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Old 04-16-2015, 10:58 AM   #1
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Default miss and backfire

Hello, I have a supercharged 3.8 it runs fine going down the road. Half throttle is responsive but at wide open throttle the car will miss and backfire and will even die if you don't let off in time. I just bought the vehicle a few weeks ago and have no experience with this motor. What could cause this? Sometimes it will idle up and down while parked (not a/c drag) , don't know know if the 2 issues are related, maybe a vacuum leak? ( not audible), as in I can't hear any vaccum lines sucking. Otherwise car runs great starts right up, just idles funny sometimes, and is not responsive at Wot. Any feedback would be great I'm a carbureted small block kind of guy, I don't know much about the sideways motors.
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Old 04-16-2015, 11:57 AM   #2
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Have you scanned for codes?

Have you checked for a vac leak, by spraying carb cleaner around the engine, looking for a change in idle?

There is no such thing as WOT......how far can you press the pedal before your car acts up? Do you have access to a scan tool, to check data, especially tps?

Sure what you are feeling is not a misfire?
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Old 04-16-2015, 12:29 PM   #3
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It does throw a check engine light but it only comes on for a few seconds and goes out it is very random. Driving conditions make no difference in the light. I do not have a scan tool and I have not tried the carb cleaner trick yet. As far as the misfire goes when I put the pedal to the floor it will backfire and die sometimes but it does start to act up a little right before the floor but the enigine will pick itself back up if you don't push it all the way down
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Old 04-16-2015, 05:40 PM   #4
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It'* seeing a misfire if the light comes on and goes away like that.

I suppose you don't know when the last tune up was done do you?
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Old 04-16-2015, 06:56 PM   #5
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No I have no idea about the tune up like I said I just bought it about 2 weeks ago. Thus is my first 3800 I didntbknow if it could be something as simple as a tunebup or if it was a common problem with these motors. I did get on the interstate today for the first time and it does hesitate as soon as you increase the throttle when you are at about 60 to 70 mph its almost like a shudder or a surging but if you increase the throttle further it will straighten out
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Old 04-17-2015, 05:57 AM   #6
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Then I suggest going out and getting new plugs and wires. Might as well have an oil change done too.
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Old 04-17-2015, 06:15 AM   #7
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I agree with Mike also change the fuel filter too!
Ensure there are no vacuum leaks.
Check the Fuel pressure regulator for leaks and off the fuel rail, do a pressure test.
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Old 04-17-2015, 09:22 AM   #8
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Thanks so much for the feedback guys. I'm going to dive into it in the next day or 2, I will let u guys know if I find the fix. At least I have a place to start now.
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