A quick look at Vf1 values while cruising. Does this sound ok?

Suprapowaz!(2)

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Apr 10, 2006
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I hooked up a voltmeter to Vf1 & E1 pins in the diagnostic block. Once the car warms up the voltmeter reads 3.5v. So that looks normal. While cruising around it reads 5v (4.97) in all gears & all RPM ranges while not in boost. Anytime I touch the throttle it reads 5v wether I'm barely touching the throttle or WOT. It does this from off idle to 5000rpms off boost. I haven't look at what it's doing while under boost. I don't have my wideband hooked up yet so I don't know what my AFR's look like at the moment. So from what I understand i'm running lean and the stock ECU is trying to richen it up?

7mgte stock shortblock
550cc fuel injectors
Walbro fuel pump
stock fpr and pressure
Lexus AFM screw all the way in
new 1990 Mustang three wire Delphi O2 sensor.
 

Suprapowaz!(2)

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A little more on this. Once again, at idle with the Lex AFM it'll sit at 3.5v for a little while. Then it will move over to 5v while still idling. Anytime I touch the throttle it'll hold 5v throughout the RPM range.

I then took off the Lex AFM and put the stock AFM housing back on. 3.5v at idle and throughout the RPM range. The only time it'll spike to 5v is when it drops back down to 600RPM for an instant. It then corrects itself back to 3.5v. All of this was tested in nuetral sitting in the garage. I'll take it on the road maybe later this evening, or sometime tomorrow morning and see how it behaves.

Again, I don't have my wideband hooked up just yet so I don't know what the AFR's are doing.
 

destrux

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May 19, 2010
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Wait for the wideband. It's helpful to use the VF1 learned fuel trim output to get the fuel trims "centered" and to check the stock O2 sensor to see if it's working properly but for any sort of tuning or A/F readings you're better off just using the wideband.

I also believe you're using the VF1 terminal incorrectly for your idle reading (I could be wrong though). I'm not going to rewrite it, so I'll copy/paste where I found my info for the VF1 usage.

http://alflash.com.ua/vf1.htm
 

GrimJack

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Also, keep in mind that a 5v or 0v reading on vF doesn't necessarily mean your engine is running way outside of it's regular values - what it means is your ECU *thinks* it's running outside of parameters, and is attempting to correct it by as much as it is allowed. There is a significant difference.
 

CajunKenny

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Nov 15, 2007
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It is normal to see Vf fluctuations. The ECU manages closed loop operation and will keep your engine safe in that condition.

It is NOT recommended to use Vf values for tuning open loop operations.
 

Suprapowaz!(2)

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Ok, today I went cruising around the neighborhood with the stock AFM on. All driving was kept under boost. Once the car warmed up I was getting 3.5v throughout the RPM ranges in all gears. When I came back home and parked it I was seeing 2.5v at idle. I think the stock ECU is happier with the stock AFM vs. the Lex AFM. It didn't have to work as hard to mantain its happy place. Since I'm only running 8psi at the moment I think I'm going to stick with the stock AFM. That Lex AFM with the unmetered air makes the ECU wanna fatten it up all the time. At least off boost it does.