Misfire

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callahan347

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So installed the mpfi unit and new gaskets still throwing a random misfire code. Some of the plugs were fouled so I replaced them with no change. Anybody have any idea what could be causing this to still miss and smells as though it is still running rich
 
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callahan347

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Have you looked at STFT and LTFT for both banks?
I have a scan tool to do that but dont know what I'm looking for on the fuel trims. Not sure what's good or bad or when to read them. Do I check them just sitting in the driveway idling or do I need to be out on the road
 

bigfootchiro

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Positive fuel trim numbers (especially on LT) is leaning out the motor. Negative is rich (more fuel). Your fuel trims should be fairly equal from side to side. If you accelerate, or increase RPM up to 1500-2500 and you see your fuel trims increase, then you likely have a vacuum leak or not enough fuel (like leaky FPR, bad fuel pump, clogged injectors). If they go negative, you are getting too much fuel, which could be clogged cats, bad O2s, or stuck open injectors
 
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callahan347

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Positive fuel trim numbers (especially on LT) is leaning out the motor. Negative is rich (more fuel). You’re fuel trims should be fairly equal from side to side. If you accelerate, or increase RPM up to 1500-2500 and you see your fuel trims increase, then you likely have a vacuum leak or not enough fuel (like leaky FPR, bad fuel pump, clogged injectors). If they go negative, you are getting too much fuel, which could be clogged cats, bad O2s, or stuck open injectors
Awesome thank you I'll check them tomorrow and go from there
 
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callahan347

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Positive fuel trim numbers (especially on LT) is leaning out the motor. Negative is rich (more fuel). Your fuel trims should be fairly equal from side to side. If you accelerate, or increase RPM up to 1500-2500 and you see your fuel trims increase, then you likely have a vacuum leak or not enough fuel (like leaky FPR, bad fuel pump, clogged injectors). If they go negative, you are getting too much fuel, which could be clogged cats, bad O2s, or stuck open injectors
Stft and ltft for bank 1 stay around 0 but both for bank 2 are around positive 8 to 9 at idle. At 2500 short term comes down to about positive 3 then right back up after getting off throttle. What could cause this
 

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