PE question

[maxgee]

From the factory the setting to kick in PE is at 5k rpm and ramps in slow. This would mean the commanded AFR be shooting for 14.7 until it reaches 5,000 rpm. Would that not mean more hp is being obtained until is reaches the PE AFR, as 14.7 is on the lean side of things.

[Quoll]

Nay, that 5000 PE Delay is not the point at which it enters PE.

Entering PE is conditional on the factors at the top and the throttle percentages in the Hot (and possibly cold) tables.

[schpenxel]

From the factory the setting to kick in PE is at 5k rpm and ramps in slow. This would mean the commanded AFR be shooting for 14.7 until it reaches 5,000 rpm. Would that not mean more hp is being obtained until is reaches the PE AFR, as 14.7 is on the lean side of things.

Peak horserpower is not typically at 14.7:1

[jtrosky]

I've been wondering about PE parameters myself. My 2012 Impala (3.6L LFX) comes form the factory tuned to not go into PE until 95% torque and 90% pedal!

How is it that a stock tune stays out of PE so long? I've always read that PE is there to avoid damage to your motor. Yet the stock tune basically only uses it until 100% throttle...

Does direct-injection change things at all (the LFX is direct-injected)? Or is it tuned that way mainly becuase it also comes stock with "Piston Protection" enabled as 3800 RPMs?

Just trying to understand why PE is tuned so "high" from the factory if it's so important to engine safety (most people seem to bring PE in at 50%+ throttle, with Torque% set very low so that the pedal is the main driver)...

[schpenxel]

Most people are idiots and go with whatever they read on the internet. Don't worry, I'm one of them too

Lots of GM trucks don't go into PE until you've been WOT for quite a while.. so it's not like things explode as soon as you don't add more fuel

It really just depends on the setup.. yes running richer does leave some fuel behind that can help cool things off, but it's not like things spontaneously explode on STOCK or close to stock setups running reasonable ignition timing. I've seen the math behind the "cooling" factor and it's not nearly as much as you'd think.

Once you start increasing cylinder pressures from whatever mods then you have to be a bit more careful

Running 12psi of boost on a stock bottom end that was meant for NA? Yeah, you want some extra fuel on something like that

Running NA on a totally stock setup that already has the timing fairly low from the factory? Good luck hurting that via AFR changes

[jtrosky]

Ok, thanks - I appreciate the info. Even the V6 Camaros with the same engine use the same PE parameters in the stock tune (95% torque, 90% pedal). But like you mentioned, most people seem to think that you need to bring PE on much sooner. I started comparing tunes between non-direct-inject and direct-injected V6's and PE seems to be brought in much earlerier on the non-direct-injected V6s.

The the same 3.6L engine in port-injection form (LY7) brings PE in a lot sooner. Which is why I was wondering if the difference was due to direct injection or not. Maybe it's just a difference between the older and newer style ECM's too (newer being torque based)?

Just thought it was kinda strange how differernt PE was tuned between the different motors. But, I figured that if it's safe enough to be in the stock tune, I shouldn't need to worry about it! :-)

Thanks again - I appreciate the feedback (hard to get feedback on the V6 forums!).

[schpenxel]

I don't know enough about the direct injection engines to say much about those. I know they are usually ran a good bit leaner than people are used to. If you run them too rich and get misfires you can wash the oil off the cylinders quick and the resulting piston/cylidner failure will look like it was lean but it was actually rich.

Peak power (on non direct injection engines) is usually around 12.5:1, so you also pick up some power by bringing it in earlier, at the expense of fuel mileage and being in open loop without any fueling corrections more often.

I honestly wonder why GM does things so differently on different cars sometimes.. I guess it's just different engineers/groups for different vehicles so they do things differently

[5FDP]

I always bring PE in quicker on trucks for that reason, to bring power in sooner. The stupid delays make it such a slug off the line and fuel mileage is the last of my worries when I'm giving it the business. If I can crack 19-20mpg on the open road and get 15-18 combined in the summer, thats good enough for me.

[schpenxel]

Yeah my truck is a pig until it goes into PE.. moving it earlier made a huge improvement on it. Though just thinking out loud I think the AFR spark adder table is still stock on it, so it's adding some timing at the same time.. that's probably why it's so noticeable on mine

I'm at like 16mpg right now on it right now.. I usually to randomly get 18-19 but haven't figured out why

[5FDP]

I got 11 last tank, yay winter. Sub zero temps ftw?