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10.5 AFRs all of a sudden - advice needed

Old 12-22-18, 07:16 AM
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10.5 AFRs all of a sudden - advice needed

Hi guys, my FD was running great, idling around 14:1. Then 2 weeks ago about 30min into a drive i noticed my AFRs had dropped into mid 10s at idle. Driving they see between 11-12:1. Even when driving on the highway and backing off the pedal it used to go full lean, but now it only goes from 11 to 12. I didnt change anything, im suspecting wideband sensor has died perhaps?

I'm running stock ports, stock twins, flex fuel, Adaptronic modular ecu, PLX wideband with 4.9 sensor (also handling the narrowband), Walbro 525, 4x 2000cc boschs, IGN-1A coils, R7420 10s + 10.5 plugs, and WI.

I had it tuned with e85 for the first time a week before this AFR issue happened. The car drives fine, idle feels like its getting close to wanting to stall but it hasnt stalled yet. Base pressure is 40psi, and vacuum with engine off is 112kpa.

If anyone has any ideas on what the issue could be i'd be very grateful.
Thanks!

Last edited by mikey13b; 12-22-18 at 05:11 PM.
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Old 12-22-18, 10:13 PM
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I'm not familiar with Adaptronic but most standalone ECUs should let you record datalogs of most of the inputs and calibration settings, even if you have to bring a laptop in the car and drive with it connected the entire time. You can look through those logs to see if the sensor values look reasonable, or compare these to logs from before (when the car was running right), or email them to your tuner and ask for advice. Try not to go into boost while it's running wrong, there are a few different scenarios that could cause rich running in vacuum but dangerously lean (and possibly dangerous ignition timing) in boost.
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Old 12-23-18, 06:59 AM
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Well i chucked the oem o2 sensor back in and its now showing 14.0 and idling perfectly. Meanwhile the wideband is reading 10.3 XD.

I dont suppose anyone knows the bosch 4.9 sensor part number that the PLX SM-AFR unit comes with?

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Old 12-23-18, 07:12 AM
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Talk to whoever tuned the car.
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Old 12-24-18, 10:58 AM
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Originally Posted by arghx View Post
Talk to whoever tuned the car.
For what?
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Old 12-24-18, 11:29 AM
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When you use a wideband controller, you should only be referencing the Bosch LSU 4.9 sensor the controller came with. The oem narrowband shouldn't even be hooked up to anything especially if you're running e85. Not to mention, running on AFR with mixed ethanol content will give you richer readings as ethanol has a different stoichiometric ratio compared to pump gas. I would highly recommend giving your tuner a call. I find it strange that your car would be able to run at 14:1 unless you still have an air pump that works.
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Old 12-24-18, 04:12 PM
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Double check your air pump and its electromagnetic clutch as well as your ACV if you still have them and the car runs as well as it used to.
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Old 12-25-18, 02:49 PM
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Yes I have discussed this with my tuner as we talk most days, nothing was mentioned regarding not using the OEM sensor for narrowband referencing with ethanol. I'll run it by him.
My air pump and acv are deleted.

Regarding the different wideband sensors, I plan on sourings the same Bosch sensor the controller came with, just looking to find it from a different source in Australia to save time and money..

Last edited by mikey13b; 12-25-18 at 02:57 PM.
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Old 12-25-18, 08:45 PM
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One quick way to check if a wideband sensor is dead is by removing it from the car's exhaust and doing 'the rag test', like shown in this video:

That video doesn't help with any sort of troubleshooting, and failing the test doesn't guarantee a dead sensor as opposed to a problem with the wiring or the wideband controller itself... but it's a pretty quick test you can try with just a rag and some brake cleaner. If you don't have brake cleaner, rubbing alcohol works also.


Also, does the Adaptronic really let you use the stock 1-wire narrowband O2 sensor for some sort of closed loop?
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