PEvsRPm tables are WACKY in these things!

Same in OBDI and OBDII?

 

The PE vs RPM and PE vs coolant temp are the tables used to change the A/F ratio at WOT.

 

What seems wacky should be correct if in fact you are stock. These %changes should keep you at a correct AFR at that particular RPM. Now the ifs: stock, no calibration errors in MAF.

As for AFR at idle, this is set at 14.7 AFR. Now something to note is not the computer "thinks" 14.7 AFR, it just reads how "well" (for lack of a better term) the 02's bounce back and forth across the 450 mv threshold. Its the 02's themselves that determine the AFR at anything other than WOT. This is why you have cars with rich or lean conditions based upon bad 02's.

Also WOT is a misstatement (and I use it also). To be correct, Power Enrichment mode would be better as we go into PE mode other than wide open throttle.

Ben

 

Well, you can actually lean out the PE tables from stock to produce more power, the cars were originally designed to run richer in order to better stay within emissions regulations. The stock tables do work, but you can get more power from a leaner mixture. Just make sure you don't go too lean, or you will end up with not enough fuel and start getting knock. If you plan on playing with these tables, make sure you have a data logger available to check the changes.

 

Im very familair with tunign these cars, but mainly LS1, with an intuitive PEvs RPM numbers, thats relatively straightlined and you cna tailor the curve easily. I take %95 out of the PE for LT1 cars and does nada

 

Uh, I don't know what cars you are tuning, but if you take 95% of the fuel out of the RPM tables, your going to end up with knock. Too little fuel is a very bad thing at WOT. That's another reason why they are designed to run rich from the factory, to prevent detonation as well as keep emissions down. I do all my own tuning plus local area tuning, this is the same on all LT1 cars, from my bolton 94Z to my buddies 383 stroker.

 

Agreed. However, I was not commenting on what his current AFR was or what that AFR would do for him but only the fact that is it possibly correct. In other words, if the programming says it will run 12.0 AFR at a given RPM in PE, then that is in fact the AFR that is being produced.

Ben

 

For charging $100 per hr dyno time + LT1 edit buy in fees for the shop I figured you new how to tune these things buy now?? J/K

Good luck to you....If you could actually tune a LT1 Id might let you tweek with my PCM since it seems I'm running pig rich @ 1,100* WOT on the EGT

 

I had soem mixed results soem cars respond to what Im used to doing, some dot. Tryign to rope the ones that dont

Got 26 hp out of a stock LT1 with a cutout, cold air and converter though :P

 

Explain please, how running overly rich is gonna help the vehicle better stay within emissions regulations, or was that a misprint?

 

Not a misprint, that's 100% accurate. The greater amount of fuel at WOT keeps the combustion temperatures down, therefore lessing the production of NOx gases, similar to how the EGR system works (except instead of cooling by recirculating exhaust gas, this is adding more fuel for cooling temps).

 

No, I disagree, but with reservation. Yes, it is true a lowered combustion temp WILL lower NOx. However, I see that as an afterthought and of little importance (to GM), compared to the primary (read overriding) reason for it's implementation. The EPA wants (expects) cleaner air during engine operation, but sees 'issues' if that cleaner air will not allow reliable engine durability. That is why non compliance WOT is allowed.

If an emission issue, I.E., low NOx (limiting of combustion temps), was a concern or the primary purpose at WOT, the egr function would include WOT, along with CL operation. Because emission compliance was not a concern, it had no bearing on the decision to go overrich. No, from my POV, GM's primary concern is warranty work, spelled expense. The overrich condition deters detonation, and consequently possible engine damage. Sorta like an insurance policy. No surprises welcome. Without official mfr. info/data to state otherwise, I'll maintain that stance.

Had your post not included the phrase: originally designed to run richer in order to better stay within emissions regulations, I would not have had an issue with your post. Because of the reasons noted above, I consider that phrase untrue, cuz it (running richer) was originally designed to protect engine from parts damaging detonation.

 

I think you are picking at what I said. I was referring to the original A/F ratio before tuning, not that it was their primary goal when they designed it to run rich. GM designed it to do that for 2 reasons. To make sure that there was more than sufficient fuel to prevent detonation and therefore damage to the engine, as well as to keep NOx emissions down during WOT. If you will read my original post, it will also state that leaning out the mixture too much will cause knock. Both reasons are included in the post, and they were both used to determine the A/F ratio at WOT. If you want to be picky about it, then yes, detonation was the most important part of that. But I thought that was covered well enough in my original post without having to state it deliberately.

 

Not too concerned wwhat GM wanted the car to do, its what I want the car to do.

So... any good ways for idle?

 

At idle it is controlled by either the values in the Open loop A/F ratio when you are in open loop, or by the PCM reading the O2 sensors to try to make the A/F ratio 14.7 (stoich). Unfortunately, you have no control over it most of the time, since the only thing you can adjust are the Open loop A/F ratio tables. Closed loop is what you will be in most of the time, unless you set your car to only run in open loop (and unfortunately, there isn't any way to do this only for idle).