Coasting to Accel Studder

[hiltonlo05]

Ive been scratching my head with this issue, Ive tried a number of settings under accel enrich, even to the extremes, cant seem to figure it out after a month or two of fiddling...

Upon transitioning from coasting/decel to acceleration, in this instance, light accel, I get a weird studder/jerking, as can be seen clearly in the attached datalog in the fuel PW and AE. Im thinking Ive got tunnel vision and have overlooked something basic so if you guys don't mind having a look at my tune and log and weighing in some opinions and suggestions.

It should also be noted, if I just flat out stab the throttle, the car will stall from a stand still, and at highway speeds it will fall flat on its nose for a second or two and then it will finally recover and screaming power...so something is goofy with my AE settings Im pretty sure, ive got that condition noted in other logs, but I figure I should start with the basics of the transition studder.

496BBC, MS3X, LS CNP, Multiport Seq. fuel.
Thanks in advance guys.

[Matt Cramer]

First, turn off the Enhanced Acceleration Enrichment until you have the VE table 100% dead on. The EAE is driven off the VE table, and if there's a rich or lean spot in that table, a small problem in the VE table will make a massive problem in the EAE behavior.

Next, the TPS driven AE is going to be very touchy as you have it set to activate on 15% per second - that's a very slow roll on - and the curve has it dumping a lot of fuel at that point. Consider swapping over to accelerator pump AE - a lot of users have found this one easier to understand and easier to get dialed in.

[gtmdriver]

I had a similar problem and I solved it by backing the TPS.dot AE right off.

Mine now runs from 1.5% at 20 to 3% at maximum TPS.dot.

I was dumping far too much fuel into the engine as the throttle started to open.

[hiltonlo05]

Thanks, my settings were all over the place, I've previously tried 30 and 50 for the threshold.

I only chose time based AE because the help node said it was better for MS. Accel pump made more sense to me anyway so I'll start messing with that.

Moral of the story, my activation was too sensitive and my curve was dumping WAY too much fuel?

[whittlebeast]

You have way too much AE. You are putting the fire out.

Plot MAP and Pulse Width on one trace. Then on the next trace plot MAPxRPM vs Duty Cycle. I want to see about a 10% to 15% bumps in fuel flow when AE sets in. You have huge bumps in fuel flow.

See http://www.nbs-stl.com/CRX/CRX%20AE%20Testing.png

Andy

[hiltonlo05]

Well...funny story...I probably let it creep up so high bc I would watch the wideband peg lean and I kept adding fuel. I'm guessing the lean was due to the flame going out. I've honestly been messing with it for so long that I forgot where the base tune started. I'm switching it over to accel pump as suggested...hopefully can do some testing this weekend. Thanks guys for the help, I'll report back my results...thanks for that graph too... I'll try those views

[whittlebeast]

As a side note, the more intake manifold needs to be "Wetted up" on a transition, the more AE you need. Are your injectors mounted right at the intake valve or up in some sort of throttle body?

My 10 to 15% rule of thumb assumes you are injecting fuel right at the valve.

[hiltonlo05]

As a side note, the more intake manifold needs to be "Wetted up" on a transition, the more AE you need. Are your injectors mounted right at the intake valve or up in some sort of throttle body?

My 10 to 15% rule of thumb assumes you are injecting fuel right at the valve.

I'm injecting near the valve I guess...throttle body is only used as a air door so I guess the intake walls would be considered dry?

[whittlebeast]

Yes, start with the assumption that 10 to 15% bump is in the ballpark. Not 2 or 3 times as much fuel.

[hiltonlo05]

Ok, so Ive been messing with this some more, and after setting things back to the base setting for ae, using time based or accell pump based, the car was barely able to make it out of the parking lot. Tried to stall very easily, could barely accelerate in traffic, it was just bad.... When trying to free rev it in neutral, it was very difficult to get over 4k rpm and would sputter and miss horribly, and the engine would stall on decel almost every time, couldn't catch itself so to speak... So I played with every adjustment I could think, and after getting mad with it today, just started throwing tons of fuel back at it to see what it does... And it was 10x better, crisp revs with blips, can drive again and pop the throttle, but the fuel amounts seem ridiculous. Still have minor transition issues, and I cant just flat out stab the throttle as hard as humanly possible, but overall I have crisp response and its drivable...

My bigger concern is that im only masking the underlying problem as to why this thing wants so much AE... Could I be overlooking something like a timing table, or some other obscure setting Im no aware of? Granted this is an old iron head big block chevy, so not exactly the most modern design as far as flow and combustion are concerned.

[billr]

I have AE totally turned off. There is no problem getting my BBC C3 moving, and I generally only ease the throttle open when moving because the power comes on pretty strong. In fact, in 1st or 2nd I tend to ease off the throttle as it gets into the torque peak because of wheel-spin.

So, after your recent posts about AE the last time I was driving it, about 1300 rpm in 4th, I stabbed the throttle to see what would happen. It hesitated momentarily, then took off with the throttle somewhat stuck open! I dragged the brakes hard to keep speed down, then remembered I have switches handy to selectively cut off fuel to each bank. Running on 4 cylinders, and still riding the brakes, I got home fine.

I know, this doesn't really relate to your questions, just thought it would amuse you other C3 folks...

[hiltonlo05]

I'm very new to this tuning...but with ae turned down low or off, the car is barely drivable...but I'm th400 so no clutch to play with. I know every setup is different, but mine seems to like to extra fuel until I can find what else is causing the issue.

Also, you MUST further explain this 4cyl mode with the throttle stuck open...

[billr]

The four injectors on each bank have a common 12V power wire, with a switch. Turn off the switch and the injectors don't pulse (the MS driver still pulses to ground). No fuel, no fire on that bank. I'm experimenting with it as a way to use VEAL with the engine under load, but keeping speeds and accel kinda within street-legal values...

[hiltonlo05]

Interesting...keep me posted on that... I have the same issue with veal. I like to stay under 100 but I'm not getting all parts of my map