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1997 Sierra 5.7 L. Vortec Timing Issues


Oct 16, 2019
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British Columbia
This truck was running but sometimes would make a 'popping sound' - especially under a load. I am posting for someone so know little info - as it was relayed to me. One recent morning, the truck would not start. It sounded like really low cranking compression. The back and forth movement of crank pulley indicated excess 'free-play' so next thing done was to expose the timing set to have a closer look. This confirmed chain had jumped two teeth on cam sprocket.
New parts were installed, correctly I was told, and then cover, damper and pulley re-installed. With nothing else disturbed (during repair) engine was turned over but did not sound right. It would 'labor' for a second or two and then turn normally but no indication of 'firing'. These Vortec engines are apparently timed by a cam sensor in conjunction with the computer so nothing would result from rotating distributor back and forth, however, the rotor is pointing at No.1 terminal at correct time. Is there something that was over-looked? Could the computer timing be set as for the position of the camshaft before the repair? There is a fuse that states 'Crank' but no power to it. Does this mean anything? This is about all I know from the owner and I did see and hear engine cranking. Any ideas?
The computer uses both the crank sensor and the cam sensor. The crank sensor provides the rpm signal to the pcm, the cam sensor provides a sync signal to the pcm for sequential fuel injection. In the scan tool data it is listed as cam retard, when running it can be set to zero + or -1 degree. The throttle must be snapped to raise rpm above 1100-1500 to reset the value. This will be set after the engine is running again.

When the timing chain and gears were changed did they reinstall the crank sensor reluctor wheel?
It looks like this here
Chevrolet Performance 10190917: Crankshaft Position Sensor Reluctor Ring | JEGS
If they are not sure, remove the crank sensor and it will be visible through the sensor hole. They should have installed the timing gears dot to dot.
I would start by rolling the engine over and align the timing mark on the balancer with the notch on the front cover while #1 cylinder is on TDC. Remove the distributor cap and see if the rotor is lined up with the #8 notch. See this video it will help with what I am talking about.

I would remove the distributor and check the gear for wear, I have seen plenty of worn gears.

The Crank fuse should get power when the ignition switch is in the crank position.
I hope this gives some insight and helps out.