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Headlight Restorer
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1,108 Posts
Discussion Starter #1 (Edited)
Hello all,:wavey:

I tried to street tune my car today since I never had a chance to do so since I went single four months ago.(due to lean spot on OBD I) I did the OBD II conversion and I was in 10:0's all day! woohoo time to tune.

here's my setup:
BL61 kit with stock fuel, and stock auto tranny and stall.
VPC/SAFC II
OBD II conversion(due to leanspot)
at 1.1 bar on 93 pump gas
AEM wideband UEGO

Just like you would tune on a dyno, I went WOT in 3rd gear and tried to tune around mid 11's. Well, after couple of WOT in 3rd gear and adjusting the SAFC II, I got it to close where I want in 3rd gear which was 11:3-11:7. Then, I went WOT in 1st and 2nd gear and holy SHIT! my a/f ratios were around 13:? to 14:?!!!!!! especially in 1st gear. 2nd gear, it was like 12:3-12:5

This might sound like a total noob question but.......aren't you supposed to tune based on 3rd gear pull? I was expecting the 1st and 2nd gear a/f ratios would be similar as 3rd and 4th gear pulls but damn was I wrong. I got worried about it and gave it more fuel with safc II and made 3rd gear WOT a/f ratios to be in low 10's. now the 1st gear stays in mid to high 12's and sometimes low 13's.

I was just wondering.........as long as the 3rd and 4th gear pulls are around mid 11's, is the car going to be okay/safe?(is this how you tune it for the streets?) or am I doing the whole thing wrong? What would be a conservatively tuned a/f ratio be for the streets with pumpgas?(1.1bar)
I feel really like a noob, but hey everyone has to start from somewhere!

Thanks in advance.
JP
 

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Registered
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244 Posts
What are your HI/LO throttle settings ?
What position are the knobs on the VPC ?
 

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Headlight Restorer
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1,108 Posts
Discussion Starter #4
What are your HI/LO throttle settings ?
What position are the knobs on the VPC ?
Thanks for your reply,

LO=10%
HI=50%

and all of the VPC knob positions are 12 o clock.

thanks,
JP
 

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Registered
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244 Posts
Try

LO 69
HI 70

VPC settings should be ok. You cannot tune anything below 4k rpm because it is in closed loop and you will be just fighting a loosing battle with the ecu.
 

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Wingless by choice.
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640 Posts
Shouldnt your high/low be right after each other, IIRC? My s-afc is 69% Lo and 70% Hi. ?
 

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Headlight Restorer
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1,108 Posts
Discussion Starter #7
Try

LO 69
HI 70

VPC settings should be ok. You cannot tune anything below 4k rpm because it is in closed loop and you will be just fighting a loosing battle with the ecu.
I will give that a try. but what will that exactly do?

thanks,
JP
 

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Wingless by choice.
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640 Posts
IIRC if you have the lo set to anything under 69% the ecu will try to correct it over and over again no matter what your settings are, therefore, the ecu trying to get a stoichometric reading from the 02 sensor by changing fuel/timing thoughout the rpm band through each gear, thats why your af's are so jumpy. Try the 69% lo and 70% hi and you should be golden. You want the hi setting to be the next number up so it steps over @ the right time, otherwise I'm sure the ecu would take over between the crossover of hi-lo if you had it, say 5% apart such as lo-65% hi-70%. So you want it to crossover completely to get your fuel settings going right then and to your tune instead of what the computer wants. Basically you can only change in open loop mode. Anyone else? amirite?!
 

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Registered
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IIRC if you have the lo set to anything under 69% the ecu will try to correct it over and over again no matter what your settings are, therefore, the ecu trying to get a stoichometric reading from the 02 sensor by changing fuel/timing thoughout the rpm band through each gear, thats why your af's are so jumpy. Try the 69% lo and 70% hi and you should be golden. You want the hi setting to be the next number up so it steps over @ the right time, otherwise I'm sure the ecu would take over between the crossover of hi-lo if you had it, say 5% apart such as lo-65% hi-70%. So you want it to crossover completely to get your fuel settings going right then and to your tune instead of what the computer wants. Basically you can only change in open loop mode. Anyone else? amirite?!
You are correct sir. I have been PMing JP about his problem. He says he still has a problem with holding steady A/F ratio in all the gears.
 

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Boost Junkie
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12,625 Posts
That doesn't make much sense. If anything you should be richer in 1st and 2nd since the load on the engine is less in those gears.

Steve
 

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The need for speed
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1,653 Posts
I've seen this issue too with VPC/AFC cars. Always leaner in 1st and 2nd compared to 3rd and 4th. That's why I run the AEM now, but that's besides the point. If lo-throttle is on 65% and hi-throttle is on 70%, then the AFC should take the average of the values between that range. At least that is how I understand it. Maybe this applies only to the s-AFC2
 

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Headlight Restorer
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1,108 Posts
Discussion Starter #12
thanks for all your replies you all. I still havent have a chance to set her at 69% LO and 70% HI and test it out. I will be doing this tomorrow and keep you guys updated.

The last thing I want to do is to change out the fuel management system.
well, wish me luck.
Thanks,
JP
 
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