An Intricate Misfire.

Hello,

I'm hoping someone can help me with my problem.
I have a pretty intricate misfire going on. It's very random.

This is something that has been happening with my car for quite a few months now.
At first, it was very, very subtle. Now, it happens almost every time I accelerate heavily.
Half the time I can get it to do it on command. Other times, it doesn't feel like doing it.

So, here's when it occurs...
We'll say we're riding in 4th gear. If you ease into the throttle by pushing the pedal down gradually to the point where it wants to shift (but doesn't just yet), the car will start jerking back and forth. It does it pretty badly if you hold the throttle to the point right below where it wants to shift. However, it also just...acts up when it wants to anyway.

Like I said -- it happens sporadically.
Another thing to note...only 1/100 times will it throw the SES light.


I was on my way to school one day. It was acting up pretty bad to begin with. Usually when it starts acting up, I just get off of the throttle and then get right back on it. Well, I wanted the car to throw a code so I could find out if it actually was a misfire.
So, I held it at the shift point. It was riding like hell, and then it finally threw on the SES light. After that light came on, all hell broke loose and it felt like I was driving with one cylinder.

So, I got to school and put the scanner on it. Said cyl6 misfire.

Not so sure I'm convinced that it's an injector or coil.
If you want to see my reasoning on that, you can read this: http://www.bimmerfest.com/forums/sho...d.php?t=631854
But, there's always the chance that I'm wrong.


Any input is much appreciated.

have the intake valves been cleaned?

Injector or coil is the most likely cause. I had the exact symptoms you described on mine, and it was the coil.

The car ran fine, but would misfire under boost, then operate roughly and with reduced power until I shut it off and restarted it. I have I-Drive, so the screen would tell me which cylinder was misfiring.

The simple test is to move the coil to another cylinder, make it throw a code again, and see if the misfire is on the new cylinder.

Frederic

Misfires under load like this are almost always the secondary ignition. My first guess would be a bad spark plug, and is the cheapest to test out.

If you change your plugs and are still having the issue, you can try swapping the coil on #6 with the one on #1 and see if the misfire moves to #1.

Originally Posted by Orient330iNYC

have the intake valves been cleaned?

Not that I know of.
Why would they need to be?

@TXFred I played that little swap game 500 times (refer to the link I posted).
The misfire has no pattern.

Originally Posted by Braumin

Misfires under load like this are almost always the secondary ignition. My first guess would be a bad spark plug, and is the cheapest to test out.

If you change your plugs and are still having the issue, you can try swapping the coil on #6 with the one on #1 and see if the misfire moves to #1.

I have new plugs in it. NGK Platinums or something. The car has 71.5k miles on it now. I believe I put the plugs in at 69k.

New plugs doesn't mean one isn't bad.

What do you mean by "the misfire has no pattern"

Do you mean the cylinder that misfires isn't always 6?

Originally Posted by Braumin

New plugs doesn't mean one isn't bad.

What do you mean by "the misfire has no pattern"

Do you mean the cylinder that misfires isn't always 6?

In the past several months this has been happening, I've only gotten it to throw one code...and that was cyl6.

Back when I had the tune in my car (in the link I posted), the misfire just had no pattern.
For example...
I'd swap the coils. The misfire would follow. Then I'd swap that coil with another, and the whole problem would go away. A couple drives later, a misfire would happen at a completely random cylinder.
So, instead of swapping this time, I'd just buy a new coil. Replaced it, and the misfire stayed with that cylinder. Swapped the new coil with another cylinder's coil, and the problem would go away.
A couple drives later, it would come back and be another random cylinder.

the N54 is prone to carbon building on the intake valves, this leads to generally bad performance.
i suspect that at your mileage, this may be a factor in your misfires and stumbling
unfortunately, a walnut shell blasting of the valves is not cheap- 5-600 dollars, but the only way to clean it if you have the buildup. its visible if you pull the intake manifold.

Hmmm. I love random misfires. They're tough but very satisfying to figure out. With your engine we have to start by agreeing that the misfire isn't the cause but the effect. Something is going bad and it results in different cylinders misfiring. Based on the symptoms I think we can assume that your compression is good, and that your mechanicals are all functioning properly.
That leaves the problem with spark or fuel. Either you are randomly not getting spark or not getting fuel. The fact that you are not always getting a CEL tells me a lot about what it isn't, not an answer, but we're making progress. If I had your car in a bay I would take a look at short term fuel trim to see if you are constantly running borderline lean, that would point to either a bad air/fuel ratio sensor (you call it an oxygen sensor), or a bad mass airflow sensor, or a bad throttle position sensor, or a bad intake air temperature sensor.
The whole key is that the engine is not immediately setting a code.
Why? Because the computer thinks the bad device is sending a good signal, in other words the signal may be bad but it's plausible! Example: You install a Super Duper oil soaked intake air filter. The oil vaporizes and condenses on the mass airflow sensor. It cokes up over time and insulates the sensor wire. At 50 mph when the sensor should report 42 grams per second of air it reports 35. The condenser then commands enough fuel for 35 grams of air which results in a very lean mix. The mix gets critical under stress conditions (like accelerating) and a cylinder -or many cylinders- run so lean they missfire. Then the A/F ratio sensor sees all those unburned hydrocarbons going down the exhaust and -guess what?- CUTS BACK on the gas because it assumes you are rich when in fact you are lean. Now your engine is shaking like the San Andreas Fault on a bad day. You let off the gas and things get a little sorted out for a while.
See? It gets complicated. I doubt we are going to be able to help you resolve this problem without good information and without a graphing scanner you can't give it to us.

Or your intake valves could look like the La Brea Tar Pit. Tip o' the hat to Orient. His record is good on this subject.

Originally Posted by DSXMachina

Hmmm. I love random misfires. They're tough but very satisfying to figure out. With your engine we have to start by agreeing that the misfire isn't the cause but the effect. Something is going bad and it results in different cylinders misfiring. Based on the symptoms I think we can assume that your compression is good, and that your mechanicals are all functioning properly.
That leaves the problem with spark or fuel. Either you are randomly not getting spark or not getting fuel. The fact that you are not always getting a CEL tells me a lot about what it isn't, not an answer, but we're making progress. If I had your car in a bay I would take a look at short term fuel trim to see if you are constantly running borderline lean, that would point to either a bad air/fuel ratio sensor (you call it an oxygen sensor), or a bad mass airflow sensor, or a bad throttle position sensor, or a bad intake air temperature sensor.
The whole key is that the engine is not immediately setting a code.
Why? Because the computer thinks the bad device is sending a good signal, in other words the signal may be bad but it's plausible! Example: You install a Super Duper oil soaked intake air filter. The oil vaporizes and condenses on the mass airflow sensor. It cokes up over time and insulates the sensor wire. At 50 mph when the sensor should report 42 grams per second of air it reports 35. The condenser then commands enough fuel for 35 grams of air which results in a very lean mix. The mix gets critical under stress conditions (like accelerating) and a cylinder -or many cylinders- run so lean they missfire. Then the A/F ratio sensor sees all those unburned hydrocarbons going down the exhaust and -guess what?- CUTS BACK on the gas because it assumes you are rich when in fact you are lean. Now your engine is shaking like the San Andreas Fault on a bad day. You let off the gas and things get a little sorted out for a while.
See? It gets complicated. I doubt we are going to be able to help you resolve this problem without good information and without a graphing scanner you can't give it to us.

Or your intake valves could look like the La Brea Tar Pit. Tip o' the hat to Orient. His record is good on this subject.

After trying everything that I did...the only thing I could think of would be a bad O2 sensor.
That, and maybe a clogged cat. Does that sound plausible?

I don't know...I'm still an apprentice technician going through school.


The car is under warranty. I WOULD just take it to BMW, but the idiots won't give me a loaner because I'm not 21. I guess people under 21 shouldn't take their car in for repairs.

Originally Posted by Hemorrhage

After trying everything that I did...the only thing I could think of would be a bad O2 sensor.
That, and maybe a clogged cat. Does that sound plausible?

I don't know...I'm still an apprentice technician going through school.


The car is under warranty. I WOULD just take it to BMW, but the idiots won't give me a loaner because I'm not 21. I guess people under 21 shouldn't take their car in for repairs.

Clogged cat is very unlikely, but could result from continued driving with a bad miss. There are ways for the computer to pick up on potential major damage and will throw an immediate blinking CEL. So far you're good.
You need to take it to BMW if it's on warranty. This could easily turn into a $500 to $1500 repair bill otherwise. And it's not going to be something you can handle on your own anyway. Sorry kid, the thing is just too complex and sometimes you gotta know when to fold 'em. These types of problems take an L1 diagnostician (the best of the best) and a whole lot of experience to figure out.

Another reason I'm skeptical about taking it to BMW is that they're idiots.
I asked, "Is this covered until my CPO warranty?"

She goes, "There are hundreds of things that could cause it. Once we diagnose it, we will tell you."

Meanwhile, a customer came to my shop because he had a misfire. BMW told him he needed a new computer.
Whereas, in reality, he just needed an injector...

So, I'm assuming they're going to do what they can to get money out of me.

Originally Posted by Hemorrhage

Another reason I'm skeptical about taking it to BMW is that they're idiots.
I asked, "Is this covered until my CPO warranty?"

She goes, "There are hundreds of things that could cause it. Once we diagnose it, we will tell you."

Meanwhile, a customer came to my shop because he had a misfire. BMW told him he needed a new computer.
Whereas, in reality, he just needed an injector...

So, I'm assuming they're going to do what they can to get money out of me.

I read the July thread twice, and this one again as well. There's nothing I can do to help you because you can't be helped. There are many lessons to be learned when you're in college. Most of the good ones don't occur in the classroom.

Originally Posted by DSXMachina

I read the July thread twice, and this one again as well. There's nothing I can do to help you because you can't be helped. There are many lessons to be learned when you're in college. Most of the good ones don't occur in the classroom.

What do you mean by "you can't be helped"?

Originally Posted by Hemorrhage

What do you mean by "you can't be helped"?

Because you gave us the history of the car, asked for advice, were given advice -the only practical advice, and you don't want to follow it.
Frankly, it would be easier to diagnose a brain aneurysm (if you had access to an MRI) than it will be to diagnose your problem. You've been dealing with this for three months and are not one bit closer to a diagnosis than you were in the beginning. So what more can be done?

I'm just trying to gain as much information as possible before committing.

It's inevitable that I have to take it to get fixed since I'm too much of a novice to figure it out...
But I'd like to get as much insight as possible so they can't feed me bull **** when the time does come.

so you're getting a check engine light... which indicates cyl6 misfire... why dont you start with that.

try swapping coils and see if the misfire follows.

yes you can check to see your adaptation values but if the car was running that lean it would have set adaptation codes already and you'd be running rough at all times.

So, I took my car to BMW last week.
They were baffled.
But, I guess it's understandable if you can't replicate the problem on command.

I brought up the idea of built up carbon in the intake valves. They were pretty certain that that is what's causing it, but they weren't able to pull the intake manifold and verify it.
They mentioned that if that IS the problem, it wouldn't be covered under my warranty. So, I told them to just ignore it and asked for my car back so I could afford the bill.
Luckily, they didn't charge me for the X hours they spent messing with it.

However, I can't understand how it isn't covered under my CPO warranty. The power train is covered, and built up carbon on the intake valves is part of the engine...
Anybody know anything about that?

Originally Posted by Hemorrhage

So, I took my car to BMW last week.
They were baffled.
But, I guess it's understandable if you can't replicate the problem on command.

I brought up the idea of built up carbon in the intake valves. They were pretty certain that that is what's causing it, but they weren't able to pull the intake manifold and verify it.
They mentioned that if that IS the problem, it wouldn't be covered under my warranty. So, I told them to just ignore it and asked for my car back so I could afford the bill.
Luckily, they didn't charge me for the X hours they spent messing with it.

However, I can't understand how it isn't covered under my CPO warranty. The power train is covered, and built up carbon on the intake valves is part of the engine...
Anybody know anything about that?

No, but I'd read the fine print on the warranty if I were in your shoes.
There are easier ways to check the intake valves than pulling the intake manifold. In fact, I rarely would. One way is to remove the throttle body and run a borescope down the intake. The latest model has high resolution video out, and records in color. By twisting the lead as the scope passes down the manifold it is possible to access most ports and get a good idea if that's the problem.

A second way is to pass a borescope down the sparkplug hole after rotating the engine so that the intakes are open. You can then inspect the area right behind the valve head which usually has the worst accretion. Given my druthers, I'd go through the throttle body. It gives me a better look at all the nooks and crannies.

Expect to pay a couple hundred bucks for the exam it the throttle body is removed. Gaskets included.

Originally Posted by DSXMachina

No, but I'd read the fine print on the warranty if I were in your shoes.
There are easier ways to check the intake valves than pulling the intake manifold. In fact, I rarely would. One way is to remove the throttle body and run a borescope down the intake. The latest model has high resolution video out, and records in color. By twisting the lead as the scope passes down the manifold it is possible to access most ports and get a good idea if that's the problem.

A second way is to pass a borescope down the sparkplug hole after rotating the engine so that the intakes are open. You can then inspect the area right behind the valve head which usually has the worst accretion. Given my druthers, I'd go through the throttle body. It gives me a better look at all the nooks and crannies.

Expect to pay a couple hundred bucks for the exam it the throttle body is removed. Gaskets included.

I looked over the "what's not included" section of the CPO warranty.
Can't say I found a concrete statement saying why it isn't covered.

Originally Posted by DSXMachina

There are easier ways to check the intake valves than pulling the intake manifold. In fact, I rarely would. One way is to remove the throttle body and run a borescope down the intake. The latest model has high resolution video out, and records in color. By twisting the lead as the scope passes down the manifold it is possible to access most ports and get a good idea if that's the problem.

----

Expect to pay a couple hundred bucks for the exam it the throttle body is removed. Gaskets included.

What boroscope are you using; whatsa resolution? Wireless comm?

OP, on the second para, don't neglect the relatively easy DIY - I've received the BMW parts from Tischer in anticipation of reaching 60k mi some day.

Originally Posted by CALWATERBOY

What boroscope are you using; whatsa resolution? Wireless comm?

OP, on the second para, don't neglect the relatively easy DIY - I've received the BMW parts from Tischer in anticipation of reaching 60k mi some day.

Oh, I definitely plan on doing it myself now that I have a pretty good idea that that is the problem.
I'm just not understanding why it's not covered.

Another thing I don't understand is...why would carbon build up cause a misfire?
I've also been paying attention to the problem and found something else out...why would it only happen at full operating temperature?

Originally Posted by Hemorrhage

Oh, I definitely plan on doing it myself now that I have a pretty good idea that that is the problem.
I'm just not understanding why it's not covered.

Another thing I don't understand is...why would carbon build up cause a misfire?
I've also been paying attention to the problem and found something else out...why would it only happen at full operating temperature?

Poor seal; obstruction to flow.

Did I post this?

Originally Posted by CALWATERBOY

What boroscope are you using; whatsa resolution? Wireless comm?

OP, on the second para, don't neglect the relatively easy DIY - I've received the BMW parts from Tischer in anticipation of reaching 60k mi some day.

Snap-On, second gen. with optional extended length probe. Unsure of resolution, easily able to see 1/32" objects though. Not wireless though some of my tools are Bluetooth. This one has the screen on it.
Snap-On now has a remote screen, Bluetooth enabled borescope but I would have no use for it.