Here's something that I came across trying to cure a surging problem I had during light throttle acceleration from a stop. First of all I'm using SAUJPv4 $8d 7730 ecm. I was having a really bad surging/jerking while accelerating from a stop. I've been messing with the AE tables trying different combinations with no results. I finally came across the constant AE, MIN TPS% for AE. It was set at 3.9%. I knew I had a problem with AE causing this jerking so I figured let's enable it at a later tps% so I changed it to 5%. Guess what? No more surging/jerking from a stop. It seems that the light acceleration fueling is coming straight from the VE tables and once I reach 5% TPS, then AE kicks in. By that time the car is already moving at a nice speed to where the surging is not even noticeable. What do you guys think?

 

Mine is a auto trans and
is set at 1.2. AXCN is set at 3.9

 

I set it also to 1.2 a few minutes after reading this and the surging got WAAAY worse than when I had it at 3.9%. I think I have whiplash. I set it to 5% and take off is smoother than a babies a$$cheeks.

 

Glad it worked for you

 

Thanks! It was embarrassing to pull up to a hangout with the car jerking all over the place.

 

It does take the fun out of driving a vehicle, BTDT.

On port setups (MPFI) the AE is tough to tune in. It is so sensitive that many times, as you found out, there are better ways. What I've found GM to do, and found out on my own, is to use the minimum AE as possible. Then allow the INT to make up for some of it.

And at the same time cover some AE requirement via the VE table. If you check the path through the VE table that the engine transverses during pulling out those cells can be fattened up. This is typically done at lower RPM, say 800 - 1600. And at loads that are only used during acceleration.

One thing to watch for is that you don't want the AE to drive the INT down. This usually ends up causing a lean sag as the INT then needs to recover. Adjusting the VE higher to the point that the INT still increases some from rolling into the throttle is better.

RBob.

 

Interesting find, I'll have to try that with my dads car since I can't seem to get the jerking at low speed, light throttle to go away.....

-jason

 

Want an easy way to see if the jerking is AE related?
Use the new dataword in V4 (displays in error word 5 that isn't used) and the AE bits should not come on under light throttle. I found that my lopey cam was hitting AE pretty continuous at just off idle too. The display of these bits for TPS AE and MAP AE helped to figure it out.
I did raise my value there also to stop it from being triggered early.
HTH

 

Describes the way AE is setup on my truck to the tee. Not that I had planed it that way, but that is what I wound up with just trying to "give the engine what it wants". I had assumed that I was wrong for having AE setup this way and have been considering retuning.

Thank You for saving me a lot of time and effort.

 

Mine was set at 1.2%. It's only one change so it should be noticable if it gets terribly weird. Won't be able to play with it for a few days.....weather is crappy.

 

I see that there are 5 bits (0-4) in Error word 5 that aren't used. Do I check all of them?

 

I'm running in open loop. Does the INT still apply?

 

Nope, the INT is inactive in open loop.

Running in open loop is quite a bit different then running in closed loop. Much more freedom to give the engine what it wants. Can also do away with PE mode as there is not transition from closed loop to open loop.

Set up the open loop AFR table to taper into PE level AFR ratios. Same can be done with the SA table(s). This provides for a smoother running engine as the jump to hyper space no longer exists (unless the bottle is involved ).

RBob.

 

From the V4 document, It shows what the bits represent in the added configuration. Can use any datalogging program you want.
The screenshot is from DataMaster

 

So any changes made in the PE AFR and PE SA tables will not yield any results in open loop?

 

If the calibration is still set up for PE mode, then the PE mode tables will still have an affect.

PE mode is designed to move the ECM from closed loop operation to a power producing mode. Then upon throttle lift quickly return back to closed loop. Recall that when in closed loop the AFR is commanded to be stoich.

When PE mode is invoked the commanded AFR is richer while also adding spark timing. Hence the hyper-space reference. On a high(er) performance engine this transition from closed loop to PE mode can be quite sudden.

To the point that in the EBL software I set up the PE spark advance to attack over time. This smooths the transition into PE mode. Otherwise it was sudden and uncomfortable, like flipping a switch.

When closed loop isn't used, there is no need to use PE mode.

Since the engine is always in open loop it is better to set up the open loop AFR table and SA table to do what PE mode does. As the load increases taper the AFR to the rich PE mode setting. The adjust the SA table(s) for the proper power and smoothness.

Disable PE mode by some means. IIRC, with $8D even if the TPS% table is set to 100%, PE mode is still entered at 100% TPS. Maybe there is an RPM or MAP threshold that can be used to completely disable PE mode in $8D.

If not, then set the PE mode SA to all zero's, along with nulling out the AFR changes (percentage of stoich IIRC). Then just run from the open loop AFR table(s) and the main and extended SA tables.

RBob.