Decided to run a compression test on my motor today....


BTW For those interested in doing the compression test its quite simple.. just gets really hot.. especially during summer.

Heres step by step for you DIYers. Im sure its somewhere on CL but yea.

1). warm up engine to operating temp.
2). turn off and start getting into the sparks.
-remove intake assembly
- remove coil packs and spark plugs
3). remove EFI fuse (i removed the EFI Relay aswell).
4). attach compression test to cylinder
5). open intake throttle by pressing down on gas all the way
6). crack engine. I did 5-6 cracks per cylinder. try to keep it consistent.




Specs

1998
Lexus
GS400
156,XXX Miles i believe.

Car is completely stock.

Here are my results.




Should i be worried about cylinder 1? It read really low compared to the other cylinders. After adding a table spoon of oil down the tube the reading went back up to normal.

please share some knowledge


btw. i understand different kits yield different results. I was mainly looking for consistency and cylinder 1 kinda freaked me out.

Safe to say i can say.. boost?

 

I'd be a little alarmed. Thats pretty low. If it was above like 160 or so (dont know the exact recommendations) 125 is pretty down there.

 

get a new car

 

The minimum is 142 psi.
The number one cylinder is having problems sealing, hence, when you add a teaspoon of oil to it, it increased.

I suggest you do a running compression test and report back.

 

a leak-down test will reveal all.

 

It's not so much of what number it's reading and trying to target one specific number. What you want is a even number across the board. For example if you have 185(+/-10psi) in all 7 cyl and 1cyl has 130psi, then you have a problem. However, if you have 155psi in all 8 within 5-10psi of each other then you're fine. Is the car smoking, misfiring, or having a hard time starting? Unless there's something wrong, I would just keep driving it. To fix the low compression would require a full engine teardown and rebuild.

 

This test is a good test to see if your valves are stuck open or not seating properly. Do this test and open the oil filler cap and listen if you can hear air leaking through, if yes, you got an open intake valve. If not, listen if there's air going through the tailpipe, if yes, you got an open exhaust valve.

 

also open the radiator cap and look for bubbles in your cooling system as well.

its a good test to do!

 

Why did you decide to do a compression test? Is your car smoking/misfiring/ect?

 

Looks like cylinder one needs a ring replacement. Is it smoking at all?

 

yea it freaked my out a bit. kinda curious if i didnt tighten the tester all the way or not...


whats a running compression test?


i would like to do this test but dam its sooo time consuming .

no smoking or misfiring. and does not have a hard time starting. Engine runs good and feels smooth (at least to me).

isnt that a test to burp the system? to prevent air trapped in the engine block? I do this when i do my coolant change.


why? Secret and no smoking or misfiring or anything.

no smoke.

 

Well, since your #1 cylinder is having lower readings than others, and I'm assuming you did everything correctly. I suspect you have a sealing problem on that cylinder. In order to find out if your valves are seating properly, you should do a cylinder leak down test to check if the intake or exhaust valve is leaking. This test is a good test to see if your valves are stuck open or not seating properly. Do this test and open the oil filler cap and listen if you can hear air leaking through, if yes, you got an open intake valve. If not, listen if there's air going through the tailpipe, if yes, you got an open exhaust valve.And if you don't have a tool like that then get a good vacuum gauge and hook it up anywhere to manifold vacuum. Tell me what's your reading.

 

no secret....<spoiler alert> lol we know u fixing to reinstall that RMM SC u got sir and wanted to test the engine first

 

whats that?

 

so what's the update?