LS1 hesitation at launch, smooth everywhere else? th400
07-08-2013, 10:53 PM
#1
LS1 hesitation at launch, smooth everywhere else? th400 Kinda pissed at the moment since my car launches like a turd. Having a problem that so far everything I have checked out seems ok.
Free revving my car is smooth. Rolling at about 25 mph and punching it, car is smooth. Holding the brakes and bringing up the rpm to launch on the street, the car seems to get stuck at around 2500-3000 rpm for a few seconds and then takes off. I have been trying to get the suspension tweaked and practicing launching and my car is horrible.
Problem only happens when I hold the brakes for a second or two to bring the rpm up, and then launch it from a dead stop. The car has seemed to bog down sometimes for half a second, sometimes for up to 3 seconds and runn like crap for that small instance. Never consistant. I can get the rpm up to about 2500 on the street and feather the pedal and keep it at the absolute limit before the tire break loose, but it will roll for at least 30+ feet and not increase rpm by more that 50, then is seems to pull out of its sluggishness and go. It won't just launch, sota just gets stuck for a bit till it can work its way out of the problem, then go. Its very hard to explain and the vids I took of the tac have glitches, so I have to try a different camera to show.
Car is a forward valve body th400, no trans brake, 3600 stall verter, heads, cam, 9" car. Only puts down a pitiful 382hp /348tq on the pony dyno, 235/240 649/609, 111LSA, ported 243's. Ever since I upgraded to these heads / cam, I do notice that the car is sluggish untill it passes 3ooo rpm, then it feels like it goes over a hump and then the power comes, even from a roll w/ a moderate pedal pushing. Foot braking and launching it just seems to amplify the problem. It literally gets stuck in that low rpm for anywhere from 1-3 seconds after I release the brakes, then seems to clear itself, and takes off like there is nothing wrong.
I will try to get a vid after work tomorrow. I was looking through the GM service manual and checked what I could. Fuel filter is new today, old had minimal dirt. MAF is clean and new (GM 85mm), Plugs are new TR6's w/ .045 gap (reccomendation from my tuner)-only 400 miles on them ,pretty new MSD wires that don't contact any metal, so no arcing, never any problem with the coil packs (300,000 mile D585 heatsink truck ones), cleaned the IAC motor, Put a volt meter on the TPS sensor and opened and closed it a few times and didn't see any inconsistant voltage readings. I have only ever had one DTC- I think a PO155 bank 2 sensor 1 O2 heater.
There is no problem from a roll, but I have been building my car for the strip, and if I can't launch the car from a stop, I've wasted a long time and a shitload of $$ building this car. Cam or convertor? I am stumped at the moment. Can't be a fuel issue, injectors are not maxed out (FAST 36 lb) and 255 GPH pump, clean fuel filter. Unfortunately the dyno chart starts at 3k, and the chart looks pretty smooth to me.
It does feel sluggish below 3000 rpm with moderate acceleration, but I feel that it's due to the 3600 converter. But basically it feels great from a roll. Just mostly works like a turd foot braking it to launch. My brakes can really only hold the car to about 3000rpm before it will start to roll. Sometimes from a stop and bringing the rpm up there is no problem but that is rare. But holding the rpm I think amplifies the feel of sluggishness below 3k when rolling. It's horrible when everyone can launch like a slingshot, and your car gets stuck in an rpm for 1-3 seconds before it picks up. Used to never have this problem. Used to **** people off that challenged me because I was quick off the light and could keep my car from spinning. I've lost that now.
Only thing I changed over winter was that I went from tr55's gapped at .060, to TR6's gapped at .045, and went from stock rockers w/ upgraded trunions, to HD 1.7 rollers. I wish I knew someone local that could plug my car into HP tuners and watch some things to see if they spot any abnormalities. If anyone has any ideas I am all ears. I need to get this situation fixed.
After I let off the brake, the car will literally get stuck in a certain RPM for 1-3 seconds even if I put more pedal into it and not move more that 50 rpm from anywhere from .5 seconds all the way up to 3 seconds, then "clears" itself out and pulls smoothly. Amplified by foot braking only, almost un-noticeable from a roll.
I can post pics of the dyno graph, and hopefully a vid of what my tac shows after work tomorrow, Won't stop raint atm. I apologize if I typed the same thing many times, just trying to explain it at easily as possible, plus being pissed and not sober doesn't help
Thank you for any help
-mark jr.
Free revving my car is smooth. Rolling at about 25 mph and punching it, car is smooth. Holding the brakes and bringing up the rpm to launch on the street, the car seems to get stuck at around 2500-3000 rpm for a few seconds and then takes off. I have been trying to get the suspension tweaked and practicing launching and my car is horrible.
Problem only happens when I hold the brakes for a second or two to bring the rpm up, and then launch it from a dead stop. The car has seemed to bog down sometimes for half a second, sometimes for up to 3 seconds and runn like crap for that small instance. Never consistant. I can get the rpm up to about 2500 on the street and feather the pedal and keep it at the absolute limit before the tire break loose, but it will roll for at least 30+ feet and not increase rpm by more that 50, then is seems to pull out of its sluggishness and go. It won't just launch, sota just gets stuck for a bit till it can work its way out of the problem, then go. Its very hard to explain and the vids I took of the tac have glitches, so I have to try a different camera to show.
Car is a forward valve body th400, no trans brake, 3600 stall verter, heads, cam, 9" car. Only puts down a pitiful 382hp /348tq on the pony dyno, 235/240 649/609, 111LSA, ported 243's. Ever since I upgraded to these heads / cam, I do notice that the car is sluggish untill it passes 3ooo rpm, then it feels like it goes over a hump and then the power comes, even from a roll w/ a moderate pedal pushing. Foot braking and launching it just seems to amplify the problem. It literally gets stuck in that low rpm for anywhere from 1-3 seconds after I release the brakes, then seems to clear itself, and takes off like there is nothing wrong.
I will try to get a vid after work tomorrow. I was looking through the GM service manual and checked what I could. Fuel filter is new today, old had minimal dirt. MAF is clean and new (GM 85mm), Plugs are new TR6's w/ .045 gap (reccomendation from my tuner)-only 400 miles on them ,pretty new MSD wires that don't contact any metal, so no arcing, never any problem with the coil packs (300,000 mile D585 heatsink truck ones), cleaned the IAC motor, Put a volt meter on the TPS sensor and opened and closed it a few times and didn't see any inconsistant voltage readings. I have only ever had one DTC- I think a PO155 bank 2 sensor 1 O2 heater.
There is no problem from a roll, but I have been building my car for the strip, and if I can't launch the car from a stop, I've wasted a long time and a shitload of $$ building this car. Cam or convertor? I am stumped at the moment. Can't be a fuel issue, injectors are not maxed out (FAST 36 lb) and 255 GPH pump, clean fuel filter. Unfortunately the dyno chart starts at 3k, and the chart looks pretty smooth to me.
It does feel sluggish below 3000 rpm with moderate acceleration, but I feel that it's due to the 3600 converter. But basically it feels great from a roll. Just mostly works like a turd foot braking it to launch. My brakes can really only hold the car to about 3000rpm before it will start to roll. Sometimes from a stop and bringing the rpm up there is no problem but that is rare. But holding the rpm I think amplifies the feel of sluggishness below 3k when rolling. It's horrible when everyone can launch like a slingshot, and your car gets stuck in an rpm for 1-3 seconds before it picks up. Used to never have this problem. Used to **** people off that challenged me because I was quick off the light and could keep my car from spinning. I've lost that now.
Only thing I changed over winter was that I went from tr55's gapped at .060, to TR6's gapped at .045, and went from stock rockers w/ upgraded trunions, to HD 1.7 rollers. I wish I knew someone local that could plug my car into HP tuners and watch some things to see if they spot any abnormalities. If anyone has any ideas I am all ears. I need to get this situation fixed.
After I let off the brake, the car will literally get stuck in a certain RPM for 1-3 seconds even if I put more pedal into it and not move more that 50 rpm from anywhere from .5 seconds all the way up to 3 seconds, then "clears" itself out and pulls smoothly. Amplified by foot braking only, almost un-noticeable from a roll.
I can post pics of the dyno graph, and hopefully a vid of what my tac shows after work tomorrow, Won't stop raint atm. I apologize if I typed the same thing many times, just trying to explain it at easily as possible, plus being pissed and not sober doesn't help
Thank you for any help
-mark jr.
07-09-2013, 11:10 PM
#2
Well the vid is crap. Looking at it now it doesn't look like much but it is horrible waiting for the car to do anything after you let off the brakes and is extremely noticable to any passengers.
The vid below shows the foot braking it at 2500. Once it is there, my foot is completely off the brakes and the car is rolling for the 500 rpm till it gets to 3k. Then the car will pull. It's like a complete dead zone. Car just won't launch like it should. A Honda could take me off the line. Hopefully someone can tell from the vid.
http://s131.photobucket.com/user/Bla..._5664.mp4.html
The vid below shows the foot braking it at 2500. Once it is there, my foot is completely off the brakes and the car is rolling for the 500 rpm till it gets to 3k. Then the car will pull. It's like a complete dead zone. Car just won't launch like it should. A Honda could take me off the line. Hopefully someone can tell from the vid.
http://s131.photobucket.com/user/Bla..._5664.mp4.html
07-10-2013, 08:59 AM
#4
I can get it to almost 3k before the brakes can't handle it anymore. Anything higher and the tires will just spin on the street. Unfortunately when I got the rear narrowed in the car last year I had to chop the e-brake brackets off and narrow them down because they hit the backing plates. Haven't had a chance to re-weld them together.
It definately feels like is bogging down. When I get it up to 3k, sometimes it bogs less, sometimes the full 3 seconds. Never consistant. I tested it last night a few times and yesterday seemed the worst yet. Kinda stumped at what I should be looking at next. Luckily today I am off work so I will be researching and see if I can find somethng else to look into.
It definately feels like is bogging down. When I get it up to 3k, sometimes it bogs less, sometimes the full 3 seconds. Never consistant. I tested it last night a few times and yesterday seemed the worst yet. Kinda stumped at what I should be looking at next. Luckily today I am off work so I will be researching and see if I can find somethng else to look into.
07-10-2013, 11:07 AM
#5
I don't know your combination, carb, efi, etc, do you have plenty of timing at that rpm?
Sounds to me like it needs a little looser converter now to get to where the engine makes power. What I mean is, if you can only get it to 3000 rpm, and it doesn't pull well there, then you need a higher stall to get into the power.
Sounds to me like it needs a little looser converter now to get to where the engine makes power. What I mean is, if you can only get it to 3000 rpm, and it doesn't pull well there, then you need a higher stall to get into the power.
Last edited by Bowtie316; 07-10-2013 at 03:18 PM.
07-10-2013, 02:26 PM
#6
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yeah when your launching at 2500 rpm you havnt even reached your 3600 stall you might want to try 2500 or 3000 stall, either that or launch from higher rpm.
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07-10-2013, 04:08 PM
#8
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What gears are in this car? That is a stout camshaft you have. Who built the converter? If it's a 3600 and is only foot braking to 3000, either something is a miss or that thing must be super TIGHT. Can you take a video from a stand still and just punching the gas to show us what the converter flashes to? Did you swap from a 4l60e? Keep in mind the difference in first gear ratio from a 400 to a 4l60e is quite big. My honest feeling, from the video, is that it has nothing to do with tuning. I think that converter is too tight and you need more gear. Fill us in with answers to those questions I asked if you don't mind.
07-10-2013, 05:28 PM
#9
First question I have, is after you let go of the brakes, are you FLOORING the throttle? In your first post you said it does it whether you floor it afterwards or not. So just to be clear, you obviously are going to want to floor it, otherwise you are probably not going to enter PE mode in the ECM.
But besides that, I am almost 100% certain that your car is doing exactly like mine is. Mine is pretty much the SAME setup as yours: 380whp, TH400 (Except mine has a transbrake), 3600rpm stall, and a 9 inch rear. Mine would take off faster than yours, but it was still the fact that we can only get our cars to about that 3000rpm mark, where (Because of our huge cam) we make no power at all.
The solution.... You need more gear in your car, and possibly you need to have the tune looked at. I made sure I put in as MUCH timing as I could in the 3200-4000 range so that I would have as much power as I possibly could at the launch in the car.
I had 3.5 gears in my car recently, but I am in the process of swapping to 4.57's, so I will let you know what kind of difference it makes. Hopefully it is the difference between noon and midnight. lol Good luck!
But besides that, I am almost 100% certain that your car is doing exactly like mine is. Mine is pretty much the SAME setup as yours: 380whp, TH400 (Except mine has a transbrake), 3600rpm stall, and a 9 inch rear. Mine would take off faster than yours, but it was still the fact that we can only get our cars to about that 3000rpm mark, where (Because of our huge cam) we make no power at all.
The solution.... You need more gear in your car, and possibly you need to have the tune looked at. I made sure I put in as MUCH timing as I could in the 3200-4000 range so that I would have as much power as I possibly could at the launch in the car.
I had 3.5 gears in my car recently, but I am in the process of swapping to 4.57's, so I will let you know what kind of difference it makes. Hopefully it is the difference between noon and midnight. lol Good luck!
