Issue: Balancer read timing versus Tunerpro

[rsicard]

I am using nothing more than this thread as my basis for judging what you know about this system.

The terminology that you can't wrap your head around is used in the factory manual. It is the same terminology used by many people who work with these systems, both mechanics and do it yourself-ers. It is the same terminology found in many threads and articles on the internet. The basics of system operation are also in the factory service manual and are described in articles and videos on the internet. Yet you have asked the same question multiple times even when the answers seem to have been provided, and you have not provided answers which would have revealed what you already know about this system. It seems as though you do not have a basic understanding of EST and you may be asking us to provide it. This is why I said I believe you need some foundation work and why I asked if you have a manual.

FYI:

REFerence is the signal to the ecm from the ignition module.
EST is the signal from the ecm to the ignition module.
These signals consist of square waves, pulses, that represent crankshaft position and the beginning of spark.
This information is available between section 6E in the factory manual and the notes for codes 42 and / or 43. It may be harder to locate in Alldata.

The EST signal lags behind the REFerence signal. The time difference between corresponding points on the two signals, accounting for the number of crankshaft degrees between pulses and the ignition module spark latency, represents spark advance. Measuring spark advance using the time differenc will allow you to see if measured timing at the balancer matches measured timing at the distributor. This information is not so easy to glean from the manual. I gave you this information but you did not know the names of the signals or you did not make the connection.

I'm sure we are both busy people. I don't mind helping. It would be good if you have a reference sheet with, or a technician's level understanding of, EST operation and the names of the signals between ecm/pcm and the distributor. It seems like some of what you are asking can be answered by reading the manual or Alldata as a reference. It seems as though knowing some of the terms and names used in regards to this system would allow you to perform searches on the internet to find additional quality information and further your understanding.

Thanks much for explaining. Did an extensive search of this forum for posts on the subject of ignition. Finally found one post by Dave W. in which he posted a schematic of the distributor ignition module. The terminology used to describe the inputs and outputs of the module are misleading. Yet gained an understanding of what is within the module. The ECM processor and memory must derive RPM based on counts from the pickup of the reluctor wheel in the distributor. Once the RPM is established, the time for one revolution at a particular RPM can be established, then the processor can predict a cylinder firing pulse based on processor and memory table derived timing such that the firing pulse comes in at a smaller revolution time. This process repeats at the main executive loop time in the software governing the processor. Just came up with this as I can presently imagine same. Need to think it through further. Still need to think further about the relationship of ECM timing as seen in TunerPro and that strobed off the degrees graduated balancer. Or hook up a O'scope to these signals and hope to find the relationship of the two. Now have a positive schematic of inputs and outputs of the ignition module. Need to instrument the 350 Vortec on the run-in stand and do the same to the 350 V8 pickup and compare the two. May provide more insight.

Like to know what makes these thing tick.

[damanx]

How did I miss this thread......

I've noticed the same issue when using a timing analyzer and comparing the reading to what tuner pro shows.

For what it's worth, because I am running a C3 ecm, I don't put much faith in the tunerpro timing reading. I do know that the different analyzers I've tried are accurate.

I have 3 different analyzers:

• All-Test 3800, digital readout using a magnetic pickup in conjunction with the inductive clamp on the number one plug wire.
• Kal-Equip 3821, digital readout using a magnetic pickup in conjunction with the pulse coming from the coil.
• Kal-Equip 4020, analog meter using a magnetic pickup in conjunction with the inductive clamp on the number one plug wire.
• I also have an Equus 5568 timing light that has the "advance" function on it.

All three work and all three accurately read the mechanical timing properly, but, as I recall, the timing reading in TunerPro was always different, although I don't remember how much.

I finally realized that the readings in TunerPro for timing did not really matter, because what did matter, was knock counts and where it was occurring.

I've questioned the purpose of the spark latency table and the best understanding of it that I've gotten, (may not be entirely correct r complete), is that it's function is to correct to frequency and duration of the reluctor pulse at different RPM's. This table varies in values based on things such as distributor size for example.

If you google "gm spark latency table", you will find some "white papers" that discuss this further.

This is my two cents, YMMV.

Edit to add video: (note that the timing in tunerpro is off by 3 degrees or so, and, I believe that the reason for that is that the analyzer is more "real-time" than what TunerPro is showing due to the 160 baud rate of the ECM I'm using.

[rsicard]

How did I miss this thread......

I've noticed the same issue when using a timing analyzer and comparing the reading to what tuner pro shows.

For what it's worth, because I am running a C3 ecm, I don't put much faith in the tunerpro timing reading. I do know that the different analyzers I've tried are accurate.

I have 3 different analyzers:

• All-Test 3800, digital readout using a magnetic pickup in conjunction with the inductive clamp on the number one plug wire.
• Kal-Equip 3821, digital readout using a magnetic pickup in conjunction with the pulse coming from the coil.
• Kal-Equip 4020, analog meter using a magnetic pickup in conjunction with the inductive clamp on the number one plug wire.
• I also have an Equus 5568 timing light that has the "advance" function on it.

All three work and all three accurately read the mechanical timing properly, but, as I recall, the timing reading in TunerPro was always different, although I don't remember how much.

I finally realized that the readings in TunerPro for timing did not really matter, because what did matter, was knock counts and where it was occurring.

I've questioned the purpose of the spark latency table and the best understanding of it that I've gotten, (may not be entirely correct r complete), is that it's function is to correct to frequency and duration of the reluctor pulse at different RPM's. This table varies in values based on things such as distributor size for example.

If you google "gm spark latency table", you will find some "white papers" that discuss this further.

This is my two cents, YMMV.

Edit to add video: (note that the timing in tunerpro is off by 3 degrees or so, and, I believe that the reason for that is that the analyzer is more "real-time" than what TunerPro is showing due to the 160 baud rate of the ECM I'm using.

Thanks ever so much for chiming in. After proceeding from your hints, found a lot of ign timing latency stuff over at TGO. Built an informative file with that stuff. Expanding knowledge of ign timing.