VEC2 Tuning?

[HOdbleFman]

I just installed a new cam as well as ported heads. Now I am trying to tune with the VEC2 and having some difficulties. I've got the diagnostics software and have been logging engine data as I'm tuning. The O2 sensor voltage at idle has been running extremely low indicating an extremely lean condition in closed loop operation. However, the long term fuel trim adaptives say that they are maxed out removing fuel. According to the instructions if the long term adaptives are negative, then you need to remove fuel trim. Doing this seems to not have much effect on the O2 sensor voltage or the trim adaptives. The car seems to run fine in open loop, but not so well in closed loop. It has a "miss" in it when the my laptop shows the fuel system in closed loop operation. Help please.

 

[Jack B]

At what rpm and vacuum is the miss and what scanner software are you using.

 

[HOdbleFman]

Jack, I was hoping you would respond to my post. I'm using the scanner software that Roe sells. I played around with the VEC2 settings some more after I posted this and have just about got it. I ended up trimming 1.66 ms off bank 1 and 1.75 ms off bank 2. It idles well now. The trim adaptives are now less than 8% and the miss is gone. It was late when I got to this point and I figured the neighbors wouldn't like it too well if I kept tuning driving around the neighborhood. It still smells a little on the rich side and when it goes to open loop under medium acceleration the a/f ratio goes to 12.5:1 according to the scanner software. I've actually got a copy of the VEC2 program that you and Rich worked on for his car. I figured it would be a good place to start with mine. I had to modify it for my use though. Greg Good did my heads and cam. I think the cam is a little bit bigger than the one in Rich's car. What should the a/f be during closed loop at idle? What vacuum should I have in the engine during idle?

 

[Jack B]

You cannot look at a/f under idle, the nature of the beast is that the a/f at idle is very cyclical. The average should be approx 15:1. A stock viper engine will have a vacuum of 10-12 at idle. With a cam you should be somewhat lower.

Did you mean .175 msec of trim.

 

[HOdbleFman]

No, I mean 1.75 msec. I was getting around 7 inHg vacuum at idle.

 

[HOdbleFman]

I take that back, I am running between 5.5 and 6 inHg at idle. Could this be why I'm having to trim out so much fuel?

 

[HOdbleFman]

Bump, Jack.

 

[Sean Roe]

I take that back, I am running between 5.5 and 6 inHg at idle. Could this be why I'm having to trim out so much fuel?

Yes.
Stock vacuum at closed loop idle is typically 12.5 inches plus.
It's normal to have to take that much fuel out if your idle vacuum is that low.

Regards,
Sean

 

[HOdbleFman]

Sean, will it hurt anything to take that much out? Do I need to compensate for this at other load or rpm conditions? I took it for a drive today with the diagnostics software hooked up to my laptop, but I think the serial port is so slow that I couldn't get data quick enough to see what I was doing in real time. Also, what kind of voltage would the stock 02 sensors put out if the a/f was beyond the range of the sensor, say at 11:1?

 

[Sean Roe]

No, it won't hurt anything. You are in fact doing what it needs and helping, not hurting, driveability.
Yes, you'll end up compensating for the cam profile by going into vacuum a bit to create your fuel enrichment on the Fuel Load page. Take a look at some of the Fuel Load and Fuel RPM pages on the NA and SC sample programs to se what we do normally.
In order to get a higher resolution signal with the EASE OBD2 Generic, only view the bare minimum of signals you want to view. It counts through the signals you're reading. A smaller number of fields means they get updated faster. I double click on the two or three that I want to see (putting them in the yellow box), then I turn off the green box.
11:1 will be greater than 1 V.
Regards,
Sean

 

[Greg Good Cylinder Heads]

WV, it's all Rich's fault. If he hadn't have complained about his cam being too small I'd have never sold you the one you have.

Thanks Sean and Jack for helping him with it.

 

[J DAWG]

No, I mean 1.75 msec. I was getting around 7 inHg vacuum at idle.

my heads/cam setup yields around 8 in vacuum at idle and when I had my VEC2 on I had to take out 2.25 ms on 1 side and 2.51 ms on the other to get my lt adap around 0%.

 

[HOdbleFman]

JDawg, do you mind sending me a copy of your program?