91 LQ1 Compression Pressure?

[intimidatorz34]

Hi Guys, new to this forum, not new to efi, wbody. etc.
Anyways, just wondering what the pressure reading should be out of a 91 Lq1 when running a compression test. I am searching for a coolant leak, and a slight miss, thought it was intake gaskets, changed them and no luck. I wanna lean towards a head gasket or cracked head but Im trying to verify it.

[4spdz34]

varies on motor condition and the cams u have. my old motor 93 would put out 200 and my new motor would only put out 170. if your timing is off your readings will be off.

[RacerX11]

The absolute pressure reading isn't as important as the cylinder-to-cylinder pressures. They should all be pretty close to each other. If you do have a bad gasket or cracked head, there should be one or more cylinders that are grossly lower than the rest.

Marty

[intimidatorz34]

Well my buddy and I checked the front 3: 70, 70, 60 for cylinders 2, 4, and 6 respectively. Altho I question the readings since it was a rush job, so I am going to run it again tomorrow morning as well as do one of the rear cylinders. But I know he did make a comment on how they were low, he was expecting 120 or so. However, he also made a comment about how it was a pain to get the testor tight because of the cam carriers.

[Juglenaut]

I got 215

[RacerX11]

A lot also depends on how you run the test. Did you remove all 6 spark plugs?

Here is how I run the test: Remove all plugs. Connect the tester. Open the throttle wide. Crank the engine for 5-6 revolutions, or until the presure gauge stabilizes. Be sure to crank the same period of time for all cylinders.

I have seen people run the test without opening the throttle, or without removing all the plugs, both of which can lead to low (but consistent) readings.

Also, some gauges read lower than others.

Marty

[intimidatorz34]

we had all the plugs in except for the one we tested, and turned the car over for maybe 3 seconds at idle speed. I guess it just matters how the rear head tests.

[4spdz34]

the gm spec is above 100 psi and every cylinder within 30%