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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4724
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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1994 mercury EFI started bogging down and would not plan the

Customer Question

1994 mercury EFI started bogging down and would not plan the boat. tried starting the next morning and it will not start. thought maybe a fuel issue due to sitting for some time. changed fuel water separator filter, bulb and hoses, drained system. turns over but will not start. coughs slightly but will not crank.
Submitted: 1 year ago.
Category: Boat
Expert:  Jeff G. replied 1 year ago.

Can I get the serial number please?

Customer: replied 1 year ago.
0G041782 1994 Nitro XRI 200 HP was built for the nitro boats by Mercury it is the throttle body fuel injection
Customer: replied 1 year ago.
It ran fine Monday and then when I went to take off Tuesday it bogged down and would not plane the boat. This morning it coughed by cranked once I gave it some throttle in neutral and then dies and will not start. It had been sitting for about 2 years and was just brought out of storage about a week ago . Ran fine for several outings and then started this
Customer: replied 1 year ago.
Changes oil water separator filter today and thermostats and bulb and hose from bulb to motor. Seems to have pressure from fuel pump in that it will spray fuel when pressing the detention on the pressure check just after the pump. I pulled the small diaphragm bowl that has the fine screen filter to protect the injectors and it was slightly dirty but cleaned anyway. Also drained the tank prior to the pump.
Customer: replied 1 year ago.
also changed the thermostats today just because they had not been changed in awhile. both of course. I will check fire tomorrow to see if something is up. just weird that it would run great and then start giving issues all of a sudden. This is only the second time any issues with the motor. the only other thing that I have notice was that the last several years when using. it was low on power when trying to plan and also when trying to drive onto trailer. But attributed it to the prop that I am running. A 4 blade 26P double cupped stainless prop. still seems low on low in power for a 200 HP. runs like a scalded dog on top end once planned. not sure if this was a sign that something was going on earlier. The only other issue I had was the oil injection module. which I replaced about 10 years ago. other than that trouble free.
Expert:  Jeff G. replied 1 year ago.

I'm suspecting ignition problems. Do you have a spark tester? If not get one from any auto parts store. Set it to 7/16" gap and check for good spark. Make note of which cylinders aren't firing properly. From the back of the engine looking forward the #1 is top starboard (right) #2 top port (left).

I would also look into getting a fuel pressure tester. Many of the larger chain parts stores will rent/ loan you one.

Do you have a voltmeter that can read resistance?

Let me know about the spark asap.


Customer: replied 1 year ago.
Will do I will try and pick up spark tester if anything is open tomorrow with it being a holiday and yes have a volt, ohm meter and compression gauge. Will try and test tomorrow
Customer: replied 1 year ago.
Happy Thanksgiving to you and your family and thanks for the help!
Expert:  Jeff G. replied 1 year ago.

I'll check back tomorrow.

Customer: replied 1 year ago.
okay purchased a spark tester and I am getting spark at each plug on all 6 cylinders. Looks week but this is a universal tester from the local auto parts store and not sure if the internal gap is correct. I am seeing reddish orange spark internal to the see thru plastic. I tested the fuel pump and was getting no pressure reading at the check valve just prior to the screen assembly before the injector rail connection. Changed the pump and left disconnected and it shot a stream about 3 feet in the air, 3/8" in diameter but still will not build pressure. Is there a check valve on the system that could be stuck open?? and is there a screen in the VST that could cause the pump to not be able to get enough fuel. Seems unlikely in that it was able to pump such a strong stream disconnected. Also disconnected the kill switch circuit from the key switch and still no luck.
Expert:  Jeff G. replied 1 year ago.

I'm going to give you the fuel injection chapter as it is was to cumbersome to try and troubleshoot step by step here. Follow the instructions. You will need a fuel injection tester. You can get one inexpensively at a discount tool store such as Harbor Freight.

Your ignition seems OK. Same with the kill switch.

Customer: replied 1 year ago.
today I tested and found the fuel pressure regulator was sticking and not allowing it to build pressure. Took apart cleaned, lubricated and activated with a vacuum pressure pump, reinstalled and building to 38 PSI according to fuel pressure gauge. holding steady so I believe now we have enough pressure and supply to the injectors. Plugs seem a little damp with oil and gas when I pulled them to do the test so think I am getting fuel to the cylinders. Everything now looks good. checked engine compression on all cylinders and from 115 to 120 on all 6 cylinders so don't see an issue there. according to specs anything close to 120 on a cold motor is excellent and considering the age of 21 years it seems to be good. Now leaning towards ignition but do not know what test to perform to narrow down.
Expert:  Jeff G. replied 1 year ago.

Have you tried to run the boat since the regulator was repaired?

You can check timing with a timing light and we already did a ignition output test.

Run it and post back how it does.

Customer: replied 1 year ago.
Tried to start again and will not start. Retested all of the plugs with spark tester and I am seeing spark but still looks weak to me put using a universal spark tester and it looks slightly orange inside the plastic cover on all cylinders! Does not look like a very hot spark to me! Should be blue if around 40000 volts as per specs I found in Internet not sure what to check next for voltage or resistance across coils.
Customer: replied 1 year ago.
Boat is sitting in the water at my dock so I have been trying every time that I check something. Specs on Internet says to unplug black yellow wire for kill circuit but there is not a wire of that color anywhere in the motor area. Checked all connections that I could find and no luck!
Expert:  Jeff G. replied 1 year ago.

To check voltage you need a special voltmeter and peak reading voltmeter. I wouldn't bother measuring the coil resistance as it is highly doubtful all 6 are bad. You can remove the kill wire, the black yellow, at the switchboxes. The top row if connections, red, blue, white black and black yellow.

Do you have an inductive timing light? You can check ignition with it as well.

Crank the engine and check for spark that way.

The stator is usually the weak link in the ignition, here we can do a few tests with an ohm meter but still rely on the peak reading voltmeter.

Do you have a good volt/ohm meter?