Understanding the concept of Cam Sync preceeds cylinder - XFI

Blazer406

Mechanical Engineer
Joined
May 2, 2002
Lets see if I got this right.... XFI...... 109 Turbo V6.....running a dizzy.....and the factory crank trigger.... with all tabs broken off the reluctor wheel in the dizzy...except one of them.....According to the help.... it doesn't matter which tab stays... as long as all but one get taken off..... you must set the "Cam Sync Preceeds Cylinder" correctly so the XFI can make the timing and fuel corrections to the appropriate cylinder if you are using the individual cylinder tuning control feature.

If I understand the concept...... Really the cam sync can occurr anywhere.... as long as it isn't within 10 degrees of the crank sync..... you must srt the "cam sync preceeds cylinder" correctly and verify it is correct by testing the retard on a couple cylinders using a dial back timing light... and verifying that the cylinder you tell to retard..... actually retards.....

Is this correct?
 
Yes, also make sure your rotor is phased correctly

Do I verify that it is phased correctly by checking ignition timing with a light and verifying the timing matches what the fast says? I think ours is set to 10 deg.... and we have verified it is like maybe 1/2 degree off.... (assuming you have zero'd out any idle trim or ATS based timing corrections)

Also... the Cam Sync BTDC in the XFI..... master dash..... that number reported.... it appears that is the degrees (I'm assuming relative to TDC compression stroke for #1) the cam sync actually occurred..... Is this correct?
 
You are confusing rotor phasing with the crank referance angle. The rotor phasing is when the rotor is pointing directly at the post on the distributor. On most Buicks, I set this around 25 degrees BTDC. Turning the distributor won't affect timing but it will affect the cam sync and more importantly the rotor phasing.
 
You are confusing rotor phasing with the crank referance angle. The rotor phasing is when the rotor is pointing directly at the post on the distributor. On most Buicks, I set this around 25 degrees BTDC. Turning the distributor won't affect timing but it will affect the cam sync and more importantly the rotor phasing.

In the case I have... the XFI is reporting 118 deg as the cam sync BTDC. How is this number achieved? Is it measured by the XFI? In the case I have the cam sync preceeds has to be set on #4 for the ignition retard to follow the correct cylinders....

edit: I think I have it:

Per a page on efisupply.com:

Rotor phase and crank/cam reference angles must be properly configured for proper operation of an aftermarket ECU.

Rotor phase is an often overlooked factor. In order to prevent crossfire it is important to "phase" the rotor, which is nothing more than ensuring that the rotor is in line with the terminal on the distributor cap during ignition (spark). Though not all distributors will permit independent rotor phasing, most applications will permit the distributor to be rotated to provide proper rotor phasing. If the crank sensor is in the distributor, turning the distributor will require a change in the "Crank Index Offset/Crank reference angle" value (found in the Engine Configuration/Operational parameters screen). The most foolproof way to confirm proper rotor phase is to drill a hole in the top of the distributor cap between the number one terminal and the coil terminal. When the engine is running and a timing light is connected to the number 1 spark plug wire, the timing light can be used to observe the position of the rotor during ignition.

Basically I must verify that the rotor is lined up with the terminal for #1 when it is supposed to be lined up with #1..... for the ignition to properly fire.... much like adjusting an old HEI distributor.... except the timing doesn't move when you turn the dizzy.....I must make sure (with small hole in distributor cap) via a timing light... that the rotor is in fact in the correct position......if it is too far off.... the next cylinder would possibly cross fire.....??
 
Bump.... attn:!! OLD THREAD!!!!!

Trying to sort out some gremlins...... XFI was reporting 16 deg for the "Cam Sync (BTDC)". I am told this is no good...... and I need to fix this by modifying the reluctor wheel so I can adjust it.... and line the reluctor tab up around 70-80 deg BTDC of #1 compression stroke......

As I understand it..... once reluctor wheel is modified with set screws......drop it in the whole at 25 deg BTDC for # 1 on the compression stroke.....make sure rotor button is looking at the # 1 terminal.......

Then pull rotor button off..... and roll motor to 70-80 deg BTDC for # 1 on the compression stroke.....

Now adjust reluctor wheel so that it hits the window (Is this under the hole that is to be drilled in the distributor cap between the #1 terminal and the coil terminal???)..... then put rotor button back on.....and fire it up.

If I do the above steps right..... the "cam sync preceeds" will be set to 1 ..... and when I retard 10 deg on #1 .... I should be able to verify this with a light.....

Sound plausable?
 
You got it! :cool:

The only thing I would caution you, is the car can not be idling when doing the individual cylinder. There are a couple of ways to handle this. I feel the easiest is to just go into View/System Configuration/Sensor Calibration/TPS Calibration and raise the green line on the far left up to 20%. This will "trick" the computer into not idling and allow the Individual Cylinder Correction to work. As a side benefit, it will get rid of the idle timing trim and get you a much more stable timing light.
 
You got it! :cool:

The only thing I would caution you, is the car can not be idling when doing the individual cylinder. There are a couple of ways to handle this. I feel the easiest is to just go into View/System Configuration/Sensor Calibration/TPS Calibration and raise the green line on the far left up to 20%. This will "trick" the computer into not idling and allow the Individual Cylinder Correction to work. As a side benefit, it will get rid of the idle timing trim and get you a much more stable timing light.

Last night we had a washer under the throttle screw... it had the TPS @ 7%. According to the "help" in the XFI software...... the only requirements for individual cylinder corrections to work was:

  1. TPS % must be above whatever is set under "max TPS for idle"
  2. ECU must be receiving a cam sync signal.
  3. ECU must be in sequential mode.

In our case, the "max TPS for idle" was set to 5%..... so I figured the washer under the throttle putting the TPS @ 7% was satisfactory.

Long story short...we never could get the timing to change (on #1) after applying 10 deg of retard 1 cyl at a time....until I had applied it to all cylinders at the same time. It was at this point when we were asked what the "Cam Sync (BTDC)" was....... and once I started the car... went online with the ECU.... pulled up the master dash......and saw the ECU was reporting 16 deg for this.

I had just went in and bumped up the TPS calibration to like 70% across the board so we could do the checking with the motor at a lower RPM. I was told that 7% may not be enough to make it kick into the individual cylinder correction..... that it needed to be 20% or more on the TPS percentage....

This is where we went no further.... until we modify the reluctor wheel and re-phase everything.
 
I remember those days.. can get confusing then one day it just becomes clear.
 
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