The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Compression Test on 200k LQ4

bsampson · 05-22-2022, 04:02 PM

I have a 200k mile LQ4. I have it on an engine stand, and am planning to put in a new cam, lifters, lifter seals, timing set, oil pump, and rear and front main seals.

The engine has been sitting for over a year. Old oil is still in the pan.

I wasn't going to pull the heads, but after doing a compression test, I got higher numbers than expected. The compression tester is a new, $25 amazon tester.

Front of Engine
(1) 225 (2) 235
(3) 235 (4) 225
(5) 235 (6) 60 (260 after 1Tbs oil)
(7) 235 (8) 230

On cylinder 6, I test multiple times. It did hold pressure fine, just wouldn't pump up well. I went to lunch, and came back and it held 100psi for probably 45minutes. In subsequent tests, it seemed to increase and got up to around 150 psi. Once I squirt a little motor oil in the cylinder, it quickly went up to 260 psi. And held.

Question 1 - Does the high pressure mean I have a crappy gauge, or lots of carbon buildup?
Question 2 - Should I be concerned with cylinder 6?

05-22-2022, 04:02 PM	#1
bsampson Registered User Join Date: Jul 2012 Location: Central IL Posts: 63	Compression Test on 200k LQ4 - Question on Results I have a 200k mile LQ4. I have it on an engine stand, and am planning to put in a new cam, lifters, lifter seals, timing set, oil pump, and rear and front main seals. The engine has been sitting for over a year. Old oil is still in the pan. I wasn't going to pull the heads, but after doing a compression test, I got higher numbers than expected. The compression tester is a new, $25 amazon tester. Front of Engine (1) 225 (2) 235 (3) 235 (4) 225 (5) 235 (6) 60 (260 after 1Tbs oil) (7) 235 (8) 230 On cylinder 6, I test multiple times. It did hold pressure fine, just wouldn't pump up well. I went to lunch, and came back and it held 100psi for probably 45minutes. In subsequent tests, it seemed to increase and got up to around 150 psi. Once I squirt a little motor oil in the cylinder, it quickly went up to 260 psi. And held. Question 1 - Does the high pressure mean I have a crappy gauge, or lots of carbon buildup? Question 2 - Should I be concerned with cylinder 6?