Compression and Leak down test anaylsis

easyloader

Seaman
Joined
Apr 25, 2014
Messages
68
I performed a compression and leakdown test on my 4.3 mecruiser engine. The engine blows smoke on start up and when in gear idling. It only used 1/2 quart of oil in 60hrs.. Below are the results. I'm going to change the gauge on the compression tester. It seems that the motor is getting tired even though it only has 400 hrs on it.
What do you think????????????????
CylinderLeak Down percentageCompression PSI
17.5%120
613.8%125
512.5%120
417.5%130
311.3%125
210.0%120
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
I performed a compression and leakdown test on my 4.3 mecruiser engine. The engine blows smoke on start up and when in gear idling. It only used 1/2 quart of oil in 60hrs.. Below are the results. I'm going to change the gauge on the compression tester. It seems that the motor is getting tired even though it only has 400 hrs on it.
What do you think????????????????
CylinderLeak Down percentageCompression PSI
17.5%120
613.8%125
512.5%120
417.5%130
311.3%125
210.0%120

Compression is good and all cylinders look fine for an engine with that many hours. One half quart in 60 hours isn't bad either. Think maybe most your smoke your seeing could be running rich
 

JustJason

Vice Admiral
Joined
Aug 27, 2007
Messages
5,319
Me thinks your gauges are not reading accurately. According to your numbers the cylinder with the highest leakdown percentage also has the best compression... when it should be the other way around.
 

CVX20SPRINT

Petty Officer 1st Class
Joined
Sep 9, 2009
Messages
213
Compression is good and all cylinders look fine for an engine with that many hours. One half quart in 60 hours isn't bad either. Think maybe most your smoke your seeing could be running rich

Or valve seals.Valve seals would make it smoke on start-up and take a couple of minutes to clear up at idle.
 

easyloader

Seaman
Joined
Apr 25, 2014
Messages
68
All dodge-Running Rich? The motor has efi. Not sure how to correct it or test it. The plugs are wet?
All dodge- I figured valves seals for start up smoke, but motor has warmed up and get the smoke at idle in gear
just justin- I was surprised with my readings on number 4 cylinder. I was consistent with the tests and triple checked #4. I know it's correct. I thought my overall compression was low that's why i wanted to try another gauge. I was hoping to see around 140+ on all the cylinders.
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
All dodge-Running Rich? The motor has efi. Not sure how to correct it or test it. The plugs are wet?
All dodge- I figured valves seals for start up smoke, but motor has warmed up and get the smoke at idle in gear

My MPI 502 was doing the same thing for years, was going to dig in and figure it out but decided to do a total repower. You could have an issue with your MAP or Temp sensor which could cause the engine to run rich. If either of the sensors are not sending the correct info the computer can send to much fuel, or to lean. This can also be caused by your injectors leaking, fuel pump pressure or both. Before I decided to repower I was going to send my injectors off to have them professionally cleaned. Injector testing and cleaning cost around 20 to 25 each plus shipping. Was going to go thru everything because my scanner said everything was fine.
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,620
The numbers for leak and compression look OK. You could re-do the leak test and isolate the source(s) of leak to give you further analysis of the engine's condition. The absolute value of the compression has a bit to do with how fast the starter is turning the engine. Battery charge, starter condition, etc come into play.

I tend to agree with the valve seal diagnosis, given the idle and start-up smoke.
 

JustJason

Vice Admiral
Joined
Aug 27, 2007
Messages
5,319
If anything you might want to throw a borescope down #4 and see if the cylinder walls have gouges in them. If they do, you can still show a decent compression number as the gouges will have oil in them as the engine is cranking over. At the same time, when you put compressed air into the cylinder, that blows the oil out of those gouges. It would explain all 3 of your symptoms if the #4 cylinder is gouged .
 

easyloader

Seaman
Joined
Apr 25, 2014
Messages
68
I notice that #4 has more blow by from the valve cover than the other cylinders. It sounds like your on to something there.
The start up smoke is probaly valve seals.
When replacing the seals do I coat the valve stem and where the seal goes with oil, or clean the valve stem off and then put the seal on.
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
. The plugs are wet?

With the plugs being wet tells me your running rich, but I'm the only one it appears

When replacing the seals do I coat the valve stem and where the seal goes with oil, or clean the valve stem off and then put the seal on.

When replacing vale stem seals put a light coat of oil on the stem so the seal slides on easy.
 
Top