sp361t

Hi All,
I have a 1990 Corvette, 383 with a LT1 intake installed.

I am having issues with the car going lean during moderate acceleration, the Tip-In seems to be fine but once Delta is applied to the throttle and then is stationary with RPM still rising the car wants to go lean (between 15-16 AFR).

This seems to be after the change is applied and the computer reverts back to the VE table.

My question is do i need to focus on the VE tables or something in the Accel Enrich tuning? i feel it is the VE table but i have not had any success fixing this.

I hope i explained all this clearly, thank you for your help.

Rob

DanielRicany

Your computer should be correcting the AFR from the input from the oxygen sensor during closed loop. It may be highway mode causing those readings. Did you enable highway mode?

fl_799

Rob, You are on the right track. As a test, add a few percent (8-10) to the VE tables across the board and see how the car behaves. On speed density cars and motorcycles I usually do a full correction on all VE tables. My car is an MAF '89 but we've tuned my brothers '90 a few times as he's modded his car. Usually start with datamaster 32 to correct the VE tables and then switch to tunerpro RT to pinpoint fine detail.

Once the base VE tables are squared away, then tip in lean conditions can be handled through the AE table(s), and PE adjusted for optimum WOT A/F ratios etc. Probably a million ways to skin this cat, just an idea.

James

bjankuski

You need to adjust the VE table in the area where it is lean. Scan the car and note the RPM and MAP readings where the car is lean, then adjust those cells on the VE table.

MrWillys

After doing a datalog you can play it back and get the blm averages for each cell based on vacuum, and rpm. So, lets say at 1200 rpm and 50 kpa your blm average was 136. You take 136 divided by 128 (sometimes I use 124 and 126 to be on the rich side), and this creates the multiplier for the ve cell number. You also need to increase the cylinder volume from 713 to 785 milliliters now that it is a 383.

sp361t

thank you all for your suggestions here is were i am at currently:
I look at my BLMs and ALL that i have logged last week show Rich, it seems the the car can correct but is having to pull alot of fuel out.
So i have been leaning those out and i added fuel to the AE Decay value which has helped the lean issue.
I think it is all in the AE section due to the fact that all my BLMs are showing rich to way rich.
While we are on AE what AFR do you guys shoot for when tuning AE? i have a few areas were i am getting into 10 and even 9:1's which i think is way to rich. but before i get into that i think i need to get my BLMs straited out.

Thank you all for your help,

Rob

fl_799

Just a suggestion. Take it one piece at a time. Take A/E completely off the table for the moment. You don't even need a wide band for this.

Next data log: Get the car up to operating temperature, begin the datalog, and slowly run through 1st gear to redline, do the same in second gear if you can. Repeat to capture as many clean data points as possible across the map as various vacuum and RPM tables with NO A/E or PE mode. Then kill the logging, analyze the BLM's and correct/smooth the VE tables. Repeat until your BLM's are at 128 (or slightly under) repeating the tests above and during normal cruising conditions. If your VE tables are up to 100 and these areas of the map are still lean, you will need to add fuel by lowering the injector constant or increasing fuel with an adjustable fuel pressure regulator. Repeat.

Once this is completely nailed down, next step!

Once this is set, then move on to the A/E tables. Shoot for 12.5 or slightly lower A/F ratio on tip in. Look for knocks or timing retard on tip in, add fuel via A/E accordingly. Then move on to PE and WOT A/F ratios etc.

I could be wrong, but I think that there is some unnecessary influence between A/E and VE going on. Once the VE tables are corrected, everything else will fall into place much more easily IMHO.

Keep us posted, I love this stuff!

James

sp361t

yes i agree i just needed to get the lean condition under control before i was seeing 16 or 17 AFR way to lean but i have gotten it alot better.

now i am following FL_799's advice and working on the VE table only, my main concern is how do you know if the car is adding fuel for AE? do the BLM numbers only reflect the VE table or everything together?

Also i am not sure if i can pull enough fuel at certain ares due to my pressure regulator. i can only go to about 38 PSI fuel pressure. it is not horrible but at idle for example i am at high 13's to low 14's no madder how much fuel i pull.

and i agree "I love this stuff" and always remember: if it was easy everybody would do it!

thank you for your help,
rob

MrWillys

I try getting the flowrate closer before working the VE. IE: let's say your blm's are averaging 140? Take 128 / 140 = x current flowrate. This way your VE adjustments will be closer, and none will want to be above 100.

fl_799

I agree, bringing the flowrate into line will make corrections much easier especially if your running that lean. More fuel pressure, lower injector constant in the tune.

Nice writeup on AE on the F body forum.

http://www.thirdgen.org/techboard/di...e-thing-i.html

And VE correction methods, more great work.

http://www.thirdgen.org/techboard/di...ttle-fuel.html

sp361t

ALl,

sp361t

All,
My flow rate is correct at 24 Lbs (24Lbs injectors) i do not feel that i am way off with my VR table and it is running rich across the board. the only lean issue i have is with acceleration.

I have been doing come logging and i have made some headway with the VE table.

Thank you all for your help