FAST tuning opinion sought.

[Rickerbucks]

Can someone give me there impressions.

For the last 6 weeks I have been pottering with the FAST. I sufferred from some problems that just did NOT want to go away. I would get decel popping which I eventually solved by increasing my VE tables to about 80 'ish and I also had popping whilst holding the car at cruise levels. The AFR would be about 12.5 to 13.5 whilst this was happening.

I would also get an intake backfire sometimes on tip in. Logging also indicated a lean spike on tip in. That being said, once the car was up into the mid to high range it felt reasonablly good.

None-the-less, driveability was a major issue.

So a buddy came by to give me some time. He has an 8 sec stang and although has not worked on a lot of cars, he has spent a LOT of time with his own.

We go for a drive and he richens the VE tables up A LOT. I mean a TON. Mid range VE is about 90. The AFR is reading 9 -10's but there is absolutely no denying that the car is rtunning very well. We may have to do a little more tuning at idle as it is a little rich.

We of course is saying, "this doesn't seem right. The VE numbers are WAY to high and the AFR reads really rich but..." I do NOT have black smoke pouring out the back. We pulled a plug and it looked great.

BUT here is the variable. The car has been burning oil - this was on a freash rebuild. In addition, at one point I pulled the O2 and "cleaned" it with WD40 which I have now been told is a 'no-no'

So can anyone provide some insight. Is the O2 faulty? Is there some calibration of the AFR/ wideband and the VE tables that are out of sync?

Or is it a case of "whatever works, don't worry about it?"
Thanks guys

 

[bobc455]

Boy! We have Rickerbucks, RickWI, and Ricky T. This is getting confusing.

Nevertheless, it sounds like you may be running very rich in order to compensate for an incorrect AE table.

A lot of people seem to be confused about AE, so allow me to take a moment to talk about it...

ROUGHLY, when you suddenly snap the throttle open, the pressure in the intake tract increases suddenly. This causes some of the gasoline that is suspended in the airstream to suddenly cling to the wall of the intake- since the gas is now on the intake tract wall and not in the airflow, the cylinder will see more air and less fuel. AE will add some enrichment to compensate for this temporary condition.

On a carb, there is a device called an "accelerator pump" that does the same thing- as you increase throttle position, it squirts extra gas into the intake tract.

I think a lot of people are confused about AE because they see the word "acceleration"- this means that the air in the intake tract is accelerating, not that the car is accelerating.

The FAST system uses two forms of AE- AE compared to change in TPS, and AE compared to change in manifold pressure. On a non-boosted car, you only need AE vs. TPS- as the FAST sees the TPS change at a certain rate, it adds fuel to comensate the change in pressure. On a turbo car, where the pressure will generally continue to change even though you are not moving the TPS (as the turbo spools up and creates more boost), you also need to add AE vs. MAP enrichment.

Rickerbucks, if you stab the throttle and the engine doesn't respond, chances are it was because of a lean condition- I suppose you can overcome this problem by just driving around rich as heck, but it's not the right way. I think you have to go back and look at your AE.

One more note. The only reason to be changing the VE table is to get the A/F ratio from your A/F table. You should NOT use the VE table to change the A/F ratio- if you want to run at 10:1, then put 10:1 in your A/F table, and leave your VE table alone!!!!

THE VE TABLE IS A CALIBRATION TABLE, NOT A TUNING TABLE. Once your VE table is calibrated to understand the airflow charachteristics of your engine, then if you want to change the A/F ratio DO IT ON THE A/F TABLE!!! That is why it is there.

The ONLY purpose of the VE table is to make the target A/F match the actual A/F.

Make sense?

-Bob Cunningham

 

[RickWI]

Bob, nice job explaining things. I'll just add that if I do not have any AE Vs Map added into my program I do get a delayed backfire out the TBody. So it can be helpful even on N/A cars.

Just to mention some of the same things maybe a different way. What I like to do is drive around with the A/F ratio map up. I look at what the ratios are under different driving conditions and make SURE they make sense. Like idle at around 14.7, cruise at around 14.7 - 14.9, medium loading in the 13.3-13.9 range, WFO 12.6-12.9. This would be for a rough out for an N/A, not turbo motor. THEN I go to my VE table and drive around and tune in cells. I do this in open loop and tune in as many cells as I possibly can. I don't like to drive aroudn in closed loop with the (L) learn button being pressed all the time. I go up hills and hold speeds in different gears I cruise flat and hold the brake to get into difficult cell ranges, I hold low gears under high vaccum conditions to get a lot of those lower rows, and so forth. I don't care about it farting or belching somewhere while I try to get to a cell but I do make sure and wait a few seconds to let the engine stabilize in the cell range to get an accurate correction value. I also have found that using a highlighter over the cell ranges that are dialed in is a nice way to remember which cells are correct and which ones are not. The ones you can't get to can them be smoothed based on the corrected values surrounding it. I will also draw a box around cell areas that I want to go back and concentrate on if I think I have a problem, or did not get enough corrected. Of course with a typical water based highlighter all you need to do is clean the screen with alcohol and it comes nice and clean.

After those two steps are done then I look at the spark map. I did forget to mention that prior to all this I do the same with the spark map as with the A/F Map. Rough it in while observing it just to get in the ball park. With the spark map at this point I try to get better throtlle response by advancing the timing under light load conditions, making sure timing gets taken out under higher load conditions, dialing in high advance at normal hwy sspeeds of 60-70. Just getting a feel for what it likes at cruise, tip in, moderate accel and so forth. I still have the upper cells conservative, like in the LOW 30's just in case something is not right to keep out of detonation. I don't try and experiment with total timing until I get most everything else dialed in.

Then I deal with trying to fine tune the AE. I like to rough out the AE Vs TPS while in park with the motor HOT. I lean it out to get the motor to hesitate and then richen up. I try to get it crisp. Then I put it in drive and give it quick jabs of gas while watching the tps position screen, and the road, again to get things crisp. When it is good, of course is when the hood rises and or the rear tires bark and squirm. Then I go into the AE/Map screen and rough that out while giving it 4-5 seconds of moderate to hard throttle from a stop, slow speed and cruise. Like I said, if this is too lean I find I get a backfire out the Tbody.

That is what's worked for me over the past couple of years.

 

[Rickerbucks]

Great Stuff Bob.

It was my intent to play aroundin the VE tables to get the AFR close to the final result and then set the target AFR from that experience.

It seems that the original AFR that I had set as targets were indeed too lean, although now I suspect I'm too rich.
Are you suggesting that the VE tables need only be a little close, and then spend all my time in closed loop playing with the "target AFR" to get the performance results I want?

That WOULD be easier

 

[Reggie West]

I have been following this thread for a while and I can share your pain .

That said the real ease of using this system is to let the wide band sensor tell you how close or far off you really are in getting the A/F ratios correct.

That means setting the A/F tables at levels they should be. For instance at idle 14.0 to 1 and so on.

Make all of your changes in the VE table, that is where you should be spending most of your time.


Getting the basics with the motor down first is very important. That means setting the TPS sensor, getting the car to start like a stocker ( yes it really can be done with this too) and so on.

No two motors are the same but the FAST can allow for that and it will work well.

 

[bobc455]

Rickerbucks,

I think you understand correctly. You should be playing with the A/F table if you want to change your A/F ratio.

I suppose you could say that the VE table tunes the computer, and the A/F table tunes the engine. Once your Target A/F matches your actual A/F, there is no more need to touch the VE table.

Reggie,

You say "Make all of your changes in the VE table, that is where you should be spending most of your time". That can kinda be misleading with regards to the current discussion- it is certainly true that most of the time spent tuning the system is done in the VE table (following around the bouncing ball to see if actual A/F = target A/F).

However if you feel that the engine needs to run richer or leaner (tuning as you drive or as you are on the dyno or whatever), you should be changing the A/F ratio table. For instance if you are on the dyno and you want to try running at 11.5:1 instead of 12:1, you should change your A/F table from 12 to 11.5 in the appropriate cells. If, on the other hand, you find that your target A/F ratio does not match your actual A/F ratio, then (and ONLY then) play with the VE table to get them to match.

It would be nice if the computer could magically figure out where our engine runs best- but alas that is up to us to do (watching for ESC retard, feeling engine hesitation or studdering, watching for blue smoke, etc.). It doesn't know if you are more efficient at 15:1 for cruising than 14.5:1- that is why everyone's A/F ratio must be somewhat different as Reggie says.

-Bob C.

 

[bruce]

Originally posted by Rickerbucks

Or is it a case of "whatever works, don't worry about it?"
Thanks guys

It a matter of giving the engine what it wants
Key is understanding what the engine wants. Sometimes it ain't what you think.

Generally for drivibility too rich and too much timing feels real good by the buttometer. Trouble is it wastes gas, and build excesss carbon in the engine. Excess carbon leads to burnt/pitied exhaust valves, as a min..

Just to follow up on the AE a lil.
Gases *boil* *vaporize* more at lower pressure levels., all things being equal. So at light load when the manifold is in VACUUM, the gas is more vaporized. So when you open the throttle the vac level changes, and what was vaporized gas, now forms droplets and lands on the runner or plenum floor. So this gas needs replaced, and for an instant air flow can about stop, when you really snap open the throttles fast. See air has inertia, and it takes a moment to change speed/and or direction. Also, explains why a long runner motor can get lazy coming off of idle.

For really getting AE correct you want to use a LED type display, and I don't mean some 5 element one from a oem O2 sensor setup. Second place is lots of data logging to see exactly what your engine wants and where.

TPS AE generally makes a car fun to drive, MAP based AE gets a car to launch. Sometimes the lack of injector forces sharing the load between the two.

Too much AE, and as well as too much VE fuel can gas wash the cylinders. When you get too far off in your timing you can get into an area where adding timing, shows leaner on the WB, and retarded rich. So you have to be aware of indicated and true.

Tuning takes time,
taking accurate notes saves you from repeating yourself, and allows for seeing trends. People get lazy about notes, and miss ALOT of minor things. These minor things are called details, and what can often win races.

HTH,