Occasional bad misfire on startup and after heavy throttle usage
10-10-2011, 12:49 PM
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Occasional bad misfire on startup and after heavy throttle usage Hello everyone! I have "lurked" around the forum for some time now and learned a lot. However, in all my searching over the past few months I have been unable to find the answers to a problem I am having. Any assistance would be greatly appreciated.
So, I bought (stole might be more appropriate) a 99 Trans Am back in May. LS1 of course with an auto. Car has about 135k on it and a factory WS6 hood with Ram Air lower box and SLP lid. It had been sitting for some time (maybe 1.5 to 2 years). After some fresh gas, battery charge and some new fluids and filters she came right to life. Occasionally, it would have a severe misfire upon startup. Maybe 1 in 10 times of starting it. Usually it would come out of it on its own but definitely would clear right up and purr like a kitten if you warmed it up, shut it off and then fired it back up. Then it might be fine for a day, week or month. No real rhyme or reason. All different temps, times of day, fuel levels, etc. By severe, I mean completely dropping a cylinder and of course setting off the SES light. Then I noticed it started doing the same thing every time I would get pretty heavy with the loud pedal. Again, it might eventually come out of it on its own but almost always clear right up if you shut it off and restarted. First course of action was all new plugs and MSD wires, took the TB and MAF off and cleaned them all real well. No change. Always throws a cylinder 4 misfire so I went with a new coil. No change. I have checked all wires and plugs. None are damaged or cracked and all are seated good. It's the intermittent thing that gets me. This car will drive awesome majority of the time but every once in a while it will completely drop cylinder 4 when you start it up cold or get a little dominant with the foot feed. Starting to pull my hair out. Injector???? Would cause it all the time I would think. Fuel pressure??? Why just cylinder 4? O2's????? Again, why just cyl 4? I have searched and searched to no avail. Any thoughts? Many thanks in advance.
So, I bought (stole might be more appropriate) a 99 Trans Am back in May. LS1 of course with an auto. Car has about 135k on it and a factory WS6 hood with Ram Air lower box and SLP lid. It had been sitting for some time (maybe 1.5 to 2 years). After some fresh gas, battery charge and some new fluids and filters she came right to life. Occasionally, it would have a severe misfire upon startup. Maybe 1 in 10 times of starting it. Usually it would come out of it on its own but definitely would clear right up and purr like a kitten if you warmed it up, shut it off and then fired it back up. Then it might be fine for a day, week or month. No real rhyme or reason. All different temps, times of day, fuel levels, etc. By severe, I mean completely dropping a cylinder and of course setting off the SES light. Then I noticed it started doing the same thing every time I would get pretty heavy with the loud pedal. Again, it might eventually come out of it on its own but almost always clear right up if you shut it off and restarted. First course of action was all new plugs and MSD wires, took the TB and MAF off and cleaned them all real well. No change. Always throws a cylinder 4 misfire so I went with a new coil. No change. I have checked all wires and plugs. None are damaged or cracked and all are seated good. It's the intermittent thing that gets me. This car will drive awesome majority of the time but every once in a while it will completely drop cylinder 4 when you start it up cold or get a little dominant with the foot feed. Starting to pull my hair out. Injector???? Would cause it all the time I would think. Fuel pressure??? Why just cylinder 4? O2's????? Again, why just cyl 4? I have searched and searched to no avail. Any thoughts? Many thanks in advance.
10-10-2011, 02:35 PM
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usnfenix,
Thanks for the input. It does seem to be getting worse. I was really starting to suspect the O2s given the whole once warmed up and then restart it deal but don't understand why it is just affecting cylinder 4. Thanks again!
Thanks for the input. It does seem to be getting worse. I was really starting to suspect the O2s given the whole once warmed up and then restart it deal but don't understand why it is just affecting cylinder 4. Thanks again!
10-10-2011, 03:06 PM
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02 sensors can cause some issues. My problems seemed to happen once the car was warm though. Cruising at lower RPM and all of a sudden it starts jerking/surging, SES light is blinking on and off. Started getting a high idle, ran the codes and bam! bank 1 sensor 1. Replaced it and been fine since. Try rockauto.com for Densos. Or you could go ahead and get the Bosch13111's that usnfenix spoke of. Especially get them if your gonna do LT's in the future. That way you won't have to mess with extending them.
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10-10-2011, 07:38 PM
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thanks man. I had just washed it and it was at distance. Car spent a lot of years in the Texas sun and from the doors forward are starting to get faded, hood too. Gotta wax it all the time, but i've seen cars in worse shape that weren't 13 years old.
11-05-2011, 01:02 AM
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Hello everyone! I have "lurked" around the forum for some time now and learned a lot. However, in all my searching over the past few months I have been unable to find the answers to a problem I am having. Any assistance would be greatly appreciated.
So, I bought (stole might be more appropriate) a 99 Trans Am back in May. LS1 of course with an auto. Car has about 135k on it and a factory WS6 hood with Ram Air lower box and SLP lid. It had been sitting for some time (maybe 1.5 to 2 years). After some fresh gas, battery charge and some new fluids and filters she came right to life. Occasionally, it would have a severe misfire upon startup. Maybe 1 in 10 times of starting it. Usually it would come out of it on its own but definitely would clear right up and purr like a kitten if you warmed it up, shut it off and then fired it back up. Then it might be fine for a day, week or month. No real rhyme or reason. All different temps, times of day, fuel levels, etc. By severe, I mean completely dropping a cylinder and of course setting off the SES light. Then I noticed it started doing the same thing every time I would get pretty heavy with the loud pedal. Again, it might eventually come out of it on its own but almost always clear right up if you shut it off and restarted. First course of action was all new plugs and MSD wires, took the TB and MAF off and cleaned them all real well. No change. Always throws a cylinder 4 misfire so I went with a new coil. No change. I have checked all wires and plugs. None are damaged or cracked and all are seated good. It's the intermittent thing that gets me. This car will drive awesome majority of the time but every once in a while it will completely drop cylinder 4 when you start it up cold or get a little dominant with the foot feed. Starting to pull my hair out. Injector???? Would cause it all the time I would think. Fuel pressure??? Why just cylinder 4? O2's????? Again, why just cyl 4? I have searched and searched to no avail. Any thoughts? Many thanks in advance.
So, I bought (stole might be more appropriate) a 99 Trans Am back in May. LS1 of course with an auto. Car has about 135k on it and a factory WS6 hood with Ram Air lower box and SLP lid. It had been sitting for some time (maybe 1.5 to 2 years). After some fresh gas, battery charge and some new fluids and filters she came right to life. Occasionally, it would have a severe misfire upon startup. Maybe 1 in 10 times of starting it. Usually it would come out of it on its own but definitely would clear right up and purr like a kitten if you warmed it up, shut it off and then fired it back up. Then it might be fine for a day, week or month. No real rhyme or reason. All different temps, times of day, fuel levels, etc. By severe, I mean completely dropping a cylinder and of course setting off the SES light. Then I noticed it started doing the same thing every time I would get pretty heavy with the loud pedal. Again, it might eventually come out of it on its own but almost always clear right up if you shut it off and restarted. First course of action was all new plugs and MSD wires, took the TB and MAF off and cleaned them all real well. No change. Always throws a cylinder 4 misfire so I went with a new coil. No change. I have checked all wires and plugs. None are damaged or cracked and all are seated good. It's the intermittent thing that gets me. This car will drive awesome majority of the time but every once in a while it will completely drop cylinder 4 when you start it up cold or get a little dominant with the foot feed. Starting to pull my hair out. Injector???? Would cause it all the time I would think. Fuel pressure??? Why just cylinder 4? O2's????? Again, why just cyl 4? I have searched and searched to no avail. Any thoughts? Many thanks in advance.
