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Bad Compression??

28K views 50 replies 11 participants last post by  DannoXYZ 
#1 · (Edited)
Hello all.

Did a compression test on my corolla today, older brother performed it for me with his new compression gauge, we removed all the plug wires and plugs, and stuck the gauge in one cylinder at a time, and heres what it read

Un-lubed, by the way:

Cylinder #1 : 113 psi
Cylinder #2 : 108 psi
Cylinder #3 : 113 psi
Cylinder #4 : 111 psi

Is this low? As I understand it, the compression for this engine is fairly high, being 10:0:1 or something like that, but I don't think that's correct, I only read that at one source.

For clarification, this is a 1995 1.8 liter 4cyl, 16v dohc, 7A-FE, with 129665 miles on the supposed clock.

I've been running non-ethanol gas in it, since it's better for your car - I would only assume that this would leave me with improved results on this test, versus nasty ethanol gas.

My last vehicle was an 87 ford ranger, with about 134K miles on the clock it tested out at 160-155-160-165, from 1 to 4, respectively. However the test was done a little differently - Only one plug and its wire was removed, the other 3 were left alone, and the gauge stuck in one at a time, cranking it twice per test (it fired up every single time on the second crank, on 3 cyls!)

So it was done by just removing a single plug at a time, not by removing all four at once - as I understand it, the supposed proper method is to remove them all at once and test each cylinder individually, not just remove one plug at a time and test.

Suggestions? Is this proper compression? If not, what psi is considered healthy? Again, 1995 7A-FE 1.8l engine.
It seems to run quite well really, it never misses or hesitates or stalls or stutters or anything, its just a straight up sewin machine. Has good acceleration and excellent uphill pull, even with a removed cat replaced with straight pipe, and a flowmaster exhaust.
 
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#3 ·
Oh, no....I didn't

I didn't push the gas pedal at all. Lol.

Just pushed the clutch in and turned the key, also it takes my car a good 10-15 minutes of driving (if it hasnt ran that day) to start blowing hot air, and it took me less than 10 minutes to get to my brothers place, so god knows it wasn't completely warmed up either.

What does pushing the throttle have to do with it? Just a curious question.. I shall definitely re-do it at WOT, tho.

Thx alot halo ^.^
 
#4 ·
Do a dry and wet test also to compare how well the rings are sealing (or not sealing) so you can see if it's a ring issue causing low compression. Those do sound like numbers I'd expect to see on a cold engine, a hot engine can show numbers 50-75% better depending on the health of the engine. Is it having an issue or were you just curious? If you do have low numbers due to ring issues try doing a piston soak with some assorted nasty solvents over night to try to clean and free them up some. That's not a terrible amount of miles but who knows what kind of oil or how often it was changed by the previous owner.
 
#8 ·
Re-did the test today, with the engine at operating temperature and throttle floored, results coming up to 118 psi across all four cylinders. Is this low, or normal?

Again, the car runs quite well, has good acceleration, great pull, good gas mileage (30 mpg+ minimum), the works. Smokes very little when revved hard, a clear/white smoke. Not burning any oil, not idling rough, not missing or hesitating, etc.

I would REALLY love it if someone could tell me what the compression ratio is on my car. Tis a '95 1.8l 7a-fe engine. Doesn't seem to state it in either of my owners manuals, ratio nor what the numbers should be, and I absolutely can Not find it anywhere online...

Just for clarification it was performed by removing all the plugs and plugwires, and inserting the gauge into each plughole one at a time, and cranking it over 5-6 full rotations. Ignition system not "disabled", engine at operating temp, and at WOT.

Suggestions, if any?
 
#11 ·
Re-did the test today, with the engine at operating temperature and throttle floored, results coming up to 118 psi across all four cylinders. Is this low, or normal?
No!

It's awesome! I mean I don't know if 118 is good, but it's very consistent. All four cylinders are the same? You couldn't ask for anything better, as long that number is well within spec.
 
#10 ·
I checked mine last year, and my results (IIRC) were similar to yours (low 100's). I have it written down somewhere, and I will look tomorrow (if I remember!). I DIDN'T do the WOT thing, though. My 7A-FE had around 77,000 miles at the time, so I'm assuming the engine is pretty solid. So, just how much difference does it make doing it without WOT? I see people saying theirs is 175psi, 200psi, or even higher. Maybe my 30 year old tester is no good? I know the 'o' ring isn't good (has a split), but the threads must hold in the vast majority of the compression, right? Hell, I'm gonna get an 'o' ring and retest with WOT!
 
#16 ·
Just for sake of consistency I'm going to have it tested again at the same place my rangers compression test was done.

That way, instead of all the plugs and wires being removed at once and the gauge being stuck in each hole individually then cranking, this is how it will be done :

Remove one plugwire and the plug, insert compression gauge, crank a couple rotations, and stop before it fires up. Then crank it again, and it will probably fire right up on 3 cyls, unless theyre designed not to do so. THEN I will get what I feel will be proper results. This way the other 3 plugs and wires are still connected and in the engine, it will be actually running and doing its compressing during the test.

Are there any dangers in doing this on an engine of this size / strength? I know the head is aluminum, my trucks entire block however was cast iron, and it was the turbo block so it was pretty much literally indestructible.

Any explosion / engine damage issues i need to worry about when I do it this way?

thanks for all the feedback guys, it really helps me alot
 
#17 ·
I don't know if that's proper procedure. I took out all my plugs and wires, and removed the EFI fuse and relay just to be safe when I did my compression test. Having an engine run on 3 cylinders won't blow it up (had to limp a Miata home on 3 cylinders, it was fine), but I don't know if it's the proper way to do it. Compression doesn't rely on combustion, just the piston moving up and compressing the air through movement. The starter provides the force.
 
#18 · (Edited)
Not sure about the compression-test on running engine. It would certainly give higher results than a non-running engine. But the idea is to standardize on a specific procedure. Then ALL tests on different cars by different people using that same procedure can be compared. Most useful in comparing the same engine to itself in the past to determine trends. What I've run across most often is:

1. warm up engine
2. remove all plugs
3. disconnect ignition/computer
4. insert comp-tester into cylinder
5. hold throttle 100% open, crank 5-6 times
6. repeat for each cylinder
7. squirt some oil into spark-plug hole and repeat test for all cylinders

The oil test will help determine if rings or valves are worn. The manual states normal compression is 191psi, minimum of 142psi with a max-variation of 14psi between all cylinders. Due to the oil-burning in these cars, there's a lot of soot built-up on the pistons and can actually raise compression above normal. As long as you're not getting pinging/detonation, that should be OK.
 
#20 · (Edited)
Could I by any chance get a page number just for reference so i can check that in my own manual?

I couldn't find anything about what psi the compression should be in my manual, And I would assume if 142 psi is the minimum, then you'd be experiencing some issues below 142. mine being at 118 across all four, My only guess is that the compression gauge we used must've been reading incorrectly. Theres no pinging or detonation, and it runs just as smooth as silk. Absolutely nothing wrong with the performance to me, no lack of power or response, no power fluctuation, anything. Either the gauge is wrong, or the manual is wrong (which I highly doubt), the way I look at it..

Thanks for the help tho guys. I may try running a few more tests on it here in the near future, will report back when I do.
 
#21 ·
You should have a fully charged battery, so it cranks at 250+ RPM. And like v8440 said, you crank until it stabilizes. It sounds like you were only letting it spin twice. If you don't have all the spark plug wires removed, then you need to disable the distributor by pulling the proper fuse or disconnecting it.

Does you compression tester screw in or do you just hold it in? It's possible that it's not sealing well enough to hold the pressure and give a good reading.
 
#22 · (Edited)
I'm not sure if people are reading my posts well enough -

I let it crank 5-6 whole times (5-6 entire engine rotations). I heard the starter reset 5-6 times, and stopped (it would stabilize by 4 whole rotations, but i do a couple extra just to be sure.) cranking when the reading stabilized.

Again, this is with All plugs and all plug wires removed from the engine. Yes, the compression gauge screws in. I didn't disconnect anything, no ignition system, no fuel system, etc. Just yanked the plugwires and plugs and got to cranking. Putting the throttle to the floor as I understand it, if it's fuel injected, asides from moving the throttle plate out of the way, also puts the engine in clear flood mode, which disasbles the fuel injectors, so the fuel system is bypassed by that (please correct me if im wrong) - The only purpose in disabling the ignition system, as I understand it, is just to keep spark from happening without having anywhere to go. So both the fuel system and ignition system (practically) are disabled. If disabling the ignition system serves some other purpose, please feel free to correct me on this.

I feel I have done the process correctly, and either one of two things is occuring - the gauge is wrong, or I've made some mistake during the performing of the test itself somewhere along the way. Because I know theres no way the manual (atleast according to DannoXYZ) is wrong - and my car runs way too smooth to indicate such low compression would actually be occuring - and btw, upon re-scouring my entire 1995 corolla owners manual, couldnt find a single world on the compression ratio or what psi each cylinder should rate at.. any chance I could get a reference page?

Thanks again guys.
 
#24 ·
and btw, upon re-scouring my entire 1995 corolla owners manual, couldnt find a single world on the compression ratio or what psi each cylinder should rate at.. any chance I could get a reference page?
Owner's manual wouldn't have that. You need to look at the factory repair manual - and what I'm writing here is directly from the factory repair manual.

Short answer: normal is 191 psi or more, minimum is 142 psi. Difference between each cylinder should be 14 psi or less

Long answer:


  1. Warm up and stop engine
  2. Disconnect distributor connectors
  3. Disconnect high-tension cords from spark plugs
  4. Remove spark plugs
  5. Check cylinder compression pressure
    1. Insert a compression gauge
    2. Fully open throttle
    3. While cranking the engine, measure pressure. Always use a fully charged battery to obtain engine speed of 250 rpm or more.
    4. Repeat for each cylinder.
Notice: This measurement must be done in as short time as possible.


If the reading is low, repeat with small amount of engine oil into cylinders. If that helps it's likely piston rings and/or cylinder bore. If it doesn't help it's likely sticking valves, improper valve seating, or leaky valve seals.


Again, all of this is from the factory repair manual, no "color commentary" inserted
 
#23 ·
Thanks for clarifying. The info wouldn't be in the owners manual, only in a repair manual. In the Toyota repair manual in the Engine Mechanical section I think. Sounds like the guage could be bad. You could test it on another car or better yet if you could connect it to an air pump with a pressure guage to compare.
 
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