Using a sqrwave generator to switch between flex and gas tables?

[Akturboguy]

I've looked through methods of reducing timing via a switch with the p59 pcm and come up with just the typical IAT mod the N2O guys use. I was trying to find a pinout to see if there was a traction control ground out pin or something I could use to activate that spark table but I've found nothing for hptuners, just some thing for efilive.

Which led me to thinking about the flex tunes and the flex fuel sensor. I've never messed with a flex tune since we have no ethanol fuels here and I dont know how fast the PCM can switch the tables without throwing a code or something. But what if I made or bought a small 5v squarewave generator that output the proper signal to trigger the flex settings and used a push button switch to change it's output from 50 to 150hz (0% to 100% ethanol)?

Could I copy over all the fuel tables and AFR settings and make everything identical except the spark tables? That way I could change spark for octane or traction with a switch?

[kingtal0n]

what are you trying to do exactly


In theory it might work but there are risks. What is the current draw or supply of such a device? Will it interfere with or burn up the computer due to transient voltage issues?
car electrical systems are not stable, clean signals. They often need some kind of induction and capacitance to help even out their voltage waves and prevent spikes from frying components.
Such a device may need an amplifier, and you would definitely want to put an oscilloscope on it to ensure operating as intended.


IAT and CTS are much easier targets because their sensors operate on principle of resistance. You can take a variable resistor and wire it through the iat for example then simply tune the supplementary IAT map in the computer however you want for temperatures which are impossible to reach naturally. For example here in Florida it never reaches -20*F or whatever, so I have cold regions set to add a bit of timing whenever I dial my IAT down that low. Of course the computer also adds fuel by itself due to lower IAT so this is a great way to both enrich and throw some timing simultaneously.
The ecu also has a cta/iat bias you can play with to combine the effects.

Traction control wise, I've never had an issue tuning the spark map for the exact tire situation the vehicle faces right then and there. Just find the region of timing map that the engine enters just before breaking loose the tires and pull timing until it doesn't.

[Akturboguy]

It's a p59 pcm in a '84 chevy body. I don't have an speed sensor on the front wheels, just the back. It's a th400 so I can't take or add spark by gear. So I was trying to find a method to pull 6-8 degrees on a button so I can pull timing in 1st after the launch. I'm not really after a 2 step function, just taking spark away for traction.

[Alvin]

I've done it before on Gen 4 ECM's Gen 3 E85 support is a bit spotty especially for cable driven applications. On Gen 3's I've used the traction control pin to retard timing for launch or for a shot of gas. You have to be careful though some OS's have a time limit for how long that retard stays active.

We did it to run a dry nitrous kit on a junkyard 5.3L build.

[kingtal0n]

It's a p59 pcm in a '84 chevy body. I don't have an speed sensor on the front wheels, just the back. It's a th400 so I can't take or add spark by gear. So I was trying to find a method to pull 6-8 degrees on a button so I can pull timing in 1st after the launch. I'm not really after a 2 step function, just taking spark away for traction.

yeah but the region the map hits from 1st gear is completely separate from the region where it will shift 2nd and 3rd,

in other words it only brushes that one region of the timing map once during a launch, and then from that point on it will never go near that spot again.

So why not just program the timing map the way you need it for that momentary launch

[Akturboguy]

I've done it before on Gen 4 ECM's Gen 3 E85 support is a bit spotty especially for cable driven applications. On Gen 3's I've used the traction control pin to retard timing for launch or for a shot of gas. You have to be careful though some OS's have a time limit for how long that retard stays active.

We did it to run a dry nitrous kit on a junkyard 5.3L build.

Do you happen to know which pin the traction control activation is? And is it just grounded or given voltage? Ive seen this method referenced one other time and the instructions were to max out the maximum activation time to 410sec. I think he mentioned pin 56? The problem was it was all in refrence to an LS1 pcm from 1999 or 2000 with blue/red harness. I have a 2003 express van PCM with a blue/green harness modified for DBC.

Talon, the traction control spark retard is only referenced to engine RPM in the table. I make more than 10psi by 4000 rpm and 10psi(1.20g cylinder airmass) is the last cell in the timing table so I can only limit by RPM in the last row but if I do that I lose spark after first gear too where I don't want to. Getting around that and using the main spark table would require an electronic boost controller with MAP sensing capabilities and boost by rpm control. That's like a $600 solution though.

It's a long bed 2wd pickup. I have a list of stuff I can do for more traction(caltracs, better boost control, ballast, relocating batt and fuel tank, etc...) but it's not regularly used at the track. I just go there and make runs to tune and have actual proof of how fast the truck is if i go to sell it ever. I just want a quick button to steal 100hp and torque from the engine...if its safe and possible.

Also, because I spray water/meth i didn't want to do the IAT mod because I have the IAT table setup to yank tons of timing if the water/meth injection pump fails so I don't want to send an artificial signal to that table. The ECT table might be an option...