Spark Advance Initial GM TPI

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51Plymouth
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Joined: Mon Jun 22, 2015 6:58 am

Spark Advance Initial GM TPI

Post by 51Plymouth » Mon Jun 22, 2015 7:17 am

I'm working on a 1991 Camaro transplant in a '32 Ford.
The Spark Advance Initial shows 50 degrees timing in the data logging dashboard. The Spark Advance Initial (distributor initial) is set to 10 degrees advance in the parameter table and the distributor is physical set to 10 degrees.

Problem is timing doesn't advance with engine rpm or load. Timing is static at 10 degrees. I scoped out all waveforms and distributor and electronics seem to work OK. It appears the constant timing is being commanded.

Anybody got any ideas?

Thanks

Mike

JP86SS
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Post by JP86SS » Mon Jun 22, 2015 7:55 am

You did not plug in the "Bypass" wire after you set the static timing.
The ECM is not controlling it.
You may see a small change with RPM but not nearly what would be called from the program.
Image

51Plymouth
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Post by 51Plymouth » Mon Jun 22, 2015 10:05 am

I bugged the wire from the ECU to the distributor and it's plugged in and connected. When I disconnected it to "set the timing" and re-connected after static timing was set.

The leading edge of the spark is exactly aligned with the reluctor signal from the distributor. I have a spare ECU and tried that but got exactly same result. I changed the electronic module in the distributor and got the same result.

I bugged the wire from the ECU to the distributor and they are all connected and I get the same waveforms on either the ECU pin header or the distributor connector.

51Plymouth
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Post by 51Plymouth » Mon Jun 22, 2015 11:08 am

What bugs me is when I use TunerPro RT the baseline distributor setting pops up at 50 degrees. I re-set it to 10 degrees but on the "dashboard" of the RT tuning program is shows up as 50 degrees.

I suspect that the baseline timing (50 degrees) virtually exceeds the max timing of 50 degrees and therefore, the ECU has no control of the spark advance.

The question may be why can't I reset the baseline spark to anything other than 50 degrees?

Again, anybody run into to this strange problem?

Thanks

Mike

51Plymouth
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Post by 51Plymouth » Wed Jun 24, 2015 8:09 am

PROBLEM SOLVED - I think....

I was using an emulator from Moates and Turner Pro RT to do some tuning.
The ECU is a gm p/n 1227730 (p/n replacement 16198262) that has a UV EPROM in the MEMCAL. I picked up a chip, download stock tune to emulator, made some changes everything worked fine (so I thought).

However, I found I used a 27C512 chip instead of 256K or 128K. I put the original MEMCAL back in - no chip, no emulator, all back to stock and my timing now moves around just like the spark table says.

Pretty dumb mistake and I wasted a lot of time.

I have no analysis of WHY?

Any comments? Any related experiences?

Thanks for the replies and suggestions.

Thanks again,
Mike

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Six_Shooter
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Post by Six_Shooter » Thu Jun 25, 2015 6:34 pm

Sounds like you may have had the offset incorrect when you programmed the EPROM, and therefore you were in LHM (Limp Home Mode), in which timing is controlled solely by the dizzy and the module found within.

Was your CEL (Check Engine Light) on when the timing wouldn't advance?

If you were using an emulator and didn't disable checksum, some strange things can happen where data will still read, but changes made will not actually be read by the ECM. This is why it's very important to disable checksum for emulation.

51Plymouth
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Post by 51Plymouth » Fri Jun 26, 2015 4:00 am

B I N G O You nailed it.

I was using an emulator and did not disable check-sum.

It kept showing timing offset beyond 50 degrees and did go to the limp home mode. The car (32 Ford) was a 1991 Camaro transplant and no check engine light was wired.

I sure learned a lesson on this one.

Problem was identical to having "set timing" wire disconnected.

Good catch - thanks

Mike

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