1996 lt4 stall and studder help!!!!!!!!!
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Heel & Toe
Joined: Mar 2017
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1996 lt4 stall and studder help!!!!!!!!!
Okay so i have a 1996 lt4 obviously 6 speed... i did a cat delete x pipe in place of the resignator and magniflow mufflers about 4 months ago, and i get a constant check enginle light because of the cat delete, but it wasnt causing any problems so i wasnt worried about it. But about 2 months ago my icm went out and in the process of trying to figure out the problem of my car not starting i replaced the opti, all new plugs and wires, the coil, and then the icm last 
But none the less the car fired up and ran, but i now have a studder right at 5000 rpm and i cant figure out the problem. Its almost like it hits a rev limiter at 5000 rpm in any gear every time, i cant go past it.
And yesterday i replaced a broken roller rocker hoping it was the problem, and it not only didnt fix the studder problem i now randomly stall when i come to a stop... the car idles way down to around 300 or 400 rpm and just dies, but fires right back up and i can drive away fine.... the stall problem is random, somtimes it does it and somtimes it doesnt.... but the studder at 5k its consistant and i can't figure it out...
SOMEONE PLEASE HELP ME!!!
But none the less the car fired up and ran, but i now have a studder right at 5000 rpm and i cant figure out the problem. Its almost like it hits a rev limiter at 5000 rpm in any gear every time, i cant go past it.
And yesterday i replaced a broken roller rocker hoping it was the problem, and it not only didnt fix the studder problem i now randomly stall when i come to a stop... the car idles way down to around 300 or 400 rpm and just dies, but fires right back up and i can drive away fine.... the stall problem is random, somtimes it does it and somtimes it doesnt.... but the studder at 5k its consistant and i can't figure it out...
SOMEONE PLEASE HELP ME!!!
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Last edited by antfarmer2; Mar 19, 2017 at 07:20 PM.
Thread Starter
Heel & Toe
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***UPDATE*** i havnt looked into the o2s yet, but now the car will die if i even try to drive it and most of the time wont start... i cleaned the IAC very well, and found a couple vacuum leaks using starter fluid. I replaced the bad line, and any others that i thought could be a problem... didnt help at all... at idle it runs like crap and will die. When it does die it wont start back up, i have to wait for a while then it will fire up and repeat... 
Le Mans Master
Joined: Jan 2006
Posts: 5,621
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From: Orlando FL
At 5000 RPM the throttle is probably close to wide open and the O2s are out of equation. They are not used for A/F calculation at high power. You have to have it idle first before you worry about the high end. Have you checked the EGR for leaks and proper operation with a vacuum gauge and the vacuum release checked.
I would get a professional smoke test and make sure the manifold is sealed properly as well as the other areas. I would also have a good scanner connected to check the IAC counts, fuel trim and o2 voltage swings.
I would get a professional smoke test and make sure the manifold is sealed properly as well as the other areas. I would also have a good scanner connected to check the IAC counts, fuel trim and o2 voltage swings.
Team Owner
Joined: Jul 2004
Posts: 28,430
Likes: 3,282
From: Hartford WI
I would do a WOT run to see if it holds pressure. IF so, the pump is good. After that, I'd check the IAC counts. If it holds at 20-30 counts when it is at stable operating temp with everything but the motor off, I doubt there is a leak. OTOH, if he can't do that simple thing, it means there is a leak somewhere and the ECM won't let the IAC open which explains why he would turn the screw all the way out and still have 0 counts.
Drifting
Joined: Jul 2004
Posts: 1,353
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From: MA
At 5000 RPM the throttle is probably close to wide open and the O2s are out of equation. They are not used for A/F calculation at high power. You have to have it idle first before you worry about the high end. Have you checked the EGR for leaks and proper operation with a vacuum gauge and the vacuum release checked.
I would get a professional smoke test and make sure the manifold is sealed properly as well as the other areas. I would also have a good scanner connected to check the IAC counts, fuel trim and o2 voltage swings.
I would get a professional smoke test and make sure the manifold is sealed properly as well as the other areas. I would also have a good scanner connected to check the IAC counts, fuel trim and o2 voltage swings.
I agree that the O2s won't cause a problem at 5000RPM (I doubt this could be your problem). If you have good fuel pressure 40-45psi at idle, I suspect your new optispark.
Le Mans Master
Joined: Aug 1999
Posts: 7,339
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From: WilkesBarre PA
Are the rockers still the stock 10mm stud, non adjustable ones or were they replaced with adjustable 3/8 ones? If they are adjustable and you over tightened it it will cause a rough condition.
Thread Starter
Heel & Toe
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Thanks for all the responses guys! The 5k studder acurred after i changed the opti, icm, ect... other than not being able to go past 5k it ran fine in the bottom end. My new problem (dying, rough idle) acurred right after i replaced the roller rocker, but the car sat for a month waiting on the rocker...
They are stock studs and non adjustable, but my concern is the rocker i baught is not an oem, and it came with an adjustable nut (with a set screw in it)?? I just used my stock nut from the other rocker... i could not find a direct replacement? Could that be a problem? If so where can i find an oem lt4 1.6 ratio rocker?
Thanks guys
Thanks guys
Safety Car
Joined: Sep 2001
Posts: 4,155
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From: Glenbeulah Wi
Lt4 engines do not have EGR valves. I would look at the new optispark you replaced, there are a lot of new defective/inferior ones out there!
I agree that the O2s won't cause a problem at 5000RPM (I doubt this could be your problem). If you have good fuel pressure 40-45psi at idle, I suspect your new optispark.
I agree that the O2s won't cause a problem at 5000RPM (I doubt this could be your problem). If you have good fuel pressure 40-45psi at idle, I suspect your new optispark.
This sounds like an ignition problem.