BotakBeng

Appreciate if i can get some info on compression test.

Here are some overviews on my 99 with 150k on the clock with new fully charged battery and it drives fine,
Just replaced the engine oil and it looks fine.


Coolant pretty messed up (will be doing a radiator flush),


Valve cover leaking (replacing),


Spark plugs looks fine,


Here are the dry result with COLD engine,
#1 60
#2 50
#3 48
#4 51
#5 50
#6 50

Questions,
1)Should i do compression with cold or warm engine?
2)Avg 60psi bad?

Pls help.
Appreciate all comments.
Thx!

xjchase

You should do it again but squirt some oil in the cylinder before you put the gauge on. It should jump up to 120 or so. This is to make sure your valves are seating, no cracks, and head gasket is good. I would say most would be at 60 with 150,000 on the clock.

BotakBeng

Thx for the input....
But my understanding is, if there is a major change with dry and wet pressure, that would mean a BAD piston/engine.

Should i be doing the test with a warm or cold engine?

Thx.

jronald

Compression test are an indicator, and should be taken as 1 portion of the diagnosis. From afar, plugs look ok, but need to know how long they have been in the engine. Compression is about equal, which should mean you have equal wear. Overall they are on the low side would like to see over 100 psi. Try the wet test with oil and lets see if they come up.

Ron

thakmfb

Yea, a squirt of oil will only show if the ring are leaking. Make sure you are letting the engine make at least 4 compression strokes while doing a compression test. Can be seen with each spike of the of the needle. Make sure your batter is fully charged and if needed put it on a charger while doing a compression test. A weak battery can cause flawed compression readings
Compression should be as follows per AllData

Compression Pressure 827-1034 kPa (120-150 psi)

BotakBeng

K, i'm gonna try a wet test now.

So is fine doing the test with a cold engine?

freegdr

cold or hot either way your good

Slick761

As said before 4 compression strokes... I do 5. That looks like you did 1. If you did 4 or 5 this is bad compression. The psi isn't as important as the difference between the top and bottom numbers. Your solitary is 20%... shouldn't be more then about 10 to 12.

BotakBeng

Thx again ya.


Yeah, i did 5 compression strokes yo.


Here are the results for cold compression test,
....Dry Wet
#1 60 60
#2 50 70
#3 48 76
#4 51 60
#5 50 66
#6 50 74

Any thoughts?

Could a bad valve cover gasket cause a bad compression?

Thx.

Slick761

You're at 13%... not bad but not great. No a vc gasket won't effect the compression. I'm gonna do a compression test soon for ****s and giggles.... let you know how that goes. Different cams will give you different cranking compression too. Some cams are designed so they bleed off compression at low rpm. The 99 probably does, my 90 probably does not.

DFlintstone

"leak-down test" is to point up or down. Improvement with oil points to rings, less improvement points to valves. (like chase said)

Spray a little starting fluid around #6 intake manifold (running)to find the leak making your #6 plug bright?

BotakBeng

Not bad is OK, but how can i make it great or at least better without breaking the bank.
I'm in a dilemma cause i have a 00' that runs great and i just bought a stock black 99' with HP d30 w/ C8.25 and grey interior with i really like to like instead of the 00'.
I REALLY like the cherokee and i intend to keep it forever



Too late .
Hook everything back on with new spark plugs.
Start just fine except white smoke filling up my garage , didn't manage to fine out where it came from, gonna take it out for a test drive.
I'll report back (i'm assuming the white smoke is from the oil when i did the wet compression test, huh?).

Wish me luck.

jronald

Smoke is the oil, sorry did not think to mention that.

Ron

DFlintstone

??"leak-down" test is what my dad called what you just did, adding oil. which yes makes a cloud when you start it! I've never done it cold unless the engine wouldn't run. Guess I learned something here.

Carefully, sparingly, preferably with an extinguisher near by, some short bursts of starting fluid around where the intake meets the head may reveille any vacuum leaks. Usually by an increase in RPM. Any change indicates a leak. Mine has leaked around #6, and I see your plug is a tad bright. On mine those bolts are a real pain, would make McGiver cry like a little girl.

Nicely done post by the way. D.

Slick761

You can use carb cleaner.... its a little less volatile.