87 Camaro 5.0, Strange Missfire?
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Joined: May 2006
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Car: 87 Camaro IROC-Z
Engine: 5.0 LB9 Stock
Transmission: T-5
Axle/Gears: Stock BW 3.45
87 Camaro 5.0, Strange Missfire?
Hi everyone,
I've got an 87 Camaro 5.0 TPI 5-Speed. The car is bone-stock except for headers (Edelbrock), upgraded coil (MSD) and ignition module. I am having a problem that I have had since I bought the car and it continues until now. What's happening is this: When the car is cold, it will seem to miss under very light to 1/3 throttle in ANY gear. It's not horribly bad but definitely noticeable as you can hear the smoothness of the engine change when it does this. The tach also jerks slightly when this happens. 1/3 or more throttle and it will be just fine. It NEVER misses under heavy throttle/load. After the car warms and is in closed loop, the car will only do this "miss" in 5th gear under the same light throttle as above (up to 1/3). If I'm on the freeway going 75 in 5th gear and my foot is steady and light on the throttle, the car will sometimes just miss a couple times a minute. Other times the entire car will begin shaking violently. The tach will bounce (about a 500 RPM range up and down) and as long as the pedal remains in the same position, the car won't stop shaking!! However, the moment I change pedal position (either letting up or giving more), the shaking will stop. If I resume a light throttle position and hold it, the shaking will begin again. The best way I can describe the shaking is when you are going really slow in say, 1st gear, and you suddenly mash on the pedal from your foot being all the way off. I have lots of ideas as to what the problem could be but I want to know if anyone else might have any. Here's a list of things I have done to the car:
Changed: O2 Sensor (Twice), Plugs (Several Times), Wires (Twice), Distributor, Ignition Module (Twice), Coil, CTS, MAT, EGR Valve, EGR Temp. Sensor, IAC Valve, Fuel Filter, Air Filters (now 2 K&N's)
About a month ago I had a valve job done b/c the car burned oil like crazy. The plugs used to get fouled up pretty bad and I originally thought that this was the ultimate source of the problem, but after the valve job it still happens, even though the car now burns NO oil. I have checked the plugs and they are all gapped at .035 and are nice and a light gray/ash color. The wires are also perfectly fine. They aren't arching or grounding to anything. Timing is dead on at 6* and TPS is set correctly. I've tested the TPS and there aren't any dead spots or abnormal voltage fluctuations throughout its travel. There aren't any loose connections to any sensors and from what I can tell, all wiring seems to be in good shape. Just a reminder, this "miss" has never happened under WOT or under any heavy or moderate load, only LIGHT throttle. I am lost here but if anyone has any ideas, please let me know.
Thanks a lot!
Chris
I've got an 87 Camaro 5.0 TPI 5-Speed. The car is bone-stock except for headers (Edelbrock), upgraded coil (MSD) and ignition module. I am having a problem that I have had since I bought the car and it continues until now. What's happening is this: When the car is cold, it will seem to miss under very light to 1/3 throttle in ANY gear. It's not horribly bad but definitely noticeable as you can hear the smoothness of the engine change when it does this. The tach also jerks slightly when this happens. 1/3 or more throttle and it will be just fine. It NEVER misses under heavy throttle/load. After the car warms and is in closed loop, the car will only do this "miss" in 5th gear under the same light throttle as above (up to 1/3). If I'm on the freeway going 75 in 5th gear and my foot is steady and light on the throttle, the car will sometimes just miss a couple times a minute. Other times the entire car will begin shaking violently. The tach will bounce (about a 500 RPM range up and down) and as long as the pedal remains in the same position, the car won't stop shaking!! However, the moment I change pedal position (either letting up or giving more), the shaking will stop. If I resume a light throttle position and hold it, the shaking will begin again. The best way I can describe the shaking is when you are going really slow in say, 1st gear, and you suddenly mash on the pedal from your foot being all the way off. I have lots of ideas as to what the problem could be but I want to know if anyone else might have any. Here's a list of things I have done to the car:
Changed: O2 Sensor (Twice), Plugs (Several Times), Wires (Twice), Distributor, Ignition Module (Twice), Coil, CTS, MAT, EGR Valve, EGR Temp. Sensor, IAC Valve, Fuel Filter, Air Filters (now 2 K&N's)
About a month ago I had a valve job done b/c the car burned oil like crazy. The plugs used to get fouled up pretty bad and I originally thought that this was the ultimate source of the problem, but after the valve job it still happens, even though the car now burns NO oil. I have checked the plugs and they are all gapped at .035 and are nice and a light gray/ash color. The wires are also perfectly fine. They aren't arching or grounding to anything. Timing is dead on at 6* and TPS is set correctly. I've tested the TPS and there aren't any dead spots or abnormal voltage fluctuations throughout its travel. There aren't any loose connections to any sensors and from what I can tell, all wiring seems to be in good shape. Just a reminder, this "miss" has never happened under WOT or under any heavy or moderate load, only LIGHT throttle. I am lost here but if anyone has any ideas, please let me know.
Thanks a lot!
Chris
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Those symptoms can indicate poor atomization from one or more injectors. At low throttle angles and low intake air flow, the injectors flow very little fuel, and this fuel is normally sprayed as a very fine mist in a conical pattern. This helps the fuel evaporate into the air as it enters the cylinder. If an injector is partially clogged or fouled at the tip, the spray can actually be more of a dribble or stream of fuel, which does not atomize easily in the low volume of intake air. At higher throttle angles, the streaming or dribbling is less of a problem since more air is drawn into the cylinder and tends to vaporize the fuel better. The problem is exacerbated when the engine is colder, since the fuel tends to vaporize even less in a cold intake runner and heat.
I had a similar bout with my '86, and fought it quite a while before pulling the injectors and having them cleaned and flow-matched.
Those symptoms can indicate poor atomization from one or more injectors. At low throttle angles and low intake air flow, the injectors flow very little fuel, and this fuel is normally sprayed as a very fine mist in a conical pattern. This helps the fuel evaporate into the air as it enters the cylinder. If an injector is partially clogged or fouled at the tip, the spray can actually be more of a dribble or stream of fuel, which does not atomize easily in the low volume of intake air. At higher throttle angles, the streaming or dribbling is less of a problem since more air is drawn into the cylinder and tends to vaporize the fuel better. The problem is exacerbated when the engine is colder, since the fuel tends to vaporize even less in a cold intake runner and heat.
I had a similar bout with my '86, and fought it quite a while before pulling the injectors and having them cleaned and flow-matched.
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