Extremely low O2 switch points for LT1

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07-01-2014
Maxzillian

Extremely low O2 switch points for LT1

Here's a brain teaser for some of you guys. I have a fuel injection conversion on my 85 C-10 that is using a 96-97 LT1 PCM with a 350HO crate engine and TPI intake. It has long tube headers with the O2 sensors installed after the collectors and a bung for a wideband at the X-pipe that follows shortly after. Tuning software is Jet DST and ScanPro XL for datalogging. The wideband is an Innovate LM-2.

In tuning this truck I found that I had to lower my O2 switch points (or swing points) to as low as .05-.1 volts in order to make the wideband register 14.5-14.7:1. I've verified that the O2 sensor heaters are working and both banks register the same as far as datalogging is concerned. I've thought about air leaks, but I would think the wideband wouldn't disagree with the other sensors if that were the case.

Running the stock settings of around 0.3-0.5 volts would register around 12.5-13:1 on the wideband... great for power, but poor for mileage. Commanding WOT from the truck has the O2 sensors registering around 0.85-0.95 volts as one would expect.
07-02-2014
lionelhutz

You don't change the switching point to change the AFR the engine runs at. You change the VE and MAP tables.
07-02-2014
Maxzillian

Quote:

Originally Posted by lionelhutz

You don't change the switching point to change the AFR the engine runs at. You change the VE and MAP tables.

I think you're ignoring closed loop operation. When I tune the VE map per the long term fuel trim that is controlled by closed loop operation and those switching points, the engine ends up running around 12-13:1 while cruising. I looked at the tune again last night while doing some other work and found the switch points are currently around 0.15 volts, not 0.05-0.1 as I reported initially.