Very Important To Have Your Air/Fuel Ratio Verified Post Modifications

[Larry Macedo]

A forced induction Viper arrived at our shop and after performing a baseline dynomometer test on the vehicle, we found the A/F to be 13.5 to 14:1. Apparently a shop close to our client performed a dyno test and found the same results 6 months ago, although they found higher hp and tq numbers than we did. I would recommend anyone installing their own parts have this procedure done.

 

[Qualitywires.com]

What system are you talking about? Lean is mean, but when it's that lean..yikes!

 

[Simms]

A forced induction Viper arrived at our shop and after performing a baseline dynomometer test on the vehicle, we found the A/F to be 13.5 to 14:1. Apparently a shop close to our client performed a dyno test and found the same results 6 months ago, although they found higher hp and tq numbers than we did. I would recommend anyone installing their own parts have this procedure done.

Exactly why mine is on its way down to you Larry!

 

[J DAWG]

I think this is an important topic. I watch mine constantly and have been amazed at how much it can change solely from outside conditions. I have tuned with the VEC2 in 90 degree heat and had my a/f around 12:8:1. Well cooler weather comes in and at the track the other night the same setup yielded a/f readings above 14:1.

I only have heads/cam car, but was really surprised how much variance there was with my setup. I think alot of people would be shocked to find out what their "tuned" car is actually reading a/f wise. I am no expert by any means, but I have been surprised how much it can change.


Another interesting thing I was thinking about is that these cars are tuned on a dyno in 4th gear(that's my understanding). Well has anyone logged a/f from other gears at other rpm's? Under load running thru all the gears seems to yield quite different a/f readings that one pull in 4th from 2000 to 6000 rpms. Just my observation from the a/f I have logged on my car.



I am guessing probably less than 5% or less people actually monitor a/f on these cars that are laying down huge power, BUT maybe they are reliable enough and consistent enough not to watch it, BUT I wouldn't bet my motor on it. I would like to hear more "expert" opinions on this.



John

 

[Jack B]

Well stated - It has always amazed me at the number of viper owners that dyno without taking a/f readings. Probably a small percentage of the burnt pistons and exploded ring lands have been made common knowledge.

As long as you use the oem PCM you will have a variation in the a/f baseline due to the triggered offsets adapting to ambient conditions. I have seen the same as you about one point variation for environmental extremes.

The only difference in the dyno and the road (at peak hp) is the slight leaning due to air flow and the added losses in the fuel system for vertical piping.

 

[Daniel Cragin/DC Performance Inc]

Larry is right, the air fuel requirements vary from engine to engine. Just changing the cats will dramatically change the fuel requirements.

On supercharged engines we like to see the air-fuel around 11.0-12.2 to 1.

 

[Bad_Byte]

Larry is right, the air fuel requirements vary from engine to engine. Just changing the cats will dramatically change the fuel requirements.

On supercharged engines we like to see the air-fuel around 11.0-12.2 to 1.

Dan or anyone, I would think that changing the cats (or cat delete) would affect the gen II much more so than a gen I mostly due to the fact that a gen I does not have O2 sensors after the cats. Is my thinking correct?

 

[Schulmann]

Forced induction Vipers has to be tuned constantly which means AFR has to be monitored. A basic AFR tool costs $500.
The probleme is with the Oxygene sensor in the Viper. It only monitors above 12.0 AFR. In addition the PCM cuts the input from the Oxygen sensor as soon as you hit full throttle. PCM passes in open loop. Everything below 12.0 AFR is static unless you have a PCM that can use a wide band Oxygen sensor. Unfortunately I haven't seen PCM that for Vipers yet.

Factory made turbo or SC cars come with wideband oxygen sensor and PCM that dynamically adjuste AFR curves. The best kit that I ever seen is made by Subaru. It can adjust the AFR at any time there is no open loop.

 

[Bugeater]

"PCM passes in open loop". or Open loop mode...

Shulman or anyone for that matter,
Can you please explain what it means when you say the PCM passes in open loop? I have read this term many many other times and have yet to grasp the concept.

Any analogies laying around to better illustrate the term?

 

[J DAWG]

Forced induction Vipers has to be tuned constantly which means AFR has to be monitored. A basic AFR tool costs $500.
The probleme is with the Oxygene sensor in the Viper. It only monitors above 12.0 AFR. In addition the PCM cuts the input from the Oxygen sensor as soon as you hit full throttle. PCM passes in open loop. Everything below 12.0 AFR is static unless you have a PCM that can use a wide band Oxygen sensor. Unfortunately I haven't seen PCM that for Vipers yet.

Factory made turbo or SC cars come with wideband oxygen sensor and PCM that dynamically adjuste AFR curves. The best kit that I ever seen is made by Subaru. It can adjust the AFR at any time there is no open loop.

maybe I am not understanding everything completely and it is probably due to me being up for >40 hours as well. I have an Innovate a/f meter with the Bosch(I think) sensor they sent to plug into my exhaust. I have it at the collector. My car inheriently ran rich with a/f readings in the low 11's. I can get them corrected with the VEC2 back to 12.8.

When I hit the nos the a/f dips momentarily to mid 10's and then comes back around 11.2 or so. So my readings do read <12 and are not static with my setup. I have my factory 2001 pcm and the upstream o2 sensors are still in place, even though they see nothing during my runs.

 

[Jack B]

Bugeater:

Real simple - when the car is in closed loop (high vacuum) the PCM controls the a/f by varying injector pulse. The input for this PCM control comes from the O2 sensors. The oem O2's are not wideband and only have resolution about one point above and below 14.7. Due to EPA constraints there is little need for the wideband O2's which are accurate several points above and below 14.7.

To continue - when you go WOT (low vacuum)the PCM does not use the O2 sensor input, instead it uses a fixed matrix (cells for timing and fuel that correspond to an rpm value). These are values that have been programmed by DC for what it believes are ideal. Ideal for a street car is not ideal for max hp.

The problem with a modded car is that the engine now breathes more efficiently in WOT and gets more air into the chamber relative to the amount of fuel that is fixed by the DC matrix in closed loop. In our engines this is especially true in mid range, thus, the reason a device like the VEC2 extracts so much more power from the engine in the mid range. All you have to do is bring the lean mixture down (enrichen) by adding more fuel in the midrange. The VEC2 also controls timing, but, that is a different topic for a another day.

This is where the aftermarket wideband O2 has value, this sensor can read a/f over a wide range and gives you a full 0-5 volt output for monitoring. It is not used for conrol of the PCM, but, for the purpose of plotting and tuning the a/f thru a device like the VEC2.

 

[Qualitywires.com]

Well said Jack!

 

[Schulmann]

What would be a great thing is to build a VEC3 which can read the input from a wide band Oxygen sensor. Basically that would elliminate all hassle around tuning our cars.

 

[Qualitywires.com]

What would be a great thing is to build a VEC3 which can read the input from a wide band Oxygen sensor. Basically that would elliminate all hassle around tuning our cars.

Yeah that would be nice to have. I am using a split second Box and the one I have does not have that ability, but I heard that Split Sec does have a box out there that does data log wideband signal info. My tech Edge Wide Band also has an input for various parameters, but the two devices I have don't seem to work together that well as far as data logging....but I maybe wrong. I haven't really dove into the tech egde wide band as of yet.

 

[RedGTS]

What would be a great thing is to build a VEC3 which can read the input from a wide band Oxygen sensor. Basically that would elliminate all hassle around tuning our cars.

It already exists but it's called AEM.

 

[Joseph Dell]

Not to turn this into a discussion on wideband O2s, but the Techedge device (about $500 complete, web site is www.wbo2.com) allows some datalogging as well. It will datalog RPM, wideband 02, plus up to 3 user inputs. that is nice so I have the MAP sensor from my boost gauge hooked up for data logging. One could also do things like TPS or anything else that reads 5v.

It would be nice if something could automatically compensate for your desired A/F ratio. Can the AEM do that?

JD

 

[KenH]

What would be a great thing is to build a VEC3 which can read the input from a wide band Oxygen sensor. Basically that would elliminate all hassle around tuning our cars.

I talked to Sean yesterday and ordered the latest upgrade for the VEC2. I'm pretty sure he said that part of that upgrade included the ability to link to a WBO2. I have a WBO2 installed permanently on my car, so I hope to play with that feature in the near future.

Here is his post about the upgrade: http://vca2.viperclub.org/forums/showflat.php?Cat=&Board=UBB24&Number=469631&page=0&view=collapsed&sb=5&o=&fpart=1

 

[ViperRay]

This may be a silly question (based upon my limited knowledge) but here it is...

Would it make a difference if you use a Mustang dyno (with load) vs. a dynojet to adjust the A/F mixture?

The reason I ask is that my heads are with Greg Good as we speak and I want to make sure the subsequent tuning is done correctly.

 

[Jack B]

The Dyno type will not change the a/f logging. One thing to watch for is the placement and type of O2 sensor, a good dyno operator can get the the vacuum assisted (tail pipe) O2 to read accurately, however, the dyno's O2 sensor is still better off in the front oem well. If you use the tail pipe sensor, remember the graph of power and a/f will be off by approx 500 rpm's.

A little insight into wideband devices. The Innovate logger just gets better and better. It won the Best of Show at SEMA last year. They have just upgraded the software and the auxiliary input box. They are also releasing a 1/2 deep gauge that includes both a digital and annular readout.

 

[Schulmann]

AEM is strong on Japanese cars ...
Honda Civic etc
Yes they make for the Civic the right PCM.

There is also a great AEM tool to log AFR data that we can use on our Vipers. But the AFR curve is still static.

 

[RedGTS]

AEM is strong on Japanese cars ...
Honda Civic etc
Yes they make for the Civic the right PCM.

There is also a great AEM tool to log AFR data that we can use on our Vipers. But the AFR curve is still static.

I'm not sure what some of that meant, but if you're trying to say you can't tune the AEM to dynamically seek a particular a/f ratio for a given circumstance, I think you're mistaken. The AEM has an O2 feedback tuning parameter that you can activate and do exactly that.

 

[Qualitywires.com]

AEM is strong on Japanese cars ...
Honda Civic etc
Yes they make for the Civic the right PCM.

There is also a great AEM tool to log AFR data that we can use on our Vipers. But the AFR curve is still static.

I'm not sure what some of that meant, but if you're trying to say you can't tune the AEM to dynamically seek a particular a/f ratio for a given circumstance, I think you're mistaken. The AEM has an O2 feedback tuning parameter that you can activate and do exactly that.

Man Ronnie, I am going to have to make a trip down in your neck of the woods to see how that AEM works!

 

[2MANYTOYS]

AEM is strong on Japanese cars ...
Honda Civic etc
Yes they make for the Civic the right PCM.

There is also a great AEM tool to log AFR data that we can use on our Vipers. But the AFR curve is still static.

I'm not sure what some of that meant, but if you're trying to say you can't tune the AEM to dynamically seek a particular a/f ratio for a given circumstance, I think you're mistaken. The AEM has an O2 feedback tuning parameter that you can activate and do exactly that.

Man Ronnie, I am going to have to make a trip down in your neck of the woods to see how that AEM works!

Me too!

 

[RedGTS]

Me too!

Hey buddy you better worry about keeping that yellow airplane of yours on the ground!

Adam, anytime--you know I've got some things I need to fabricate. Will your MIG welder fit in your trunk?

 

[J DAWG]

if the AEM can actually do that............maybe it is worth the money.

 

[Joseph Dell]

It definitely would be worth it. Consider hot summer day vs. cool summer day... night vs. day. Most of the "dumb" systems are tuned once and don't get tweaked at the track for maximum efficiency. if the AEM can do it automatically (and dynamically), it is well worth it.

JD

 

[Jack B]

Joseph

I don't believe the AEM (viper version) can do dynamic fuel and timing compensation at WOT. Perhaps someone who has done a viper can chime in. If that were the case the development curve would not have been as long and it still appears that some hiccups remain if you read between the lines.

 

[RedGTS]

Jack, this is from the AEM user manual:

To control the engine's fuel delivery system, the EMS can be programmed to run
open loop and/or closed loop O2 feedback. Closed loop uses feedback from the
oxygen sensor to make temporary but immediate corrections to the injection to
maintain a target AFR. The type of an O2 sensor will determine how O2 feedback
can be controlled. Due to the nature of standard narrow band O2 sensors, 14.7:1 is the only air fuel ratio that can be accurately maintained in closed loop. However, wideband O2 sensors can be used in almost every feedback condition. When the fuel system is open loop, the O2 sensor is ignored and the injector pulse width relies on the fuel map and fuel compensators to adjust injection duration. Open loop is necessary during engine starts when the O2 sensor has cooled below its operating temperature. It may also be necessary when Coolant Temp temperatures are low. In this state, the fuel vaporization is poor and the engine will require a richer mixture to properly operate. When under heavy load, the engine typically requires an air fuel ratio that is out of a narrow band O2 sensor's standard range and open loop will be necessary.

* * *

O2 FB Maximum Load

Units: Engine Load
Description: O2 feedback will operate when the engine load is below this value.
Typical Use: When using a narrow band O2 sensor, O2 feedback is typically not
used at high engine loads because of the sensor's inaccuracy outside the
stoichiometric range. However, O2 feedback can be used at high engine loads with a quality wideband O2 sensor.

So it appears to me you can use O2 feedback at WOT so long as you're using wideband O2 sensors. As far as I know, this function is applicable to the Viper unit, although I don't know whether anyone has actually done so, or if not, why not. I'm told WOT tuning with the AEM is pretty simple compared to the driveability tuning, and it may be that the experts don't think it's necessary to use O2 feedback.