Misfire

[callahan347]

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

 

[bigfootchiro]

Did you check O2 sensors?

 

[callahan347]

Did you check O2 sensors?

Replaced them last fall and have checked them with a scan tool and they appear to be reading well no lazy signals or anything like that

 

[bigfootchiro]

Have you looked at STFT and LTFT for both banks?

 

[callahan347]

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]

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

 

[callahan347]

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

 

[callahan347]

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

 

[HiHoeSilver]

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

Vacuum leak on bank 2.

 

[callahan347]

Vacuum leak on bank 2.

Cant find a vacuum leak. Pulled plugs 2 and 4 are wet with fuel but 6 and 8 look great. Did find a vacuum leak behind the cats where the flange is could that cause it?