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Setting the timing on a 96' model
Good morning,
just wondered what all was involved in setting the timing on a 96' blazer, 4.3 Thanks |
Get the distributor installed correctly and then you have to use a scan tool capable of reading cam retard and adjust it to +/-2. Once your there the computer will do the rest as far as timing is concerned.
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Technically, you don't adjust timing at all on these. The computer controls timing completely and fires the coil/plug based on the crank position sensor input.
What you adjust is the position of the dizzy (cap and rotor) relative to the crank. The data you need from the scan tool live data is called "CMP offset" or "CMP retard." It needs to be zero +/- 2°. You adjust like you adjust timing on an older engine, at the dizzy. There isn't much adjustability in the clamp, though. If you need more, there are two options. You can grind/file the hole in the clamp for more clearance. The washer will cover it. Obviously take the clamp out to do this. Or, you can run to your local parts place, go over to the "hot rod and engine dress up" area and find a Mr. Gasket 1009 chrome dizzy clamp. Throw away the "wrench" style clamp that engages the flats on the Vortec dizzy and use the older style clamp and you can adjust away. If it's running, you can probably drive it to a parts store and use their scan tool to check CMP offset/retard. Around here, O'Reilly has the best "loaner" scan tool. If it's not running, or if you have a DTC (P1345, "Camshaft To Crankshaft Position Correlation Fault Condition"), you installed your dizzy one tooth (or more) off. Take it out and try again. Also, when moving the crank to TDC, watch cylinder #4, center, passenger side bank. You want that piston at the top right after the rocker for the exhaust valve finishes closing. That's TDC on compression for cylinder #1. It's pretty easy to install things 180° out of sync (at the dizzy) if you only look at the marks on the crank (at the harmonic balancer and front cover). Don't ask me how I know this. |
I've been driving it since the intake gasket replacement and it's not bad. I'm certain I have the correct tooth but with the metal backed updated gaskets and a helical gear, the etched marks I made wouldn't go back exactly. I believe the newer set of gaskets are slightly thicker which would rotate the setting a small amount.
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Being off at the dizzy doesn't change timing. It might make for the rotor being out of position at extreme ends of the timing curve, though, leading to misfire and/or excessive rotor/cap post wear from arcing inside the cap.
To answer the question you actually asked, "what is involved in setting the timing?" The only way to mechanically set (change) the ignition timing on these engines is with an offset key at the reluctor wheel for the crank position sensor at the crank pulley. If you lie to the PCM about the crank position, timing will actually change based on what the PCM sees as the current crank position. Everything at the dizzy is about keeping things in proper alignment when the PCM decides to fire the coil to a spark plug. You could also electronically change the timing by updating the PCM with new timing curve specifications. That could be a reflash, or replacing a PROM chip in the PCM. |
Originally Posted by Racer_X
(Post 665838)
Technically, you don't adjust timing at all on these. The computer controls timing completely and fires the coil/plug based on the crank position sensor input.
What you adjust is the position of the dizzy (cap and rotor) relative to the crank. The data you need from the scan tool live data is called "CMP offset" or "CMP retard." It needs to be zero +/- 2°. You adjust like you adjust timing on an older engine, at the dizzy. There isn't much adjustability in the clamp, though. If you need more, there are two options. You can grind/file the hole in the clamp for more clearance. The washer will cover it. Obviously take the clamp out to do this. Or, you can run to your local parts place, go over to the "hot rod and engine dress up" area and find a Mr. Gasket 1009 chrome dizzy clamp. Throw away the "wrench" style clamp that engages the flats on the Vortec dizzy and use the older style clamp and you can adjust away. If it's running, you can probably drive it to a parts store and use their scan tool to check CMP offset/retard. Around here, O'Reilly has the best "loaner" scan tool. If it's not running, or if you have a DTC (P1345, "Camshaft To Crankshaft Position Correlation Fault Condition"), you installed your dizzy one tooth (or more) off. Take it out and try again. Also, when moving the crank to TDC, watch cylinder #4, center, passenger side bank. You want that piston at the top right after the rocker for the exhaust valve finishes closing. That's TDC on compression for cylinder #1. It's pretty easy to install things 180° out of sync (at the dizzy) if you only look at the marks on the crank (at the harmonic balancer and front cover). Don't ask me how I know this. |
Dang, you guys went over my head pretty quick...lol
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Originally Posted by Graveyard
(Post 665835)
Good morning,
just wondered what all was involved in setting the timing on a 96' blazer, 4.3 Thanks |
Yes I did have it out to replace the lim gaskets. used the updated set along with valve cover gaskets, grommets, upper plenum (cracked) fuel injector, (the newer one).
Just spent a lot of cash and wanted to make sure everything was just right. |
also replaced rotor and cap with ac delco parts
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