2003 540i M62TU Exhaust: "Pre cat delete"

[BradleyDanger]

I know the topic of exhaust has been extensively discussed, debated, and otherwise deliberated countless times on this forum and others, but I've been doing a bunch of research on the M62TU pre-cats attached to the headers and not coming up with a lot of answers.

A little background - I just bought a 2003 540i M Sport (auto), 111k miles. Seemed to be in good shape aside from some cosmetics and the PPI showing valve cover gaskets needed. Well, after buying and letting it sit for a couple weeks, it started up, idled like crap, then died; and wouldn't stay running again after that, even with some throttle. Long story short, I had it towed to a local BMW shop here in Denver and this brings us to the catalytic converters...

The shop looked it over and told me it was having issues because the pre-cats were extremely clogged, getting bank 1 and 2 codes (didn't tell me the code numbers). This seemed odd to me, but ultimately (to save myself about $2500 in new exhaust pieces plus labor) they ended up gutting the pre-cats to clear them, changing oil and fouled spark plugs, and now it's purring like a kitten. Only set me back $580. A win in my book compared to the alternative. No codes, no SES, no problems so far. I'm not sure if I lost any power, since it was not likely running at peak with clogged cats when I bought it, but seems to have plenty of get up and go.

My question, with some followups: has anyone else hollowed out/gutted their pre-cats? If so, why? Has it caused long term issues? Short term? Changes, good or bad, in performance? Anyone done this in a state or county with emissions and still passed (I still have to have it tested)? How? Has anyone done this and changed, as a result of or not, other pieces of the exhaust to compensate, or add more performance?

I'm not in the camp of changing exhaust purely for sound. I think the M62 V8 sounds wonderful through the stock exhaust, honestly, and I know a lot of you will disagree - change my mind. The only reason I would swap anything from stock is to gain some performance, and this particular change was not one I intended.

Thoughts?

[MotorMouth93]

If you're worried about passing emissions you can check the emissions status with any Bluetooth/Wifi OBD reader and a phone app.

[JimLev]

I put headers on my 540 3 years ago which meant the OE engine headers with the pre-cats had to go.
I've had them in my garage laying on the floor for the last 3 years.
2 weeks ago I cut the cats off (still good) and tossed the rest.
I don't get any codes but it does smell just a little bit when first stared up when cold. It's doesn't last long.
If you don't have a CEL on you should be OK.
Back when I use to live in MA (different car) we'd dump in a alcohol with the gas so it would burn cleaner, didn't have a problem when they checked emissions.

OldExhaust.JPG

Header_28.JPG

[Iamthebull]

Jim which headers are those? I keep going back and forth between trying to get a hold of the A1 headers, or going all out for the Unicorn headers. Or ditch it all together and save towards a turbo build. All costly options.

[JimLev]

I bought them from Schneidermann (sp?) they are actually made in Italy and for an M5. Same head/bolt pattern.
They are stainless, I had them ceramic coated inside and out.
You will need to have some custom welding done to connect them to the main CAT's. I bought V-band clamps for the collectors to the main CAT's.

[jicaino]

Don't worry, pre cat delete won't even give you a code or increase the amount of C0 emissions. As a matter of fact my car went from 50 ppm to 70ppm doing a full decat. Now that I have a stronger tune and colder tstat it's 85 PPM.

You'll be safe, and happy about the deletion too!

[BradleyDanger]

I figured having less restriction in the system would be a good thing, especially right out of the headers (which have their own bottleneck issues), so I didn't complain about a decreased cost to gut them as an alternative to replacement. But I also don't know enough about this topic to know if it would be a performance enhancer, limiter, or no change option. My main concern was with emissions, and causing more stress, and lower life expectancy to the main cats further back. I know there are ways to cheat the emissions center to pass (my mechanic - though he'll deny ever saying so - suggested 4 gallons of e85 mixed with 91 octane to run hot enough to pass. That was a new one), but if there's no need, that's even better.

[BradleyDanger]

I put headers on my 540 3 years ago which meant the OE engine headers with the pre-cats had to go.
I've had them in my garage laying on the floor for the last 3 years.
2 weeks ago I cut the cats off (still good) and tossed the rest.
I don't get any codes but it does smell just a little bit when first stared up when cold. It's doesn't last long.
If you don't have a CEL on you should be OK.
Back when I use to live in MA (different car) we'd dump in a alcohol with the gas so it would burn cleaner, didn't have a problem when they checked emissions.

OldExhaust.JPG

Header_28.JPG

I'm sure you havent looked back since installing new headers. Performance worth the price?

[JimLev]

Performance worth the price?

Ummm, maybe for the die hard guys that like to wrench, has grease under their fingernails, and love the smell of gas.
I did all the work installing them, with the extra parts needed I've got at least $2K into this mod.
It does pull better and is a lot lighter than to OE exhaust.

[Iamthebull]

If I do decide on getting a set of headers, I'll do it when I replace my clutch & flywheel, diff, and other maintenance items involved.

[BradleyDanger]

Alright, I've got to revive the thread.

Since my original post the car has basically been in and out of the shop, getting a ton of engine love and needed refresh. Needless to say, I didn't get around to actually registering and emissions testing it until late November 2019. It didn't pass then, and hasnt passed since, even with 4 gallons of e85 in the tank. So now I have a car I cant drive, with temporary plates that are expired until I fix this issue.

My mechanic is convinced the gutted precats are the issue, and unfortunately I am now getting check engine lights as well. I can clear the codes, but they always come back within a few days of driving.

I'm at a loss - and after tons of research the M62TU vanos engine is the only in the line of e39 vehicles that has this particular design flaw. I can buy a set of used catted headers and hopefully fix the problem, but what's the point when the design is inherently restrictive and used cats will eventually fail also? Is there anything else that could be causing the emissions failure? Are there ANY after market catted headers out there?

[jwetz]

If you've already done the initial emissions test, go to air care Colorado.com
They post, and update, dates, times & locations that the emissions testing vans will be at. There's a certain timeframe before emissions are due when re-registering your car that you can drive by the vans on 2 different days & "pass" the emissions test.

If your car passes, they'll let you know on that little reminder card they send you, that a test isn't required, but you still have to pay the "testing fee" with your registration.

If you haven't ever done emissions on the car, then all bets are off, you'll actually have to take it in to Envirotest for the emissions...but only the first time if it passes. Afterwards, try what I described 2 years down the road.

Sent from my SM-G892U using Tapatalk

[jwetz]

Alright, I've got to revive the thread.

Since my original post the car has basically been in and out of the shop, getting a ton of engine love and needed refresh. Needless to say, I didn't get around to actually registering and emissions testing it until late November 2019. It didn't pass then, and hasnt passed since, even with 4 gallons of e85 in the tank. So now I have a car I cant drive, with temporary plates that are expired until I fix this issue.

My mechanic is convinced the gutted precats are the issue, and unfortunately I am now getting check engine lights as well. I can clear the codes, but they always come back within a few days of driving.

I'm at a loss - and after tons of research the M62TU vanos engine is the only in the line of e39 vehicles that has this particular design flaw. I can buy a set of used catted headers and hopefully fix the problem, but what's the point when the design is inherently restrictive and used cats will eventually fail also? Is there anything else that could be causing the emissions failure? Are there ANY after market catted headers out there?

Once you hit $700 cost in parts & labor to fix the emissions, you can get a waiver, at least, that used to be the rule here in Colorado. You might want to look into that. Or else see if you can find an e39 that's being parted out, that has what you need. Maybe see if the same model year/engine X5 has compatibility & is getting parted out?
Check the part # on both models on realoem.com
If they're the same # then they'd work.

Sent from my SM-G892U using Tapatalk

[JimLev]

If you can't pass emissions and need a set of pre-cats I saved mine when I cut them off to install headers.

[ross1]

If you can't pass emissions and need a set of pre-cats I saved mine when I cut them off to install headers.

ding, ding, ding, ding, ding

https://www.bimmerforums.com/forum/s...7#post30389487

- - - Updated - - -

Alright, I've got to revive the thread.

Since my original post the car has basically been in and out of the shop, getting a ton of engine love and needed refresh. Needless to say, I didn't get around to actually registering and emissions testing it until late November 2019. It didn't pass then, and hasnt passed since, even with 4 gallons of e85 in the tank. So now I have a car I cant drive, with temporary plates that are expired until I fix this issue.

My mechanic is convinced the gutted precats are the issue, and unfortunately I am now getting check engine lights as well. I can clear the codes, but they always come back within a few days of driving.

I'm at a loss - and after tons of research the M62TU vanos engine is the only in the line of e39 vehicles that has this particular design flaw. I can buy a set of used catted headers and hopefully fix the problem, but what's the point when the design is inherently restrictive and used cats will eventually fail also? Is there anything else that could be causing the emissions failure? Are there ANY after market catted headers out there?

Design flaw?
You wrecked your cats, can't pass smog and blame it on BMW? What have I missed here?

[BradleyDanger]

I'm emissions testing for the first time to register the car, so the drive by van testing won't work. It's true that $700 spent and proven will get a waiver, but I also don't want to spend that kind of money unless it's to upgrade and I know it will pass afterwards. I'm looking at realoem.com right now, the diagrams between the TU vanos engine, and say an M5 engine of the same year - parts are certainly different. What I can't figure out is how an M5 of that year differs in emissions control that drastically to only need one set of cats (which mine still has mid-way).

I may take you up on those pre-cats if they're in good shape @JimLev. I assume they'll need to be welded on at this point?

[BradleyDanger]

ding, ding, ding, ding, ding

https://www.bimmerforums.com/forum/s...7#post30389487

- - - Updated - - -


Design flaw?
You wrecked your cats, can't pass smog and blame it on BMW? What have I missed here?

You missed the part where the car wouldn't run without replacing the cats, or gutting them. I took the chance and went the cheap route because $4000 parts and labor to replace them is unspeakable - Which brings us to the design flaw, which is inherent ONLY to facelift e39 M62TU vanos engines where the entire exhaust manifold has to be replaced when the cats inevitably fail, and they will. Any other e39 only has 1 set of cats downstream, making it a MUCH simpler process to swap them when needed. All of this and the OE exhaust manifolds themselves are still a complete bottleneck and restriction right out of the heads.

The point is, $4000 to replace the OE headers/cats makes no sense when there are other options that cost much less, AND provide better flow and increased performance. I am attempting to explore those options while also determining how to pass emissions.

[Frankie]

My mechanic is convinced the gutted precats are the issue, and unfortunately I am now getting check engine lights as well.

When I read your original post from June 2019, I suspected the car was for sale precisely because the cats had failed.

Anyone who "guts" cats from their exhaust will fail emissions, period. Your mechanic - who should have known better - is partially responsible for even suggesting such a thing. And now he acknowledges this. Funny. And ideas of magical potions to put in your gas tank are embarrassingly naive.

This is because car manufacturers have gotten much better at preventing attempts at bypass emissions controls. Furthermore, cat sensor feedback is now an integral part of engine control software, and required in order to prevent engine knock, mixture faults, and numerous other codes. If cat faults exist, your car will not only run poorly but will burn excessive amounts of fuel and produce very stinky exhaust...which is intentional and commanded by the ECM. With BMW, this occurs with TU engines onward, and especially with SULEV engines (M54) in the 525, 530.

How do I know? Because it happened to me (with a 2003 530i).

I'll get to the point: you're in trouble. Big trouble.

No way around it: If you want to keep this car, you must replace the exhaust headers.

Yes, you could buy used headers, but you simply don't know what you're getting. It's a gamble. They may fail after a short time and require a repeat of this expensive service. That's what happened to me. As a car owner, it was the worst experience I've ever encountered.

The only permanent solution is to buy factory-original, new parts. $855 each. Only then can you be sure.

A couple side notes:

The reason factory cats are so expensive is because of the considerable precious metal content inside, used to absorb and mitigate emissions. Aftermarket cats don't have nearly as much of this content and are therefore less expensive. This also leads me to believe they won't do as good a job at keeping the check-engine light at bay.

You can thank your legislators for this situation. Emission controls have become so stringent they are now the primary factors driving cost increases in new cars. Due to this, cars have become so complex that computer diagnostics are no longer optional. This also results in much higher cost of ownership for used cars (such as ours), especially after the warranty period. Almost all the engineering that BMW and others do centers around this topic.

Good luck.

[JimLev]

I may take you up on those pre-cats if they're in good shape @JimLev. I assume they'll need to be welded on at this point?

They are in good condition, I'll post pics of them later today.
Yes they will need to be welded on.

[BradleyDanger]

When I read your original post from June 2019, I suspected the car was for sale precisely because the cats had failed.

Anyone who "guts" cats from their exhaust will fail emissions, period. Your mechanic - who should have known better - is partially responsible for even suggesting such a thing. And now he acknowledges this. Funny. And ideas of magical potions to put in your gas tank are embarrassingly naive.

This is because car manufacturers have gotten much better at preventing attempts at bypass emissions controls. Furthermore, cat sensor feedback is now an integral part of engine control software, and required in order to prevent engine knock, mixture faults, and numerous other codes. If cat faults exist, your car will not only run poorly but will burn excessive amounts of fuel and produce very stinky exhaust...which is intentional and commanded by the ECM. With BMW, this occurs with TU engines onward, and especially with SULEV engines (M54) in the 525, 530.

How do I know? Because it happened to me (with a 2003 530i).

I'll get to the point: you're in trouble. Big trouble.

No way around it: If you want to keep this car, you must replace the exhaust headers.

Yes, you could buy used headers, but you simply don't know what you're getting. It's a gamble. They may fail after a short time and require a repeat of this expensive service. That's what happened to me. As a car owner, it was the worst experience I've ever encountered.

The only permanent solution is to buy factory-original, new parts. $855 each. Only then can you be sure.

A couple side notes:

The reason factory cats are so expensive is because of the considerable precious metal content inside, used to absorb and mitigate emissions. Aftermarket cats don't have nearly as much of this content and are therefore less expensive. This also leads me to believe they won't do as good a job at keeping the check-engine light at bay.

You can thank your legislators for this situation. Emission controls have become so stringent they are now the primary factors driving cost increases in new cars. Due to this, cars have become so complex that computer diagnostics are no longer optional. This also results in much higher cost of ownership for used cars (such as ours), especially after the warranty period. Almost all the engineering that BMW and others do centers around this topic.

Good luck.

Thank you for the thorough response. I suspected this was likely the case. What I'm trying to figure out now is if/how I can eliminate the catted headers altogether, and reduce emissions further down the exhaust so I don't have to deal with this again, a setup similar to the M5 exhaust. There has to be a way to replicate the controls and exhaust dynamics so an M5 style exhaust could be used on a 540i TU engine. Right? Or am I way off base here? Below are the diagrams from realoem, first the M5 exhaust - manifolds then front section. Second the 540 exhaust - manifolds then front section:

2003 M5

M5 headers.JPG
M5 front exhaust.JPG

2003 540i
540 Headers.JPG
540 front exhaust.JPG

The main difference I can see is in the arrangement of the upstream and downstream O2 sensors, and perhaps much more robust cats on the M5. Where the M5 has an upstream o2 sensor much further down the pipe before the main cats, and downstream after, the 540i has an upstream sensor directly on the manifold before the cat and not again until after the mid cats. I'm just spitballing here, and I'm no engineer, but couldn't this be replicated on a 540i with more efficient than stock mid cats?

[Frankie]

if/how I can eliminate the catted headers altogether?

You can't.

Unless you want to re-engineer the entire exhaust system, sensor inputs, and ECM mapping. It would be easier to swap an M62 engine. But that would cost more than simply buying new headers.

[JimLev]

Doing the M5 setup is possible but it's going to cost you a boat load of $$$$, probably a lot more than just putting pre-cats back on your 540.
I'll get you some pics of the outsides and the cell area this afternoon.

[Santaclaus4]

I read your first post and you mentioned gutting the CAT's and replacing the fouled spark plugs. Is it possible the spark plugs were the actual problem? Perhaps the CAT's didn't need gutting in the first place.
I've dealt with several cars in the past with clogged CAT's and the car will start normally and run for a few minutes and as the exhaust warms up it will start to make a wheezing sound and lose power. In both cases the car would still idle fairly normally and it did not cause the spark plugs to foul. In both cars I open the housing and removed the material. You could see the honeycomb structure had stuff wedged in it causing blockage. I still have a chunk of it in my tool box at work so I can show people what a clogged CAT looks like.

[BradleyDanger]

I read your first post and you mentioned gutting the CAT's and replacing the fouled spark plugs. Is it possible the spark plugs were the actual problem? Perhaps the CAT's didn't need gutting in the first place.
I've dealt with several cars in the past with clogged CAT's and the car will start normally and run for a few minutes and as the exhaust warms up it will start to make a wheezing sound and lose power. In both cases the car would still idle fairly normally and it did not cause the spark plugs to foul. In both cars I open the housing and removed the material. You could see the honeycomb structure had stuff wedged in it causing blockage. I still have a chunk of it in my tool box at work so I can show people what a clogged CAT looks like.

No way to know at this point, unfortunately. What you describe is more or less what happened. I started the car and let it idle for about 3 minutes, then it died and wouldn't start again. Shop told me it was the cats, and after gutting them, it started, but was still running ragged, so they replaced spark plugs.

Sounds like the only way to solve this problem is buying $1700-$2400 worth of headers (depending where you buy) and having them installed again. What a mess. Anyone know what the typical lifespan on these cats is supposed to be? Or why they might clog sooner than later? This car only has 111k on it.

[BradleyDanger]

Anyone tried the Magnaflow manifolds with cats for these cars? https://www.hottexhaust.com/Magnaflow_50450 and https://www.hottexhaust.com/Magnaflow_50451. Design looks much less restrictive than stock, and about the same price. I guess at this point, I'm just comparing options if I'm going to have to spend the money anyway.