AE tuning question

[90c1500tbi]

I've been viewing this site for a while, but this is my first post. I'm a FAST newbie, and this site has been a big help!

I'm having trouble getting rid of a stumble when I open the throttle quickly. Opening at a slow to moderate rate is smooth, but when I punch it (from idle or at slow speeds), the engine nearly dies until I back off. Logs indicate a lean condition, so I've increased AE vs TPS Rate at the higher rates. It got better, but now I'm maxed out at 4.0 mS @ 15 cts/4mS and the problem is still there. My AE vs TPS Position is 100% until 21, slopes down to -20% at 43 and levels off. My TPS position is 17 at idle, 93 at full throttle. Right now, I have the AE vs MAP Rate at zero because I read that it wasn't really necesary for a mild naturally aspiriated engine. Could it be that the two large fuel injectors I have in the 2-bbl TBI (see signature) can't keep up with the demand? Do I need to change the injector opening time setting (1.0 mS right now)? Since there are two 90 lb/hr injectors for eight cylinders, I put 22.5 lb/hr (90*2/8) for the injector flow rate in the system config. Is this correct? Do I need to add AE vs MAP?

Any advice would be greatly appreciated!

 

[RickWI]

go into the AE vs MAP demo screen and load that template in. You should notice a difference. Also make sure the AE parameters are setup as well. Usually if things are super lean you tend to get a backfire through the intake. Has that ever happened?

 

[90c1500tbi]

I added AE vs MAP and MAP AE Parameters with the same values as in the demo.gct file. The problem is still there. There is no backfiring, just silence when I push the throttle quickly. The logs show the actual AF ratio goes to 15.94 and stays there when the throttle is open, then when I close the throttle, it goes way rich, (9.19). If I open the throttle quickly and then back off a little, the engine smooths out and the O2 correction eventually catches up (back to near zero).

 

[RickWI]

Are you sure the cell values in those VE map ranges are high enough? Overlay your log on the VE map and make sure you have those cells tuned up.

 

[bobc455]

901500,

I run with zero AE vs. MAP and I bet you could also. Something else doesn't sound right.

I would also raise up your AE vs. TPS at the lower rates (the left side of the graph)- that is where I think you'll see the biggest improvement.

-Bob Cunningham

 

[90c1500tbi]

Thanks for the tips guys. Rick, I think you may be right about the VE cell values in the high load, low RPM areas. I've spent most of my time tuning the cells from idle to cruise and moderate acceleration (cells it runs in while driving around town and on the highway). I'll try lowering my AE vs TPS Rate and start increasing the VE values in this area to see what happens.

 

[Otto J]

WHILE IT IS RUNNING watch the bubble in the VE tables, You will have to probably raise the VE table in the are in which you are when you floor it, It should not go to 15.94 that is pegged lean.

 

[Ricky Trussell]

A few questions on set-up.

1) Do you have 02 correction to where it can add 20% at wot?

2) Are you sure that it is lean and not fat?

3) What is injector DC%?

 

[clemsgn]

Don't forget the AE vs Coolant temp. If it's not high enough when coolant is warm, you may experience this bog. Does it happen at any temp or just when warmed up ?

Hope this helps.

 

[90c1500tbi]

When I floor it, the AF ratio immediately goes to 15.94 and the O2 correction increases slower up to 24.2. The injector duty cycle goes up into the high 50's and increases into the mid-70's as the RPM increases at WOT. All this is when the engine is fully warmed up, so AE vs. Coolant temp is 0.

I've been slowly increasing the VE numbers in the cells at low RPM/high MAP and it seems to be helping. Right now, it only happens when I floor it from idle - when I floor it from cruising (TPS < 30), there is a slight hesitation, but it has improved quite a bit since I started.

 

[Otto J]

TAke all the numbers in the general are and up them by 30% and try it, If it s adding 25 and is still lean upon tip in that will help but it may need more. Send me a log and a current file and ill look at it.
Otto

 

[90c1500tbi]

Now that I've increased the VE values in area it jumps to some more, the throttle response is better, but there is still a bad hesitation when I floor it from idle or from a slow roll.

Otto - I'll email you the latest files. Thanks a lot!

 

[RickWI]

This should take you less than 45 minutes to tune out unless something else in the programming is way off.

Go into your A/F screens and make sure your upper rows are in the 12.8 A/F range. The rows around 98 Kpa and above, assuming you are naturally aspirated. The row just under dial in 13.1. That is a good general wide open throttle air fuel ratio.

Start a datalog and punch the pedal to the metal and run it through a couple of gears. Pull off the side of the road and go to your VE screen. Overlay your datalog and with the arrow key run the cursor through the run. Watch what the corrections are doing on the O2 and go back into the VE screen and dial them in, based on those corrections. Corrections in the upper lefthand side of the mapping are where you are having a problem.

That should get you in the ballpark a bit better.