2012 3.0L TKS runs great with muffs, but slow on lake...

[alldodge]

There is no place to get a vacuum reading from this motor

 

[cyclops222]

Post #3 said your spark gap tester shows a reddish glow ? BAD. Should be white or blue very thin arc in air. Testing arcs with no load on the prop can be useless.
Have you adjusted the carburetor float correctly ? There are 2 dimensions

 

[GeorgioP07]

Post #3 said your spark gap tester shows a reddish glow ? BAD. Should be white or blue very thin arc in air. Testing arcs with no load on the prop can be useless.
Have you adjusted the carburetor float correctly ? There are 2 dimensions

Hi.
The sparks are blue and white and strong. Once in a while, I see a yellow one.
The carburetor float height and float drop adjusted to exact mm listed in the Mercruiser service manual, with no effect to this situation.
Rebuilding the carburetor actually did nothing to make things better, other than some peace of mind on that side of the engine.
I just received the M16x1.5 T-Adapter to measure the fuel pressure at idle and at high throttle, so I will test that in a few hours and post the results with video here.

One last thing that I never mentioned, and maybe because this sounds crazy, is that I noticed that when driving in the speed zone at a local lake at WOT, the engine would "open-up", and run fast as expected (RPM>3200) when making a medium-to-sharp left turn!
If I went to slow down, or if I shut it off, I could not get back to the higher RPM's though.
That led me to think that it might be a sticking throttle or shift cable, or exhaust valve, or something that by moving the throttle lever and cables back and forth, or when that left sided pressure was applied, or right side pressure of that component was relieved, then something "opened up" or got "unstuck", and returned to motor spec, and the motor responded with normal operating parameters leading to expected throttle response.
I could not re-create this phenomenon every time, but it was happening about 1/2 the time.
I should mention that this speed zone runs counter-clockwise, so I didn't get a chance to test a hard right turn at WOT yet.
I know... it sounds nuts.

 

[nola mike]

Hi.
The sparks are blue and white and strong. Once in a while, I see a yellow one.
The carburetor float height and float drop adjusted to exact mm listed in the Mercruiser service manual, with no effect to this situation.
Rebuilding the carburetor actually did nothing to make things better, other than some peace of mind on that side of the engine.
I just received the M16x1.5 T-Adapter to measure the fuel pressure at idle and at high throttle, so I will test that in a few hours and post the results with video here.

One last thing that I never mentioned, and maybe because this sounds crazy, is that I noticed that when driving in the speed zone at a local lake at WOT, the engine would "open-up", and run fast as expected (RPM>3200) when making a medium-to-sharp left turn!
If I went to slow down, or if I shut it off, I could not get back to the higher RPM's though.
That led me to think that it might be a sticking throttle or shift cable, or exhaust valve, or something that by moving the throttle lever and cables back and forth, or when that left sided pressure was applied, or right side pressure of that component was relieved, then something "opened up" or got "unstuck", and returned to motor spec, and the motor responded with normal operating parameters leading to expected throttle response.
I could not re-create this phenomenon every time, but it was happening about 1/2 the time.
I should mention that this speed zone runs counter-clockwise, so I didn't get a chance to test a hard right turn at WOT yet.
I know... it sounds nuts.

Doesn't sound nuts...sounds electrical. Though could also be that the carb is fueling differently because of the angle. Any change when hitting a wake?
Have you checked spark at speed? Rereading the thread I see that the spark was checked at idle, but not under load? I'm broken record about this, but throwing a timing light on the coil wire/each plug wire is invaluable for tracking down a high speed miss. Also, have you wiggle tested the connections? Just grab some wires and see if anything changes when you shake em...

 

[GeorgioP07]

Alright, I did a test run tonight with the fuel pressure gauge inline.
I was reading 4.5PSI at idle and 4.2PSI at 2500RPM.
Tried using a hand-held tachometer to validate the dash tachometer, was not working, will try that again later.
The motor started up well into this run.
Please take a look at the video and let me know what you think.
You can definitely hear the sucking sound of the TKS, as the engine was cold just before this video.
Right after this run, I tried to restart it just as before, and it would not restart, after two tries, I called it a night. Thanks,

 

[Scott06]

Alright, I did a test run tonight with the fuel pressure gauge inline.
I was reading 4.5PSI at idle and 4.2PSI at 2500RPM.
Tried using a hand-held tachometer to validate the dash tachometer, was not working, will try that again later.
The motor started up well into this run.
Please take a look at the video and let me know what you think.
You can definitely hear the sucking sound of the TKS, as the engine was cold just before this video.
Right after this run, I tried to restart it just as before, and it would not restart, after two tries, I called it a night. Thanks,

I think when it doesnt restart take a spark gap tester see if you have spark if you do dribble some gas down the carb , if it restarts then you are missing gas. Just gotta figure out if its spark or fuel. Hard to tell form the keyboard but if yo have good spark and timing is right it should fire if you dribble gas down unless it flooded. if flooded you open throttle wide to clear it just be ready to pull it back if it catches...

 

[alldodge]

After the run did the loud sucking sound stop?

Looking down the carb right after turning motor off, was there any fuel dripping?

 

[GeorgioP07]

I think when it doesnt restart take a spark gap tester see if you have spark if you do dribble some gas down the carb , if it restarts then you are missing gas. Just gotta figure out if its spark or fuel. Hard to tell form the keyboard but if yo have good spark and timing is right it should fire if you dribble gas down unless it flooded. if flooded you open throttle wide to clear it just be ready to pull it back if it catches...

Hi, There is always spark to all 4 cylinders. I already did the spark gap test on all 4 cylinders. Timing was tested a month ago and it is correct. I never replaced the ignition coil because the consensus here was, - it's all or none. Are you saying to pour gas into the carburetor when it does not start? Thanks.

 

[GeorgioP07]

After the run did the loud sucking sound stop?

Looking down the carb right after turning motor off, was there any fuel dripping?

Hello, The TKS Sucking sound stops after a few minutes.
I'll have to take off the flame arrestor and check for gas dripping after turning off the motor.
There seems to be about 4PSI in the fuel line at all times, according to the inline pressure gauge that I installed.
If 4.0 PSI is my baseline inline fuel pressure while not running, and running at idle is 4.5 PSI, and running at 2500 RPM goes to 4.3 PSI, - does that sound like enough gasoline would be reaching the carburetor inlet if I bump it to 3000 RPM when the boat is on the water? I does that when on muffs. Would the fuel pressure inline from the pump to the carburetor change when the motor is under a real load on the water compared to running on muffs?
Thanks.

 

[GeorgioP07]

Also, have you wiggle tested the connections? Just grab some wires and see if anything changes when you shake em...

Hi, I did unplug and re-plug in each wire while running and noticed the same 200-300RPM drop on the tachometer. What else could I do to test for mis-fires? Please watch the video and let me know if you can hear any. Thanks.

 

[Scott06]

Hi, There is always spark to all 4 cylinders. I already did the spark gap test on all 4 cylinders. Timing was tested a month ago and it is correct. I never replaced the ignition coil. Are you saying to pour gas into the carburetor when it does not start? Thanks.

Yes I know you had spark , but when it wont run verify it again to determine why it went from running to not running.

yes dribble some down the carb to see if adding gas changes things.

Also as all dodge suggested look down carb bores when you shut it off to see if bowl is over flowing and flooding it out.

Basically need to look at a few things to see what has changed why wont it run. Do I not have spark now, is there too little/no gas, or is there tooo much gas because carb bowl is over filling and dumping gas and flooding it at shut off.

 

[nola mike]

Hi, I did unplug and re-plug in each wire while running and noticed the same 200-300RPM drop on the tachometer. What else could I do to test for mis-fires? Please watch the video and let me know if you can hear any. Thanks.

I'm talking about all connections everywhere, not just the plug wires. I already mentioned how to test for misfires under load. At 3k rpm you might not hear much. your fuel pressure sounds fine. I'm also in the minority here where sometimes it is the coil.

 

[alldodge]

Hello, The TKS Sucking sound stops after a few minutes.
I'll have to take off the flame arrestor and check for gas dripping after turning off the motor.
There seems to be about 4PSI in the fuel line at all times, according to the inline pressure gauge that I installed.
If 4.0 PSI is my baseline inline fuel pressure while not running, and running at idle is 4.5 PSI, and running at 2500 RPM goes to 4.3 PSI, - does that sound like enough gasoline would be reaching the carburetor inlet if I bump it to 3000 RPM when the boat is on the water? I does that when on muffs. Would the fuel pressure inline from the pump to the carburetor change when the motor is under a real load on the water compared to running on muffs?
Thanks.

Your fuel pressure is good so this is no longer part of the problem

If the carb is flooding the motor than that is why it won't start, but if it's not dripping then it's not fuel and it's spark

It could be after things warm up and motor is turned off something isn't getting enough power. This would not explain why you can't get the rpm just why it won't start

 

[Scott06]

has a sample of fuel been taken and put in a clear jar to see if there is water or contamination?

Did this with my buddies boat this summer and it turned milky in about 5 min...

 

[ESGWheel]

A quick story and then some of my thoughts and my suggestions.

I have had 1 experience with a bad coil. Really 2 if you count my oil-fired furnace “coil” that was intermittently failing and blew up my furnace. The first was, as a young and inexperienced mechanic in the 70s, I was working at a British Leyland dealership. I was sent to a customer’s house that had an MGB that sometimes had difficulty starting. Would crank but not always catch was the complaint. Back then these cars had a manual choke. I get there on a cool morning, pull out the choke and varoom, starts right up. Thinking perhaps the customer was unaware of the manual nature of the choke, I asked him. To say the least I was taken off the job and the guy (“Joe”) in in the next bay was assigned. We gave the customer a loaner and had his car for several days while Joe finally figured out the coil was intermittently failing. He was kind enough and walked me thru his process which was first to determine no fuel issues and then hooked up a timing light to a spark plug wire and had the light rigged up to be always on and noted the one time it did not start there was no flashing. Knowing the cap, rotor, points all good, he replaced the coil and was fixed.

Georgio, you have really stuck to this, and I admire your tenacity. This is a head scratcher and now there are two issues, perhaps unrelated: unable to get to max RPM under load and difficulty restarting. And from watching the video it appears there is a 3rd issue that may be unrelated to the others > the engine seems to stumble, especially at the end when you came down off the high RPM (about 1:45). Others with experience on these 3.0s may be able to say if it is normal. It’s a stretch, but if the coil is intermittently failing or for some reason not being triggered properly 100% of the time, it could explain all three issues. My suggestion is to see if you can rig up a timing light like in my story. It would require carefully placing and securing everything to not get caught up in the belt, etc. If that is not a good option for you then suggest replacing the coil.

Prior to doing that two things:

• Fuel test as mentioned by Scott06 (I do not recall if this was done already) and
• Second, if you are up to it, a partially blocked exhaust (by a damaged / unworking flapper valve) has not been ruled out. To check this does require pulling the riser, so best to get a gasket beforehand.

BTW: nice install on the fuel pressure gauge. And the handled tach you are using is an optical one. These work on a contrast delta, meaning you need to put a white dot on the pully some distance from the center, like 2 inches. Then the tach sensor sees ‘black’ with a flash of ‘white’ for every revolution of the pulley and thus calculates the RPM. The white dot I saw when the engine was stopped was right in the middle.

Please keep trying and posting > this is fixable!

 

[GeorgioP07]

Knowing the cap, rotor, points all good, he replaced the coil and was fixed.
Georgio, you have really stuck to this, and I admire your tenacity. This is a head scratcher and now there are two issues, perhaps unrelated: unable to get to max RPM under load and difficulty restarting. And from watching the video it appears there is a 3rd issue that may be unrelated to the others > the engine seems to stumble, especially at the end when you came down off the high RPM (about 1:45). If that is not a good option for you then suggest replacing the coil.
The white dot I saw when the engine was stopped was right in the middle.
Please keep trying and posting > this is fixable!

Thank you for all the insight and analysis into this.
Over the weekend I was able to go out and start up the motor. It was cold, had not been ran for a few days. Ambient temperature was about 78 degrees Fahrenheit and it started right up.
I let it run for 2 minutes at idle, and I wiggled the spark plug wires, shift cables, but heard no difference. I tried to wiggle anything other wires, hoses, connectors, harnesses, cables to mimic the experience I had when I made a hard left turn and the motor RPM's ran consistant and nothing seemed to change the RPM's.
I shut off the motor. I looked immediately down the carburetor.
There is no fuel dribbling from the venturi down into the throat as soon as the engine stops, so I don't believe that there is any carburetor flooding going on here. A minute later, started it up and it started right back up again. Apparently this stop/ start issue is intermittent.
The 3.0L must know when I am at the dock, and when I am in the garage?
I did not bother to check the spark. It must have been there. It started right up so. I'll go back to:
1. The ignition coil is original and has possible burns/shorts in the coil itself, or a bad ground..
Can this be tested with a DVM while running, or am I just better off to replace it?
2. The gas is brand new(ish) - The tank was emptied 3 months ago & three times I put 7 gallons of fresh 87 pump and so the oldest the gas could be now is 90 days.
3. Will re-run the optical tachometer RPM testing with the reflective tape off center.
4. Will re-visit the timing light testing again as soon as I can get to that.
Thanks for the continued support, and let me know what else I can try to test for next.

 

[Scott Danforth]

its not your coil

 

[ESGWheel]

For the coil test underway > the only way I can think of is described above with the timing light.
Agree does not appear to be contaminated fuel
You are doing all the right things (pulling on wires, etc., etc.)

I am still hung up on the restricted exhaust. I know you were reluctant to pull the valve cover (post #30) but you are clearly capable IMO.

The only other thing I can think of is the engine coupler, but you would be smelling that (burning rubber) and I believe it would rapidly deteriorate (like a slipping clutch in a standard shift car > once it starts to slip and keep using it will slip even more). So, unless you are smelling a burning rubber you have not yet mentioned, I do not think it’s that.

So, I am running out of options > coil which can be tested as above or restricted exhaust is all I got. But I will continue to think on it. That same “Joe” in my story once told me: “It can always be fixed”. I have since adopted that but say it this way: “It did not come from the factory running this way" implying it can do so again.