Lt1 383 stroker missing at 4000-5000 rpm, NEED A GENIUS!!!
08-10-2006, 04:33 AM
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Lt1 383 stroker missing at 4000-5000 rpm, NEED A GENIUS!!! Hey I have posted before and have fixed half the problem. I have a 1995 LT1 camaro with the new 383 stroker (12.5:1) compression. The motor has approx 1200 miles on it with Llyod Elliot stage 2 heads and stage 2 cam. It has an LT4 intake manifold, 58mm throttle body, no cats and Slp loudmouth exhaust (which is really failing miserably to calm her down). 30 lb injectors, 255 walbro, great fuel pressure (adjustable fuel pressure regulator on it), new plugs, wires, MSD opti, new coil, new coil wire, clean MAF screen free from random intake debris. I checked to see if I had spark at the coil itself using a test-light and the spark is very strong and bright blue when it jumped onto the test light. The fuel pressure reamains constant with the Key on engine off position (not running). It also has a brand new TPS sensor. There is no check engine light on.
This is what the car is doing. If it is being started for the first time of the day, it fires right up and holds a beautiful lopey idle just like I want to hear. Idles at 1000 rpms. Now if the car is hot, or ran for more than 5 minutes and I try to start it, it take a good 5-10 turns before it will finally fire and then the throttle response is really sluggish for a few seconds, never really getting crisp or instant throttle response. The car runs a little rough while under 2000 rpms while I am driving but accelerates BEAUTIFULLY until I hit 4000-5000 rpms and then the engine starts to miss really bad and will just keep missing until I let off the throttle. It happens everytime at about the same rpm everytime too. I notice once the car is warmed up and it comes down from anything higher than 3000 rpms, the car barely catches its idle (drops to 400-500 and while it is that low the service engine soon light comes on until the car adjusts up to the 1000 rpm idle or I give it gas to save it from stalling. If I leave it at the 400-500 rpm range for long it will stll completely within 15 seconds. The fuel filter has approx 1200 miles on it as well as the fuel pump. I am getting great power from the battery and alternator has been checked and is perfect also. Basically everything in the car is new or has less than 1200 miles on it.
Note: During the 1200 miles of breaking in the motor there was a time (200miles worth of time or so) when the motor would scream all the way to 6500 rpms without missing at all (but constant at a constant speed you could feel the car miss/hesitate slightly). The missing was a sudden change so something changed for this extreme missing /hesitation at high rpms to occur. You can also feel the car slightly missing if it is held at a constant speed at any rpm, it kind of spits and sputters unless you are accelerating. It accelerates very smooth until 4000-5000 rpms and then misses really bad to the point where the whole car jerks and almost shuts off completely. It will continue to miss until I get off the gas, like I am hitting some kind of rev limiter or something. I was thinking it has to be fuel relate, like fuel cut was happening but I haven't the slightest clue as to what I am talking about with diagnosing these cars correctly. Could it be a bad injector or wouldn't that make the car miss all the time when I was accelerating. I know 99.99% sure its not the opti because that was changed to the new MSD opti and the car runs the EXACT same as it did with the other opti I thought was bad. The car finally hits a real boost of torque at 3500-4000 rpms and its like as soon as I start to feel like the car is a rocket this miss happens and ruins everything. Any help is greatly appreciated. Thanks so much.
This is what the car is doing. If it is being started for the first time of the day, it fires right up and holds a beautiful lopey idle just like I want to hear. Idles at 1000 rpms. Now if the car is hot, or ran for more than 5 minutes and I try to start it, it take a good 5-10 turns before it will finally fire and then the throttle response is really sluggish for a few seconds, never really getting crisp or instant throttle response. The car runs a little rough while under 2000 rpms while I am driving but accelerates BEAUTIFULLY until I hit 4000-5000 rpms and then the engine starts to miss really bad and will just keep missing until I let off the throttle. It happens everytime at about the same rpm everytime too. I notice once the car is warmed up and it comes down from anything higher than 3000 rpms, the car barely catches its idle (drops to 400-500 and while it is that low the service engine soon light comes on until the car adjusts up to the 1000 rpm idle or I give it gas to save it from stalling. If I leave it at the 400-500 rpm range for long it will stll completely within 15 seconds. The fuel filter has approx 1200 miles on it as well as the fuel pump. I am getting great power from the battery and alternator has been checked and is perfect also. Basically everything in the car is new or has less than 1200 miles on it.
Note: During the 1200 miles of breaking in the motor there was a time (200miles worth of time or so) when the motor would scream all the way to 6500 rpms without missing at all (but constant at a constant speed you could feel the car miss/hesitate slightly). The missing was a sudden change so something changed for this extreme missing /hesitation at high rpms to occur. You can also feel the car slightly missing if it is held at a constant speed at any rpm, it kind of spits and sputters unless you are accelerating. It accelerates very smooth until 4000-5000 rpms and then misses really bad to the point where the whole car jerks and almost shuts off completely. It will continue to miss until I get off the gas, like I am hitting some kind of rev limiter or something. I was thinking it has to be fuel relate, like fuel cut was happening but I haven't the slightest clue as to what I am talking about with diagnosing these cars correctly. Could it be a bad injector or wouldn't that make the car miss all the time when I was accelerating. I know 99.99% sure its not the opti because that was changed to the new MSD opti and the car runs the EXACT same as it did with the other opti I thought was bad. The car finally hits a real boost of torque at 3500-4000 rpms and its like as soon as I start to feel like the car is a rocket this miss happens and ruins everything. Any help is greatly appreciated. Thanks so much.
08-10-2006, 03:46 PM
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Not sure if you can do any data logging but that would at least give you an idea. My guess or gut feeling would be spark. If it was fuel related I do not believe that it would run rough until 2000 rpm and then also run good until 4000-5000 rpm. If you could data log it you could determine a few things thatmight help like if it was running lean or rich, this should be able to give you a hint lean if it is a fuel issue and rich if it is a spark problem because it wouldn't be burning all the fuel correctly.
03-11-2015, 08:21 AM
#7
I had a 4000+rpm studder in my stock 95. Put a data logger to it, did a little thinking and decided to replace the O2 sensors. Problem solved.
I only had the issue when the car was "warm" or "hot" as well. This would be due to the fact that the PCM does not use the O2's as a source of information until the water temp is warm enough for it to go into closed loop.
I only had the issue when the car was "warm" or "hot" as well. This would be due to the fact that the PCM does not use the O2's as a source of information until the water temp is warm enough for it to go into closed loop.
