Timing Vortec engines

[planedude]

When timing the Vortec 4.3 5.0 5.7 etc. I have read many peoples opinions saying this timing is not adjustable. Why is it that there is a circuit comparitor between the cam and crank sensors. This I was told has to be 0 the give the computer its base to be able to control timing. On my 96 the distributor is adjustable because it has an elongated slot cut in the holder. Can anyone clarify this situation because right now my truck is set at 0 degrees cam retard. Thks

[Thunderbolt]

I know the v-8 timing is adjustable, But I believe the v-6 is not. Someone else on here explained to me about the v-6 and I am not familiar with them. The v-8's timing is supposed to be 0 degrees plus or minus 2 degrees and is only adjustable if you have a scanner. A timing light does not work on them.

[planedude]

yup I have a scanner, I was just wondering why the v6 is different or if in fact it is, and if it needs to be set to 0 degrees cam retard.....the principle of the crank needing to know where the cam is should still be relevant. Thks for the info though.

[planedude]

GMMERLIN maybe you can shed some light.

[skipr]

here you go:


TEST PROCEDURE
The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following:



With the ignition OFF, install a scan tool to the DLC.
Start the engine and bring to normal operating temperature. IMPORTANT: Cam Retard Offset reading will not be accurate below 1000 RPM.
Increase engine speed to 1000 RPM.
Monitor the Cam Retard Offset.
If the Cam Retard indicates a value of 0°+/-2°, the distributor is properly adjusted.
If the Cam Retard does not indicate 0°+/-2°, the distributor must be adjusted.
ADJUSTING PROCEDURE


With the engine OFF, slightly loosen the distributor hold down bolt. IMPORTANT: Cam Retard Offset reading will not be accurate below 1000 RPM.
Start the engine and raise engine speed to 1000 RPM.
Using a scan tool monitor Cam Retard Offset.
Rotate the distributor as follows:
4.1. To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
4.2. To compensate for a positive reading, rotate the distributor in the clockwise direction.

Repeat step 4 until 0°+/-2°, is obtained.
Turn the ignition OFF.
Tighten the distributor hold-down bolt to 3 Nm (25 lb. ft.).
Start the engine, raise engine speed to 1000 RPM and recheck Camshaft Retard Offset.

[planedude]

Thank u for the clarification. This is how i thought it was suppose to be. Perfect explanation. Thks

[Thunderbolt]

Skipr, Were you giving the instructions for a V-6 or V-8 ?? When I did the intake on my 5.7 I set the cam retard to 0 degrees at idle because that is what I was told to do. How much difference will it make ?? When I put the distributor back in I had it marked well and the retard was already at 0 degrees. Should I recheck it ? One more unrelated question, In your post you were able to use the symbol for degrees. At the risk of sounding like an idiot, How do you do that ??

[skipr]

lol good eye! How did I do that? No, really I just scanned the page from my OEM service manuals second edition (4000 pages in 4 volumes). then high lighted the paragraph I wanted copy/cut then paste in reply. Didn't u notice it's worded like a nerd is explaining it? I don't use those fancy words like: IMPORTANT, COMPENSATE and PREVENT....etc.

[GMMerlin]

Neither one of these engines can be "timed" in the way you are used too.
The distibutor housing holds the cam sensor, The PCM calculates the timing by measuring the crank signal and the cam signal.
What you are seting by turning the distibutor housing is the correlation between the 2 sensors.
On the V-6 model, the housing holddown bracket is fixed to the housing so if you return the rotor to the proper position when reinstalling the housing, the engine should be at the correct cam sensor position setting.
Believe me I have seen them installed incorrectly
I don't know why they did not fix the holddown bracket to the V-8 models, it would have saved a lot of headaches.

To set the correlation between the 2, you will need a scan tool that can read camshaft position offset.
With the engine RPM over 1200 adjust the offset too 0 degrees.

[planedude]

This is fine for a new engine but a non adjustable disributor on an older engine, I think would cause some trouble. The timing chain stretches, the disributor shaft wears, gear wear causes the timing "correlation" to slowly drift. I just checked a v-6 with 200,000 on it and the cam retard was off -16 degrees. Not enough to put it ahead another tooth and I can't figure out why. Any comments on this situation.

[Jeremy-WI]

Thunderbolt
On a computer running windows you can go to the start menu, select run, type charmap and click ok. Character map may also be in accessories folder. Once you have the character map running you can select what symbols you want and copy them from there and paste them where you want.

Planedude
Are there any problems with the way the engine runs? I think the cam retard spec on the V6 is 0° +/-20°

[planedude]

Yep my scanner picked up 11000 misfires.

[brokesilverado]

skipr is good he heped me out on my truck.
by the way skipr i still have not had time to get that check engine light off yet. I have to get my hands on a scanner.

[Thunderbolt]

Originally Posted by Jeremy-WI

Thunderbolt
On a computer running windows you can go to the start menu, select run, type charmap and click ok. Character map may also be in accessories folder. Once you have the character map running you can select what symbols you want and copy them from there and paste them where you want.

Planedude
Are there any problems with the way the engine runs? I think the cam retard spec on the V6 is 0° +/-20°

Thanks Jeremy !!

GMMelin, When I did my intake on my 98 5.7 I had the engine idling when I set the cam retard. How much do you think it would be off and what effects would it have ?? The truck runs fine. Should I reset it ??

[Jeremy-WI]

I have heard that putting a distributor cap with brass contacts on a 4.3 helps with misfires and the 5.0 and 5.7's have had some problems with distributor gear wear. It could be a possibility on a 4.3 but I haven't heard of it being a problem. You may want to check for slop in the distributor since there is wuite a bit of plastic and the bushings could be worn