LS1 hesitation at launch, need scanned / tune tweaked?
07-09-2013, 11:20 PM
#1
LS1 hesitation at launch, need scanned / tune tweaked? I have this posted on some other sites trying to figure this out, possibly trans / converter, or engine (yeah, I narrowed it down). Trans guys say it w/ the tune. Would like to know your take on this
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, 92/92. 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 while slowely sweeping it. 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. If it sounds like something that needs HP Tuners to check, I will have to make a call to the last shop that tuned it.
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.
-------------------------------------------------------------------------------------
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
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, 92/92. 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 while slowely sweeping it. 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. If it sounds like something that needs HP Tuners to check, I will have to make a call to the last shop that tuned it.
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.
-------------------------------------------------------------------------------------
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
