2003 silverado 4.8no compression?

[tracmekanix]

I just purchased an 03 silverado it will not start. I pulled the spark plugs and they look good (used not new) I checked the compression and it has from 25 to 75 psi. Does G.M. still use fiber coated camshaft gears or do I have big problems? Thanks Jerry

[16th hippy]

pull a valve cover and see if the valves move. if so, then big problems. if not, start with timing chain.

[tracmekanix]

I pulled valve cover and rockers are moving plenty. I loosend them off a couple of turns no help. I squirted oil in one and comp came up from 60 to 70 on a good cyl.

[16th hippy]

how many miles on the engine, and what condition was it in before this happened....was it running rough, or just up and died with a no start?

[maxwedge]

Before you torture yourself here, make sure you have spark and fuel pressure that gage may be wrong or the engine cranks too slow or you are not holding the throttle open.

[tracmekanix]

Originally Posted by 16th hippy

how many miles on the engine, and what condition was it in before this happened....was it running rough, or just up and died with a no start?

The eng has 94000 on it. It is a bank repo I never heard it run. I've replaced a few timing chains before but I was told these have either double roller or gear drive. I haven't been able to turn crank by hand and watch rocker arm movement until I get a helper.

[tracmekanix]

Originally Posted by maxwedge

Before you torture yourself here, make sure you have spark and fuel pressure that gage may be wrong or the engine cranks too slow or you are not holding the throttle open.

It has good spark but would not try to run priming it. Gage is probably close if not correct a couple of the cyls. I can hold my finger over.

[maxwedge]

I'd do a leak down test on the engine and see what you come up with, seems hard to believe the engine would loose this much compression on all the cylinders, if you bring the engine up to tdc on #1 you should be near the mark on the damper. If the valves are stuck/not seating you will hear the air escape from the intake or exh.

[fleettech]

if its a bank repo chances are the previous owner gernaded it before they came and got it. or did something to destroy it.

[tracmekanix]

Originally Posted by maxwedge

I'd do a leak down test on the engine and see what you come up with, seems hard to believe the engine would loose this much compression on all the cylinders, if you bring the engine up to tdc on #1 you should be near the mark on the damper. If the valves are stuck/not seating you will hear the air escape from the intake or exh.

I tore engine down and it looks like the oil was never changed. All the rings were stuck except for a couple of top rings. They all still have plenty of tension. Bore and crank look good. I'm doing the heads and going back with new bearings and rings.

[tykrz]

Makes you wonder what the rest of the powertrain is like. Make sure you measure up the crank and bore with proper instruments to make sure nothing is out of round and taper within tolerances. If you're this far into it, i'd definately do a complete overhaul.