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CEL after NA header conversion, only in certain scenarios


aac0036

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Hiya, about 5 years ago I had a Legacy GT header modified to fit an '07 naturally aspirated Legacy. Yes, it was needlessly expensive etc. However I still have and am very much in love with my car. But the intermittent CEL is grating on me...

 

P1153 (manufacturer control) seems to show up for most when an O2 sensor is bad, but I get this only in certain scenarios. There are loads of threads on P1153, but I figure my issue is a bit different because I'm sure it's a result of the header conversion. I have a code reader, and it is allllways this same code. I only have the LGT header and a custom Y to JDM Legacy STi mufflers. Not a full catback. I had a road tune a few years ago just to maximize daily drivability, but obviously this did nothing to address the CEL popping up in the situations listed below. I'm assuming this isn't a standard O2 sensor gone bad because it's off most of the time and only comes on in the scenarios below, and has done so consistently for years. I'm able to clear the code without issue..

 

CEL WILL come on:

-If cruising above 65 mph (above 2.5k revs)

-When accelerating to merge onto the highway (again, above 2.5k revs for more than a few seconds)

-Usually more in colder months than summer time

CEL will NOT come on:

-In only city/suburban driving

-Changing gear at 3k revs or more in city driving (for less than a second)

 

I think it's just an airflow reading/metering issue since the LGT header doesn't have a cat and the stock 2.5i header does. And when accelerating enthusiastically the sensor is able to pick up the increased exhaust flow. Is there any way to correct this issue? It's embarrassing when carting people around, and also a huge drag when taking road trips and not being able to use cruise control because of the CEL. Should I be worried about my cat's longevity due to the tripped CEL? I heard that might be an issue.

 

Any advice would be great, thanks :icon_conf

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If you're in Beverly - drive over to Enhanced Street Performance- they are right in there Beverly....

 

Dave and Team are super easy to work with - but be prepared to hear most places suggest you replace the malfunctioning part with one that is appropriate for the application - although I would still stop in and talk with ESP - they will at least help with ideas.

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Bern Tuning is fairly close to you, I'd call them and ask what they think. May be they can fix your issue.

I was road tuned by Matt Miner, I was planning on checking with him.

If you're in Beverly - drive over to Enhanced Street Performance- they are right in there Beverly....

 

Dave and Team are super easy to work with - but be prepared to hear most places suggest you replace the malfunctioning part with one that is appropriate for the application - although I would still stop in and talk with ESP - they will at least help with ideas.

In Beverly, or Beverly Road in Sterling? ;)

 

Thank you. In my own research I found that it could be something as simple as a loose O2 connector or damage from the installation. I'm not sure, but will report back. Any other ideas welcome.

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Yup - Corrected - ESP is in Sterling.... But yeah any of the experts who will listen may at least have an idea.

 

Another thought - can you try an extender/spacer/isolator:

http://hydrogengarage.com/o2spacer.html

https://www.amazon.com/O2-Sensor-Spacer-Adapter-Extender/dp/B00CZFCPQU

 

 

When I had a custom exhaust on my 99 N/A LGT - the shop that built it stated that with high flow cats the flow is increased outside factory flow specs - and it throws codes - the spacer moved the sensor within the flow path - and it supposedly helps to reduce the chance of codes - could be worth a shot - as it sounds like the issue they described...:cool:

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Skip the extender, anti-fouler, etc. that isn't your issue. You modded the UEL turbo manifold to fit your 253, that's fine but where are your sensors located ? Specifically your orange (AFR) and gray (O2)? Next have you changed/cleaned the MAF ever/recently?

 

The ECU/MAF measures incoming air, which is dictated by your camshafts, you didn't change them, so the same amount of air is being drawn in on the intake stroke as before the mod. Gases getting out faster due to less restriction, for an N/A, won't drastically improve the scavenging affect. Might be worse since you went from EL to UEL but that is another thread.

 

Since you have provided some conditions for the CEL, the ECU is unhappy when referencing the extremes of the various control tables (torque request, fuel, TPS) associated to the higher RPM range.

 

Say you step on the throttle the MAF reads a certain voltage and the ecu references the associated value for that voltage for the various actions needed to speed the car up (more fuel, timing, torque, etc) if the MAF is failing but the other conditions are monitored to be increasing that would cause the CEL. SO think about the chain of inputs/event to help you diagnose the problem.

 

My take is you have a bad/failing MAF and/or AFR

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Thanks for taking the time to respond.

 

where are your sensors located ? Specifically your orange (AFR) and gray (O2)? Next have you changed/cleaned the MAF ever/recently?

I believe the 2 sensors are housed within the 1 unit I have, which was welded in where the up pipe would normally be on a turbocharged car. I think the NA models have them on the header itself, beneath the 2 banks? I cleaned the MAF 2-3 years ago and this had no effect. Could one of my sensors/wires just have been damaged during the installation? Heard they can be finicky.

 

The ECU/MAF measures incoming air, which is dictated by your camshafts, you didn't change them, so the same amount of air is being drawn in on the intake stroke as before the mod. Gases getting out faster due to less restriction, for an N/A, won't drastically improve the scavenging affect. Might be worse since you went from EL to UEL but that is another thread.

I know it wasn't the wisest thing to have done... live and learn. Have considered going back to the original header but then considered the costs associated with fabrication etc.

 

Since you have provided some conditions for the CEL, the ECU is unhappy when referencing the extremes of the various control tables (torque request, fuel, TPS) associated to the higher RPM range.

 

Say you step on the throttle the MAF reads a certain voltage and the ecu references the associated value for that voltage for the various actions needed to speed the car up (more fuel, timing, torque, etc) if the MAF is failing but the other conditions are monitored to be increasing that would cause the CEL. SO think about the chain of inputs/event to help you diagnose the problem.

 

My take is you have a bad/failing MAF and/or AFR

 

This sounds reasonable, although I'm not sure why this would fail so early on if that is the case. It first appeared around 50-60k when I did the mod, and where I live we only have extremes in temperature without worry of dust or other environmental hazards. Here I am at 114k and it only appears in the conditions described, which is basically under moderate/heavy load. Either way, both sound like a DIY and are possibly less costly than reverting to the standard exhaust. Will look into replacements and see if that has any effect.

 

Thanks guys

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Yeah on the 2.5i header the AFR is right in the mix in front of the cat below the passenger side head and the O2 is directly after the cat in the same location. That location plays into the ECU being happy or not with the cat being able to heat up to light-off temp fast and start converting gases to less crappy gases.

 

If you have a pic of you setup that would help.

 

I would check the wiring to the AFR, MAF and O2 make that is all intact. But if you dont have a way to monitor the ECU (Tactrix 2.0 cable) you should consider reverting to the stock setup just to see if the problem persists.

 

If you can find a Tactrix 2.0 Cable for sale or buy one you can use it to log and that will tell you the exact problem and will be much cheaper and give you the ability to eliminate the P0420 and get your car tuned down the road.

 

Without some data or hard diagnostics (voltmeter probing circuits) it may be tough to track down the problem.

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3fd26fd471f34e0e214fc120f71c79de.jpg

 

This is the only bung I can see from underneath, after the passenger side cat. Ignore the CV juice lol. It just doesn't make sense because it honestly seems to depend on my fuel level too.

 

d98e6f225b619abe483eded17db7e05a.jpg

 

 

Here we see a 50 degree day below 1/2 tank and I'm able to get up to speed and even cruise above 2500 revs. If I filled up and did the same it's a guaranteed P1153. I've never had a P0420. I think logging the issue as you suggested would be ideal, I'll get help with that.

 

 

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Is there another sensor in there upstream of that one?

 

Not to my knowledge, I'll have to try poking around. Hard not having a garage! Upstream meaning closer to the engine?

 

Tried the resistor trick?

 

Not familiar with this?

 

 

 

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Yeah if you arent running a AFR sensor that is your problem. Your ECU switches between open and closed loop based on certain conditions. To keep it simple think about it like this:

 

At low loads the ECU knows: xRPM + xMAFv = XFuel to inject to be safe (This is Closed loop)

At higher loads (like when you go above the mentioned RPM to throw the CEL) the ECU knows: xRPM + xMAFv + xAFRv + xSpeed = xFuel to inject to keep things as close to 14.7:1 AFR as possible. (This is Open Loop)

 

If you dont have a functioning AFR the ECU can't solve the calculation for xAFR. It gets unhappy and throws the code, that code is saying "i dont know if the AFR is even present" vs "The present AFR Sensor is above/below expected voltage"

 

The quickest way to tell is open your hood look down hear the passenger side cam cover. There should be two connections plugged in if there is only 1 you dont have a AFR.

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  • 2 weeks later...
Interesting, I have to look. Why would there not be an AFR?? Thank you and sorry for the delay. Having trouble getting together a cable etc for logging.

 

The shop/the owner that did the conversion may have overlooked it honestly and since the WRX/LGT stock manifold only has 1 bung the O2 got put in and not the AFR

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You can take it to a shop and have them weld in a bung so you can screw in your AFR sensor, then reset your ECU.

 

Still would like to see some detailed pics from under the car to see the whole manifold and from the top down (looking down from the top of the front of the engine in the space between the radiator and the timing cover) just to be 100% sure you are missing your AFR

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I'll take more photos. If the AFR is in fact missing where should the bung be welded in and connected to? After an ECU reset could that really solve it?

 

 

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Alright, so apparently I forget what my own exhaust system looks like. Blame it on this being done 5ish years ago and not having my own garage where I can take my time for the past 2. Thanks again for your help and your patience, now on to the photos.

 

39eecc0a1a17de2e169b0b6b68d632a3.jpg

 

9317514323d905d9fffd9f399c0b6be4.jpg

 

2064632a3a3385163255dbdcb8b1b63b.jpg977e03f927a5b2bb09d91f7d952f4c7f.jpg

 

 

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Assuming that the lack of an AFR is no longer a standout, and that logging is needed to check values? Or could I try replacing the AFR sensor assuming it was damaged during the installation, since they're fragile?

 

 

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