Compression test results 4.3L V6 2005 what do You think?

[Kubaat3lover]

Hello,
the summer season is over and Ive decided to do a compression test on my engine.
Here are the results, what do you think?
Warm engine, WOT, DRY TEST:
#6 - 170 psi #5 - 145-148 psi
#4 - 175 psi #3 - 175 psi
#2 - 178 psi #1 - 170 psi

I did WET test on #5 (added 5ml - tea spoon of 25W40)
and #5 jumped to 162, 165 psi.

Here are the plugs:
Ive noticed that #5 is very light brown, not like the others
also noticed on #6 some oil on the thread (??)

 

[alldodge]

Ya need a new gauge
Do a leak down test to see if its the valve or rings on 5

 

[Kubaat3lover]

Gauge is a new one, with schrader valve. Not chinese crap

 

[alldodge]

Then your flooding or other liquid in the cylinders. Compression should not be that high unless motor was rebuilt with high compression parts. If you have a air compressor, check with tank pressure

In any case, still leak down

 

[Kubaat3lover]

How about #5? I dont have gauges for leakdown test yet,
do You have any tip to set certain cylinder to TDC for that leakdown test?

Take care,

 

[alldodge]

The leak down test will tell if its rings or valves for the low compression. You can do it just to 5 but figured doing the test might as well get readings on the rest.

The plug doesn't look bad but all show signs of rich

 

[Kubaat3lover]

plug on #5 is more orange/brownish than the rest, why?
also on #6 ive noticed that thread was little oily.
My choke was set too richy maybe thats why, ive leaned it a little now as You probably remember from my previous posts

 

[alldodge]

5 is not firing very well and most likely do to low compression

6 the thread being oily might just be because the valve cover is leaking slightly. Don't think its the valve seal because there isn't much of any carbon build up

If the choke was not opening all the way "ever" then this can cause it to run rich. If its not adjusted right and runs more rich while cold, but then does fully open it should not show the black. If carb is causing the rich mix then this would by why they all show black

 

[Kubaat3lover]

Ok so what do You recommend?
Choke is opening now all the way when warm, it was set too rich and engine was doin a lot of black smoke and rough idle when cold, ive leaned the choke and its fine so far, smooth idle and no black smoke when cold.
I did also carb rebuilt before this summer season. Do you think the idle mixture screw needs adjustment??

Can I try for example to pour some snake oil/marvel mystery oil/sea foam to the cylinder to unstick the ring ?

5 is not firing very well and most likely do to low compression

 

[alldodge]

Ok so what do You recommend?

Verify compression gauge
Do a leak down test

Right now your compression is way to high.
If your cylinders are actually 150 to 160 except 5 then that would mean 5 is 116.
If compression is accurate then need to find out why their to high. This is caused by liquid or carbon build up. If it was carbon build up I would expect the motor to "run on" (diesel) when shut off

If there where no high readings I would still do a leak down test. Then look into float level and want to know more about the carb

 

[Kubaat3lover]

Right now your compression is way to high.
If your cylinders are actually 150 to 160 except 5 then that would mean 5 is 116.
If compression is accurate then need to find out why their to high. This is caused by liquid or carbon build up. If it was carbon build up I would expect the motor to "run on" (diesel) when shut off

If there where no high readings I would still do a leak down test. Then look into float level and want to know more about the carb

its 2bbl Mercarb, new brass float, new needle and seat, float set to the level point,

 

[alldodge]

Hey @Bondo @Scott Danforth a little help please

 

[Kubaat3lover]

Do you think this running rich is because of carb? Not choke ? Idle screw set according to manual and @achris suggestion’s

 

[Scott06]

Do you think this running rich is because of carb? Not choke ? Idle screw set according to manual and @achris suggestion’s

I'll play the other side of the fence.

The difference between the stated compression of 150 psi and what you see is the accuracy of the guage ( i know you bought a good one...). There doesnt appear to be evidence of water in the combustion chambers and assume the engine runs well based on your comments and doesnt smoke?
If it were mine I wouldnt worry about the compression and enjoy the boat.

Make sure the choke opens 100% every time. Your plugs are failry typical of a carbed engine-You made adjustments to the carb but did you clean the plugs afterwards or change them.?If you were idling a long time before you pulled the plugs lean the idle mix out some.

 

[Bondo]

Hey @Bondo @Scott Danforth a little help please

Ayuh,...... Could be a deviation in the gauge for the high numbers,...

I'd richen it up abit, 'n run it,.....
A couple of plugs look alittle lean,.... To rich is better than to lean, especially in a boat motor,.....

 

[Kubaat3lover]

Yes I’m idling for 5-10 minutes because of marinas no wake zone, my boat is sitting in the water for the summer.
Also I was warming up the engine on fast idle before this test. Nevertheless I’m bit confused because “starboard side looks more rich to me than the port side..(?)

 

[Kubaat3lover]

I'll play the other side of the fence.

The difference between the stated compression of 150 psi and what you see is the accuracy of the guage ( i know you bought a good one...). There doesnt appear to be evidence of water in the combustion chambers and assume the engine runs well based on your comments and doesnt smoke?
If it were mine I wouldnt worry about the compression and enjoy the boat.

Make sure the choke opens 100% every time. Your plugs are failry typical of a carbed engine-You made adjustments to the carb but did you clean the plugs afterwards or change them.?If you were idling a long time before you pulled the plugs lean the idle mix out some.

Yes the boat doesn’t smoke

 

[Scott Danforth]

new engine cranking compression numbers for a 2005 4.3 are published at 150 psi by both GM as well as Mercruiser and VP

I suspect the gauge is off, and cylinder 5 has a manifold leak and rust on the valves.

 

[tpenfield]

Cylinder leak test on #5 and keep an eye on it year-over-year.

 

[Kubaat3lover]

Will do, any ideas Why only this one cylinder is weaker? I don’t know the weak points this V6 blocks but would like to know