DIS Ignition

[81 TransAm]

Hi Danny, Scott. We're working on a buddies car. We are putting a DIS system on it, and we are having an issue with the timing below 2200 RPM jumping around. It will jump (at the crank) 10° ahead at idle. The amount the timing jumps is consistent, but the frequency it happens is not. Once above 2200 RPM it does not jump around.
It's on a 400 SBC. He's using the Holley 60-2 wheel, with what I believe is a Cherry sensor you recommended he use on another thread. The air gap is at .025", but the sensor is slightly off center. He's also using a EFI Connection cam sync unit: https://www.eficonnection.com/home/p...nd-bbc-engines
We recorded a datalog as well as a System Log. We don't see any missed events in the System Log.
My first thought was to center the sensor and reduce the air gap a little to eliminate that as a cause.
Do you know of any other things we should be looking at? Here's a zipped copy of his Global File (V4), datalog & System Log.

[Danny Cabral]

As you stated, center the crank sensor, and .025" sensor gap should be fine (that's what I run). Also, is the Inductive Delay correctly adjusted (LINK)?

[81 TransAm]

Yes, the Inductive Delay is set. It was off a few degrees and it needed to be raised.

[Danny Cabral]

We are putting a DIS system on it, and we are having an issue with the timing below 2200 RPM jumping around. It will jump (at the crank) 10° ahead at idle. The amount the timing jumps is consistent, but the frequency it happens is not. Once above 2200 RPM it does not jump around.

Have you tried temporarily disabling the Idle Spark control (Idle ICF)? Does this happen when using the Enable Static Timing Set?
The Global File & Datalog look fine. Did you notice something wrong in the Datalog you posted? If so, at what time (seconds)?

It's on a 400 SBC. He's using the Holley 60-2 wheel, with what I believe is a Cherry sensor you recommended he use on another thread.

Since it's a SBC, why isn't he using the Holley 554-117 Hall-Effect crank sensor that's included in the kit?

[81 TransAm]

The Idle Spark control is disabled. We did not try enabling the Static Timing Test. We will try that next time we look at it. He bought the DIS Kit used, so it didn't have the correct sensor.

[Danny Cabral]

He bought the DIS Kit used, so it didn't have the correct sensor.

Is this the person from this forum thread: LINK?

[81 TransAm]

Yes, that's him. Thanks.

[81 TransAm]

Hi Danny. I was just reading your thread on Crank & Cam Sensor Setup: http://forums.holley.com/showthread....m-Sensor-Setup
It states: 2.2 Cam Sync setup when using a 60-2 crank input.
When using a 60-2 crank sensor wheel, this cam sync signal trigger MUST occur:
• Before cylinder #1 is at TDC on the COMPRESSION STROKE, make sure that it is not occurring on the exhaust stroke.
• It also MUST occur at least 8 teeth (approximately 50 degrees) before the “missing teeth” are read by the crank position sensor.

By the look of our cam signal, it's happening on the 4th tooth after the missing teeth. This would make the signal happen late. Am I correct that I would need to advance the cam sync distributor housing, until the signal happens at least 8 teeth before the missing teeth?

[Danny Cabral]

I was just reading your thread on Crank & Cam Sensor Setup: http://forums.holley.com/showthread....m-Sensor-Setup

First ensure the 60-2 trigger wheel is properly positioned. Read page 2 of the installation manual (LINK).
Just so we're clear, and because it's a common mistake:
With the #1 cylinder at TDC, the 9th-12th tooth after the two missing teeth (in direction
of engine rotation), needs to align with the crank sensor (not the TDC mark on damper).

A 60-2 crank trigger gets its signal from the two missing teeth on the 60-2 trigger wheel (#1 cylinder), and the 10th tooth after
the missing teeth (Ignition Reference Angle - read next paragraph). The two missing teeth send the TDC signal every time #1
cylinder is up (near TDC of compression stroke and near TDC of exhaust stroke). It doesn't know when the #1 cylinder is ONLY
on the compression stroke, hence the need for a cam sync sensor for sequential injection and/or CNP ignition. If you don't need
or want sequential injection/CNP ignition, then you just need an oil pump drive plug.

The ECU needs an Ignition Reference Angle, so it can control the synchronized timing.
The TDC Tooth Number (amount of teeth after missing teeth) is the Ignition Reference Angle.
On a 60-2 trigger wheel, each tooth equates to 6 degrees. 60 x 6° = 360°.
The Ignition Reference Angle needs to be at least 10° higher than the maximum amount of timing used.

12 teeth is 72° of Ignition Reference Angle, which allows you up to 62° of timing advance (in the Base Timing Table).
11 teeth is 66° of Ignition Reference Angle, which allows you up to 56° of timing advance (in the Base Timing Table).
10 teeth is 60° of Ignition Reference Angle, which allows you up to 50° of timing advance (in the Base Timing Table).
9 teeth is 54° of Ignition Reference Angle, which allows you up to 44° of timing advance (in the Base Timing Table).

It gets confusing because for a 60-2 crank trigger, the EFI software uses the term "TDC Tooth Number" to describe the Ignition
Reference Angle. Which is fine, since the amount of teeth (after the missing teeth) is more of a definitive method to identify it.
http://www.masterenginetuner.com/top...all-fails.html (Crank Reference Angle Importance)

• Before cylinder #1 is at TDC on the COMPRESSION STROKE, make sure that it is not occurring on the exhaust stroke.

Yes, ensure you're not on the exhaust stroke.

• It also MUST occur at least 8 teeth (approximately 50 degrees) before the “missing teeth” are read by the crank position sensor.

Yes, that's at least 48° before the two missing teeth. Each tooth is 6 degrees (60 x 6° = 360°).
It also states, "If the crank sensor is setup such that the 10^th tooth after the missing teeth is at TDC, position
the cam sensor such that it's between 110°−250° before TDC on cylinder #1. This will create a proper position."

By the look of our cam signal, it's happening on the 4th tooth after the missing teeth. This would make the signal happen late.

I don't know how or why that happened.

Am I correct that I would need to advance the cam sync distributor housing, until the signal happens at least 8 teeth before the missing teeth?

Turn the crankshaft to 180° BTDC, on #1 cylinder compression stroke, and align the cam sync sensor on the falling edge of the vane. It's that simple.

[81 TransAm]

Hi Danny. Thanks for the response, and as usual, you are a fountain of information. We are using the 10 tooth as top dead center, and have a reference angle of 50. Our Timing Offset is at 0. The timing at idle, at the crank with a timing light, lines up properly to our commanded timing. Since his balancer only has #1 TDC marked on it, and since we know that one tooth is 6 degrees; I will count back from the 10th tooth after the missing teeth, rotate the engine back until I get to the proper degrees BTDC. Then set the falling edge of the cam sensor. Then I will record another System Log, to make sure the falling edge of the cam sensor falls in the proper area.