Mercruiser 4.3 maxes out at 2200 RPMs at WOT - Please Help.

[Boat Doctor1]

Heres what u do=== with engine off- put throttle lever all way to full/fast position. Remove flame arrestor on top carb. Look down to see if carb butterflys are fully open /vertical.If not?? either controll cabel is bad / not adjusted or controll box is bad . IF those all check out - likel;y just a fuel delievery problem!! Start with replacing fuel filters! even one in carb inlet aftre fuel line goes into carb-may / may not have one?? also make sure the 1 way valve @ top of fuel tank is clean & flows great!! I have seen those bad! Id also look into removing the fuel tank vent hose & blow compressed air thru that from tank hose out!! If all that is fine?? pull carb & clean it!

 

[alldodge]

Found he timing line. No scale - just a single line. I'll have to pull the procedure to see what it says.

The marks should be on the vibration dampener

 

[acevedor2]

Did the oil smell like gas at all or thinner than it should be?

Yes it does and yes it is! Smells like gas and is definitely thinner than it should be. I didn't put two and two together when I was removing the oil because it was very hot and just been run. This also explains how it could be so overfilled. I am extremely...meticulous...and there is no way I could have put an extra three quarts in. I also checked it again a little while ago and though it isn't as high, the level has definitely risen from where it was when I removed oil earlier.

A few questions come to mind...
1 - What causes this? Bad/faulty fuel pump?
2 - Is it likely any damage has been done, or can I replace the pump, oil and filter and optest it?

 

[acevedor2]

The marks should be on the vibration dampener

You're right Dodge - they are. Didn't notice them at first. Thanks!

 

[alldodge]

OK now I;m going bald from scratching my head so much. Your getting fuel in the engine from a 2008 model engine which should have an electric fuel pump and not a mechanical one. There is no mention of smelling gas, engine running bad or anything else I can remember of the issue.

Next question which should have been my first, what is the engine serial number?

 

[acevedor2]

Dodge - sorry if I was confusing. To be honest, this has been confusing to me as well. I definitely appreciate all of your time and help. I definitely noticed it today - the engine is running rough - particularly under load in the water. It used to run smooth with a lot of power. Now - not so much. When I was riding through the no wake zone, it was definitely running rough. In other words, I could feel the engine more - if that makes sense. It was as if it was vibrating more and not smooth. What was confusing me was that the RPMs are not jumping around that much when at idle or low RPMs (1200-1400). When I went to WOT today - as mentioned above - it stopped at 2200 for a few seconds, and then went up to 4100, and then would surge and fall back between 3500 and 3700.

I am fairly positive that I have an electric fuel pump because when I was doing the compression test I noticed that it seemed to run a lot - but in truth, I did not know really how much it was supposed to run. But given that I was in neutral, it seemed to run more than I would have thought. As far as fuel smell, I really didn't notice a heavy fuel smell in the boat. The bottles of used oil I removed from the boat today definitely have an odor of gas, but it is not extremely strong. I am sure it has gas in it though, because of the smell and also - it is definitely thinner than it should be and it's definitely not water.

\Thoughts?

Serial is 1A311898. Date of manufacture is Mar 2008

 

[alldodge]

Serial is 1A311898

This engine has an electric fuel pump so if it leaks the fuel does not go in the crank case, that verifies that issue. If there is gas in the oil then it means the carb is flooding and the engine is getting to much gas.

Fun Times mentioned that it looked like 3 quarts to much oil, if this is true then the carb should be almost pouring fuel in though the carb. If this is happening then plugs will be black, smoke coming out the exhaust and a lot of other smelly stuff.

So if we start over and think this as a fuel issue we need to know what the carb is doing, Don't know need some clarification on the issues

 

[alldodge]

Wait a dang minute, your serial number is for a TBI not a carb

 

[acevedor2]

No Title

Plugs are definitely black. Here is a vid of it running on muffs yesterday.
http://www.youtube.com/watch?v=ykq_GgObuSI

 

[acevedor2]

Think I might have a thought. I think the TKS system might be faulty. I don't know if that would be the main problem, the only problem, or just one of other problems.
Though the hissing definitely gets lighter after it is warm, I still think I can hear some hissing. I don't remember hearing this before. It used to pretty much go away completely when it was warm.

Could this cause the carb to dump more fuel?

 

[Rick Stephens]

No such thing as checking WOT on muffs or in a shop. Can't be done without the boat being dropped into a tank or floated. I s'pose a shop could hook up a dyno, but never seen one done for less than a race boat. Big dollar facility and limited usefulness.

The only test that matters at WOT is putting the engine under full load, horsepower to water. No way to do that without either dropping it in the drink or attaching to a dyno.

RIck

 

[Fun Times]

The serial number comes up as an MERCRUISER 4.3 TKS A 4.3L ALPHA.

Here's some helpful tips at reading spark plugs, http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp?mode=nml

I haven't read the whole topic, but have you done a compression test and checked fuel pressure while under load while the problem is occurring?

Though I don't believe you'll find anything wrong, in the following link are some tests you can try doing. Since you're thinking maybe there's a problem with the TKS system, be sure to read page 2 of 3 (TESTING FOR VOLTAGE AT THE TKS MODULE)... Also there's some trouble shooting/testing inside Mercruiser's TKS service manual # 41 available online. The TKS temp switch testing is in section 6A for example.

TKS (Turn Key Start) carburetors. When the engine is warm ...

Having access to an prop shaft dynamometers sure helps makes jobs like these a bit easier so should you decide to get outside help, be sure to ask if the marine service shop has a prop shaft dyno. http://es.land-and-sea.com/prop-shaft-dyno/marine-dyno.htm

 

[acevedor2]

No such thing as checking WOT on muffs or in a shop. Can't be done without the boat being dropped into a tank or floated. I s'pose a shop could hook up a dyno, but never seen one done for less than a race boat. Big dollar facility and limited usefulness.

The only test that matters at WOT is putting the engine under full load, horsepower to water. No way to do that without either dropping it in the drink or attaching to a dyno.

RIck

Thanks Rick - understood. Haven't tried to do WOT on muffs. I was out on the river yesterday testing her out.

Since I know this thread is on page 5 - a recap of current symptoms and what I have done to resolve.

Symptoms: Engine starts with no issues. Overall running is a little rough. You can feel it - especially in low RPMs, but this is not reflected greatly in the tachometer. The RPMS are not steady, but they do not fluctuate much - for example - it idles at about 600-650 and seems to surge back and forth as opposed to idling smoothly. With the boat in the water and I throttle down to WOT, instead of jumping up and running like the scalded rat she should, she starts moving, but seems to labor at first. The RPMS go up to about 2200 - stay there for a few seconds, and then start climbing and she starts moving as she should. The RPMS get to about 4100 but are not steady. They will fluctuate between about 3500 and 4100 at WOT with no change in throttle position. The engine did backfire 2-3 times while at higher RPMs yesterday while running on the river. There is no real bad smell of gas in the engine compartment. I am still not sure if the engine sounds normal or if there is a little hiss still remaining when it is hot indicating the TKS may not be functioning properly. Video above is of engine when warm.

While checking the oil yesterday - on the water and anchored - I found it to be about 3 quarts high. I definitely did not put three extra quarts in there - so I pulled in, removed about a qt and a half and re-launched the boat. Same symptoms as above. Oil removed does have a gas smell and is thinner than it should be, leading to the though that there is gas in it. It also explains the excess oil level. The boat is a 2008 Mercruiser KS Carb 4.3L boat with an electric fuel pump.

What I have done so far:
1 - While on land on the trailer - pulled the plugs, and conducted a compression test. All cylinders were sat at 180 psi.
2 - Plugs were black indicating rich condition (pics above)
3 - Removed outdrive to locate missing exhaust shutter. Located and removed it. Reinstalled Outdrive.
4 - Replaced impeller and drive lube.
5 - Replaced fuel/water separator (twice) and inspected the inline fuel filter at the carb. It is plastic and was clean with no obstructions.
6 - Replaced anti-syphon valve.
7 - Verified - with engine off - that carb butterflies both open as the should when throttle is placed at WOT.

I have NOT yet:
- verified timing
- check fuel pressure under load. I am not sure how to accomplish this.

What should my next move be? Thanks!
.

 

[Eric 3.7LX Alpha 1]

I wonder...... if somehow a cracked intake could allow gas into the lifter valley?

 

[acevedor2]

Well today was the first day I could get around to doing any checking since taking her out on Sunday. I pulled the plugs and checked compression again and I also checked the timing.

Compression was 190psi all cylinders. This is higher than the 180 I got last time but that is because this time I checked the compression after the engine had warmed up - last time I did it the engine was cold.

Timing was a little interesting. I broke out my timing light. It's a good think I have an advance timing light because there is only ONE mark on the timing cover indicating TDC. You adjust the advance on the timing light to match the mark on the balancer up with the mark on the cover. In base mode the reading was consistent. 12 deg BTDC. Out of base timing mode it was 16 degrees initially, but when I checked it later, it was 10 degrees. I might have misread it the first time, because after reading it several more independent times (starting and stopping the engine) and putting it in and out of base timing mode. I got a fairly consistent 12 deg BTDC IN base timing mode, and 10 deg BTDC out of timing mode. Spec calls for 10 dec BTDC while in base timing mode, so I don't think 12 is that far off. I don't, however, have any idea, how normal 10 degrees is out of base timing mode.

Plugs are still fouled and somewhat wet (gas not water). Any thoughts?