BimmerFest BMW Forum banner

Z4M: Throwing misfires - codes - why?

7K views 42 replies 11 participants last post by  CHITOR 
#1 ·
Finally got a code reader to see what faults were thrown the three times the car light up the SES and went into 'limp mode'. Each time I pulled over, stopped the engine and restarted without incident. Codes are:

20
c29d2 Misfire, Cyl. 6
c29Cd Misfire, Cyl. 1
c29CC Misfire, several Cyls

These are the only codes - cummulative for the three incidents.

Then, it happened again today (fourth time), but no new code showed up. I did not clear the old codes - just did a read, so I assume this new one today is same as one of the above codes. Correct?

This happens under normal highway driving conditions - not in or after a hard push or rev run up. And it's intermittent. Driving under the same conditions just last weekend was fine. I had no problems.

The first time it happened I thought it was the K&N air filter in conjunction with RPI scoop, but I took the filter out and went back to stock filter after the first incident. Then I thought it might be the gasoline I am using, but I use the same gas from the same gas station (Chevron) practically every time. Then I searched around on different forums for possibliities and read one case of valve damage, but I have never over-revved the engine in a down shift or gone above the yellow during warm up.

My questions: what could it be? what should I check next?
 
See less See more
#2 ·
Has this happened when it was moist or damp/raining?

Did you pull the coilpacks and spark plugs to check for anything out of the ordinary?
 
#4 ·
Has this happened when it was moist or damp/raining?
Nope. It never rains in California...

Did you pull the coilpacks and spark plugs to check for anything out of the ordinary?
Not yet - but makes sense. I want to hear what else I should check once I break out the tools.
 
#9 ·
If you suspect the K&N, then perhaps there's still some residue/oil left over on the MAF sensor. Use elec contact cleaner spray and clean it... see if it goes away. I've used Wurth on prev cars. On my M Coupe, didn't have an issue w/ RPI/BMC combo. GL.
Definitely worth trying out, but as blau said misfires are usually always bad gas or something related to the ignition system (coils, plugs etc). Def change gas stations as a start, pull the coils and check (its not uncommon to see premature coil failure on german cars) and clean the MAF.

BTW, were you running the K&N without the second carbon air filter?
 
#12 ·
Today I got the chance to have a diagnosis done at the dealer for this problem. I watched the complete test first hand. Thanks for your help BMW tech! Here is the result.

The detail read out on the fault code shows statistics like, mile/km at reading, engine temp, max rpm during misfires, min/max relative load during misfires, last ambient temp, last ambient pressure, voltage, and a few more statistics. It's actually quite impressive what measures are taken. Anyway, everything looked normal -that is within tolerance - except one. The two techs looking at the results thought the Last atAmbient pressure might be too high - perhaps twice normal. If so, they suspected it could be either extra pressure at intake or not enough back pressure at exhaust or both that would cause of too lean mixture and hence a misfire.

Still, what's not clear to me that the intake pressure is/was part of the problem. The read out says Last atAmbient pressure 997.664 mbar. But now that I am home and had the chance to look it up that reading is pretty close to standard atmospheric pressure at sea level which = 1013.25 millibars.

Anybody know where this reading comes from? Outside or inside the induction path? If inside, then isn't the read out normal? And with a scoop shouldn't it be higher than one atmosphere inside induction?

At any rate, there was no recommendation for a remedy, except to test a fix by isolate each change that I have made - the scoop and the exhaust - and see if it throws a fault again.
 
#13 ·
At any rate, there was no recommendation for a remedy, except to test a fix by isolate each change that I have made - the scoop and the exhaust - and see if it throws a fault again.
While I am sure the techs have some reasoning behind their suggestion, it looks to me they gave you the very typical "your mods are causing the problem and we dont want to bother with it" excuse.

I have seen some very creative reasoning from dealers about problems with a "modded" car- one of my Audi dealers one told me that my TT was overboosting at 13 psi (when the factory docs say that the car is programmed for about 12-14 psi) because I had replaced the defective factory Diverter Valve with a more solid aluminium one (they called it the "red box") ... I knew it was a MAF problem when I brought the car in and they did not fix it. I ended up buying a MAF myself and replacing it; Light gone and car was happy.
 
#17 · (Edited)
Thanks for all your posts and sharing your experiences. In looking at these and the range of fixes I realized that it really is pretty daunting to do all of them so I arranged the possible causes fall into four categories and then ranked them (for my benefit) lowest to highest probability of cause:

1. Fuel & fuel system - bad gas or water in the tank; fuel pressure
2. Coils and plugs - degenerate
3. Exhaust - too much or not enough back pressure
4. Induction - too much pressure; incorrect flow

1. Fuel system seemed to have the lowest probability of cause ***8211; especially given how much gas stations storage systems are regulated and monitored by the state and particularly in my local area by more than one county agency and the EPA. Even so, it has been suggested that I consider a fuel additive that is rated to remove water. I am not sure how sensitive our Ms are to fuel additives. However, if it can tolerate a fairly good level of alcohol the suggestion is to run a couple tanks with additive then replace the fuel filter. That said, I was a little surprised that no one even mentioned the fuel filter. Even when we tested I did not see any diagnostic that included fuel pressure. If I had it do again, I would ask if it matters and where the pressure is monitored - if closer to injectors or back at pump. The multiple misfire would seem to rule out a faulty injector. Draining the tank seems kind of extreme and saved for last.

2. Coil and plugs might be higher on the probability list except that the car is almost new and the code reads that misses were across multiple cylinders. Statistically that reduces the probability of this being a root cause.

3. From all I read on this board and others, when it comes to exhaust and induction it seems pretty clear this engine is tuned/set to the point of considerable sensitivity. So, it's not unreasonable - as the techs pointed out to me ***8211; with any modification to exhaust (too much back pressure or not enough) that MAF sensor could conflict with the values sent by O2 sensor and other fuel management nodes downstream. I wont explain this well, but it is it's this condition could confuse the computer when it's trying to feed the injectors thereby creating a lean injection and misfire.

4. The BMW techs pointed to the many cases where they had seen lean misfire codes on cars with modified air box or CAI ***8211; and not just the S54. They mentioned this bulletin which Ron has posted for all of us to see: http://www.bimmerfest.com/forums/showpost.php?p=2878954&postcount=25

As I mentioned in post #12 it's not clear to me what part intake pressure is/was the root cause of the problem. If anyone knows where 'Last atAmbient pressure' measurement is taken - outside or inside the induction path ***8211; please post the answer. Also, if inside and you know what the pressure should be, then please post that value as well so I can compare. ***8211; Cheers.
 
#18 ·
1. Fuel & fuel system - bad gas or water in the tank; fuel pressure
2. Coils and plugs - degenerate
3. Exhaust - too much or not enough back pressure
4. Induction - too much pressure; incorrect flow
Before you do anything, drive around for a couple of gas tanks (preferably with some Techron or BG-44K or similar fuel system cleaner- not sure what the S54 guys usually prefer) and see if the problem resurfaces. If not, then you had a bad tank of gas and any gunk should be cleaned out by the cleaner.

If it does come back, (4) is easy enough to do ... start by swapping out the RPI duct and then the K&N panel filter. Drive for a couple of weeks (a few hundred miles and a some restart cycles) and if all is silent and good, you should be fine.

It is highly unlikely that mufflers will trigger a light ... now if you had race cats and a huge X-pipe, its a different story.

If you are mechanically average, pulling out the coils and plugs for a visual inspection and installing them back is never a bad idea.

Good luck and keep us informed. The more concrete information you give us, the more useful we can try to be.
 
#19 ·
Put the OE air box and filter back in as Pal suggested. It is highly likely the aftermarket intake is causing you problems. Even DINAN does software upgrades for their intakes to compensate for the change in breathing.
 
#21 ·
Well. It's definately not the RPI scoop. Last weekend I put stock "cup" back on and threw in some Techron and I be damned if it didn’t happen again. Same conditions; cruising at about 60-70 mph. I am just plain peeved this point so I am taking in for service next Monday to let the dealer sort it out. I have another problem they need to fix anyway. When the brakes are warm and I apply 'soft' brake I get a font end shimmy (warped rotor?). My brave hope is they will fix both issues without question since I bought the car there as a CPO and it's still under warranty.
 
#22 ·
Well. It's definately not the RPI scoop. Last weekend I put stock "cup" back on and threw in some Techron and I be damned if it didn't happen again. Same conditions; cruising at about 60-70 mph. I am just plain peeved this point so I am taking in for service next Monday to let the dealer sort it out. I have another problem they need to fix anyway. When the brakes are warm and I apply 'soft' brake I get a font end shimmy (warped rotor?). My brave hope is they will fix both issues without question since I bought the car there as a CPO and it's still under warranty.
Front rotor damage sounds to be the symptom. BMW brakes are a definite weak point in this car especially if you push it hard. I know, I had brake failure yesterday on the ring...:bawling:
 
#25 ·
One more update on this - hopefully the last. I took the car to the dealer yesterday and got it back today. For the misfire problem they replaced the coils on cylinder #1 and #6. For the front end shimmy they replaced both front end rotors and brake pads. Fair enough. All parts and labor done under warranty at no-charge.
 
#30 ·
Thanks for your post Ron.

So I interpret what I read to mean that drive cycle condition 1, 2, 3, or 4 (or time length of trip for that matter) has no bearing on misfire detection because it is permanently monitored. Correct?

I am reading elsewhere on M3 / S54 mifire. Some techs recommending checking valve clearances.

At any rate I am just trying to figure out how to prod the dealer in the right direction. They were reluctant to replace the coils last go round...
 
#33 ·
Another update. I took it to the dealer on Thursday. I got it back with a new injector for cylinder 6 and an explanation that it was likely heating up and going bad. I took it out today for 140 mile run with no incidents, but the real test comes next weekend with a much longer trip.
 
#34 ·
cmsnow,

Since your last post, late august last year, did you get any other incidents like these until march? I had my oxygen sensors replaced last month after my check engine light came on, and today I got it again, after an instant hesitation at half throttle. So, to geta back to my question was the injector the remedy to your issue?
 
#36 ·
UPDATE - The inspector from BMW never came to look at the car but the directive from him to the dealer is to takeoff the head and inspect the lifters and valves on Cyl 6 because they have seen this problem before and it has always been Cyl 6 and "a sticky lifter".

This makes no sense to me or my dealer service rep because the problem is remedied after turning off the engine and restart. How is it that a lifter could be so random sticky and be normal after restart? Wouldn’t you see some indications of a problem in the smooth running values?

At any rate I am told I will be Z-less for a couple of weeks and they will "make good" for the continued inconvenience.
 
#41 ·
UPDATE - The inspector from BMW never came to look at the car but the directive from him to the dealer is to takeoff the head and inspect the lifters and valves on Cyl 6 because they have seen this problem before and it has always been Cyl 6 and "a sticky lifter".

This makes no sense to me or my dealer service rep because the problem is remedied after turning off the engine and restart. How is it that a lifter could be so random sticky and be normal after restart? Wouldn't you see some indications of a problem in the smooth running values?

At any rate I am told I will be Z-less for a couple of weeks and they will "make good" for the continued inconvenience.
Hi,

Just wondering what ever happened to your car? Did you already resolved the problem? Im having the same issue but mine is a Z3. I have a misfiring issue during high speed/high rpm. And will run fine after an engine restart. Just want to know if your issues were solved already before I buy any parts to change such as coils, plug wires, O2 sensors, etc.

Thanks.
 
#37 ·
Man, these issues don't ever seem to get resolved. My 2001 M Coupe is having an issue where, in 3rd gear, and only in 3rd gear, if I exceed 6000rpms, I get thrown into limp mode, the car feels like it hits the redline, and then in any gear, the car won't accelerate beyond 4000rpms and has NO power at all. It's not until I pull over, turn the car off, turn it back on that it goes back to normal. There are NO check engine lights and no codes. I had a code and check engine light for an exhaust camshaft position sensor, replaced it, and still have the problem.

I'm about to take the car to VAC Motorsports for diagnostics, however, it looks like not even bmw knows what is going on with these sorts of issues.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top