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3.0 toks keeps dieting after a few seconds

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Tc2663

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New carb, new oil pressure sensor, new spark plugs. The boat will start up and idle for about 10 seconds, then die almost like you turned off the ignition. The more you try the worse it gets till it just won’t start. Was running fine then started one day out on the water. To me it seems like a sensor but any suggestions would be appreciated. 2008 mercruiser 3.0
 
Tc2663 said:
New carb, new oil pressure sensor, new spark plugs. The boat will start up and idle for about 10 seconds, then die almost like you turned off the ignition. The more you try the worse it gets till it just won’t start. Was running fine then started one day out on the water. To me it seems like a sensor but any suggestions would be appreciated. 2008 mercruiser 3.0
Click to expand...
New carb, new oil pressure sensor, new spark plugs. The boat will start up and idle for about 10 seconds, then die almost like you turned off the ignition. The more you try the worse it gets till it just won’t start. Was running fine then started one day out on the water. To me it seems like a sensor but any suggestions would be appreciated. 2008 mercruiser 3.0

I also put the fuel line into a jug to see if it had pressure and fuel pump seems to be working great. New fuel filter as well. Any other info needed just ask.

This is my first post so again thanks for any help. I can’t figure out how to edit my spelling errors but TKS ignition not toks also the motor is dying not dieting ….
 
After it won't start, remove flame arrestor, look down the carb throat while someone opens the throttle fully... Should see fuel squirt.
If not fuel problem.
 
Tc2663 said:
We are still getting fuel. Seems like something keeps killing the spark.
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verify if you have spark hook up timing light see if you are getting spark when it dies. Also verify timing is correct and distributor hasn't moved

When it dies if you try to restart it what happens. Have you tried adjusting the idle speed screw in (higher) a tad or played with the idle mix screws?

When you say new carb - is it a rebuild or aftermarket?
 
Oem carb from merc cruiser. I figured it would be already adjusted. But I would think those aren’t the problem. When I first start it up I have held the throttle at 2k rpm and it still does, so I would think the idle screws wouldn’t be the issue would they? I can maybe try give them a turn or 2 and see if it helps. I’ll have to check the timing when this rain in Michigan stops.
 
NO carb, new or rebuilt is set up for operation. YOU MUST adjust both main idle speed and air fuel mixture.

Main Idle speed should be 650-750 rpm in gear in the water.

If you can achive this then adjust idle air.fuel mixture screw(s). Starting point is, turn mixture screw(s) all the way in carefully until seated/stop. (Do not over tighten) then back out 2 complete turns. This is only a starting point.

If boat will idle at 650-750 rpm then asjust mixture screw(s) to reach max rpm. Once done readjust main idle to spec above.
 
kghost said:
NO carb, new or rebuilt is set up for operation. YOU MUST adjust both main idle speed and air fuel mixture.

Main Idle speed should be 650-750 rpm in gear in the water.

If you can achive this then adjust idle air.fuel mixture screw(s). Starting point is, turn mixture screw(s) all the way in carefully until seated/stop. (Do not over tighten) then back out 2 complete turns. This is only a starting point.

If boat will idle at 650-750 rpm then asjust mixture screw(s) to reach max rpm. Once done readjust main idle to spec above.
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this, if you want to complete the tune up verify your timing is correct as well. Its close to 2 k rpm when you start seeing fuel coming off the boosters and thus are fully off the idle and transition circuit.

good you bought an OEM one instead of chinesium.
 
Okay sorry for the long delay. I had stuff come up. But I just checked and I loose spark and engine dies simultaneously. It idles at about 1200 for about 10-15 seconds and dies.
 
I was wondering if some of the wiring might have got messed up. Can anyone tell me what all these wires are for? Also I plan on redoing the connectors that are messed up but would like it to run first.

2 purple and white coming off distrib.

1 orange, 1 brown, and one black. Located near the top/rear of the engine

And 1 purple and 1 black and white on the top near the carb.

Someone obviously got into this wiring already
 
Tc2663 said:
I was wondering if some of the wiring might have got messed up. Can anyone tell me what all these wires are for? Also I plan on redoing the connectors that are messed up but would like it to run first.

2 purple and white coming off distrib.

1 orange, 1 brown, and one black. Located near the top/rear of the engine

And 1 purple and 1 black and white on the top near the carb.

Someone obviously got into this wiring already
Click to expand...
I had pictures but they did t upload I guess. I’ll have to try again if you guys think it will help
 
Tc2663 said:
Okay sorry for the long delay. I had stuff come up. But I just checked and I loose spark and engine dies simultaneously. It idles at about 1200 for about 10-15 seconds and dies.
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So it starts and runs when on the starter then pretty much immediately dies? I would check the man overboard switch on the shifter. B/c the coil gets 12v off the starter during cranking, then via the ignition circuit (purple wire) from the key via the man overboard switch when key is in run position if switch is tripped it will run and start then immediately die as there is no power to the positive side of coil.

Google the mercruiser wiring diagram you will find some thing that is close enough.

you can test this by putting a volt meter or test light on positive side of coil. should see 12 ish volts when cranking and check to see if it drops out when key is in run. Also can jumper 12v from positive battery terminal to the + side of coil see if it stays running.
 
Which type of switch was used for the safety lanyard, the toggle or plastic clip that presses a tiny button? If the latter, press on the pin while it's running, to see if it continues. If it does, it needs a new lanyard and I have seen this in boats that had the clip in place constantly, especially in hot places- the plastic relaxes and loses the needed pressure.

The rest of the recommendations should allow you to find the problem.
 
Tc2663 said:
I was wondering if some of the wiring might have got messed up. Can anyone tell me what all these wires are for? Also I plan on redoing the connectors that are messed up but would like it to run first.

2 purple and white coming off distrib.

1 orange, 1 brown, and one black. Located near the top/rear of the engine

And 1 purple and 1 black and white on the top near the carb.

Someone obviously got into this wiring already
Click to expand...

In order to get wire info reply to this with ALL OF YOU ENGINE INFO!!
Some of this info may be missing to better understand your system.

Engine aerial number.
Year of boat, which typically matches year of engine.
Type of carb, Mercarb or TKS (this is easy to determine, carb will have what looks like a solenoid with a two wire connector)

I think I am seeing responses related to older models but lets get the specifics so we can answer your questions more accurately
 
Okay, so it is a tks ignition system. It is a 2008 3.0It does not come with a man overboard switch. So that shouldn’t be the issue. But I can still check the voltage. I will get back to you guys with the serial number because I am at work.

When I first start it it seems to run fine for about 10-15 seconds then dies. Start it again it will run for 8 seconds, then 6,5 until it won’t start at all. Let it rest for a while and it will idle for 10-15 seconds again. It might putter/run ruff for a second before it dies but it does pretty quick once it starts.
 
Attached is All I could find in my collection of manuals.

from left to right- TKS Manual schematic (first two images) Third on right is from Manual for 1997 3.0 liter and newer which is all I have but may not be for your model year but I added it anyway
 

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kghost said:
Attached is All I could find in my collection of manuals.

from left to right- TKS Manual schematic (first two images) Third on right is from Manual for 1997 3.0 liter and newer which is all I have but may not be for your model year but I added it anyway
Click to expand...
Sn : 1a309159
 
I have never been the best with electrical but I’ll do my best. I figured/remembered the purple wires I was talking about were for timing.

One of the white and black ones is for the shift interrupter. I’m still trying to figure the rest
 
Tc2663 said:
Okay, so it is a tks ignition system. It is a 2008 3.0It does not come with a man overboard switch.
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Would be surprised if it is not a small red lever switch located just below the shifter as seen below.

powerboatsupply.com

Mercury MPC 4000 Finger Release Remote Control - Black (Sterndrive - Power Trim) 8M0011214

OEM Quicksilver/Mercury Remote Control- Black 8M0011214 Please confirm fitment of MerCruiser parts with your serial number. Photos and descriptions provided via Mercury may not always be accurate. All of our Mercury parts are sold and priced EACH.
powerboatsupply.com powerboatsupply.com
 
IF anyone is still interested I have finally found the issue. After testing every kill/safety switch, chasing every ground and wire, and changing a ton of parts that didn’t need changing it was the distributor module aka ignition module. It would keep time for a few seconds and then loose time and die. Maybe something to consider next time y’all are stuck. Thanks for all the input last year!
 
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