Surging when Coasting
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
Surging when Coasting 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?
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?
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
I'm coasting with 34 degrees of timing. I kept adding it... that and adding airflow to the TF/TC made light throttle possible without bucking. But it hasn't helped on decel.
TECH Addict
Joined: Dec 2004
Posts: 2,177
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From: Florida
my truck was real bad about this. i think i adjusted the dfco to fix it. it still does it until its fully warmed up though. i havent figured out how to fix that.
4.8/4l60e/0411/efilive/cos5/olsd
4.8/4l60e/0411/efilive/cos5/olsd
Staging Lane
Joined: Nov 2015
Posts: 96
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You've got the same spark for coasting and decel... decel should be less. You want the engine to unload completely in decel. Try reducing your spark to just below idle spark (maybe about 27°) for the 0.08 and 0.12 grams cells in the 1400-2400 rpm range and for the 1200 rpm cells set it half way between that and idle (maybe about 30°). You might have to go a bit lower, but that's a good starting point.
If you can't get it better with that, then log the usual things you'd log but be sure to include IAC counts, MAP, spark and wideband.
If you can't get it better with that, then log the usual things you'd log but be sure to include IAC counts, MAP, spark and wideband.
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Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
I've played around with the timing quite a lot to get it to act pretty well with light throttle and no throttle. In fact, adding as much timing as I did made it more manageable with 0% TPS... I was surprised I needed 34+ degrees.
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Joined: Nov 2015
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I've had a good look over your tune now and WOW... you really are putting a lot of air into your engine with your throttle cracker and follower. With that much airflow, your decel is more like an off throttle coasting. I can see why you need that much spark in your decel.
We need to figure out what's causing you to need so much airflow. Your VE table doesn't look quite right to me... maybe a symptom of bad injector data, but I don't know if that's enough to cause this.
See if you can get a log for me.
We need to figure out what's causing you to need so much airflow. Your VE table doesn't look quite right to me... maybe a symptom of bad injector data, but I don't know if that's enough to cause this.
See if you can get a log for me.
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
I'll get a log today.
I added airflow there to take away the bucking. As I said - it used to buck pretty bad (16 degrees of overlap) when locked up. I found that adding airflow took it away and made decel better too. Then adding timing made it even better... but it's not quite right.
I swapped the injectors this year for GM L9H Flex Fuel injectors. Data is from GM. VE table has always been incredibly lean down low. Even when I had Ford 47lbs injectors in to start with. Looked pretty similar.
I added airflow there to take away the bucking. As I said - it used to buck pretty bad (16 degrees of overlap) when locked up. I found that adding airflow took it away and made decel better too. Then adding timing made it even better... but it's not quite right.
I swapped the injectors this year for GM L9H Flex Fuel injectors. Data is from GM. VE table has always been incredibly lean down low. Even when I had Ford 47lbs injectors in to start with. Looked pretty similar.
Joined: May 2004
Posts: 1,593
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From: Halfway back on the Highway to Hell...again!
I have this in my 94 Impala SS with a 24x swap. Another guy on the Impala forum had the same issue and he made some changes in the dwell tables. He said he used the dwell tables from a 5.3L truck program and it completely solved his problem.
I haven't had a chance to try this yet since the car is away for the winter. But come springtime I'm gonna do some testing.
I haven't had a chance to try this yet since the car is away for the winter. But come springtime I'm gonna do some testing.
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
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.
Drive shows temp at 160 with me driving around. Ok shows as I let it warm up to temp in my neighborhood as I drove slow. Tune attached as well.
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.
Drive shows temp at 160 with me driving around. Ok shows as I let it warm up to temp in my neighborhood as I drove slow. Tune attached as well.
Not sure if this will help your coast down, but for the idle dip, try setting minimum transient pulse to 0.010 down from 0.020, and the minimum transient RPM, increase to 700 from 450, since your idle speed is 900, not stock.
Another thing would be in your derivative RPM low table, put a small (0.10000-ish) value in for 0.03 and 0.04 columns. This should anticipate the rpms dropping too far and add a smudge of air preemptively
Another thing would be in your derivative RPM low table, put a small (0.10000-ish) value in for 0.03 and 0.04 columns. This should anticipate the rpms dropping too far and add a smudge of air preemptively
Something else I noticed is your idle timing is set to 33 degrees, which I'm betting matches the minimum MAP reading?
If this is true, your idle adaptive spark won't work quite right. If you advance spark to gain RPM, you'll actually LOSE torque, resulting in either a drop in RPM or more air needed.
If you're game, try setting your idle spark to 28 degrees instead. Then, in your idle underspeed spark table, go like this:
everything else....-100...-75...-50...-25...0
4.........................4.......3......2.......1 .....0
In your overspeed table, go like this:
0....25...50...75...100...125...150...175...200... everything else
0.....1.....2....3.....4.......5......6.......7... ...8..........8
If this is true, your idle adaptive spark won't work quite right. If you advance spark to gain RPM, you'll actually LOSE torque, resulting in either a drop in RPM or more air needed.
If you're game, try setting your idle spark to 28 degrees instead. Then, in your idle underspeed spark table, go like this:
everything else....-100...-75...-50...-25...0
4.........................4.......3......2.......1 .....0
In your overspeed table, go like this:
0....25...50...75...100...125...150...175...200... everything else
0.....1.....2....3.....4.......5......6.......7... ...8..........8
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
That's correct. MAP minimum is in the 68-70kPa range at 32 degrees. I have it set at 28 in park since there's no load. But with the A/C on and with power steering, the added spark makes it less prone to dipping RPM if I'm in a parking lot for example. But that may be an airflow problem.
Staging Lane
Joined: Nov 2015
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Darth V8r is right, you need less spark at idle. I'd be inclined to set idle even lower than he recommends... maybe to about 26. Then you'll need more airflow to idle properly, which is a good thing as I think you don't have enough base airflow now which is why you have to throw so much air at it with your cracker table.
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
RAF has been set. The airflow in the tune are actually higher than what the RAF process called for because it was so low. I think I added around 1/g sec vs what the RAFconfig needed. I logged it from warmup in drive and park.