3900 Trouble starting Code59 swap

[Guest]

Cranks over and runs for about 2 seconds then dies out as accelerator is pressed and rpm starts to climb ending with backfiring.

TPS sensor is reading properly
MAP Functioning
MAT sensor working
Timing advancing as expected

Fuel changing and spark adjustment isn't making to much of a difference at the moment.

I believe I'm the only person using Code59 with DIS so their maybe a problem that hasn't been worked out although it is setup for DIS in this application.

I'm going to check the base timing. I have the cam fully advanced now and noted good vacuum coming up on the gauge during starting compared to what it used to be but I'm at a loss for why it keeps backfiring and will not run continuously.

[Superdave]

Did you change the spark ref angle to 59.8 degrees and set the number of cyls?

[Joseph Upson]

Did you change the spark ref angle to 59.8 degrees and set the number of cyls?

Yes, I did all of the typical stuff. I started with a known working bin for a 6 cylinder. I believe there is a problem with other timing limits causing the problem as it starts up fine and as soon as the ECM starts taking over timing things go wrong.

After further testing performed after the response deteriorated to a miniscule sign of ignition, and changing bins and ecm's had no effect, I pulled out the timing lights and the oscilloscope and found intermittent firing at times and a far from normal crank sensor signal especially when compared to the nice one produced on my first test of the 7x ring.

So when I return for another try I'll have new ignition parts in hand and hopefully a properly configured bin.

[Scott_68B]

Joesph -- You probably already read this but, if not, it might help.

http://www.diy-efi.org/twiki/bin/view/Gmecm/DISdist

-- Scott

[Joseph Upson]

Joesph -- You probably already read this but, if not, it might help.

http://www.diy-efi.org/twiki/bin/view/Gmecm/DISdist

-- Scott

Thanks. Hope to have another shot at it in a couple weeks. One important discovery after the fact is that my crank position sensor wires were not twisted together after the harness change. GM specifically states not less than 9 turns per foot for those two wires on some instead of all DIS associated wiring diagrams. That probably explains the very unusual tracing I noted on the oscilloscope test of the sensor compared to what I had seen in the past.

I would never have known had I not read it although I wondered why they went through the trouble to twist them together from the start. The wire twisting is important to reduce electrical interference that can cause a misfire.

As for the timing, I don't believe the actual final value requested is a negative value as set in the example in the link you posted. A simple check of the code59 spark limits against the 8F TGP code would revealed quite a bit, like the much higher 80,20 max advance and max retard setting.

The code59 settings were around 47,0. So chances are the spark logic test failure resulted in 0 degrees advance on an engine that needed at least 20 deg to have a chance at running, which would it explain why it ran nicely briefly until the ecm started to take over timing.

It took finding the following thread that in my opinion is a Phd level explanation about how spark timing is arrived at to help me get a better grasp on how to approach the matter. It's unfortunate the author, Grumpy, has passed away. Scroll down a little in the link to see his masterpiece of an explanation;

http://www.thirdgen.org/techboard/diy-prom/317768-timing-logics-anyone.html