Car stutters upon acceleration after cold start up, possible vaccuum leak???
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Car stutters on acceleration to 3000rpm after cold start up, possible vaccuum leak???
I don't know why my car is doing this, but upon cold startup the car stutters really bad at low rpms (up to roughly 2500rpms-3000rpms or so) upon acceleration. The engine is shaking pretty badly, and if feels like I'm only running on say 5 or 6 cylinders. The car accelerates as if it only had about 150-200hp. During acceleration, all of a sudden without warning, the engine just goes back to normal at around 2500-3000rpms and pulls great.
The shop that installed my LSX intake as well as a buddy of mine both checked for vaccuum leaks around the manifold and found nothing.
I'm stumped and can't figure out what might be causing this. My brakes seem really mushy as of late too, and of course, I'm down about 40rwtq down low and about 30rwhp/30rwtq down from where I should be all around.
Any suggestions? I've swapped MAF sensors to no avail, and changed the valvetrain around. I'm going to test if the weatherpack plug on the MAF sensor tomorrow, but other than that I'm stumped. Any ideas?
The shop that installed my LSX intake as well as a buddy of mine both checked for vaccuum leaks around the manifold and found nothing.
I'm stumped and can't figure out what might be causing this. My brakes seem really mushy as of late too, and of course, I'm down about 40rwtq down low and about 30rwhp/30rwtq down from where I should be all around.
Any suggestions? I've swapped MAF sensors to no avail, and changed the valvetrain around. I'm going to test if the weatherpack plug on the MAF sensor tomorrow, but other than that I'm stumped. Any ideas?
Last edited by verbs; 03-24-2004 at 05:55 PM.
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Originally Posted by Damian
Sounds like normal cold start up surging to me. My cam does that a little bit when cold, kinda stutters below 3K until it's warm and then goes away. Your cam is a LOT bigger than mine, so it'll probably be a bit worse...
The car will idle fine after about a nice 20 second warm up.....what I'm referring to almost feels like a mini earthquake in my engine about 1-2 minutes after startup after the initial cold start surging takes place.
Last edited by verbs; 03-24-2004 at 05:48 PM.
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Originally Posted by Damian
Gotcha. Could have a problem somewhere. That kinda stuff is hard to diagnose over the internet
Dude all things considered, the G5X3 is almost twice the size of your old cam. I wouldn't be suprised in some major surging @ cold startup...
Dude all things considered, the G5X3 is almost twice the size of your old cam. I wouldn't be suprised in some major surging @ cold startup...
I'm hoping someone else has seen this same issue before and found a fix.
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kinda feel like the gas gets pinched off then, all of a sudden the gas turns on again and the car accelerates normally? Mine does this too, The engine is new and so is the big cam. I'm thinking vacuum leak around the intake manifold. My car falls flat on its face when I try to accelerate, then past 3500 it wakes up and goes??????
I just don't want to spend 50 bucks on stock LS1 intake manifold gaskets again
I will be ripping into it tomorrow, maybe my knock sensor harness got under the intake manifold funny and it lifted one side????
Let me know if you find out what it is.
I just don't want to spend 50 bucks on stock LS1 intake manifold gaskets again
I will be ripping into it tomorrow, maybe my knock sensor harness got under the intake manifold funny and it lifted one side????
Let me know if you find out what it is.
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Originally Posted by frcefed98
kinda feel like the gas gets pinched off then, all of a sudden the gas turns on again and the car accelerates normally? Mine does this too, The engine is new and so is the big cam. I'm thinking vacuum leak around the intake manifold. My car falls flat on its face when I try to accelerate, then past 3500 it wakes up and goes??????
I just don't want to spend 50 bucks on stock LS1 intake manifold gaskets again
I will be ripping into it tomorrow, maybe my knock sensor harness got under the intake manifold funny and it lifted one side????
Let me know if you find out what it is.
I just don't want to spend 50 bucks on stock LS1 intake manifold gaskets again
I will be ripping into it tomorrow, maybe my knock sensor harness got under the intake manifold funny and it lifted one side????
Let me know if you find out what it is.
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Originally Posted by CANNIBAL
May be your 02 sensors. My brother's car did the exact same thing, usually when it was wet, as soon as he'd hit a certain RPM it'd be fine. Also, it would completely go away after about 2 minutes regardless.
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Originally Posted by verbs
When I logged my o2 sensor activityduring dyno runs I noticed they weren't switching as fast as they should be. It's probably time to replace them and that could very well be it.
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Same problem
I am currently having the same problem on cold start ups. So far I have installed new plugs which where fouled but did not solve the problem. With Auto Tap I am seeing a high number of misfires on Bank 2. I started to monitor my O2 sensor. When cold it reads 1150mV, after start up about 20 seconds later when the engine gets to about 120F, the O2 sensor starts to responed an then I get the misfires. I beileve when the car is cold the sensors should reas 200 mV or less. I am going to get a new O2 sensor and see if this fixes the problem.
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Originally Posted by verbs
I don't know why my car is doing this, but upon cold startup the car stutters really bad at low rpms (up to roughly 2500rpms-3000rpms or so) upon acceleration. The engine is shaking pretty badly, and if feels like I'm only running on say 5 or 6 cylinders.
Just thought what about the flywheel and clutch assembly? Has that been messed with?
Last edited by kossuth; 03-24-2004 at 07:45 PM.
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I assume this is only under load?
I had a similar symptoms not too long ago.
I changed my plugs.Of which four turned out to be heavily fouled I had to clean the soot off of one of my o2 sensors.
Is there any chance you have a loose/damaged plug wire or did have for awhile?
If the problem is not only limited to when you have a load on the engine
Check and double check for vacuum leaks. Spray carb cleaner,starting fluid,wd40,etc. (whichever YOU feel comfortable with-No suing me if the ether blows up on you ) around areas you suspect leaks. Idle will generally increase if any of these chemicals are drawn into the intake via vacuum leak. If you're extra paranoid or have painted parts underhood you can use water and wait for the idle to fall off. Water is nowhere near as quick as the others though.
You can use a spray bottle to mist water on your exhaust headers/manifolds to check for a non firing cylinder(due to lack of fuel or spark). Spray all of the exhaust tubing on one side of the motor if one takes much longer to boil off the water that cylinder is not up to temp. Check the plug,wire,coil,injector,etc. there.
Use a screwdriver or a mechanics stethoscope to verify proper function of your injectors. Listen to each individually and see if any one or two sound different from the rest.Obviously you'll hear a rapid ticking from all of them. One pulsing significantly slower would signal some kind of problem.
Good luck! Hope you get the problem wrapped up soon.
I had a similar symptoms not too long ago.
I changed my plugs.Of which four turned out to be heavily fouled I had to clean the soot off of one of my o2 sensors.
Is there any chance you have a loose/damaged plug wire or did have for awhile?
If the problem is not only limited to when you have a load on the engine
Check and double check for vacuum leaks. Spray carb cleaner,starting fluid,wd40,etc. (whichever YOU feel comfortable with-No suing me if the ether blows up on you ) around areas you suspect leaks. Idle will generally increase if any of these chemicals are drawn into the intake via vacuum leak. If you're extra paranoid or have painted parts underhood you can use water and wait for the idle to fall off. Water is nowhere near as quick as the others though.
You can use a spray bottle to mist water on your exhaust headers/manifolds to check for a non firing cylinder(due to lack of fuel or spark). Spray all of the exhaust tubing on one side of the motor if one takes much longer to boil off the water that cylinder is not up to temp. Check the plug,wire,coil,injector,etc. there.
Use a screwdriver or a mechanics stethoscope to verify proper function of your injectors. Listen to each individually and see if any one or two sound different from the rest.Obviously you'll hear a rapid ticking from all of them. One pulsing significantly slower would signal some kind of problem.
Good luck! Hope you get the problem wrapped up soon.
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Originally Posted by lerajie
I assume this is only under load?
I changed my plugs.Of which four turned out to be heavily fouled I had to clean the soot off of one of my o2 sensors.
Is there any chance you have a loose/damaged plug wire or did have for awhile?
I changed my plugs.Of which four turned out to be heavily fouled I had to clean the soot off of one of my o2 sensors.
Is there any chance you have a loose/damaged plug wire or did have for awhile?
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Originally Posted by 99 Black Bird T/A
How much long do you let the car warm up before putting in gear and driving?
Could a faulty cam position sensor cause any of the erratice behavior?
Could a faulty cam position sensor cause any of the erratice behavior?
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Originally Posted by verbs
I don't know why my car is doing this, but upon cold startup the car stutters really bad at low rpms (up to roughly 2500rpms-3000rpms or so) upon acceleration. The engine is shaking pretty badly, and if feels like I'm only running on say 5 or 6 cylinders. The car accelerates as if it only had about 150-200hp. During acceleration, all of a sudden without warning, the engine just goes back to normal at around 2500-3000rpms and pulls great.
The shop that installed my LSX intake as well as a buddy of mine both checked for vaccuum leaks around the manifold and found nothing.
I'm stumped and can't figure out what might be causing this. My brakes seem really mushy as of late too, and of course, I'm down about 40rwtq down low and about 30rwhp/30rwtq down from where I should be all around.
Any suggestions? I've swapped MAF sensors to no avail, and changed the valvetrain around. I'm going to test if the weatherpack plug on the MAF sensor tomorrow, but other than that I'm stumped. Any ideas?
The shop that installed my LSX intake as well as a buddy of mine both checked for vaccuum leaks around the manifold and found nothing.
I'm stumped and can't figure out what might be causing this. My brakes seem really mushy as of late too, and of course, I'm down about 40rwtq down low and about 30rwhp/30rwtq down from where I should be all around.
Any suggestions? I've swapped MAF sensors to no avail, and changed the valvetrain around. I'm going to test if the weatherpack plug on the MAF sensor tomorrow, but other than that I'm stumped. Any ideas?
Try increasing yout RAF values at the temps affected.
Has all this happened since the intake install?
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Originally Posted by gojo
Try increasing yout RAF values at the temps affected.
Has all this happened since the intake install?
Has all this happened since the intake install?
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Originally Posted by verbs
all this just started happening since the intake/cam install.
When I tuned mine, I had to reduce the IAC and RAF's by about 4. I did that across the board until I got rid of racing startups. I had to go back and raise the RAF's across the board and then a little more in the cold temps to smooth out running until the engine warmed.