1999 M3 not passing smog, no codes. High hydrocarbons

[dakar786]

Hello bimmer community,

I recently tried to smog my car and failed (3 attempts) NO CHECK ENGINE LIGHT OR CODES

I just got the car and here are the things i did before i smogged it.

Car has 129k miles and its a 1999 M3

seafoam in gas tank + through brake booster vacuum line let it sit in hot engine and got alot of black smoke.

changed sparked plugs

changed oil (doesnt really make a difference)

changed air filter

Here were my first results at my smog attempt:

15mph ..... HC (PPM) came out to 147 .... max is 54 *fail*
25mph...... HC (PPM) came out to 33 ...... max is 37 *pass*


2nd attempt was me not really changing anything but getting the engine super hot driving hard and idling and revving for about 15 min before smog:


Here were my results the 2nd time :

15mph......HC (PPM) came out to 83 .... max is 54 *fail*
25mph......HC (ppm) came out to 31..... max is 37 *pass*


3rd attempt I visually inspected the car furthermore and found a hole in the intake boot near hole that leads to ICV.

Replaced intake boot

Cleaned ICV

Cleaned MAF sensor

Changed Fuel Filter

This time i got the engine super hot! idled on about 3k rpm for about 15 min right before smog.

Here were my last results :

15mph.......HC (PPM) came out to 157..... max is 54 *fail* even higher than the first time.
25mph.......HC (PPM) came out to 31.......max is 37 *pass*


So heres what I had in mind,


The car eventually reaches its operating temp ( needle in middle) but seems like it takes a while to get there. Could a bad thermostat cause high hydrocarbons and nox?

Also, a bmw tech told me it could possibly be the upstream (near head) o2 sensors lagging. I thought o2 sensors usually throw a code when they go bad but i could be wrong. Could this possibly be the culprit?

Alot of people are telling me to get the liquid gtp (guaranteed to pass) from the local auto store but wanted to find the root cause of the issue. car averages about 19mpg.. normal?

HELP

[bluptgm3]

19 mpg seems low for S52 OBDII E36, but I don’t know how you drive.
Drive to get cats hot, no stationary running. Need load to run properly.
Old Pre-cat O2 sensors can cause rich mixture if they are slow to respond.


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[TostitoBandito]

As you said, it could be the pre-cat O2 sensors in the headers. When they go your engine will default into a rich mixture which will lower mileage and also degrade your cats over time. I'm not sure on the codes for those, but you'll likely need a scan tool plugged into the port under the hood to get that level of detail. My other guess would be that the cats might be shot. 19mpg does seem a bit low; that's around what I get driving around town but I also have a 3.46 diff and wider wheels/tires so I burn more gas.

Engine temp should have nothing to do with it as long as you're at operating temperature in the middle when you test.

I'm about to replace all my O2 sensors when I drop the exhaust to swap my driveshaft this weekend, partly because I've been getting intermittent codes from them or for cat efficiency so I think one or more are dead/dying and I want to address it before they ruin my cats. My cats still have to make it 4.5 more years before I can remove them.

[Hova]

Over the years I've seen a number of tricks, but the most common is to get the cats VERY hot. The best way I've seen this done is by putting a lot of load on the engine. Go do some 0-60+ mph runs. Then bounce off the rev limiter going into the smog parking lot, lol.

High hydrocarbons should be burned up in the cats, which is making me think they might not be hot enough.

Should also consider changing all of the O2 sensors if you can't get it to pass. Just because they are slow doesn't mean they are out of range according to the ECU, so they might not throw a code.

[bluptgm3]

The dash temperature gage is not very accurate and you could be running a bit on cool side.
And/or O2 sensors.
As mentioned pull the stored codes or get INPA to read the live data.


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[jclausen]

Read the coolant temp with infrared heat gun, if it takes a long time to reach halfway your thermostat is probably done.. is this ca a daily driver or does it sit a lot also you need to get the cats good and hot and get it on the machine, no sitting around

[Hankdoll]

I feel for you. My car has been just at the max for HC for the last 8+ years. I’ve done everything you mentioned before each smog check, and replaced the pre cat O2 sensosors too. Cannot figure it out, but since I always squeak by, I leave it for another day. I only drive the car 1k a year at most. I used to get 23 mpg on average, but get about 19mpg now. I,m thinking it has something to do with the 10% ethanol CA starting allowing in the gas. The timing lines up with the decrease in my mpgs (and high hydrocarbons).

[marvinstockman]

Are you burning oil? If so, what weight oil are you using. At least for the test, you might try a 15w-50.

Also, if you had really bad O2 sensors, they should bring up a check engine light.

What is your long and short term fuel trim? What is your air-fuel ratio?

[tjm3]

A bad thermostat combined with the engine not reaching normal operating temp would cause high HC at idle, but the cooler running engine wouldn't increase the NOx. If the O2 sensors are suspect then a quick check with even the cheapest code reader would allow you to view the live data from ALL of the O2 sensors. But the best way to verify that info is to capture the Min/Max voltages AND the averages directly from the pre-cat sensors using a good DMM. Easily done at the connectors on top of the engine. You would be looking for a LEAN biased sensor that would cause the system to pump in more fuel (that's more HC), if that actually is the cause of the problem. If you don't see that lean bias then it's NOT the O2 sensors. If you've been running rich for a while then the cat is also suspect. A cat efficiency test wouldn't be out of line. By the way, driving the crap out of it before a smog test doesn't get done to warm the engine, it's to superheat the cat to make it work a little better.

[Hova]

A bad thermostat combined with the engine not reaching normal operating temp would cause high HC at idle, but the cooler running engine wouldn't increase the NOx. If the O2 sensors are suspect then a quick check with even the cheapest code reader would allow you to view the live data from ALL of the O2 sensors. But the best way to verify that info is to capture the Min/Max voltages AND the averages directly from the pre-cat sensors using a good DMM. Easily done at the connectors on top of the engine. You would be looking for a LEAN biased sensor that would cause the system to pump in more fuel (that's more HC), if that actually is the cause of the problem. If you don't see that lean bias then it's NOT the O2 sensors. If you've been running rich for a while then the cat is also suspect. A cat efficiency test wouldn't be out of line. By the way, driving the crap out of it before a smog test doesn't get done to warm the engine, it's to superheat the cat to make it work a little better.

This.

[dakar786]

Marvin,
Im burning quite a bit but was told it shouldnt effect smog too much.
I read the forums in the past and people were recommending 10w40 and currently thats what im running..... I was thinking of switching back to the recommended 5w30. I haven't got the read out for my air-fuel ratio. Ill check it out soon.

Thank You

- - - Updated - - -

quick update, SO the car has a slight hesitation starting sometimes like maybe a second and half. Doesnt start up right away. Once on runs fine. I was told spacing my downstream o2 sensors with a spark plug fouler might lower the reading on the hydrocarbons and nox. Is this true?

[bluptgm3]

- - - Updated - - -

quick update, SO the car has a slight hesitation starting sometimes like maybe a second and half. Doesnt start up right away. Once on runs fine. I was told spacing my downstream o2 sensors with a spark plug fouler might lower the reading on the hydrocarbons and nox. Is this true?

Is the emissions data coming from OBDII port or tail pipe probe, I assumed a probe.
Down stream O2 sensors do not affect mixture, they are simply monitoring catalytic efficiency.

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[tjm3]

....
Down stream O2 sensors do not affect mixture, they are simply monitoring catalytic efficiency....

Not true, varies with manufacturer and engine model but especially not true for Bosch systems that use them for LTFT adjustment (Bosch Automotive Handbook).

[tjm3]

Marvin,
Im burning quite a bit but was told it shouldnt effect smog too much.
I read the forums in the past and people were recommending 10w40 and currently thats what im running..... I was thinking of switching back to the recommended 5w30. I haven't got the read out for my air-fuel ratio. Ill check it out soon.....

Here's some interesting information. Burning oil does affect the catalytic converter operation, especially with higher weight oils. Beginning after the SJ rated oils, the amount of zinc and phosphorus (ZDDP) used for high pressure wear (flat tappets, cam driven high pressure fuel pumps, etc) were cut back drastically so that newer oils (SM, SN) have about half or less of what used to be in there. They only did this for the lighter weight oils 5W-30 and lighter. The oils from 10W-30 and heavier retained close to the original amounts of zinc and phosphorus. They did this mainly for converter life. The zinc/phosphorus attacks the cats and so they cut back. So, if you're burning a lot of the heavier oil then it sure can affect the cat efficiency, especially if you've been burning it for a while. By the way, I have the Blackstone reports to back up the info.

[dakar786]

TJ,

So you recommend switching to 5w30? Do you have any recommendations as to which oil brand you recommend? Preferably one that burns less. I'm going to do an oil change as soon as possible and maybe run some of that GTP (guaranteed to pass) and get the engine hot and try again.

Thanks for your time.

[TostitoBandito]

Any of the BMW-approved 5w30 or 5w40 full synthetic oils should be fine (longlife-01 I think is what you want). Liqui-moly is a popular choice, but there are many others including oils from castrol, pennzoil, etc...

[bluptgm3]

Not true, varies with manufacturer and engine model but especially not true for Bosch systems that use them for LTFT adjustment (Bosch Automotive Handbook).

The E36 engine management system does not use post catalytic converters O2 sensors, they do not control mixture.
Spacing these with a non fouling device does nothing to alter mixture.

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[TostitoBandito]

Yeah my understanding is the only purpose of the post-cat sensors is to measure cat efficiency for emissions. If they fail or you remove them you'll get CEL codes for that but it doesn't actually impact anything about how the car runs. If you remove the cats you can just replace the sensors with a simulator to make the CEL go away.

[dakar786]

Update: I don't know if not gapping the spark plugs might have an effect on the car reading high hydrocarbons and nox. I switched the plugs to the NGK BKR6E-11 and the preset gap is 0.044 Inch....

Does anyone know the gap specs for a 1999 m3? Or should i just leave them be?

[bluptgm3]

As I recall the S50 prefers the NGK and the S52 prefers Bosch - no gaping required with proper plug.


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[TostitoBandito]

https://smile.amazon.com/gp/product/B000GX9FSY/

I'm using those. They work fine. And yes, I believe the BKR6E's are in theory the proper gap though you should still check them.

[dakar786]

Tostito,

The link you have is for the bkr6equp which are 4 electrodes as opposed to 1 electrode on the bkr6e-11. Do you recommend those over the single electrode?

[TostitoBandito]

They work and lots of people use or have used them. They will last longer than the single electrode plugs, but are a bit more expensive. There's lots of threads here and elsewhere about it. Those are the two flavors of NGK plugs I'd suggest though. Track/race cars tend to favor the single copper electrode plugs for slightly better performance and they don't care about the shorter life since they probably change them at least every year along with everything else consumable on the car.

[bluptgm3]

Boost seems to like single electrode plugs, been running the four electrode plugs non boosted for over 200k miles.


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[dakar786]

does anyone recommend any hoses in the vacuum system to be changed? Hoses that might effect the high hydrocarbon reading ? theres a small hose that connects to the secondary air pump near the exhaust that i will change out. It is completely frail and almost completely warn out. Don't know if that might have an effect on it.