compression test question

[amalik]

Hey all,

I wanted to do a compression test before putting in new NGK plugs and wires since the old plugs were already out. First time doing it.

97 limited.

Long story short, the numbers suck. Suck to the point of being below the minimum in the FSM.

Before I get into a wet test and all the other jazz, I just realized something. Should the airflow box be reconnected for the test (taken off for left side plugs/coils)? Pretty impossible to get around with it on.

If it can be off, I dont understand the point of having to fully depress the throttle with the airflow disconnected.

Thanks

 

[4Runner_101]

when you do a compression test, the throttle should be held open, make sure your batteries good and it doesnt matter of the intake is connected or not. if the numbers for each piston are much different from each other, then your engines messed up. if the numbers are pretty close to each other, then your good and you can keep on trucken

 

[BrianSD_42]

Are there any symptoms besides low numbers?

Flashing cel, Codes or misfires?

 

[amalik]

Are there any symptoms besides low numbers?

Flashing cel, Codes or misfires?

Brian, I have a P0133 according to my Bluetooth obd2 reader, although no official CEL. I need to get on that, 02 sensor.

Would that be relevant to the numbers you think?

 

[BrianSD_42]

I'd be assume your compression is fine if it's not losing coolant, misfiring (flashing cell), throwing a miss (single insurance CEL), loss of power, white smoke etc.

I don't think an o2 sensor has much to do with compression levels, perhaps you just did the rest wrong.

If you were misfiring you would know it.

 

[amalik]

Quick update:

I tried a different gauge and the numbers look better. The numbers are still a concern, but I think I have a few due maintenance items which should help.

Thanks yall.

 

[slapdappy]

you need to compensate for altitude.
"FSM Specs:
Compression pressure
at 250 rpm STD: 1,200 kPa (12.2 kgf/cm2, 174 psi) or more; Minimum 1,000 kPa (10.2 kgf/cm2, 145 psi)
Difference of pressure between each cylinder :100 kPa (1.0 kgf/cm2, 15 psi) or less."
Until reading about altitude adjustment I was concerned because mine were 145-150. 150 at 5280' = 174 at sea level (174 x .86 = 150). All is well... excellent, in fact.

Technical Articles at Greg's Engine & Machine
"Compression data is usually based on 14.7 atmospheric pressure and 59F at sea level. There are factors to compensate for the different altitudes and the corresponding temperature differences. These are as follows:
1000' = .9711
2000' = .9428
3000' = .9151
4000' = .8881
5000' = .8617
6000' = .8359
7000' = .8106
8000' = .7860
The equivalent compression reading for a cylinder that should be 135 PSI by the data at 5000' would be 135 x .8617 = 116.33."

compression at high altitude - Forums
"I found the info here after a day of googling if anyone wants it:

Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773"

 

[amalik]

you need to compensate for altitude.
"FSM Specs:
Compression pressure
at 250 rpm STD: 1,200 kPa (12.2 kgf/cm2, 174 psi) or more; Minimum 1,000 kPa (10.2 kgf/cm2, 145 psi)
Difference of pressure between each cylinder :100 kPa (1.0 kgf/cm2, 15 psi) or less."
Until reading about altitude adjustment I was concerned because mine were 145-150. 150 at 5280' = 174 at sea level (174 x .86 = 150). All is well... excellent, in fact.

Technical Articles at Greg's Engine & Machine
"Compression data is usually based on 14.7 atmospheric pressure and 59F at sea level. There are factors to compensate for the different altitudes and the corresponding temperature differences. These are as follows:
1000' = .9711
2000' = .9428
3000' = .9151
4000' = .8881
5000' = .8617
6000' = .8359
7000' = .8106
8000' = .7860
The equivalent compression reading for a cylinder that should be 135 PSI by the data at 5000' would be 135 x .8617 = 116.33."

compression at high altitude - Forums
"I found the info here after a day of googling if anyone wants it:

Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773"

slapdappy, I really appreciate your input. Based on these numbers, I hopefully calculated ~5,800 feet correctly at ~0.8449.

Although I have 1 cylinder below the adjusted minimum, I am still happy to see 5 out of 6 are at least at or above the minimum in the FSM (after adjustment). I may also re-run a dry test on that 1, as it's weird that it was the only one so far off from the other 5.

I'm going to hopefully find time for a wet test after work today, but here are my dry results:

As I stated before, I believe I have a few maintenance items which may really help with the numbers as well (And no, I don't mean a new engine as a maintenance item), lol

 

[4Runner_101]

doing any maintenance wont help with compression, also engine codes and clearing them wont help at all either. the compression tells you whether you have a blown head gasket where in that case your coolant will mix with your oil, and/or your piston rings are fried where your engine will then burn oil depending how bad they are. only thing you can do to change those numbers is a re build

 

[BrianSD_42]

Just checking but you don't have any symptoms of a bad CYL besides the one low compression number correct?

If everything seems find then just drive it and keep some money set aside.