warms up then it has to be a cold engine fuel issue. Have you had the engine scanned to see if any problem codes are stored? For what it costs it will save you money by replacing only defective parts.
...the engine has been running for at least 5-10 minutes although the temp guage doesn't register very much heat....
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With a good thermostat the engine should be at operating temp w/in 5 mins. of idling. I'm thinking it could use a thermostat...they don't last forever. Dirty throttle plates and throats will cause poor operation on a cold engine. Clean them w/spray throttle body cleaner and NOT CARB cleaner.
 
Hi all, thanks for the replies. The thermostat seems fine and opens when motor warms. The plugs all look the same and have compression of 4@ 120lbs, 1@ 119 and 1 @ 118 (not bad for an old motor?) when engine warm.


Could it be a partial air intake blockage? There is a sucking noise coming from under the manual start flywheel but I can't get under it to have a look. Last time that it was in for a service the mechanic had a quick look and stated that it was an unusual sound for the motor to be making (he couldn;t find the source either). Am I right in saying they don't have an air filter? If not where is the air intake for the motor located?


At this stage I'll try what has been suggested and if that fails to fix the problem will take it into a Mercury dealer to hook onto a computer. Thanks for the offer of a CD (engine manual) but I already subscribe to Seloc.

Will keep you all advised.

Cheers
 
The Seloc and Clymer manuals SUCK.Both way too vague and try to fix too many motors.Spreading themselves way too thin.
Nothing beats the factory manuals.
You do the fuel pump pressure test?
If you think you have an air leak.While the motors running,spray some starting fluid up under the flywheel.
It will make the motor sounds change.
Any peculiar sounds from that area could be a loose screw rubbing on the flywheel.Remove it and check.J
 
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Hi, haven't tried the spray test yet but will next week when I get a couple of days off. Failing that will attempt to take off the manual start flywheel so I can see what is happening underneath. Is this easy to do?

Haven't done the fuel pressure test as I don't have the gear. The sound if definitely sucking sound and not a loose screw rubbing

Yes the motor does smoke when cold. I just put it down to 2 strokes. No problems with smoke when it has been running for a while and up to full operating temps.

Cheers
 
Assuming your oil injection system is still hooked up and functioning. Hard starting and excessive smoke when cold is caused by over oiling due to a $11.00 part that needs to be changed. The oil tank pressure check valve. It feeds crank case pressure to the reserve oil tank. When the engine is shut down it is supposed to relieve the pressure in the oil tank. If not working properly it will force oil into the fuel system. This part cannot be cleaned.
 
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Hi, yes it is all hooked up and working. The motor starts easily when either hot or cold. That part already been replaced as it was leaking oil into the cowling. I take it that's the brass 'T' section that you are referring to? Have tomorrow off so time to try and get under the flywheel and have a look. Cheers
 
Nope not the brass tee. Your reserve oil tank has two lines going to it. One goes to the tank on the engine and the other is the pressurizing line that goes to a check valve that is screwed into the bottom of the engine block. Follow the lines and you will find it.
 
The Duke said:
Hi all, I am having problems with throttle control when engine running cold. When first starting I always warm engine (on the trailer) to where thermostat has opened and water is flowing through the head. Then there is always a bit of low revs motoring to get the boat out from the ramp etc. When I try to get the boat on a plane there is a distinct lag in throttle response. The boat revs increase only slightly but it takes 5-10 seconds to come up to required revs. This only happens when first started and the engine has been running for at least 5-10 minutes although the temp gauge doesn't register very much heat. Any ideas? Thanks
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The reason I am asking about this valve is that it will cause poor performance for the first minutes of running (hot or cold) until the excessive oil is cleared. You cannot clean this part, you can only replace it.

Actually you can check its operation to see if it is not functioning correctly, after you have run the engine, shut it down for maybe 2 minutes. Now go to your reserve oil tank fill and remove the cap and listen carefully while you remove it. There should be no purge of air. If the tank stays pressurized, the valve is bad.
 
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The Duke said:
Hi thanks for the replies. I am running the fuel through a separate water separator and have replace the fuel filter. No water in either. The motor doesn't do it when it warms up so a little bit confused. I have put an injector cleaner additive through but nout seem to help? Cheers
Click to expand...

I have a 96 EFI 200. Similar problems Idol super rough cylinders meet the hundred and twenty or better compression it has spark. I can't find the injectors I'm looking for the fuel rail I can't even see that. I'm kind of confused on the whole deal. My boat will not go on playing it slowly got worse and now it runs very rough and doesn't have enough power to even get up on plane. I personally am going to try and take off the fuel pump and look for all the crap from the grey hose and try to clean that out. Change the filters. I was hoping to clean the injectors but I can't even find them. If you happen to know why I can't find the injectors please let me know. I feel stupid because I know where they are and everyone else's motor. I'm starting to wonder do I even have fuel injectors. LOL
 
Docksidemarineservices said:
Assuming your oil injection system is still hooked up and functioning. Hard starting and excessive smoke when cold is caused by over oiling due to a $11.00 part that needs to be changed. The oil tank pressure check valve. It feeds crank case pressure to the reserve oil tank. When the engine is shut down it is supposed to relieve the pressure in the oil tank. If not working properly it will force oil into the fuel system. This part cannot be cleaned.
Click to expand...

I have 96 EFI 200 in mine had the oil injection removed professionally and I mix the oil and I was told to run 45 to 1 just to Baby the cylinders. I'm having no power problems myself. And it runs super rough. I'm thinking I need to clean out the fuel pump because I do have gray hose connected and I can't find the fuel rail I'm feeling like an idiot. I know where all my friends are on their Yamahas but I don't know where this one is I thought it would be on the sides. Thought if I cleaned out the fuel pump change the filters and cleaned out the injectors I would be good to go. Any suggestions for me? Because I have a family vacation coming up and we already tried it and my boat into work so we cancelled it and drove all way back 10 hours and rescheduled our vacation. Can't do that again the banks and government are trying to destroy us so we are limited on funds. Any help would be appreciated.
 
You have tagged onto a 5 year old post so start a new thread back at the beginning of the Mercury OB section. Include the engine SN and year. Doing this will get you 15-25 learned viewers to help you ASAP. First thing I would do is check for strong bluish spark using a spark gap tester set at 7/16". Also connect a different fuel source.,
 
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