Timing table example?

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Aug 12, 2002 | 08:28 PM

zwede

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From: Plano TX

Timing table example?

I'm running a Commander 950 MPFI system on my '71 454. I was wondering if I could trouble someone to post a timing table? Basically needs to contain MAP reading vs RPM and the timing advance. I would like to take a look at some stock tables for various engines to get an idea if I'm running a good table. For mine, I basically emulated an old-fashioned distributor (i.e mech advance that is rpm bound + 15 dgr advance at low load).

So any timing tables you have (stock or aftermarket) would be appreciated.

Aug 13, 2002 | 12:30 AM

Hendej

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Re: Timing table example? (zwede)

Here are the tables for the 1990 SD calibration (aluminum head):
http://www.diy-efi.org/gmecm/papers/anht_hac.pdf

Here is a writeup on how the tables relate:
http://www.diy-efi.org/gmecm/ecm_inf...730/qanda.html

HTH

Aug 13, 2002 | 12:12 PM

zwede

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From: Plano TX

Re: Timing table example? (Hendej)

Thanks! Exactly what I was looking for. Interesting also... A quick look through the dump and it looks like GM does some things the aftermarket is not doing yet. For instance, highway fuel & spark, Stall saver, hot restart retard.

Aug 13, 2002 | 01:03 PM

zwede

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Re: Timing table example? (zwede)

Question: For the timing table, is initial advance added to the number in the table or not?

Looking at the table, at say 5200 rpm we have a base advance of 24 degrees at 100 kpa. Add to this the power enrichment advance of 7 degrees and we have 31.

Now will the advance be 31 degrees or will the initial advance of 6 degrees be added on top of this?

Aug 13, 2002 | 01:11 PM

Hendej

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From: Crystal Lake, IL USA

Re: Timing table example? (zwede)

I see that the ANHT hack references, but does not list the SA vs coolant table. WinBin to the rescue! Another 5 degrees is added until the coolant temp reaches 92 deg C (198F).

Also, I believe all these values are relative to the 6 degree base setting.

Also, there might be a 10 degree ALDL advance added for limp home mode in later years - I have not seen this in the MAF code, but it is supposedly used in the SD code.

Interesting that the EPA would not allow GM to use any of the highway code.

Aug 13, 2002 | 01:17 PM

Hendej

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Re: Timing table example? (zwede)

In my experience (MAF code), the base advance is programmed into the PROM, but is only used to check if the total advance PROM value would be exceeded. All the table values are relative to the base advance.

Aug 13, 2002 | 03:27 PM

zwede

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Re: Timing table example? (Hendej)

Not sure what you mean when you say it is relative. I think you mean that the value from the PCM will correspond to what is read on the timing tab?

To continue the above example: On top of the 31 dgr I listed would be another 5 dgr coolant vs SA for a total of 36 dgr. If I took a timing light I would see the same 36 dgrs, correct? I wouldn't see the 36 plus 6 initial for a total of 42?

Thanks

Aug 13, 2002 | 06:18 PM

Hendej

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Re: Timing table example? (zwede)

When the ECM calculates the SA, it adds together all the various contributions (PE, knock test, coolant comp, main, etc). This is the value used to control the module, so it does not include whatever mechanical advance you have set (the 6 degree base value). The ECM value is the same value reported through the ALDL to your scanner - the amount of electronic advance added on top of your base timing.

In the example you should see 36 + 6 = 42 degrees with a light.