Thread: Removing rear O2 sensor on 01-newer PCMs -- Things you should know

Keep it friendly.


Open loop is great, I run it but you really should own a wideband sensor and a way to adjust the tune if necessary. If you're already reading this topic or in this section, most people already have a tuner and may only need a wideband.

The 16.4 trims could be a number of things, even evap will play tricks with you.

Originally Posted by darkhorizon

I dont see any reason to get involved with a open/closed loop discussion.... But my suggestion is someone used to OBD1 / map sensor setups would probalby find it is much easier to run open loop on a maf sensor.

What are you implying? I've tuned hundreds of OBD2 PCMs so I don't see what your point is.

As far as the "different climates" and "some guy came in with a bad open loop tune" goes... I have never had issues with temperatures, elevation change, humidity, or anything hurting any of the 15+ cars I have put on open loop.

That you know of. Do all those people who's cars you've locked into open loop check the status of their tunes on a daily basis to see how well that open loop tune is matching up?

2 of the fieros I have done in michigan were shipped out to moutian areas, one in PA the other in colorado... both with widebands and they both know how to use them, neither have had to adjust their tunes...

Like I said before, if the customer has the ability to adjust the tune themselves and wants to keep a constant eye on it, then giving them a "locked in open loop tune" is certainly a "choice". However, I don't think I would base all of my reasoning on just 2 instances where it appears to be "working". I bet any other tuner could take a look at how these 2 cars you speak of are running with their open loop tunes and find something off in those tunes.

Also every open loop tune I have done will command no more fuel than about 15.1 in most cases, and at cruise it usually averages a 16:1 air fuel....

That's good on the valves and the valve seats.

Also, professional tuners like ourselfs have a few other tricks that we normally do to enhance closed loop operation with bigger cams... The laymans out there reading the stupid "tuner guide" are just going to throw a pile of crap at their maf and hope for the best.

I tune everything so the fuel trims operate within a reasonable range of as close to 0% as possible. I try to leave the closed loop and fuel trim learning enabled in all my tunes so the PCM has the ability to adjust for changing conditions. And conditions do change. I've seen it happen countless times on stuff that has been here at my shop and on scan logs customers have emailed me. While the fuel trims ultimately don't change all that much (over the year, as the weather changes), they do change some. And I would rather allow the PCM to have the ability to make the adjustments it needs rather than to just allow the engine to run stupid lean while going down the highway. Forcing overly lean AFRs on the engine for extended periods of time is not good practice if you want your engine to last; especially at the loads it is subjected to run under when cruising on the freeway.

Of course if you don't care about changing engines every year or two because you can find them for $100 at the junkyard (and you don't mind wasting a weekend to swap it out), then I guess engine durability is of little concern. How many engines have you tuned that have blown head gaskets, chucked rods out of the side of the block, or otherwise failed? Be honest...