Compression test question

[Biogenic]

Does it make any difference if you take your plugs out completely or if you do it one at a time? I’m about to run one on my 3rz-fe.

From what I recall it doesn’t but i just want to double check. I’ll disconnect all the plug wires and ignition coils and I I’ll floor the throttle all the way down for 5 seconds

Anyone know what’s a healthy value?


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[alumarine]

They should all be out so the motor spins faster.
Motor should be warm.

FSM says 178 psi or more with a minimum of 127 and the difference between cylinders should be 14 psi or less.

 

[19963.4lsr5]

And a good bigger battery charger on the battery while doing it helps also.


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[mtbtim]

Yes, all the spark plugs should be out when doing a compression test. You can lose cylinder pressure various ways, out a burned up intake or exhaust valve. Out a burned up intake or exhaust seat. It could be getting past the rings. It could be getting into a coolant channel via a bad head gasket or cracked head. And, it can leak into a neighboring cylinder via a bad head gasket or cracked head. With only one spark plug out at a time, you might be losing cylinder pressure to a neighboring cylinder and it will be more apparent there is an issue if you have that neighboring cylinder's spark plug out. It will basically make the compression more accurate and will identify a problem you will further investigate by doing a leak down test.

 

[19963.4lsr5]

Spark plugs out ensures maximum starter rpm to ensure an accurate test. 250rpm sticks in my head, however, that’s many engines ago.

To do it right and be accurate a cold engine test with all spark plugs out and throttle held Wide Open and then repeat hot will tell you what you need to know. If there is a big difference between hot and cold you got problems.


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[96RedRunner]

Do yourself a favor, download a FSM it's easy.

Complete 4Runner Service Manual 1996-2002.pdf - Google Drive

Page EM-3 covers test for 5VZ, procedure and numbers are the same for 3RZ, might dig for 3RZ version.
Manual will give you a direction to go based on results.

 

[Malcolm99]

Wide open throttle and disconnect the fuel pump!, fuel will give you false readings.

 

[Biogenic]

Wide open throttle and disconnect the fuel pump!, fuel will give you false readings.

Well I already did what 19963.4 recommended. Cold engine, took all 4 plugs out, wide open throttle and got a reading of 200 on each. On a warm engine I got 225 on each.

Does the fuel pump discontinued make such a big difference?

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[plcfcng]

those reading are fine. If your looking for a problem you can start looking else where. Plug readings are important they should be mostly white a little tan is ok on the porcelain section under the electrode. I am surprised that all your readings are all the same for each cylinder.:banana:

 

[alumarine]

Are you sure that gauge works properly?

 

[Biogenic]

Are you sure that gauge works properly?

Yup...was used not too long ago on another vehicle with totally different readings


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[Biogenic]

those reading are fine. If your looking for a problem you can start looking else where. Plug readings are important they should be mostly white a little tan is ok on the porcelain section under the electrode. I am surprised that all your readings are all the same for each cylinder.:banana:

I turned the engine over the same amount of time on each cylinder... 5 times


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[plcfcng]

The readings are good I still don't know where your going with this other than just seeing the health of the engine.
:spit:

 

[gamefreakgc]

Well I already did what 19963.4 recommended. Cold engine, took all 4 plugs out, wide open throttle and got a reading of 200 on each. On a warm engine I got 225 on each.

Does the fuel pump discontinued make such a big difference?




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That is a very healthy engine! Has a lot of miles left in it.

 

[Malcolm99]

Fuel in the cylinder would give you a false high reading for a compression test, and as you move from one cylinder to the next you will be dumping more and more fuel in the cylinders, you must disconnect the fuel pump when doing compression tests, but I'm sure your fine as the numbers are consistent which is the most important part..