View Full Version : Opinions on Compression Test Resluts, With Confounding Factors.
AlligatorBling
03-15-2004, 06:00 PM
Ok, I decided to do a compression test on my 93 240... The odometer on my car says it has about 60k, but it sticks sometimes, even though I've fixed it once... I still don't think it rolls over like it should... so this isn't accurate I'm guessing. I went to the 240sx.org FAQ section to see exactly how to do the test... In the instructions it said to release the fuel pressure... I didn't do this... I also didn't disconnect the center distributor cable... However, have I did have all 4 spark plugs out during the test, and had the gas pedal mashed to the floor for the testing of each cylinder... I got an average of about 77 PSI for the whole lot. I was hoping for 80+ :-/ Could my neglecting the steps mentioned attribute to the PSI I got? Thanks for your input.
F3600
03-15-2004, 07:22 PM
Ok, I decided to do a compression test on my 93 240... The odometer on my car says it has about 60k, but it sticks sometimes, even though I've fixed it once... I still don't think it rolls over like it should... so this isn't accurate I'm guessing. I went to the 240sx.org FAQ section to see exactly how to do the test... In the instructions it said to release the fuel pressure... I didn't do this... I also didn't disconnect the center distributor cable... However, have I did have all 4 spark plugs out during the test, and had the gas pedal mashed to the floor for the testing of each cylinder... I got an average of about 77 PSI for the whole lot. I was hoping for 80+ :-/ Could my neglecting the steps mentioned attribute to the PSI I got? Thanks for your input.
your car need to be hot (get it to the running temperature)
remove all the sparkplugs
remove your fuel pump fuse
remove the spark cable
fully press the gaz pedal ad do the test
after that, we can talk about result... all your cylinder are equal its a good thing...
and yes your neglecting steps does not help your reading :x:
AlligatorBling
03-15-2004, 07:36 PM
your car need to be hot (get it to the running temperature)
oh it was hot all right, lol. i took it for a drive before i did the test... i actually did the test a first time after only letting the car run for a min or so and got a really shxtty reading... my dad then suggested that i do the test with the motor hot. the readings from my original post are from after i took the car out and got it warmed up. im thinking that maybe because i didnt disconnect the fuel, that the gas being injected into the cylinders might be washing away the oil, thus reducing compression ... any thoughts?
F3600
03-15-2004, 08:16 PM
oh it was hot all right, lol. i took it for a drive before i did the test... i actually did the test a first time after only letting the car run for a min or so and got a really shxtty reading... my dad then suggested that i do the test with the motor hot. the readings from my original post are from after i took the car out and got it warmed up. im thinking that maybe because i didnt disconnect the fuel, that the gas being injected into the cylinders might be washing away the oil, thus reducing compression ... any thoughts?
do the test and follow all the step.. after that we can talk about your result ... but if you keep getting 77 psi.. something is not right .. good luck
on my 89 240sx my compression reading are 150 psi on all cylinder... supposed to be 190.
its for KA24E .. not sure about KA24DE
DuffMan
03-15-2004, 09:00 PM
The gas should increase your compression if anything because it would pool up in the cylinder without any sparkplugs. Probably only on the first cylinder you tested though, because it would blow out the top on the other 3.
That seems really low, I would think the car would run like total crap if it was actually that low.
AlligatorBling
03-16-2004, 04:40 AM
no, the car runs very strong... im going to try the test again today following all the steps...
AlligatorBling
03-16-2004, 06:25 PM
I did the test again tonight, this time I removed the fuel pump fuse... it did make a difference... this time i tested i got at 180 or between 180 and 181 on all four cylinders... im in quite a good mood now. lol.. thanks for all the input. =D
you dildo. i was worried for your motor
fliprayzin240sx
03-16-2004, 08:07 PM
whats the biggest difference between a compression test and leak down test? is a leak down test a reliable way to the condition of the engine?
96twofourty
03-16-2004, 08:18 PM
whats the biggest difference between a compression test and leak down test? is a leak down test a reliable way to the condition of the engine?
yes, yes it is
fliprayzin240sx
03-16-2004, 08:22 PM
K so ive seen compression rates on SRs...but couldnt find anything on leak down test. Anybody wanna enlighten me on whats a good leak down test for an SR should be? Which one is better to check the condition of the internals? Leak down or compression?
epoxy_nc
03-16-2004, 10:05 PM
K so ive seen compression rates on SRs...but couldnt find anything on leak down test. Anybody wanna enlighten me on whats a good leak down test for an SR should be? Which one is better to check the condition of the internals? Leak down or compression?
a compression test can determine 2 things
1) piston rings are bad... you get 'blow by" (oil gets passed the rings)
2) valve(s) has gone to hell
you can determine which one by adding about a table spoon of oil into the cylinder you test (do this to all 4). If the compression is better after this, then it's the rings. If not, it's probably the valves.
NOTE: be careful when doing the oil thing... the 4th cylinder will spit on you :tweak:
there can be other stuff wrong such as a warped head etc, but that is the basic run down.
a leakdown test is when you throw about 100psi of pressure in the block and you listen for air. It can be used to find out if you intake valves or exhaust valves are messed up so you dont have to search for all 16
i'm pretty sure this is all accurate... feel free to correct me!
AlligatorBling
03-17-2004, 05:52 AM
you dildo. i was worried for your motor
hahahahaha
a leakdown test is when you throw about 100psi of pressure in the block and you listen for air. It can be used to find out if you intake valves or exhaust valves are messed up so you dont have to search for all 16
i'm pretty sure this is all accurate... feel free to correct me!
you dont determine the leak down by listening for air. You have to read the guage. There is a special guage with color coded portions that says what's ok and what's not for leakage
epoxy_nc
03-17-2004, 10:58 AM
you dont determine the leak down by listening for air. You have to read the guage. There is a special guage with color coded portions that says what's ok and what's not for leakage
oh ok.... sorry about that :) i never had to do it, but i had bad valves and did a bunch of stuff.
crash153
03-17-2004, 01:03 PM
ok, what tools/gauges did you guys use to check your compression?
and what is the name of that tool for leakdown tests?
AlligatorBling
03-17-2004, 03:41 PM
ok, what tools/gauges did you guys use to check your compression?
and what is the name of that tool for leakdown tests?
for compression, the compression tester gauge thinga ma jiggy from sears, lol... a ratchet with a spark plug socket, and an extension peace to fit down in the hole... not to familiar about the leakdown tests though...
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