Newbie needs a little help tuning FAST

[mustangracer42]

I just got my car running the other day and Im having some problems getting the O2 correction to keep the "actual" af ratio to match the "desired". The problem is only at idle up to 1500 rpm. I have a desired af ratio of 13.5, the closest I can get for actual is 12.4-12.8 and that's with the correction maxed out at 25%. Like I said I'm a newbie with this stuff so if you guys can give me a few areas to start playing with I'd appreciate it.

I've already started messing with base fuel pressure and it doesn't seem to help. I've gone from 50# (recommended for my setup) down to 25# and always seem to have the same 25% O2 correction factor.

Thanks
Jeremy

 

[HighPSI]

Jeremy,
If you don't mind travelling, I can help you out. I have the Orlando track rented this weekend specifically to tune some FAST Mustangs.

 

[mustangracer42]

Cal, I wish I would've known sooner. I'm military and I'm on leave right now. I have alot of other commitments this weekend. Thanks for the offer.

 

[bobc455]

Jeremy,

That is exactly the purpose of the VE table. Have you tried to change those values?

-Bob Cunningham

 

[mustangracer42]

Bob I have not changed any of the values on the VE table. Should I increase or decrease the value. As I sit here and try to think through volumetric efficiency I can't decide which way I should change the tables. Thanks for the help

 

[JDEstill]

Think of it this way:
VE is essentially telling it how much air is the engine getting. Higher VE means the engine is getting more air for a given rpm, manifold pressure, etc.

When the FAST thinks that it is getting more air, then it adds more fuel to get the desired a/f ratio.

In your case, the engine is actually too rich. It is getting more fuel than it needs for the air its getting. The engine is getting less air than what the FAST thinks it is getting.

So... since it is getting less air real life than what the FAST thinks it is getting, you need to tell the FAST that the air flow is less. So you lower the VE. Lower VE, the FAST knows the air flow is less, and it will cut back on the fuel.

Lower VE = less air = less fuel
Higher VE = more air = more fuel

You'll have to mess with the whole VE table, trying to get the O2 corrections within 5% or so everywhere (preferably on the rich side so it is always pulling out a little fuel). Having the correction close to zero means that the air flow the FAST thinks the engine is getting = real life air flow.

Once you get to that point, if you want things to be richer or leaner you just adjust the A/F ratio table. You always want the air flow that the FAST thinks the engine is getting to = real life air flow. Don't try to make things richer or leaner by faking out the FAST with the VE table. The A/F table is there to make things richer or leaner as necessary.

Clear?

John

 

[Chuck Leeper]

????

Where is closed loop set??

 

[mustangracer42]

John, thanks for the detailed description on how the ve table works. It was very helpful and you explained it in a way that I fully understood it. I can store that little nugget of FAST info away and recall it later as I need it. Once again, Thanks

Chuck,the closed loop parameters are as follows:
Closed loop high rpm-500
Closed loop low rpm- 250
cold closed loop delay- 10
hot closed loop delay- 10
closed loop gain %- 45
max closed loop step %- 9
closed loop min temp- 60 (this was set at 121 and since it takes so long for the car to warm up because of outside temps, it was really pig rich until it hit 121. I lowered this temp and it quit smoking as much but the O2 correction was still maxed out and that's when I came to the board and asked my question)

Thanks again guys for sharing what you know
Jeremy

 

[10SV6]

How big are your injectors ? What kind of HP do you think you'll be able to make with the combo ?

 

[mustangracer42]

I have 83# injectors. As far as Hp goes, I'm not sure I think 1000-1100 would be my goal (conservative tune). This car is still very much a street car. I've been driving it around quite a bit lately w/out the blower belt on. Trying to get a feel for how it does in stop and go traffic. Seems pretty good, temp holds right at 180-190. If you know someone with desktop dyno, I'd be happy to provide all the specs. It's a pretty stout combo:
351 block (motorsport 4 bolt 9.5" deck),
TFS R's with alot of work from Brian Tooley at TEA
LAE 4" billet crank
Carillo 6.2" rods
JE custom pistons
Trick Flow custom lower intake with a custom upper from Reichard Racing
Cammotion custom grind solid roller
Lots more
I originally purchased the FAST from Mike Murillo but that was 2 years ago and this car has had it's ups and downs throughout the build process. I'm just now starting to try and tune it and I have alot to learn.
Jeremy

 

[HighPSI]

Jeremy,
If you don't get it sorted out and want my help. I'll be renting Orlando Speed World again February 8th tuning on two DR Mustangs.