One bank rich, one bank lean on 3.8 V6 (check engine light on)
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One bank rich, one bank lean on 3.8 V6 (check engine light on)
Greetings! My dad's '96 3.8 liter Windstar has 75K miles and has treated him well....but about a month ago, the Check Engine Light came on. This is what the scan tool said:
2 codes found-1 of 2
PO301-Cylinder 1-Misfire Detected
PO174 (pd) System-too lean(Bank2)
To fix the misfire, we thought we'd put in fresh plugs (they had never been changed, but were rated for 100K, I think) to see if that would help. It didn't.
He cleared the codes (he ran the battery dead and pulled the battery to recharge it), then took it for a good drive. He put around 80 miles on it when the check engine light came on again. So he bought Forscan and Torque apps for his phone, and now we have more information than we know what to do with.
We are still learning how to use these new tools (our experience is with pre-OBD vehicles).
We turned on Forscan and drove around, just to see what was happening with fuel trim. When the engine was running at part throttle,the values changed around a lot, both short-term and long-term, but usually more or less in tandem. When coasting downhill (at idle), bank 1 trim would turn very positive, while bank 2 would go similarly negative. Compression braking magnified the difference between the two banks. Forscan also showed misfires in all 3 cylinders on bank 1. In a 5-minute drive, we had around 100 each in cylinder 1 and 3, and only around 20 in cylinder 2.
When we got home, we parked the car and turned it off. After about 5 minutes, we went back out to turn it on and check it at idle. One bank runs rich, the other runs lean. Forscan showed that bank 2 trim was pegged at +25 and stayed there, while bank 1 trim was negative to a similar degree. This is at idle. And, weirdly enough, after 2 runs around town with misfires in cylinders 1,2, and 3, when we were parked in the driveway, the misfires continued, but on cylinders 1,3....and 5? 5 is on the other bank. This is while bank 1 trim was running a negative value (-15) and bank 2 was pegged at 25.
So, at idle, bank 1 and bank 2 have very different trim values, but the trim gets much closer to zero when the car is driving up the road under load (both banks tend to move about the same while the car is under load).
These symptoms seem specific enough for a diagnosis.
--warmed-up car has dramatically different fuel trim patterns from bank 1 to bank 2.
--car is misfiring on all 3 cylinders on bank 1 and none on bank 2 (though, when we returned home and idled the car in the driveway, cylinder 5 showed a misfire too).
--the difference in fuel trim gets smaller as engine runs faster.
--car has new spark plugs
--we tested for vacuum leaks by waving around a propane wand, but found no leaks with this method.
Some sites online suggested that one bank lean and the other bank rich suggested a blocked exhaust on one side. The car does have a y-pipe with separate catalytic converters for each bank, so it's possible that a failing catalytic converter could be leading to the problems...but then wouldn't the problem be better when the car is idling and worse at part or full throttle?
2 codes found-1 of 2
PO301-Cylinder 1-Misfire Detected
PO174 (pd) System-too lean(Bank2)
To fix the misfire, we thought we'd put in fresh plugs (they had never been changed, but were rated for 100K, I think) to see if that would help. It didn't.
He cleared the codes (he ran the battery dead and pulled the battery to recharge it), then took it for a good drive. He put around 80 miles on it when the check engine light came on again. So he bought Forscan and Torque apps for his phone, and now we have more information than we know what to do with.
We are still learning how to use these new tools (our experience is with pre-OBD vehicles).
We turned on Forscan and drove around, just to see what was happening with fuel trim. When the engine was running at part throttle,the values changed around a lot, both short-term and long-term, but usually more or less in tandem. When coasting downhill (at idle), bank 1 trim would turn very positive, while bank 2 would go similarly negative. Compression braking magnified the difference between the two banks. Forscan also showed misfires in all 3 cylinders on bank 1. In a 5-minute drive, we had around 100 each in cylinder 1 and 3, and only around 20 in cylinder 2.
When we got home, we parked the car and turned it off. After about 5 minutes, we went back out to turn it on and check it at idle. One bank runs rich, the other runs lean. Forscan showed that bank 2 trim was pegged at +25 and stayed there, while bank 1 trim was negative to a similar degree. This is at idle. And, weirdly enough, after 2 runs around town with misfires in cylinders 1,2, and 3, when we were parked in the driveway, the misfires continued, but on cylinders 1,3....and 5? 5 is on the other bank. This is while bank 1 trim was running a negative value (-15) and bank 2 was pegged at 25.
So, at idle, bank 1 and bank 2 have very different trim values, but the trim gets much closer to zero when the car is driving up the road under load (both banks tend to move about the same while the car is under load).
These symptoms seem specific enough for a diagnosis.
--warmed-up car has dramatically different fuel trim patterns from bank 1 to bank 2.
--car is misfiring on all 3 cylinders on bank 1 and none on bank 2 (though, when we returned home and idled the car in the driveway, cylinder 5 showed a misfire too).
--the difference in fuel trim gets smaller as engine runs faster.
--car has new spark plugs
--we tested for vacuum leaks by waving around a propane wand, but found no leaks with this method.
Some sites online suggested that one bank lean and the other bank rich suggested a blocked exhaust on one side. The car does have a y-pipe with separate catalytic converters for each bank, so it's possible that a failing catalytic converter could be leading to the problems...but then wouldn't the problem be better when the car is idling and worse at part or full throttle?
New User
Joined: May 2019
Posts: 3
Likes: 0
Greetings! My dad's '96 3.8 liter Windstar has 75K miles and has treated him well....but about a month ago, the Check Engine Light came on. This is what the scan tool said:
2 codes found-1 of 2
PO301-Cylinder 1-Misfire Detected
PO174 (pd) System-too lean(Bank2)
To fix the misfire, we thought we'd put in fresh plugs (they had never been changed, but were rated for 100K, I think) to see if that would help. It didn't.
He cleared the codes (he ran the battery dead and pulled the battery to recharge it), then took it for a good drive. He put around 80 miles on it when the check engine light came on again. So he bought Forscan and Torque apps for his phone, and now we have more information than we know what to do with.
We are still learning how to use these new tools (our experience is with pre-OBD vehicles).
We turned on Forscan and drove around, just to see what was happening with fuel trim. When the engine was running at part throttle,the values changed around a lot, both short-term and long-term, but usually more or less in tandem. When coasting downhill (at idle), bank 1 trim would turn very positive, while bank 2 would go similarly negative. Compression braking magnified the difference between the two banks. Forscan also showed misfires in all 3 cylinders on bank 1. In a 5-minute drive, we had around 100 each in cylinder 1 and 3, and only around 20 in cylinder 2.
When we got home, we parked the car and turned it off. After about 5 minutes, we went back out to turn it on and check it at idle. One bank runs rich, the other runs lean. Forscan showed that bank 2 trim was pegged at +25 and stayed there, while bank 1 trim was negative to a similar degree. This is at idle. And, weirdly enough, after 2 runs around town with misfires in cylinders 1,2, and 3, when we were parked in the driveway, the misfires continued, but on cylinders 1,3....and 5? 5 is on the other bank. This is while bank 1 trim was running a negative value (-15) and bank 2 was pegged at 25.
So, at idle, bank 1 and bank 2 have very different trim values, but the trim gets much closer to zero when the car is driving up the road under load (both banks tend to move about the same while the car is under load).
These symptoms seem specific enough for a diagnosis.
--warmed-up car has dramatically different fuel trim patterns from bank 1 to bank 2.
--car is misfiring on all 3 cylinders on bank 1 and none on bank 2 (though, when we returned home and idled the car in the driveway, cylinder 5 showed a misfire too).
--the difference in fuel trim gets smaller as engine runs faster.
--car has new spark plugs
--we tested for vacuum leaks by waving around a propane wand, but found no leaks with this method.
Some sites online suggested that one bank lean and the other bank rich suggested a blocked exhaust on one side. The car does have a y-pipe with separate catalytic converters for each bank, so it's possible that a failing catalytic converter could be leading to the problems...but then wouldn't the problem be better when the car is idling and worse at part or full throttle?
2 codes found-1 of 2
PO301-Cylinder 1-Misfire Detected
PO174 (pd) System-too lean(Bank2)
To fix the misfire, we thought we'd put in fresh plugs (they had never been changed, but were rated for 100K, I think) to see if that would help. It didn't.
He cleared the codes (he ran the battery dead and pulled the battery to recharge it), then took it for a good drive. He put around 80 miles on it when the check engine light came on again. So he bought Forscan and Torque apps for his phone, and now we have more information than we know what to do with.
We are still learning how to use these new tools (our experience is with pre-OBD vehicles).
We turned on Forscan and drove around, just to see what was happening with fuel trim. When the engine was running at part throttle,the values changed around a lot, both short-term and long-term, but usually more or less in tandem. When coasting downhill (at idle), bank 1 trim would turn very positive, while bank 2 would go similarly negative. Compression braking magnified the difference between the two banks. Forscan also showed misfires in all 3 cylinders on bank 1. In a 5-minute drive, we had around 100 each in cylinder 1 and 3, and only around 20 in cylinder 2.
When we got home, we parked the car and turned it off. After about 5 minutes, we went back out to turn it on and check it at idle. One bank runs rich, the other runs lean. Forscan showed that bank 2 trim was pegged at +25 and stayed there, while bank 1 trim was negative to a similar degree. This is at idle. And, weirdly enough, after 2 runs around town with misfires in cylinders 1,2, and 3, when we were parked in the driveway, the misfires continued, but on cylinders 1,3....and 5? 5 is on the other bank. This is while bank 1 trim was running a negative value (-15) and bank 2 was pegged at 25.
So, at idle, bank 1 and bank 2 have very different trim values, but the trim gets much closer to zero when the car is driving up the road under load (both banks tend to move about the same while the car is under load).
These symptoms seem specific enough for a diagnosis.
--warmed-up car has dramatically different fuel trim patterns from bank 1 to bank 2.
--car is misfiring on all 3 cylinders on bank 1 and none on bank 2 (though, when we returned home and idled the car in the driveway, cylinder 5 showed a misfire too).
--the difference in fuel trim gets smaller as engine runs faster.
--car has new spark plugs
--we tested for vacuum leaks by waving around a propane wand, but found no leaks with this method.
Some sites online suggested that one bank lean and the other bank rich suggested a blocked exhaust on one side. The car does have a y-pipe with separate catalytic converters for each bank, so it's possible that a failing catalytic converter could be leading to the problems...but then wouldn't the problem be better when the car is idling and worse at part or full throttle?
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New User
Joined: Mar 2019
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Have you tried the usual overheating things? When does it overheat? Could be a thermostat stuck closed, a fan that's not coming on, a clogged radiator, or something more sinister like a blown head gasket. Or maybe you're just low on coolant! 
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