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Old 07-11-2011, 10:59 AM   #1
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Default CEEM (CA Car) with Pre-CAT Woes (P0124 Error)

Hi all,

I'm new to this forum and Miatas in general, but I love my car! Best handling car I've ever owned and the closest thing to my sport bike, when it comes to the fun factor. I can't wait to add some go-fast goodies, but first, I need to get it registered.

The first issue I need to address right now is to get it to pass the smog test here in Nevada. It's a [CEEM] California car (with pre-CAT), and the only error I get is P0412 ("Warm Up Catalyst Efficiency Below Threshold"). The pain is, they fail you in NV for any CELs, so I need to resolve this issue, but I only have about $500 to do it. From what I understand, I have two basic options:

1). "The Proper Fix": Replace the headers with Racing Beat Headers for $425+ (or OBX 4-2-1 headers for $155 on eBay), then relocate the pre-CAT sensor behind the CAT (I'd have a muffler place do this stuff). I hear this would give me a nice 10% or so HP gain and make it a proper 49-state car. This could be combined with a full after-market exhaust for more goodness, but I don't have the cash for that now. I'd barely afford the OBX headers and the install, I suspect...

2). "The Short-Cut": My seller said I could just "relocate" the [California specific] sensor (where?) and it'll stop throwing the code. This sounds half-***, but if it will get me straight before the 30-day deadline AND it's legal to do this, I'm OK to do it as a temporary fix. After all, I only have about another 2 weeks to reg the car.

Any input as to which I should do (or any other options) would be greatly appreciated, because I am completely at a loss as to which way to go on this.

Also, this being a 1999 car (with 127k), I need to have my mechanic give this car a good once-over and fix any issues he may find...

Like I said, I'm tight on cash right now, and I could use any extra (after the smog fix) for this inspection and any problems that must be dealt with. I'll have more cash in a few weeks, but the deadline to register the car is before then...

I like the idea of a full tune-up too, since it IS a 12 year old car (even though the seller said it had new plugs, etc., I want to know for myself). I have all the parts for a tune-up (K&N air filter, NGKs, Rspeed wires, PCV grommet & fuel filter if that IS all I need). But money is tight, so having a mechanic install these parts seems like a waste, since I can install the parts, but I haven't worked on any Mazdas, except for my trusty B2000 & B2200 trucks... So, I'm kinda at a loss as to where my priorities should be here.

My Miata is a 1999 N/A NB with a hard top and no apparent performance parts, unless you count a ground kit and a spoiler.


The Carfax was totally clean and showed regular service from the dealership and CA emission passes up to about 110k (the last one). It was a CA car until now, but it was an auction car, so I never met the real owner...

My apologies if these are common or off topic questions... I searched the forum (and the whole web) and couldn't find anything on this code or fixing it. I DO want to add a Turbo or SC to the car, but first the essentials, right?

Thanks in advance for any advice!


-az
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Old 07-11-2011, 11:52 AM   #2
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Originally Posted by azathoth View Post
2). "The Short-Cut": My seller said I could just "relocate" the [California specific] sensor (where?) and it'll stop throwing the code. This sounds half-***, but if it will get me straight before the 30-day deadline AND it's legal to do this, I'm OK to do it as a temporary fix. After all, I only have about another 2 weeks to reg the car.
As to where, that would be after the second cat, as would be the case for a normal (non-CA) car. They all have two sensors (from '96 on), the only difference is the relative location of the two. This way, the second O2 sensor is seeing the combined efforts of the two catalysts. Will this work? Never done it myself, but the theory is sound and it's cheap to try.

I take it you just bought this car, yes? Was it sold in California or Nevada? I ask because CA law requires the seller to provide the buyer with a valid smog inspection certificate at the time of transfer.
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Old 07-11-2011, 01:56 PM   #3
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Have you tried pulling the positive terminal off the battery for 30 seconds and see how long it takes for the light to come back on? I use to get ~100 miles out of mine without any cat before it would throw a code. I bet it would be long enough to get you through smog.
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Old 07-12-2011, 05:41 AM   #4
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Default RE: Reset woes...

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Have you tried pulling the positive terminal off the battery for 30 seconds and see how long it takes for the light to come back on? I use to get ~100 miles out of mine without any cat before it would throw a code. I bet it would be long enough to get you through smog.
Good idea. The first thing I did after the smog test fail was visit the nearest auto parts store and borrow their error code reader. I confirmed the code, then deleted it (reset/delete), and the Check Engine Light went off, so I drove 15 miles or so (at the seller's advice) and took the car back for smog. When I did, the smog guy told me it would still fail and I'd be wasting my money, unless I did more like 50 miles and it was still clear, so I just got a 30-day from the DMV.

I'm guessing they can tell if you've reset the CEL recently and will [bill you for the smog test then] ask you to come back after 50 miles or whenever the ecu says it's been run long enough.

Did I guess wrong? Does anyone know if I can get away with this if I reset the ECU and just go to another place? It would be nice to get the car registered and not have to worry about all this NOW...

Also, does anyone here have experience with the OBX 4-2-1 Headers? They're made from the same metal as the RB headers for less than half the price of anything else, but that makes me suspicious in itself...

-az
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Old 07-12-2011, 05:48 AM   #5
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I take it you just bought this car, yes? Was it sold in California or Nevada? I ask because CA law requires the seller to provide the buyer with a valid smog inspection certificate at the time of transfer.
I bought it in NV, unfortunately. Also, I bought it from a dealer, so he brought all the right paperwork, even a NV Bill of Sale. Then again, my car cost less than $5k, so I'm not complaining.

-az
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Old 07-13-2011, 03:00 AM   #6
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Originally Posted by azathoth View Post
Good idea. The first thing I did after the smog test fail was visit the nearest auto parts store and borrow their error code reader. I confirmed the code, then deleted it (reset/delete), and the Check Engine Light went off, so I drove 15 miles or so (at the seller's advice) and took the car back for smog. When I did, the smog guy told me it would still fail and I'd be wasting my money, unless I did more like 50 miles and it was still clear, so I just got a 30-day from the DMV.

I'm guessing they can tell if you've reset the CEL recently and will [bill you for the smog test then] ask you to come back after 50 miles or whenever the ecu says it's been run long enough.

Did I guess wrong? Does anyone know if I can get away with this if I reset the ECU and just go to another place? It would be nice to get the car registered and not have to worry about all this NOW...

Also, does anyone here have experience with the OBX 4-2-1 Headers? They're made from the same metal as the RB headers for less than half the price of anything else, but that makes me suspicious in itself...

-az
I don't know about your area, but in Cali, it is pointless to run the smog test unless a certain number of the readiness monitors have run and passed (depends on the year). That may be why he's telling you to drive the car. If you disconnect the battery/clear codes, it sets all the readiness monitors to "incomplete". It would be an instant fail/wouldn't test the car. If you're lucky enough to get the cat monitor to not run (which would turn on the light) but the others to run, maybe you can get away with it.

Basically: Fix the car. Getting one specific monitor to not run (unless its evap) is going to be a blind guessing game.
Also, putting that o2 sensor in the same location as the post cat MIGHT work. It really all depends on what the computer is expecting to see from that sensor. If it isn't expecting a smooth signal, it might throw some other kind of code. Pre cat o2s are supposed to switch.
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Old 07-13-2011, 03:03 AM   #7
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O2 simulator?
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Old 07-13-2011, 05:34 AM   #8
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Thumbs up That decides it...

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Originally Posted by MartinezA92 View Post
Basically: Fix the car. Getting one specific monitor to not run (unless its evap) is going to be a blind guessing game.
Also, putting that o2 sensor in the same location as the post cat MIGHT work. It really all depends on what the computer is expecting to see from that sensor. If it isn't expecting a smooth signal, it might throw some other kind of code. Pre cat o2s are supposed to switch.
Thanks for the hard facts, bro.

That's more than enough for me to decide.

Based on my research (and these replies), "converted" 49-state cars are set up with the pre-CAT sensor connected to a threaded "bung" behind the CAT. I've seen these sold with after-market exhausts.

According to all accounts, the pre-CAT O2 sensor works in this area without throwing a code, because it gets an acceptable sensor reading. So I'm buying the OBX headers and making the conversion. If it still throws the code after I replace the header, I'll just swap out the ECU...<shrug>

Thanks for the help!

-az
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Old 11-30-2011, 03:44 AM   #9
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Lightbulb There's no easy way out of a Pre-CAT problem.

Just an update for the nice folks online.

OK, I did the full 49-State "Federal" conversion. Next is a turbo, of course.

If you're too cheap or poor to do have a shop do this and/or you're a a glutton for punishment like me, here's some DIY advice I wanted to share with all the other folks who will run into my same problems if/when they decide to do a CEEM to 49-state conversion, or add similar parts:

FACT: CA Version (1999) Miatas are a royal p.i.t.a. to convert to 49-state cars. If you are still shopping for a Miata, don't buy a CEEM Miata unless you live in CA! You'll suffer for it later, when the Pre-CAT or CAT goes out or you want to upgrade...

If you already have one and want to do this, here's some stuff I learned that got me through the project with a running car... I hope it helps you.

1). Buy a New or Used Exhaust Header and a CAT-Back
The 01+ headers are tubular, so you might get the "Federal" exhaust off one, or so I understand. Before you buy any Header & CAT-Back, make sure the exhaust system you buy has two holes to screw O2 sensors into. In my aftermarket setup, the first was in the header and the second was behind the main Catalytic converter, on the mid-pipe. If you read the installation instructions for the 4-2-1 Racing Beat header, you'll see that you need to buy plug extensions for each sensor, so they will reach the engine from the new locations. This is true with RB, OBX, Racleland and all the other headers I read about.
You'll also want to swap the rear sensor with the front, just like the RB header install says to do (see the last step). This will fool the O2 Sensors so you won't get a CEL after you're done.

2). Remove & Uninstall Your Stock Muffler and Mid-Pipe (CAT-Back)
Before you do anything, get some PB Blaster or Liquid Wrench and hit every bolt you're going to get at, especially the header and Pre-CAT bolts. Then you can start unbolting the muffler at the back of the car or at the mid-pipe (with CAT). The stock rubber "hangers" that your exhaust hangs from are a b!!ch to get off, so either use a lubricant or just cut them off and buy new ones (4 hangers) from a Miata parts source. I chose to buy new Polyurethane hangers, which were easier to get on and stiffer than the worn out old rubber ones.

3) Remove Your Old, p.o.s. "Boat Anchor" Stock Header
To remove a stock CEEM header, you'll need a 14mm "deep socket" to take off the 3 nuts that connect the pre-CAT to the front-pipe (it will all be replaced by the Racing Beat or fleaBay header you buy). If you can't get those bolts off, you might look at the notes under step 5.

4). Inspect Your New Header
The EGR tube is the hole on the headers that's just right of the pipes, facing toward the mid-pipe connection. Many people's headers came to them from OBX (or wherever) with either the wrong type of EGR adapter (male instead of female, so you have to replace the EGR tube behind your engine with an 01+ model), or a MISALIGNED EGR connector. My fleabay OBX 4-2-1 header was about 10-15 degrees too far to the right to fit the stock position). That meant the 20mm male threading end would NOT stretch over to the place where my EGR hole was. There wasn't enough give to move it over, either. TRUST ME, I TRIED a LOT! I heard a few people were able to thread the EGR connector onto the header BEFORE mounting it on the header studs, then man-handle it onto the studs, bending the EGR tubing to fit (may break the tubing). My header was installed, so I just hacked it in half and lengthened the tube to make it fit. I was told you could also (theoretically) run the car once the rest of the exhaust is put in until the header was red hot, then try to bend or pound the hole into the right position. This didn't work for me. The final option (if you don't care about passing smog) is to buy a 21-22mm bolt with a 20m-1.5 thread somewhere and a stop plate for the other side, on the back of the intake manifold and just block the EGR system off.

5). Install (Shiny) New Header
When it came time to finally install my cheap OBX 4-2-1 header, I realized it doesn't fit, normally. That is, it can't be installed, because there isn't enough room to get it in. It took me a few days to find the solution. I ended up having to loosen my mounting bolt on the driver side (this bolt is hidden behind the driver side wheel) and (while the car is on jack stands) put a jack under the engine and slowly jack the right side of the engine up, while loosening the bolt, trying not to completely undo it! I have NO idea how you get around this if it doesn't fit past the steering column. All I know is that if you've removed everything and it still won't quite go in from above (without hitting the valve cover), this is the only thing that will do the trick. Don't waste your time trying to remove the steering shaft, even though it's in the way. There's no easy way to do it and it'll just make a mess. Remember, this is just how mine went in. Be sure you even have to resort to such a desperate measure, before trying this. You may damage your engine mount(s) in the process. I take no responsibility for your actions.

6). Installing your CAT-Back
If you bought a 3" Aftermarket CAT-Back, like a Racing Beat or Flyin' Miata CAT-Back, and you just didn't get a gasket, here's the part # to the gasket that fit my 3" mid-pipe and Flyin' Miata rear, which was NOT stock: ROL Gaskets #EG24859 / FP- 60885. It took 5 tries to find one that fit a 3" exhaust and the very wide bolt pattern it had. If you haven't had luck, try creating a template from one end of the connection, marking the exact location of the bolts and the exact size of the exhaust hole.

7). Replacing the O2 Sensors
Assuming you have either bought O2 extensions, or you spliced and lengthened your own O2 sensors, using shrink-wrap over shrink wrap, or both (like me), Racing Beat says (for CA Cars) to swap the rear O2 Sensor (plugs in near the back of the engine) and re-install it in the front O2 hole in the exhaust. The front O2 Sensor is then installed in the new hole just aft of the CAT. Install them after installing the header/CAT-Back exhaust system and don't plug it in until you've bolted it back down or you'll twist the cable.

Again these directions were for a 1999 Miata (Base Model) CEEM (California Emissions Version) Car. Your mileage may vary. Hope this helps someone find the answers I couldn't find!

-az
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