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Full rich on bank 2 and full lean on bank 1

8K views 8 replies 5 participants last post by  Modular88gt 
#1 ·
Havingan issue with my 98 cobra, I've been chasing it since I bought it. When firstpurchased, it had a p0171 code lean bank one. We checked for vacuum leaks, replaced IM gaskets, etcdid all the grunt work. O2s voltage were good.

Itook it to the first tuning shop, who after a month apparently fixed it andtuned it. Apparently that O2 was faulty. I get it back and it startedbackfiring on the way home. It still backfires some only in the mornings or ifit sits for around 12 hours. Just recently it started dying on me when I pullinto work in the morning also and It smells like it's running fat. Now it'spulling codes for bank 2 being rich, the egr, and a code saying the pcm wasunable to finish its diagnostic test. I figured it was their tune. When Icalled to see why all of these codes were up and why it was running like this Inever got a call back.

So Itook it to the second shop powercurvemotorsports. Excellent dude! However when he was logging he noticed that bankone is full lean and bank two is full rich. He said my maf was readingcorrectly. He had an identical cobra same year as mine there and he showed methe dyno for it against mine and I'm down about 50hp and 60torquecomparatively. It feels as tho the engine has a dead miss, however no codesfor it.

Hasanyone had this issue where one side is full rich and the other is full lean?If so what did you do to fix it??
 
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#2 · (Edited)
The ECU reads oxygen in the exhaust off the O2 sensor and based on that reading adjusts fueling to bring the mix to whatever the tuner commanded in the tune. If the mix does not get there then the O2 sensor is bad or the problem lies with the injectors. If it is the injectors then you either have a wiring problem or an ECU problem. It is improbable a whole bank of injectors would fail at the same time. You should hope for a wiring problem. Ford no longer offers the ECU.


Ed
 
#3 ·
Reversed Front O2 Sensor wires

Havingan issue with my 98 cobra, I've been chasing it since I bought it. When firstpurchased, it had a p0171 code lean bank one. We checked for vacuum leaks, replaced IM gaskets, etcdid all the grunt work. O2s voltage were good.

Itook it to the first tuning shop, who after a month apparently fixed it andtuned it. Apparently that O2 was faulty. I get it back and it startedbackfiring on the way home. It still backfires some only in the mornings or ifit sits for around 12 hours. Just recently it started dying on me when I pullinto work in the morning also and It smells like it's running fat. Now it'spulling codes for bank 2 being rich, the egr, and a code saying the pcm wasunable to finish its diagnostic test. I figured it was their tune. When Icalled to see why all of these codes were up and why it was running like this Inever got a call back.

So Itook it to the second shop powercurvemotorsports. Excellent dude! However when he was logging he noticed that bankone is full lean and bank two is full rich. He said my maf was readingcorrectly. He had an identical cobra same year as mine there and he showed methe dyno for it against mine and I'm down about 50hp and 60torquecomparatively. It feels as tho the engine has a dead miss, however no codesfor it.

Hasanyone had this issue where one side is full rich and the other is full lean?If so what did you do to fix it??
Yes, I would check the Front O2 sensor wires to see if they are reversed. Common mistake when taking out engine or transmission. One sensor reads lean, so the computer works to rich it out, then the opposite bank gets the fuel, which then wants to lean out. crazy.

- - - Updated - - -

The wire diagram is in the Chiltons Repair Manual.
 
#5 ·
You can force open loop in the tune which might be what your tuner did. Other than disconnecting the sensor I think the switch to force open loop is the only way to ignore fuel trims.

Ignoring fuel trims is a good way to hurt the engine. When you do ignore the trims the ECU can no longer adjust fueling in real time to accommodate unforeseen changes in the engine's appetite for fuel. The inability to see or accommodate those changes is a good place to avoid — it is the origin of many bad experiences and wounded engines.


Ed
 
#6 ·
You can force open loop in the tune which might be what your tuner did. Other than disconnecting the sensor I think the switch to force open loop is the only way to ignore fuel trims.

Ignoring fuel trims is a good way to hurt the engine. When you do ignore the trims the ECU can no longer adjust fueling in real time to accommodate unforeseen changes in the engine's appetite for fuel. The inability to see or accommodate those changes is a good place to avoid - it is the origin of many bad experiences and wounded engines.

Ed
Thanks for that advice. I'm running out of tuners here in Charlotte. I'll have to have it looked at again by someone willing to take the time to actually tune a car vs loading a canned tune.
 
#7 ·
In my view, it was a mistake to take the car to a tuning shop as its been my experience that "tuners" more often than not are unable to properly diagnose and repair drivability issues. Many times, a "tuning" shop will make issue even worse and you mentioned that the car started to back fire and set rich codes after the car was released from the tuner shop thus proving my point about the incompetence of the tuners in general.

If I were you, I would reload the factory calibration back into the PCM and use a factory MAF sensor and go from there. By the way, It is very rare for O2 sensors and injectors to cause rich or lean codes. The usual suspects for lean rich codes, backfiring issues are vac leaks, bad MAF, bad MAF transfer function or a "tuner" allowed to do stupid stuff with the PCM, ETC.
 
#9 ·
have injectors bench tested check injector harness just incase replace all the 02 sensors and check the 02 harness, get a stock tune loaded and see if you still have the problem sounds like a lot of money wasted but if it starts acting “ normal” then you know it was one or all of these components , also if you have an aftermarket FPR I would check what it’s set to and check for vacuum leaks
 
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