Mystery misfire + solution

So where to begin. I have a 325xi '04 with an M54 engine. I have owned the car from 38,000 miles and perform 5,000 mile oil changes and 70,000 mile transmission changes. (I take very good care of the car) The car never goes over 5,000 rpm.

I am also writing this because I have run into others that have described this "mystery misfire" and have not come to a conclusion. Or have relented to BMW and installed a new engine.

4 months ago (@~140,XXX miles) while driving the car on the freeway the engine began to run rough, but by the time I got home it had returned to normal. (no warning lights)

Fast forward a week ago (@157,XXX miles), engine again begins to run rough on the freeway. This time it continues and trips the "check engine light".

I hook up a code reader and get a P0303. Misfire on cylinder #3. I assumed ignition problems (even though the plugs were changed at 120,000). I decided to test the coils by switching #3 coil with #1. Cylinder #3 continued to misfire.

I believed at this point that the spark plug was to blame and switched it out for a new one. Cylinder #3 continued to misfire.

Frustrated and short on time I took the car to BMW so they could hook it up to a computer. I believed that the DME computer might have been faulty. After two days of diagnostic labor they concluded it was not the spark plugs. (someone should give these guys a medal, but my story gets better. They decided to perform a compression test and found that #3 had only ~ 25 psi. In short cylinder #3 had no compression.

Without performing anymore tests BMW proudly announced their findings. (although when I asked for it in writing they declined to do so) BMW concluded that the rings on #3 piston had come off and that I needed to spend $8,000 for a new engine and $2,500 in labor to install. BMW also stated that the engine at 157,000 miles was far over it's "expected life". Needless to say I asked for my car back and I took it to a independent (and more motivated) BMW mechanic.

After performing a leak down test we discovered that pressure was leaking past the valves! No other choice left, we removed the head in search of answers.

With the head off it became obvious what had happened. The exhaust valve on #3 had been burnt. And as the picture shows it REALLY went! The direct cause was worn valve guides.

I am now in the process of replacing all the exhaust valves @ only 157,000 miles on the car! I have heard of exhaust valves going at 200,000+ miles but never at 150,000?

Also BMW (the manufacture) never considered that the valve guides would wear faster than the valves themselves. Therefore BMW does not offer replacement valve guides for the M54 engine. (although aftermarket ones are available) They instead provide valves with oversized stems and require you to ream the valve guide to accommodate.

**Has anyone else experienced a burnt exhaust valve before 200,000 miles?

So a couple side notes....
-cylinder wear was .0004"
-Cam wear was not measurable

I'm not really sure what to say but I'll leave you with this:



FWIW, did you race the car at all or run it in high temps or overheat it? I wouldn't think the exhaust valve would get burnt that fast.

OP- have you used chevron techron? E85 gas? What kind of gas do you pump and from where?

I've seen a handful of valves fail like this over the years. It is just a defective valve and was nothing the owner did. Just crap luck that you got one. Last one I seen was on a 98 or 99 740. Guides would not cause this. Just a bad piece of metal. Sorry for your trouble.

Doesn't look like it melted or broke. Looks like it corroded and the hole got bigger over time.

Originally Posted by e46alfonso

Doesn't look like it melted or broke. Looks like it corroded and the hole got bigger over time.

Unless OP stored the car for a long long time (and based on his 4 month mileage ) I doubt it corroded. To me it looks like the metal got brittle and then failed due to high heat and smacking on the valve seats every time.

Material-Failure - this is not "daily" ... the valves are natrium-cooled and very hard to kill ... sorry man :-(

*UPDATE*

Removed all valves and found all exhaust valves in poor shape (lots of pitting) Exhaust valve seats are fine. Also guides are not to blame. As stated above by others the metal is to blame. Intake valves are in great shape and can be reused.

This car has been a daily driver for me, I've never raced it or driven it hard (since I got the car @ 39,000 miles). It's hard for me to believe that the metal that the valves are made of is that poor? Especially when BMW wants $45 a valve as a replacement!

Any suggestions for after market exhaust valves?

Did you also use an excessive amount a oil? I add a quart of oil to my 330xi every 500 miles and i pulled up the same p0303 code. Mine only ran rough when id let it sit and idle for a while. It'd throw a cel and if i shut it off and restarted it, it would run fine. I hope i don't have the same problem although ive read a post like yours before. My car has 161k miles.

Originally Posted by CrazyHarry

*UPDATE*

Removed all valves and found all exhaust valves in poor shape (lots of pitting) Exhaust valve seats are fine. Also guides are not to blame. As stated above by others the metal is to blame. Intake valves are in great shape and can be reused.

This car has been a daily driver for me, I've never raced it or driven it hard (since I got the car @ 39,000 miles). It's hard for me to believe that the metal that the valves are made of is that poor? Especially when BMW wants $45 a valve as a replacement!

Any suggestions for after market exhaust valves?

There's no reason all of the exhaust valves should have gone bad in this short of time unless you overheated or were tracking the car (high RPM for extended periods of time).

This honestly might be something you should contact BMW NA about. They might have had a bad batch of valves in from a supplier that they should be aware of. Maybe they'll help pitch in even? Who knows, stranger things have happened.

The other valve should be resurfaced and reused. Get one new one and valve seals. After some thought I have seen one other E46 do this and the valve looked just like yours.

Still a mystery to why it burnt out the valve. All exhaust valves had severe pitting. Intake valves could have been factory new! Valve guides had .0002" wear. Funny thing... exhaust valve stems had .0015" wear, tilt test resulted in .0010".

So... obviously harden steel valves wear faster than brass alloy guides. ;v)

Wow, what an unfortunate thing to say the least. Nice that your about half mechanic. The last pic of your head brings hope.

So, I guess we're safe to say that the rings didn't fall off? Idiots!!

Think this could be my problem? My 4th cylinder was misfiring therefore causing an extreme lag in acceleration in a high gear, granted I know high gears aren't pulling gears... It does it every so often, and just had my plugs, coils, mass air flow sensor, etc... replaced. Any ideas?

I'm guessing the OP had severe issues not an "every so often" deal. A compression test would tell you whats going on. Valves can't heal themselves with holes in 'em.

Originally Posted by White_Knuckles

I'm guessing the OP had severe issues not an "every so often" deal. A compression test would tell you whats going on. Valves can't heal themselves with holes in 'em.