Advance calculation

[myburb]

I have a 6395 pcm with a BHDF bin in a 94 7.4 suburban. In the scalers there is a box for initial advance. Does the pcm use that number in advance calculations or is it just there for reference.

[lionelhutz]

It will be used. It's the timing advance the distributor should be set to. for example, if the initial is 10* then the ECM takes 10* off of it's timing advance calculations.

[myburb]

I thought that also but had some indicators that made me think differently. So today I plugged a bunch of different numbers in and it does use that in the calculation but it seems if you stray very far from the intended number it gets unhappy.

[JeepsAndGuns]

The initial advance parameter is where you enter in what your distributor base timing is set at. Most all I have seen has been 0*, but I think I have seen some 7.4L bins have around 4*.
You want that parameter to match your distributor. It does effect timing. If you set your base timing to say, 5*, and you set the parameter in the bin to match, then the ecm knows there is already 5* and subtracts that from the timing tables/calculations to account for it. That way it doesn't go over what is programmed.
However, if you have your distributor set to 5* but have the parameter in the bin set to 0*, then the ecm thinks its zero and will make no changes, while in the meantime, your getting 5* added to all your timing.
So long story short, make sure your distributor base timing and the initial timing parameter in the bin match.

[rsicard]

The initial advance parameter is where you enter in what your distributor base timing is set at. Most all I have seen has been 0*, but I think I have seen some 7.4L bins have around 4*.
You want that parameter to match your distributor. It does effect timing. If you set your base timing to say, 5*, and you set the parameter in the bin to match, then the ecm knows there is already 5* and subtracts that from the timing tables/calculations to account for it. That way it doesn't go over what is programmed.
However, if you have your distributor set to 5* but have the parameter in the bin set to 0*, then the ecm thinks its zero and will make no changes, while in the meantime, your getting 5* added to all your timing.
So long story short, make sure your distributor base timing and the initial timing parameter in the bin match.

JeepsAndGuns: I have a 350 Vortec with 7427 ECU and the ignition timing varies between 0 to 10 degrees advanced as read by a timing light on the balancer. The ignition advance table values are something totally different. Trying to make some sense of what is going on. According to your post you have knowledge of the 7427 and small HEI distributor operation. Please expand on knowledge of this ignition system workings. Please advise. Thanks.

[1project2many]

rsicard, you seem to be chasing two problems. 1) perceived lack of timing activity for an engine that is running outside a vehicle, and 2) the need to know *everything* about the ecm, ignition system, code, etc to diagnose and repair #1). Keep in mind that very few technicians have an in-depth understanding about how the timing control works, and that most tuners don't know how all the variables work together, and yet both groups are able to successfully diagnose and repair many problems related to the ignition system. As a technician, and as someone with in-depth knowledge about how the ignition system works, I don't believe your problem #1 warrants the time or effort required to successfully satisfy the conditions for #2. If you are simply chasing knowledge for curiousity's sake, that's fine. If you wish to determine whether or not your ignition timing is working as it should be, folks here could certainly help. I believe there are some unanswered questions in your original thread?