High Compression?

[CSULZER]

I recently checked compression on my 1996 5.7L Siverado 110k miles. I read between 190-210psi after 5 strokes on all the cylinders. I think the spec says 150 psi. Is this high and what could it be from? Could it be causing a loss of power which I have noticed over the last couple years?

[dstktmusa]

Carbon build up on the top of the piston can cause high compression readings.

[cantrma]

If you had that much carbon, you've have audible pinging. It is also unlikely that it would be consistent across all cylinders. I'd suspect my gage more than I would my truck at this point. Are you sure you used the right scale on the gage?

[CSULZER]

If you had that much carbon, you've have audible pinging.  It is also unlikely that it would be consistent across all cylinders.  I'd suspect my gage more than I would my truck at this point.  Are you sure you used the right scale on the gage?

 

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Thanks. I did check the gage and though I couldn't verify it at 200 psi, it was in calibration at 90 psi (air compressor) so I think it should be fairly accurate. But I guess my question is, is 200 psi abnormally high for a 1996 5.7L vortec.

[budhayes3]

What was the reading after 4 compressions strokes? That's where you should be checking it.

[CSULZER]

The readings were about 120 psi on the first compression, 150 (2nd) , 175 (3d), 190 (4th), and about 200 on the 5th.

The final readings varied from 190-210 psi on the 8 cylinders.

[mcreyaufmiller]

If I remember my old school training, if there is oil above the piston, you will get abnormal high psi readings off of a compression check. This is normally caused by a failed oil ring, but if yours is consistant across the rack, I would say as long as they are within 5psi of one another you are in good shape. As bud hayes said, you should be at 190 on the 4th stroke, your message said 200 at 5, and 190 at 4. you should be okay. Just my opnion.