Low cylinder compression

If petrol, anything north of 120psi will do as it is low compression.

Low compression on cylinder number 1 and cylinder number 2 on a 2000 Toyota Solara 2.2L engine could be caused by a few different issues. Here are a few possibilities:

1. Worn or damaged piston rings: The piston rings seal the combustion chamber and maintain compression. If the rings are worn or damaged, they may not be able to seal the combustion chamber properly, resulting in low compression.
2. Damaged or worn valves: The valves allow air and fuel to enter the combustion chamber, and allow exhaust gases to exit. If the valves are damaged or worn, they may not be able to seal the combustion chamber properly, resulting in low compression.
3. Damaged or worn cylinder walls: The cylinder walls are what the pistons move against. If the walls are damaged or worn, they may not be able to maintain proper compression.
4. Head gasket failure: The head gasket seals the combustion chamber and prevents compression from escaping. If the head gasket is damaged or blown, compression can escape, resulting in low compression.
5. Leak in the intake or exhaust system: a leak in the intake or exhaust system can cause low compression.

The dry compression test you did on cylinder 1 and 2, 80 PSI and 60 PSI respectively, are not within the normal range and indicate low compression. The wet compression test results are also not within the normal range, 95 PSI and 85

It can vary between make and model of car. However, a general rule of thumb is that 135+ average is okay. Less than 85psi is pointing at something seriously amiss in the engine.

It can vary - some cars may have 125psi as 'average' compression.

Don't expect each cylinder to give the same compression reading as there will be a fluctuation. Another general rule of thumb is that there shouldn't be more than 10% variation between the readings. That is, if cylinder No1 is 135 psi, cylinder No2 shouldn't be less than '125 ish'.

If you suspect you may have compression issues, it's quite easy to do a bit of fault finding. Warm the engine first so that the pistons are expanded in the cylinders. Then do a dry compression (normal) test.

Here's some examples of compression tests on a 4 cylinder engine:
130 127 129 127

All compression readings are within 10% of each other. Fine.

Example 2:
95 95 129 127
Here, a low compression reading on cylinder 1 and 2 suggests a problem. It may be due to a faulty head gasket/cylinder head allowing compressed gases to be transferred via the defective head gasket from one cylinder to another.

Example 3:
130 80 129 127
Cylinder No2 has a problem. It's compression is way down. The other three cylinders are fine. So .. what is the cause of the low compression on cylinder 2? It could be a broken ring/cracked piston or a burnt exhaust valve.

This is where you do a second compression test - called the 'wet' test.

Squirt some light engine oil into each cylinder. Aim for the cylinder walls so that the oil can find its way down the walls and around the piston rings. Place a rag over each spark plug hole and spin the engine to expel excess oil.

The oil that you have sprayed into each cylinder will form a 'seal' around the piston ring. Do another compression test and note down the readings. Here's example 3 again:
Example 3:
130 80 129 127
.. with the low compression on cylinder 2.

If after carrying out the 'wet' compression test you have a reading along the lines of
130 100 129 127
suggests that the bore/piston rings in cylinder 2 are at fault. The compression has increased on No2 cylinder because of the oil forming a seal around the rings.

If there is no increase in psi on the wet test i.e
130 80 129 127
This suggests a burnt exhaust valve.

How low is low? Low compression is really vague as a diagnostic method. The issue could be leaking valves, head gasket, or rings. Yes if it is losing a lot of compression then there is no fuel to ignite and it would be a misfire.

most petrol engine run 145psi ( low compression engines) to around 165 psi (high compression engines) regardless of the compression read there should not be any more that 10% difference between adjacent cylinders Hugh differences in cylinders indicates valve problems

It could be a problem in the valve train. For a car that old, before putting new parts in, you could buy a compression tester for about $30, and do your own compression test. It should tell you if the engine is good enough internally to warrant proceeding. If compression is low on any cylinders, that problem must be addressed first. If a valve is not sealing and causing the popping, that cylinder will show low compression.
For the test, the engine should be at normal operating temperature. Then pull all the plugs out, connect tester to #1 spark plug hole. Have a helper hold the throttle wide open while cranking the engine over about 5 seconds. Watch the gauge-the first revolution or two will cause the gauge to jump high at first, and successive revolutions during the 5 second span will cause the needle on gauge to climb a little each time. Record or note the compression on #1, then do each cylinder. Try to do the same amount of cranking on each cylinder, and keep the throttle wide open. What you want are compression readings on each cylinder that is well above 100 psi, and all should be close. The lowest reading should be within 75-85% of the highest reading cylinder. Example: say your highest reading is 135 psi. 85% of 135 is 115-so your lowest reading should be at least 115 psi. Some general guidelines: any cylinder with compression below 100 psi is definitely a problem-that cylinder will not have hardly any power output, even if it is firing. Worn piston rings or poor valve sealing is causing compression loss. A newer engine should have compression readings above 150 psi. As the engine wears, compression will drop. In general, for high mileage engines, you would want to see compression in the range of 125-150 psi, the higher the better, but remember, it should be balanced-the lowest should be at least 75% of the highest reading cylinder.
Post back if you have questions-good luck.

A new engine would be about 180 psi for each cylinder. As the miles add up and wear occurs, compression will get lower. The important thing is that compression is even and balanced-lowest compression reading should be within 75% of the highest cylinder's compression. Some Toyota engines had a minimum allowable compression of about 135 psi, but if compression is balanced, you could have average compression as low as 125 psi and engine would still run good, some loss of power but still acceptable, and oil consumption would not be that bad.
If cylinder compression is below 120 psi as an average, you should be looking into a rebuild event-rings and valves need attention. If any cylinder is below 100 psi, it may not even fire, certainly will produce no power, and could be a head gasket failure, very worn rings, or valve problems.
Remember the important thing is to find compression readings that are very close to each other. I have an '87 Sentra with 75,000 miles(true!)-lowest comp. is 160, highest is 165 psi-runs great, good power. Also a '79 Datsun pickup (with god only knows how many miles-about 200,000 maybe). Compression is about 125-135 psi, fairly well balanced-noticeable loss of power, very little oil burning, still runs fair to good-dependable, at least.
That should give you an idea of what to look for. Good luck.

Time for a new car, unless you want to spend the big bucks to repair your engine. Low compression, below 100 psi, means the cylinder will not fire, will miss, have low power. The reason could be a blown head gasket, worn rings, valves not seating properly-at the very least, the cylinder head will have to come off. Before doing that, though, do a leak down test to pinpoint the cause of low compression in that cylinder. If just one cylinder is low, and you have good compression otherwise, it may be worth fixing. Tercels are low value beaters, but I owned a '94 tercel, and I loved it, till the engine went south, just like yours-body was too banged up to make it worth fixing, though.

If cylinder compression is too low, the car may not even start because of it. Have a shop do a compression test or a leak-down test to check the internal health of your engine. A good engine should have pressures of 150-200 psi in all cylinders and be close to each other. A worn or high mileage engine may have pressure as low as, say 125 psi, but if still balanced (close readings), would still run decent. Compression below that, especially below 100 psi, is serious trouble. ignition spark refuses to ignite the air/fuel mixture and you get a misfire-a non-working cylinder. Low compression can be caused by worn piiston rings or poor valve sealing. Low compression in 1 or 2 cylinders can be a valve problem, burned valves or valves not seating properly.
A leak-down test will check each cylinder and if there is a problem, the test will find the cause of the problem.

valve or head gasket for that low cylinder take it that your measurement is in bars -- the 12 bars is 170 psI very good and the 9 bars is 130 psi
as it is good practice to allow only 10% difference between cylinders the 130 psi (9) is a problem cylinder
One possible fix is to check and adjust the tappet clearance or have that cylinder hydraulic followers checked for operation
other than that valve face or head gasket