Setting the timing on a 96' model
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No, I wasn't operating the scan tool. Our local O'reilly's will not rent that tool.
I also told the guy what I was looking for but I didn't verify absolutely what we were looking at. Dang, I had to go to 2 different stores before I found someone who actually knew how to get to that page on the scanner...lol
And I believe I understand what your saying about the dizzy settings. If I understand, all I'm doing by turning the distributor is getting the cap terminals positioned so that the rotor tab fires when it is directly lined up with a terminal.
I also told the guy what I was looking for but I didn't verify absolutely what we were looking at. Dang, I had to go to 2 different stores before I found someone who actually knew how to get to that page on the scanner...lol
And I believe I understand what your saying about the dizzy settings. If I understand, all I'm doing by turning the distributor is getting the cap terminals positioned so that the rotor tab fires when it is directly lined up with a terminal.
Last edited by Graveyard; Jun 10, 2016 at 09:43 AM.
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From: North Central Indiana
No, I wasn't operating the scan tool. Our local O'reilly's will not rent that tool.
I also told the guy what I was looking for but I didn't verify absolutely what we were looking at. Dang, I had to go to 2 different stores before I found someone who actually knew how to get to that page on the scanner...lol
And I believe I understand what your saying about the dizzy settings. If I understand, all I'm doing by turning the distributor is getting the cap terminals positioned so that the rotor tab fires when it is directly lined up with a terminal.
I also told the guy what I was looking for but I didn't verify absolutely what we were looking at. Dang, I had to go to 2 different stores before I found someone who actually knew how to get to that page on the scanner...lol
And I believe I understand what your saying about the dizzy settings. If I understand, all I'm doing by turning the distributor is getting the cap terminals positioned so that the rotor tab fires when it is directly lined up with a terminal.
Yes, you are understanding correctly what you are doing by turning the distributor.
Last edited by LesMyer; Jun 10, 2016 at 11:28 AM.
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Joined: Apr 2016
Posts: 325
From: North GA, USA
I suddenly have some unplanned travel in my immediate future, and some unplanned personal business.
Hence the updated "not so tech tip of the week" in my sig.
Short answers here, Graveyard, you are correct, the goal is to properly align the rotor with the posts and nothing more. If things are aligned, all the spark energy gets to the spark plug (you hope) when the PCM fires the coil for each cylinder.
The electronic timing control with a fixed dizzy was all the rage from the late 1980's up into the early 2000's. The computer controls timing based on the sensors, the dizzy doesn't move at all. That way timing isn't dependent on mechanical springs (that weaken or wear) and weights, or on vacuum lines and vacuum actuators that leak when they get old. It's also the only way to maximize power and minimize fuel consumption with knock sensors (run the timing advance until it knocks and back off a bit). It's virtually impossible to wire a knock sensor into an old mechanical/vacuum dizzy.
When most manufacturers switched over to this type of system, they made changes to the rotor and cap designs to keep the rotor element in contact with the posts on the cap over a wider angle. "Hammer head" rotors (with a "T" shaped contact) or wider contacts on the posts inside the caps were common.
On our Vortec engines, GM uses neither strategy, so they have a very narrow angle where the rotor is in contact with the post on the cap, and all ignition timing variations (up to 20° crank, or 10° inside the cap) have to fall in the angle where the post and rotor are touching (or close enough to couple). That's why cap position (and CMP retard/offset angle) is so critical on this engine.
Hence the updated "not so tech tip of the week" in my sig.
Short answers here, Graveyard, you are correct, the goal is to properly align the rotor with the posts and nothing more. If things are aligned, all the spark energy gets to the spark plug (you hope) when the PCM fires the coil for each cylinder.
The electronic timing control with a fixed dizzy was all the rage from the late 1980's up into the early 2000's. The computer controls timing based on the sensors, the dizzy doesn't move at all. That way timing isn't dependent on mechanical springs (that weaken or wear) and weights, or on vacuum lines and vacuum actuators that leak when they get old. It's also the only way to maximize power and minimize fuel consumption with knock sensors (run the timing advance until it knocks and back off a bit). It's virtually impossible to wire a knock sensor into an old mechanical/vacuum dizzy.
When most manufacturers switched over to this type of system, they made changes to the rotor and cap designs to keep the rotor element in contact with the posts on the cap over a wider angle. "Hammer head" rotors (with a "T" shaped contact) or wider contacts on the posts inside the caps were common.
On our Vortec engines, GM uses neither strategy, so they have a very narrow angle where the rotor is in contact with the post on the cap, and all ignition timing variations (up to 20° crank, or 10° inside the cap) have to fall in the angle where the post and rotor are touching (or close enough to couple). That's why cap position (and CMP retard/offset angle) is so critical on this engine.
Last edited by Racer_X; Jun 11, 2016 at 12:21 PM.
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When you rotate the distributor, you are aligning the camshaft position sensor with the camshaft, hence the name "Camshaft position sensor". You are also, simultaneously, aligning the position of the distributor cap so it aligns with the rotor when the coil fires. Factory spec is zero degrees, plus or minus 2 degrees. If it's out of spec, there will be crossfire inside the cap.
EDIT: The PCM uses combined data from the crankshaft position sensor AND the camshaft position sensor to detect, and accurately identify, cylinder misfire. If camshaft retard is within spec, you can disconnect the camshaft position sensor and the engine will perform the same as when it's connected, (without cylinder misfire detection).
EDIT: The PCM uses combined data from the crankshaft position sensor AND the camshaft position sensor to detect, and accurately identify, cylinder misfire. If camshaft retard is within spec, you can disconnect the camshaft position sensor and the engine will perform the same as when it's connected, (without cylinder misfire detection).
Last edited by Captain Hook; Jun 11, 2016 at 12:57 PM.
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From: North Central Indiana
RPMs need to have been raised above that point after starting and after each adjustment. It's OK to go back to idle.
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okay, I'm just a little hacked off. I took my blazer to my respected mechanic and ask him to adjust my cam retard to zero degrees. He hooked it up to his Snap on solus and told me I was 20 degrees advanced. Said if I didn't have an engine service light on he'd just leave it alone...not what I wanted. Went to O'Reillys earlier and couldn't really find anyone that knew how to use their scanner. Holy crap, how can I get the settings corrected properly? Seems to be running alright but I have just sunk a ton of cash on this thing and I want it timed properly. What the heck is a guy supposed to do...lol
Later
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