AFR, tip-in and related q's

[Rickerbucks]

hey guys.

I'm running with a FAST and for the moment NA until I get things sorted out.

The car is running reasonably well in the mid - high range but I have some driveability issues.

1. In the FAST, it gives you the opportunity to "target " a AFR. What should I have there. I know that at IDLE the target is 14.7, and I know at WOT I'm looking for about 12.00 (with the blower). What to i want at tip-in? What AFR do I want in 6 th on the freeway at 1700 - 2000 rpms?

2. I sometimes get a tip-in 'burp', especially when the car is colder. Just as I tip in the throttle, the car will pause, sort of 'fart' through the intake and then off we go. it is also most pronounced with a gentle tip-in as oppossed to a more aggressive stab at the gas. is this a fuel or a timing issue? is there a specific table that helps with this issue?

3. (possibly related to #2). When cruising around on the freeway, when I gently give a little gas, basically just taking up the 'slack' in the pedal, the throttle response is a little delayed. It seems to just hesitate for a moment before reacting to the gas. Again, timing, fuel or another table?

4. Decel popping. I get popping at lower revs and lower MAP quite badly. In fact sometimes just taking my foot of the gas slighthly while cruising will get a little too much burbeling. I have the bootom on the MAP richened up and that has helped a lot from what it was, but now on decel I'm about 11 - 12:1 and I think that is 'rich' enough. Before anyone asks, I had it real LEAN before and it popped like popcorn in a microwave.

Thanks

 

[T66Typhoon]

Not sure who told you target at idle was "supposed" to be 14.7

Most of the SyTy guys that I know... and mine is set at about 13.3 and some of us running variations of open loop and closed loop.

I have found, I am learning this too, that if I tried to run high in the 14's at idle.. my off idle performance was terrible. And the Syty's have a tendency to stumble when going from Park to D, etc. So running about 13.3:1 for me was good... I think whatever works for your particular application is "ideal" Just my $0.02 on that...

Again on the Typhoon I have found that the high 13 range is working good for me on the cruising part of the map. If I try to run 14.7 or 14.3.. my tip in is terrible.

I have not tuned for WOT yet... I have been told this for sure: Do not try to tune the midranges of the map for part throttle.. you will continually fight it.. make all of your adjustment for WOT and get the map pretty good in the middle when cruising. This applies if the part throttle part of your map is also a place you are going to pass though at WOT from a dead stop. With your NA application this may be the case.

I am posting what I have been hearing because I am new to this and tuning and the more information I can share.. the more direction people can give or tell me I am going in the wrong direction.. so I am no expert.... Just passes on my interpretation of what I have been told.

 

[Rickerbucks]

Thanks a million for taking the time Nick. I think I will try and richen the idle up a little then. I'm still interested in other opinions and assistance.

 

[Rickerbucks]

Craig, can you help with some thoughts?

 

[bobc455]

Ricker,

Have you tried adding more AE? I would think you might want to bump up your AE fuel vs. TPS Rate of Change at the low end of the graph. Also make sure that your AE fuel vs. TPS position is up near or at 100% at the bottom end of the graph. You might try to adjust these with a friend driving the car, so you can watch the graph while you feel the engine reacting.

Every car is a bit different, so the AFR that your car likes will take some fooling around. But on my car, for example, I run about 14.5 at idle, then I get up about 15 - 15.2 for light throttle highway cruising. If you look at it from a chemical perspective, 14.7:1 will give you best theoretical combustion, that is where all the new cars from Detroit will idle. Fowever some cars (especially those with bigger cams, etc.) need to run a bit richer to cover up some of the roughness, especially at idle (which is why some cars idle around 13.3 - 13.8) caused by ineffecient combustion at low airflows. You probably won't notice this on the highway, so I would see if I could tune it to run at 14.7 on the highway.

I would play with your AE Fuel vs. rate of change- on my car, I bumped it up a lot compared to the "sample" program.

One more note. If you are going to eventually be adding some boost, I would be sure that you are running with your 2-bar sensor now, and under "Fuel calculation parameters" make sure it is set to have a 2-bar sensor. Changing it later may cause some confusion with the VE, timing, and A/F tables, so all the tuning that you do now disappears.

Just my $0.02...

-Bob Cunningham
bobc@gnttype.org

 

[Rickerbucks]

Thanks Bob, the AE vs rate of change table did seem to solve the problem.

However, the popping from the muffler on decel is driving me nuts. I gather this is a timing issue but i don't know if I'm suppose to INCREASE the timing or reduce it. I played around a little but could not experience any differance.

I may have a SMALL leak in the exhaust. One of my exhaust clamps is ratteling suggesting I need to re-adjust things. Would that do it?

 

[RickWI]

That sounds like a VE table problem. Monitor the VE screen under decel and pay attetion to the A/F correction. It should stand right out. Those cells need to be adjusted. To adjust the high vacuum low load range I keep it in either first or second and adjust then while slowly speeding up, maintaining speed and slowing down. Best to have another person with you. First check your A/F map in this range to make sure your targets make sense. I have most of mine at 14.7 or so.

 

[bobc455]

I agree with Rick, see if you can change the VE table to eliminate the popping. Exhaust leak probably won't cause the popping, unless your O2 is trying to do some wild corrections.

-Bob Cunningham