Compression Test

[trrbo_tc]

Anyone done a compression test on a tc yet ?

anyone know what i have to do in order to do the compression test ?

i have the compression tester, and all the tools neccessary,

what i need to know is what fuse to i remove in order to stop the fuel pump from spraying fuel into the chamber while cranking.

thanks guys for your help !

[2dot4]

disconnect the ignition and the fuel - the fuel you can disconnect by unclipping the plug on the injector. The ignition, just pull the coil and make sure you don't get it near anything while you crank the motor.

That's my suggestion.

[trrbo_tc]

hmmmm .. is there any way i could just remove some kinda fuse ?

instead of unclipping the injectors ?

also, if i unclip the injectors, that doesnt mean the fuel pump stops pumping .. so if the injector is unplugged cant that be bad ?

[JoshCrane1]

here's an easy solution for you, unhook your battery.:) you dont need to crank your motor for a compression test,yo just have to have your valves closed. you pump the ball on the comprerssion tester and pressurize the cylinder until the needle(cylinder) can no longer maintain the pressure, thats your max pressure, then do the same to the other cylinders, the drop off pressure for all cylinders should be within 3-4 psi of each other, any more variation is a ring issue(or valve seats but thats another prob.). im not sure what the average psi the tc engine's can hold for a good compression test but prob in the ballpark of 10-20 psi.

hope this helps, ive done these tests with a ball pump style compression tester, looks kinda like a blood pressure tester at the doctors.

[Binder86]

the easiest way to do it is to take off your oil cap and put a business card over it. if the business card doesnt get sucked down and blows away than you fail. Another way is to take a straw place it on the pison at tdc, disconnect the fuel, hook up a vacuum guage at the exhaust, intake, block etc.. pretty much where air can escape. Then crank the engine and get your readings off the vacuum guage.

[JoshCrane1]

the easiest way to do it is to take off your oil cap and put a business card over it. if the business card doesnt get sucked down and blows away than you fail. Another way is to take a straw place it on the pison at tdc, disconnect the fuel, hook up a vacuum guage at the exhaust, intake, block etc.. pretty much where air can escape. Then crank the engine and get your readings off the vacuum guage.
compression testing with a business card doesnt seem to reliable(especially if the card gets sucked all the way in,yikes!), and it cant differentiate between cylinders.and ive never heard of the straw trick.

the tester i was talking about can be bought for less than 100 bucks and its absolute, and doesnt lie or decieve(like the biz card or straws), its what peeps use when they buy a used car and wanna see what kinda shape the motor is in. it'll tell you if your rings and valve seats are ok, cuz either one will involve tearing the motor apart, so whether its the seats or rings is irrelevant.

[trrbo_tc]

alright here are my readings from my compression test.

i did 2 tests.

the first test i cranked the motor about 8 - 10 times

the second test i cranked the motor about 4-5 times


Here are the First Test Readings

From Left to Right as you face the engine compartment -

Cyl1 : 200

Cyl2 : 197

Cyl3 : 210

Cyl4 : 200

that was test 1 where i cranked the motor about 8 - 10 times
---------------------------

now for test 2

---------------------------

Test 2 Results / Readings :

From Left To Right as You Face The Engine Compartment

Cyl1 : 190

Cyl2 : 185

Cyl3 : 184

Cyl4 : 182


iv'e been running a f*cked up turbo install for about 3 months now, i'd say compression is pretty good. i just cant get anyone to tune my bastard car properly.

anyways.. those are my readings

[JoshCrane1]

what kinda tester are you using? and what units are those? not psi obviosly.

seem pretty close, but they are inconsistent.

[trrbo_tc]

i bought the tester at autozone for about 68 bucks ...

looks pretty good, legit stuff..

remember the first test i overcranked the motor ..

the second test is more realistic whereas i cranked only about 4 -5 times.

[JoshCrane1]

i bought the tester at autozone for about 68 bucks ...

looks pretty good, legit stuff..

remember the first test i overcranked the motor ..

the second test is more realistic whereas i cranked only about 4 -5 times.
is there any instructions with it, or reference tables, like typical numbers for our cars. just goin with the second set of numbers, seems ok, only 8 between high and low. no engine teardown yay!!!!

[2dot4]

so at idle, the oil filler hole should be under vacuum? ruh-oh...I should probably run a compression check too.

[trrbo_tc]

yeah eric, i would do a test if i were you cause you ran a turbo on basically a stock ecu for quite awhile before trying to get it tuned.

make sure your compression levels are reasonable

[2dot4]

Well, on all the resources I found, nothing mentioned that you should have a vacuum in the valve train during normal operation...and from what I can remember, most cars I've had puff air from the oil filler cap while running.

It's positive crankcase ventilation - the moving pistons create positive pressure that needs to leave the engine. If that puff of air contains or smells like gasoline or exhaust, then you have a problem.

I don't think the business card test is 100% accurate, but I'm still going to check my compression regardless. I'm not exhibiting any other symptoms of piston wear (oil burning, smokey exhaust, low power, etc.), so I'm hoping I'm fine.

11:1 pistons are next on the list anyway, so even if my piston rings were bad, they'd get replaced soon enough. lol

[Binder86]

the business card is not 100% accurate cause it doenst give you any numbers, but it does let you know if there is a problem (handy tech stuff when your on the clock) The straw test is 100% accurate as long as you know where tdc and how to manually turn the crank, hook up your vacuum guage lines to your exhaust (where your o2 sensor is) intake (manifold or find a port in the actual intak tubing) and anywhere else a leak can occur, and then all you have to do is disable fuel and crank ONLY 4-5 times. Those numbers that you tested above look good but you can get faulty readings if that cylinder your testing isn't exactly at tdc.

sorry negate the last sentence of this comment and refer to the repost sorry

[Binder86]

the business card is not 100% accurate cause it doenst give you any numbers, but it does let you know if there is a problem (handy tech stuff when your on the clock) The straw test is 100% accurate as long as you know where tdc and how to manually turn the crank, hook up your vacuum guage lines to your exhaust (where your o2 sensor is) intake (manifold or find a port in the actual intak tubing) and anywhere else a leak can occur, and then all you have to do is disable fuel and crank ONLY 4-5 times. Those numbers that you tested above look good but you can get faulty readings if that piston your testing isn't exactly at tdc.

[2dot4]

I'm confused by the straw thing - I'm picturing a soda straw and it doesn't make sense to me lol.

[Binder86]

thats exactly what it is. you take off the cylinder head and stick the straw into the cylinder and rest it on the piston and turn the crank manually, this is so you know exactly where tdc is, therefore no faulty readings.

[2dot4]

take the head off? for a compression test?

that seems excessive. I may seem like an idiot, but for a minute it made sense - stick a soda straw down the spark plug hole, turn the engine manually to TDC marks, then mark the straw, so you can repeat the process without having to reset to TDC by hand each time...that's what I assumed you meant, but apparently I'm still confused lol

[JoshCrane1]

thats exactly what it is. you take off the cylinder head and stick the straw into the cylinder and rest it on the piston and turn the crank manually, this is so you know exactly where tdc is, therefore no faulty readings.
WOULDNT it be easier to just pull your plugs and stick the straw in the plug hole?

[trrbo_tc]

i dont know guys i just did a simple compression test with a compression tester .. i dont know about all that business card or straw crap .. i think he was either kidding or being sarcastic.

[JoshCrane1]

i dont know guys i just did a simple compression test with a compression tester .. i dont know about all that business card or straw crap .. i think he was either kidding or being sarcastic.
yeah idk, i was just entertaining the idea.

[2dot4]

it makes sense now - you mark the straw so you can find TDC on each cylinder - because the TDC marks on the cam gears are only for cyl1.

[JoshCrane1]

it makes sense now - you mark the straw so you can find TDC on each cylinder - because the TDC marks on the cam gears are only for cyl1.
yeah i get that part, just how do you do a pressure test with a straw stickin outa your plug holes? dont you still gotta buy a tester?

[2dot4]

yeah i get that part, just how do you do a pressure test with a straw stickin outa your plug holes? dont you still gotta buy a tester?

I think it's just to make a mark, then you remove it and......good point - I have no clue lol

[trrbo_tc]

Youtube Video Of The Compression Test How-To....

http://www.youtube.com/v/ujVhVt_rhOk

The video is being converted by youtube right now ..

if you dont want to wait and you want to download a Hi-res version of the video..

i have opened up my dedicated web server so you guys can download a hi-res version of the video.

it's 200+ megs guys ...

http://deathbydragon.com/CTESTHIGHQUALITY.mp4

[vettereddie]

FYI: From the 2005 Scion tC Repair Manual

Compression pressure: 1,300 kPa (189 psi)

Minimum pressure: 1,000 kPa (145 psi)

Difference between each cylinder: 100 kPa (14 psi)