mmaker

Picture this...
A fellow goes with his buddy to do some dyno tuning.
Intelligent buddy wires car with a $4,000 air fuel meter, special O2 sensor, scanner, and other assorted tuning tools i will leave to your imagination.

Despite having built this car on a budget over the next x hours these two guys manage to squeeze out tremendous power from this 355 small block chevy. I am talking AWESOME hp and TQ. Both guys are very happy and quickly disconnect all the tuning crap and re-insert the stock O2 sensor and rush home to tell their wives how much power they have found in the microns of chipland.

My question...during the tuning session...the engine was NOT receiving O2 sensor feedback and therefore was not adding or subtracting fuel via long term fuel trim calculations. It was reacting to whatever was being programmed/emulated at the time.

The minute the stock O2 sensor went back in the exhaust header - the engine started to adjust fuel back to 128/128 thereby negating all the effects of tuning - yes or no?

Or are y'all gonna tell me that since the runs were all WOT runs that the ecm does not use/need O2 feedback???

Sorry if this is a dumb question but i am still learning.

Going a step further if i am targeting specific afr's then do i really care if the o2 gives any feedback to my ecm. Shouldn't i just unplug that o2 and run without it and rely on the tables i have spent so much time perfecting and on my buddies $4,000 afr measurement equipment. This is supposedly what we pay the big bucks for wether our car is custom tuned by ourselves/other experts or wether we (perish the thought) order a chip.

I am assumming if the ecm does not receive o2 input it will not try to correct to stoich afr of 14.7.

My target is not 14.7 but something different. I am not sure what "something different" is but it is max hp/tq and i don't want the computer to second guess what i am trying to achieve - otherwise what is the point?

David

TRAXION

Yeeeup. That's exactly what I am telling you. The BLMs are locked at WOT because the car is in Open Loop. Thus, BLMs can't be used for tuning WOT ... which makes a lot of sense anyhow because the O2 sensor is not accurate at those AFRs.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

hectorsn

Maker, you're too concerned with WOT. All you want to do is tune WOT. Ask yourself this: how much time do you spend in WOT? This is the reason why you want to adjust part throttle tuning *first* and then move on to WOT. The $4K O2 sensor you speak of is a useful tool for tuning and especially for WOT. The stock O2 is helpful for the AFR it was intended for, 14.7 or stoich. If you get part throttle tuned first you will have a nice drive over to the dyno to tune WOT. If not, then after you tune for power you will drive home with the same performance you had before the tuning just that WOT power will be what it was on the dyno. If you don't understand what is being said you need to forget what everyone has told you and relearn the truth by going through the archives and reading everything and go to all the links in the prom intro post. There are lots of intelligent and trustworthy people on this board that are here to help you for no other reason than to further the DIY section of the aftermarket. In other words, they do this for nothing. Listen to what they have to say. Anyone else is basically trying to sell you something.

Grim Reaper

If you use Tunercat to graph your VE tables (assuming you have tuned them close to 128/128), you will notice that the graph has a specific shape that is maintained through out specific load ranges. It does not have one shape and then (@ WOT) take on a completely different shape.

By getting your VE tables very close through out the lower ranges (it is easy to get it up to 80 kpa) you can extrapolate the shape of the graph to the higher Load Values. This will get your very close to the ballpark so you just have to tweak your Power Enrichment change to the Fuel for WOT (doing some runs and basic analysis of your spark plugs and monitoring your knock retard/counts). And if you are a real junkie for power, you can even go to a dyno to tweak it for max HP. (Though what is BEST for a dyno is not necessarily the BEST for the strip...two different operating conditions).

But, by tuning for Part Throttle first, you will have an excellent starting point that makes tweaking the WOT a lot easier.

If you do it the other way (WOT first), you may get max HP, but have not done ANYTHING to your part throttle. If you start to tweak that, you just screwed up your WOT tuning and have to re-do it anyways.

Lastly, if you should want to invoke Highway Mode to save some gas while you cruise, it requirs a good part throttle table to work properly. I initially tried invoking Highway Mode BEFORE I tweaked my part throttle VE table, and I found I burnt MORE GAS in spite of my supposed "leaner" AF ratio. The reason is that Highway Mode relys on the tables to maintain the requested AF Ratio. If those tables are too rich, you may actually cause the ecm to give it too much gas as the ecm no longer uses the O2 sensor to maintain 14.7:1. Conversely, if you are too lean, you may go leaner than you intended.

Lastly, it seems you are hell bent on trying to make your engine to go to a specific AF ratio. This is not the best way to tune an engine, though it is not a bad way to initially START your tuning. By having your VE tables 128/128 perfect, you will know that you are 14.7:1. By using the PE Change to Fuel, you can then calcutate how much fuel you would want to add to get say 12.7:1 as your starting point. Then you can tune to what the engine REALLY wants after that.

TRAXION

Whooop, there it is.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

Ed Maher

What about the twin to that song, whoomp! there it is...boy that was a confusing summer

mmaker

I trust you guys - that is why i am here - to learn. Thanks for your feedback. All of you (Tim, Glen and Hectorsn).

I am concerned with tuning at all rpm and load ranges. (Blew up one motor already due to detonation so you don't have to impress upon me the importance of a properly tuned motor. I am trying to make sure i get it right the next time or my wife won't let me live it down. Besides i used up all of our cash already.)

I was just testing the theory that once an engine is tuned with an external sensor that once the stock sensor is re-inserted the ecm will start re-adjusting via Long term fuel trims.

What i am hearing is that this will happen for part throttle tuning but won't impact WOT throttle tuning.


Wife is calling me again - bye

dave

hectorsn

[QUOTE]Originally posted by mmaker:
I was just testing the theory that once an engine is tuned with an external sensor that once the stock sensor is re-inserted the ecm will start re-adjusting via Long term fuel trims.

What i am hearing is that this will happen for part throttle tuning but won't impact WOT throttle tuning.

OK, an external wide band O2 is used to get the actual AFR at WOT due to the fact that the factory O2 is not trustworthy at anything other than 14.7. I don't believe that at this time anyone has been able to run a WBO2 with GM hardware. If and when this is accomplished you will always be using the WBO2. Therefore, as of right now, you will not have to do any changing of the O2 after a WOT tuning session as the factory O2 will always remain in place. The external WBO2 will have to be monitored by something other than a scanner hooked up to the factory ECM. Usually a dyno facility will have the means to do so. As Glenn stated, you make a dyno run, evaluate the data (not from the ECM), and add PE until you get the AFR you wish. PE is extra fuel that is added to the VE table. Again as Glenn stated, this is why it's important to get the part throttle tuning right first. It makes life easier and will redude the risk of catastrophic engine failure, which by your own words is highly diserable.

Bobalos

If I might add my2c. I think that we have established for the most part that what you thought is in fact right. Tuning with the WBO2 is great & now this car is Super, Duper happy @ WOT. It will NOT make any more HP than it is making now. (provided they tuned for HP & not AFR, the "best" AFR is most likely not going to give the best HP).

BUT, Now you have the stock O2 sensor in it & you are putting along to the store (or to the track etc). this same car just might very well run like total garbage cause it is now running in CL & the ECM IS now paying attn to the O2 sensor. Now you are in trouble. the car might be pig rich or chop stick (sp) lean. In which case you might very well be beating the heck outta the pistons, cause the VE tables are still wrong.

Now you are sitting there saying, I gotta fix this up it is just UN-SAT. now you start tweeking on your VE table to get the car to run decent & what do you know, ALL your tuning @ WOT is now out the window cauase the PE is based on the VE table.

How do i know this? this is the road that I am on right now. the car runs pig rich all the time & I am getting 10 mpg with a car that ought to be getting 20. BUT it runs pretty well @ the track (12.8 last time out, NA). what to do? for me I have two bins, the one that I am working on (slowly i might add) to get the car right & the one that I put back in when I am off to the track.

start @ the beggining & when you get to the end you will be VERY happy. If you want to cut across you can but now you have to live with something that might not be what you wanted. this is more of an application call than anything really. I really dont drive the car on the street any more, but I want it right anyway, so.......

BW

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Bobalos
aka Bob W.
www.r71camaro.homestead.com
r71chevy@earthlink.net
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