Surging when Coasting

[JakeFusion]

So, I've tuned my car to be pretty good on the street, but I'm not sure what to do about the surging/hesitation that happens when I lift off the gas when the converter is locked up. I've added a ton of airflow in the follower/cracker, which helped some. But I'm not even sure how to log it. It's a feeling... and it's noticeable when I'm at say 50-55mph in traffic and I left off the gas to speed match the car in front of me so I don't ride the brakes. It's about the only thing left that's not great with the tune. Any pointers on what to look for or even log?

It's an 02 Trans Am... LS1 Heads/Cam 234/242 111 cam... so fairly aggressive. FAST 102/102 TB, Kooks 1-7/8" Headers... Circle D 4200 stall... 3.23 gears (which don't help).

[JakeFusion]

Finally was nice today, and I had time to hook up the wideband.

Tried to drive normal with a lot of coasting. The bucking is more pronounced and coast-down. But I also have a return to idle bounce around with the SD tune I don't have when I enable the MAF. So I'd like to get that corrected too. Any ideas? Temps were in the 50s... last time I tuned in October for the VE table it was in the 80s. So everything looks off a little.

I started the log once the car temp hit 160.

[LaTechGTO]

Finally was nice today, and I had time to hook up the wideband.

Tried to drive normal with a lot of coasting. The bucking is more pronounced and coast-down. But I also have a return to idle bounce around with the SD tune I don't have when I enable the MAF. So I'd like to get that corrected too. Any ideas? Temps were in the 50s... last time I tuned in October for the VE table it was in the 80s. So everything looks off a little.

I started the log once the car temp hit 160.

I battled with this same thing a few weeks ago... I found a few things that helped with the surging you're discussing. I did the exact opposite thing you mentioned though; I removed almost all of the follower and cracker air in the affected idle cells because I determined it was causing the issue. Some of the things I did:

* Tuned RAF
* Raised Cracker Enable Speed (I was experiencing some low speed surging too)
* Zero'd out all Cracker Airflow up to 1600 RPMs and at all speeds within those columns
* Zero'd out Follower Airflow in 0 and 0.5 Throttle Position % cells. I was also experiencing some light throttle surging so I lowered the Follower Airflow and multiplier.

I was going to dip into the Rolling Idle Airflow tables to at least get my coast down RPM under control by bumping it into N, but I started having luck with my adjustments. I still have the Rolling Idle Airflow disabled right now (Enable Speed = 255). If you go that route, I suggest adjusting the Rolling Idle RPM to a shade above the normal Base Idle RPM to get started with dialing it in.

Hope this helps!

[JakeFusion]

I had those zero'd out before. It surged with low throttle, so I added airflow. And that took away the light throttle surge. And lessened the off-throttle coast-down surge. But I feel like that's just a bandaid.

The other issue is my return to idle bounces around. So that's more of an A/F issue I think.

[LaTechGTO]

I had those zero'd out before. It surged with low throttle, so I added airflow. And that took away the light throttle surge. And lessened the off-throttle coast-down surge. But I feel like that's just a bandaid.

The other issue is my return to idle bounces around. So that's more of an A/F issue I think.

Yeah, it sounds like 1) your RAF isn't tuned close enough and 2) A/F needs some adjusting. I've seen the latter a lot before... Even guilty of it myself a few times, although it ends up much more pronounced on a manual car when clutching after a throttle transition before coast down.

[JakeFusion]

Just as an update... I've been working with Lorentz from LSX Power Tuning. And it's gotten much better. One thing we're working on now is the timing. A/F is still a little rich here by 4-5%, but I began taking timing out in the decel areas. When you lift your foot off the gas, the airmass drops... but if the timing doesn't drop too, it'll fight the motor. It's a bit of a chase your tail issue. So I plan to adjust the A/F a bit (lean out MAF - VE was dialed in before blending) and keep messing with the timing. The good news is, there is a noticeable improvement.

It still wants to bounce off idle as I return to idle. Which isn't a problem typically, just noticeable when coming to a stop (it may be cam surge or converter surge?) but it does become more noticeable when I'm in lower speed traffic situations since I'll be coasting at 30mph or so and very low RPM. I may end up taking all air out of follower/cracker to get rid of it. But the surge is timing related too.

Any ideas/suggestions there?

[JakeFusion]

Well, I played around with the timing a lot today. Added a lot. Took some out. It didn't really make a difference. Though not having enough timing makes light throttle buck. Taking it out doesn't seem to help or hurt. As long as it doesn't jump from say 28 with light throttle to 38 off idle. I played with A/F a little, leaned it out, and then after a few failed attempts to get the timing to do anything... I started taking air out of the cracker table. I went back to stock and then zero'd out a lot of stuff. I then re-ran RAF and took out more airflow.

That solved the return to idle bounce. But it's a chasing your tail problem. I still need to run RAF from a cold start to make sure it's right. But I was eyeballing it and taking out 2% at a time.

The coast-down issue is still there, but it's better than it has been in the 1.5 years I've driven the car. I need 3.70s or more gear to get my RPMs up when I'm locked up.

[La RPM]

did you ever try raising the Throttle cracker enable tables to like 45 or so?


IMO. if the surging gets better when you add to the cracker table. you need more RAF. I would try to fine tune the idle with RTT if you're still using the old 2.24 software.


try more RAF and raise throttle cracker enable.

[JakeFusion]

It got better taking it out of cracker. I need less RAF it appears. So I had to wait to today to re-run RAF from a cold start to get a new baseline of numbers. Playing with timing and A/F does change that (as does weather conditions). I started logging cracker and follower. So that's how I started to tune the airflow. But timing doesn't seem to play as important a role when de-loading as I thought.

I'll see if raising the cracker does anything.