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14.7 AFR at WOT on a 96LT4 ?

 
Old 07-17-2001, 03:52 PM
  #21  
ChrisB
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14.7:1 is stochiometric - where you theoretically have 14.7 molecules of air for every molecule of fuel - so you can get a complete burn. Around here is where fuel economy is the best (or pretty close - some lean burn honda engines run at 16:1).

Now at WOT you really don't want to run 14.7:1 for a couple of reasons

1) It is to lean. You are going to kick up your cylinder temperatures tremendously and very likely get pre-ignition/detonation.

2) It doesn't make as much power - you are never going to have perfect a/f charge distribution, and since air is the limiting reactant (we can put as much fuel in they cylinder as we want, it's air that's harder to get in there) we want to make sure we burn all of it. So we spray in extra fuel, which cools down the mixture at the same time ensuring all the air is combusted. NA you will find max power from 12.9-13.3 : 1 approximately


If the computer ever leaned out the mixture continuously to 20:1 the effects would be more akin to a blow torch on top of your pistons than anything else!

As for what the computer does, look above in his log. The "A/F Ratio" indicated is "Desired A/F ratio" and what the computer *thinks* it is commanding. Stock it's generally around 12:1. You are only at 14.7:1 during part throttle closed loop operation.



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Old 07-17-2001, 10:05 PM
  #22  
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I was wondering about a couple of things on the HPP powerscan readout.
1: Doesn't the PCM go into Open Loop at WOT?
I noticed Vince's readout was still showing closed loop.
2: I ran my Powerscan a couple of times but never actually checked O2 output at WOT. I did notice that my spark advance was in the 40 deg. range at low RPM. And at close to WOT was still in the 38deg. area. without any retard from Knock sensor.
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Old 07-17-2001, 11:50 PM
  #23  
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In GM terminology you aren't in open loop at WOT, but learning is disabled. Effectively it's the same thing (O2 input is disregarded) the main difference is long term fuel trims can still be applied (if you were running lean before) as a base correction.




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Old 07-18-2001, 04:19 AM
  #24  
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Tell the dyno dude to put the wide band in front of the cats! Then you'll have a really usefull reading. Also, how 'bout the old tech-read the plugs. It does still give you a good idea....



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Old 07-18-2001, 05:40 AM
  #25  
vim LT4
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Here are more numbers to look at.
I basically did the same thing as the first time but with a completely stock computer.

two runs: 2nd gear, WOT from around 1000rpm to 6200+, two different sets of values recorded from the computer through the PowerScan.

Results (sorry for the length):

TIME____RPM____AFR____Retard____Spark___ _Loop____TP(%)____
_______________(:1)____(Deg)____(btdc)__ _________(%)____
0.00_____1070____14.7_____0_____35____Cl osed_____17____
0.10_____1147____14.7_____0_____24____Cl osed_____50____
0.20_____1115____14.7_____0_____13____Cl osed_____91____
0.30_____1231____12.3_____0_____13____Cl osed____100____
0.40_____1347____12.2_____0_____14____Cl osed____100____
0.50_____1416____12.2_____0_____16____Cl osed____100____
0.60_____1515____12.1_____0_____19____Cl osed____100____
0.70_____1619____12.0_____0_____20____Cl osed____100____
0.80_____1729____11.9_____0_____21____Cl osed____100____
0.90_____1820____11.8_____0_____23____Cl osed____100____
1.00_____1931____11.7_____0_____25____Cl osed____100____
1.10_____2035____11.6_____0_____26____Cl osed____100____
1.20_____2122____11.6_____0_____27____Cl osed____100____
1.30_____2244____11.6_____0_____29____Cl osed____100____
1.40_____2346____11.6_____0_____31____Cl osed____100____
1.50_____2487____11.5_____0_____31____Cl osed____100____
1.60_____2562____11.4_____0_____32____Cl osed____100____
1.70_____2716____11.1_____0_____33____Cl osed____100____
1.80_____2777____11.0_____0_____33____Cl osed____100____
1.90_____2888____11.2_____0_____34____Cl osed____100____
2.00_____2985____11.4_____0_____34____Cl osed____100____
2.10_____3147____11.6_____0_____35____Cl osed____100____
2.20_____3262____11.7_____0_____35____Cl osed____100____
2.30_____3325____11.7_____0_____36____Cl osed____100____
2.40_____3457____11.7_____0_____36____Cl osed____100____
2.50_____3575____11.7_____0_____37____Cl osed____100____
2.60_____3619____11.6_____0_____37____Cl osed____100____
2.70_____3710____11.6_____0_____37____Cl osed____100____
2.80_____3886____11.6_____0_____38____Cl osed____100____
2.90_____4012____11.6_____0_____38____Cl osed____100____
3.00_____4029____11.6_____0_____38____Cl osed____100____
3.10_____4237____11.6_____0_____38____Cl osed____100____
3.20_____4324____11.6_____0_____38____Cl osed____100____
3.30_____4415____11.6_____0_____38____Cl osed____100____
3.40_____4551____11.7_____0_____38____Cl osed____100____
3.50_____4565____11.7_____0_____38____Cl osed____100____
3.60_____4741____11.7_____0_____38____Cl osed____100____
3.70_____4795____11.8_____0_____38____Cl osed____100____
3.80_____5024____11.9_____0_____38____Cl osed____100____
3.90_____5050____12.0_____0_____38____Cl osed____100____
4.00_____5041____12.1_____0_____38____Cl osed____100____
4.10_____5016____12.2_____0_____38____Cl osed____100____
4.20_____5238____12.2_____0_____38____Cl osed____100____
4.30_____5343____12.4_____0_____38____Cl osed____100____
4.40_____5441____12.4_____0_____39____Cl osed____100____
4.50_____5421____12.4_____0_____39____Cl osed____100____
4.60_____5682____12.3_____0_____39____Cl osed____100____
4.70_____5523____12.2_____0_____39____Cl osed____100____
4.80_____5817____12.4_____0_____39____Cl osed____100____
4.90_____5934____12.2_____0_____39____Cl osed____100____
5.00_____5886____12.0_____0_____39____Cl osed____100____
5.10_____5994____12.1_____0_____39____Cl osed____100____
5.20_____6157____12.0_____0_____39____Cl osed____100____
5.30_____5994____12.1_____0_____39____Cl osed____100____
5.40_____6275____12.1_____0_____39____Cl osed____100____
5.50_____6222____12.1_____0_____39____Cl osed____100____
5.60_____6383____12.1_____0_____39____Cl osed____100____
5.70_____6288____12.2_____0_____39____Cl osed____100____
5.80_____6275____12.1_____0_____39____Cl osed____100____
5.90_____6482____12.2_____0_____38____Cl osed______0____
6.00_____6093____14.7_____0_____38____Cl osed______0____
6.10_____5543____14.7_____0_____37____Cl osed______0____


TIME____RPM____AFR____Ho2S1B1____Ho2S2B1 ____Ho2S1B2____Ho2S2B2____
_______________(:1)____(mV)________(mV)_ ______(mV)_______(mV)____
0.40_____1007____14.7_____47____616_____ 31____702____
0.50_____1052____14.7_____31____420_____ 20____690____
0.60_____1131____14.7_____31____184_____ 20____627____
0.70_____1176____14.7_____31_____98_____ 27____180____
0.80_____1272____12.3____698____149____7 53____349____
0.90_____1381____12.2____655____341_____ 75____427____
1.00_____1469____12.1____118____369_____ 78____459____
1.10_____1577____12.1____192____400____7 18____494____
1.20_____1669____11.9____557____427____5 10____522____
1.30_____1781____11.9_____94____431____5 06____533____
1.40_____1886____11.7____314____443____4 47____541____
1.50_____1965____11.7____557____471____6 04____549____
1.60_____2070____11.6____718____486_____ 98____553____
1.70_____2181____11.6____129____478____6 04____561____
1.80_____2281____11.6____663____506_____ 90____561____
1.90_____2378____11.6____537____502____6 04____565____
2.00_____2536____11.4____141____506____6 90____569____
2.10_____2612____11.3____663____529____6 35____580____
2.20_____2764____11.1____718____537____6 98____592____
2.30_____2872____11.2____643____537____6 71____600____
2.40_____2979____11.2____608____529____2 35____588____
2.50_____3078____11.5_____78____486____1 45____580____
2.60_____3185____11.7_____98____478____1 14____576____
2.70_____3213____11.7____482____506_____ 78____557____
2.80_____3409____11.7_____86____475____5 84____522____
2.90_____3465____11.7____749____506____5 29____506____
3.00_____3557____11.7_____94____482_____ 71____435____
3.10_____3705____11.6____502____502____5 57____518____
3.20_____3771____11.6____651____506____1 57____510____
3.30_____4007____11.6____392____510____4 94____525____
3.40_____4040____11.6____141____525____6 59____510____
3.50_____4073____11.6____592____525____7 25____490____
3.60_____4207____11.6____745____541____5 57____514____
3.70_____4475____11.6____710____537____6 75____522____
3.80_____4475____11.7____714____533_____ 63____412____
3.90_____4587____11.7____710____522_____ 82____373____
4.00_____4601____11.7____694____510____1 80____384____
4.10_____4795____11.8____651____502_____ 86____361____
4.20_____4867____12.0____576____502____3 18____361____
4.30_____5041____12.0____698____510____6 90____467____
4.40_____4999____12.0____137____475____1 80____314____
4.50_____5147____12.1____161____490____4 43____380____
4.60_____5165____12.2____251____447____5 41____361____
4.70_____5266____12.2____710____353____4 47____290____
4.80_____5482____12.4____306____416____4 51____349____
4.90_____5461____12.5____329____443____5 80____349____
5.00_____5575____12.4____749____471____1 18____384____
5.10_____5607____12.3____271____467____4 39____435____
5.20_____5738____12.2____620____490____7 02____471____
5.30_____5760____12.2____624____490____6 71____471____
5.40_____5946____12.0____663____502____7 06____486____
5.50_____6043____12.0____624____510____3 14____475____
5.60_____6068____12.1____584____506____4 90____455____
5.70_____6081____12.1____463____502____2 47____443____
5.80_____6183____12.1____776____565____8 20____631____
5.90_____5994____14.7____251____675____6 04____729____
6.00_____5304____14.7____557____702____6 51____749____
6.10_____4764____14.7____553____718____6 12____757____
6.20_____4496____14.7____412____725____5 92____761____
6.30_____4448____14.7____663____722____7 57____757____
6.40_____4356____14.7____153____725_____ 35____757____
6.50_____4337____14.7_____16____714_____ _8____745____
6.60_____4262____14.7______8____671_____ _4____725____
6.70_____4171____14.7______8____208_____ _4____710____
6.80_____4231____14.7______8_____75_____ _4____180____


The air temperature was slightly lower (85 instead of 95, it was later in the day) and I had my lights on (more drag and more electrical power used, if that makes any difference). Engine temperature was slightly higher (205 instead of 190) because of the fans triggering at a much higher temp with the stock program.

It looks like those numbers could feed the debate a little bit


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Old 07-18-2001, 06:53 AM
  #26  
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It looks to me like you are running very lean still - unless your stock O2's are old or worn out! When you just drive around what are you s-trims or l-trims like? (your block learns and integrators - don't know which terminology hypertech uses?).

Also, have you had a chance to check your fuel pressure yet?



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Old 07-18-2001, 10:45 PM
  #27  
vim LT4
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Originally Posted by ChrisB
Also, have you had a chance to check your fuel pressure yet?
[/color]
Not yet, I'm still waiting on my fuel pressure gauge..


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Old 07-21-2001, 02:34 AM
  #28  
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Mez,

I was just about to comment the very same thing, it looks to me that since the rpm's are dropping the AFR is returning to normal since earlier in the run they appear normal at like 6 grand...

BTW I'm an engineer as well... electronics not that it make a difference in anything..

I ran Autotap on my car as well and had very similar readings it would drop to about 11.8 at 5100 rpms and soon as i let up on the throttle it was right back to 14.7.

I didnt look at the mv readings on the o2's... it is interesting the significant drop ..but all that asdie they look fine to me as well

Just my 2 cents,

Mo

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Old 07-21-2001, 03:13 AM
  #29  
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Originally Posted by Mo_Bandy:
[B
I didnt look at the mv readings on the o2's... it is interesting the significant drop ..but all that asdie they look fine to me as well
[/B][/color]

Did you see my reply when the above question was raised? [img]http]//www.corvetteforum.cc/ubb/smile.gif[/img]

The AFR numbers indicated in the log file are CALCULATED, not actual afr numbers - they are what the computer *thinks* the AFR is, but could be off for any number of reasons. The wideband AF meter and stock O2's both indicate a seriously lean condition.


Chris Bennight



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Old 07-21-2001, 03:25 AM
  #30  
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thanks for the correction Chris,,, its a little late...heh

Actually it was a misprint on my part, The comment I was trying to make was that with the Autotap on my car , I didnt log the mv reading to give a relative comparison but the AFR looked fine to me and was in line with what my car preformance was.

Mo

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Old 07-21-2001, 10:59 PM
  #31  
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Vince I recorded my O2 sensor data and RPM on my powerscan. I Emailed it to you because I don't now how to post it here!
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Old 07-24-2001, 10:22 PM
  #32  
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I measured the fuel pressure today.

<UL TYPE=SQUARE><LI> engine off & cold: 43psi, 45psi when pump is running (this is after having let the pump run a few times and build pressure)<LI> engine at idle: 37psi<LI> blip from idle: goes up to 45psi,down to 35, and back to steady 37psi<LI> driving around at 3k RPM with NO gas: 35psi; part throttle from there: 40psi; WOT: 45psi, maybe around 46 when WOT around 5-6K<LI> stopped in neutral: part throttle from idle to 3k RPM and maintain it at 3K: pressure goes from 37 idle to about 40 at 3K, and then drops back to 37 (still going at 3k RPM), drops to 35 when I release the gas and goes back up to 37 at idle.
</UL>

Does it look right?

Also, Grndspt sent me his O2 Sensors data from his LT4, so I graphed it (red) along with my data (blue). Note that he started his run at around 1600RPM (mine was at 1200), and we both have the hypertech program installed at this point.

I don't know what the hypertech terminology is for O2 Sensors, but we have Ho2S1B1, S1B2, S2B1, S2B2. Don't know which one is which in reality. (I'm guessing it stands for Sensor1(precat) Bank1, etc.. I lost the manual)

Ho2-S1B1:


Ho2-S2B1:


Ho2-S1B2:


Ho2-S2B2:



I definitely run lean!

Vince.

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Old 07-24-2001, 11:00 PM
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Hmmm.... Very educational topic. Please let us know what turns out to be the source of the problem.

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Old 07-25-2001, 01:24 AM
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Yep, and your fuel pressure sounds like it is fine! The gauge is vacuum referenced, and the fluctuations you noted are normal (designed to keep the pressure drop from fuel -> intake constant, so when manifold vacuum goes up, fuel pressure goes down, and vice versa).

Though again I would caution against reading to much into stock o2's (it's an old habit ) from the data it's a clear cut case of being lean (the delta is large and constant enough to tell).

I would try borrowing a known good MAF sensor from someone else (and LT1 vette or f-body will work) - a stock one, (screen doesn't matter), and see what that does with your o2's.

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Old 07-25-2001, 11:25 PM
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Vince, I don't know if it would cause this type of problem,other members are probably more experienced,but have you checked your spark plugs AC41-943? I know 4 of mine out of the 8 were missing the platinum contact on the ground side! And I noticed after I replaced them with NGK TR55-IX plugs the car revved more easily at WOT! Just a thought again not sure it would lean with a larger spark plug gap(contacts missing caused over .065 gap).
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