Low RPM hesitation on acceleration 323i

[Jager561]

I originally posted a question about my 323i last week. It has a hestitation upon acceleration between 1,000 to 2,000 RPM's. Once about 2,000 it smooths out. Some readers asked for fuel trim info. I got it today and it follows:

Adaptation, mixture 1, additive 0.08ms
Adaptation, mixture 1, multiplicative -6.7%
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Adaptation, mixture 2, additive 0.07ms
Adaptation, mixture 2, multiplicative -7.9%
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Bank1 additive (idle speed): 0.08ms
Bank2 additive (idle speed): 0.10ms
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Bank 1multiplicative (partial load): -6.72%
Bank 2multiplicative (partial load): -7.92%
Set point: -7.0 …. 11.0%

Original post is below... any and all help is appreciated! This is driving me crazy.

The car has 62,000 miles on it... new O2 sensor on bank 1 at 45,000 miles


Two dealers could not figure this one out...

My 2000 323i feels like it is misfiring at low RPM (poor acceleration and stumbling sensation), between idle and 1,800 RPM. Sometimes it just gives one or two "bucks" right a 1,800 RPM. The problem is intermitent... but will act up when asked to. The problem does not exist when the engine is cold. The car has been checked for vacuum leaks... none, I have pulled the plugs and they are clean... mass air flow sensor is reported by the dealer to be reading high and near the top of the range... but a new MAF sensor did not cure the problem... the engine light is not coming on and there are no faults store in the ECM... the dealers suggest I wait until a check engine light comes on... but I want the car to run well in the mean time... it has been 4 months already... and I don't feel like getting stranded somewhere.
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[nathan56989]

When they replaced the mass air flow meter did they clear adaptaion values if not it will not seem as if the meter has been replaced. Your trim indicates that your DME is subtacting fuel. Which meens your car is running rich. Check you air filter. A restricted filter will not let in enough air. If none of this helps have them remove the filter drive the car and see what the fuel trim does then. I had a 5 series do the same thing. I tried all the above things I listed. When I took out the air filter (new) the fuel trim came back to normal. What I did was drilled a hole in the air box after the air filter then put a course filter in the hole. This fixe the probelm. You could also have a leaking fuel injector. I would run some BG 44K in your fuel tank.

[thejlevie]

And have the pressure in the fuel rail checked. Excessive pressure will result in the DME having to use negative trim to compensate for a greater amount fuel being injected per injector pulse.

Since this seems to about the same for both banks, I'd be more suspicious of a cause common to both banks rather than something like a bad injector. I guess you could have a bad injector on each bank, but that stretches credibility a bit far.

[Jager561]

I have been doing some research on fuel management and fuel trim in particular and from what I have read the Additive (Long Term Fuel Trim or LTFT) is set or re-set based on inputs from the Multiplicative (Short Term Fuel Trim or STFT). The LTFT is a response to the short term adjustments... once the short term adjustments reach a threshhold the LTFT is changed in response to bring the fuel metering "back into line" with expected values

With that in mind... it seems odd that the LTFT is a positive value (more fuel being adminstered in milliseconds of open injector time) while the STFT is a negative value... or a reduction in fuel being administered. Basically, the STFT is trying to cancel the LTFT order for more fuel.

Doesn't this seem like a conflicting set of orders from the DME? How did the LTFT get positive if the STFT is negative... won't it reset the LTFT downward at some point?

I swapped the MAF sensor... and did not know to reset the DME fuel trim values... I did not get DME readings after the swap either. Silly question, but is there a way to reset the values through the vehicle... or do you have to have the dealers diagnostic computer. Will a scan tool like Peake allow resetting of DME values and capturing of fuel trim info?

I agree that the problem is upstream of the two separate banks... I will check fuel pressure... is crankcase pressure still a possibility? I have a brand new BMW air filter... problem existed before the air filter change. I still have a new MAF sensor and can re-install if that may help. I added duel system cleaner this morning and after 50 miles... same problem.

Thanks for all the help...
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[mfumbesi]

I am also interested in this thread. I have a 2000 323i with 156000km (approx.97500miles), I have the same problem with my car.
Below 2500 rpm the car is sluggish (it feel like it doesn`t want to move, almost deadish), as soon as its pass 2500 rpm it smooths out. I will try nathan56989 suggestions.

[nathan56989]

It is almost 100% of the time that if the one of the trims are adding and the other is subtracting it the mass air flow sensor. Oh and mfumbesi I beat my head on this car for about 2 weeks. This is very, very, very, unlikely to be your problem. Your car seems liek that becasue at 2500RPMs you disa flaps open which changes the geometry of your intake runner from long to short runners. This is normal. Please don't ask about the flaps cause I really don't wanna explain this into detail. (not to be an ass) It s pretty complicated for me to explain. Someone else may be able to give you a short description. How do they work? They just do. lol.

[Jager561]

After many frustrating months a final solution... problem persisted after new MAF and reset fuel adaptations in DME. Pressures in fuel rail and CCV all checked out... went to ignition side and bought new coil and boot... did the swap process tonight and don't you know a new boot on cylinder 5 did the trick... thanks to all who helped... only a $15 fix... dodged a bullet on that one!

btw... the new MAF sensor is staying in the car... it cured another issue of uneven or surging acceleration when I was getting on it hard...

[Mike Murcia]

So the rubber boot around the coil was the problem? My car ('99 323i also) has the EXACT same problem that you described. If I understand you correctly, it is likely due to an arcing ignition coil.

[Jager561]

The boot is the piece that connects the coil to the spark plug. It pulls away from the coil. The boot itself can be bad and is causing an arcing to the block. Mine was failing once it got heated up. The problems could also be a coil. There are codes that can be set for a bad coil, but my car was not setting the code. The boot is relatively inexpensive at $15. If you know the cylinder then you in are luck... I had to swap out 5 cylinders before I found the bad one. When replacing the boot make sure it snaps into place on the coil.

[DrCG]

Hi there,

My car (323i 99) has the same problem. You're right, it NEVER happens when the engine is cold.

Anyways, is that something I could do or should I ask my independant mechanic guy? I'm okay to switch lightbulb in my car, and that's it I have absolutely no idea what you're talking about (coil, boot, spark plug) etc... so maybe I will ask someone else..do you have pictures of what you did to fix the problem?

Luckily 'check engine' lights from time to time when this happens.

[calisupra2nr]

i posted about a problem just like this, could you give a writeup or help as to how and go about swapping as I have never worked on a bmw before.

[Jager561]

To swap the coils and boots... just buy one set... one coil and one boot... start at cylinder 1 and then drive... if problem is gone... it was that coil and or boot... if not move to #2... etc.

The coils and boot are very easy to replace... just remove the cover on the top of the engine... there are two covers on our car... the one on the left is plugs and coils... the right is fuel injection. Tow 10mm bolts hold the covers in place. Directly under the cover are the coils, unplug the coil (clip slides up and then you can unplug), use that same 10mm socket to remove the two bolts holding the coil down. Pull the coil with the attached boot straight off the plug... swap and then reverse the whole process.

I found that that the aluminum post on the coil and the boot core had some corrosion... I cleaned that up... but also... and perhaps more importantly I also found dark black coating on my plugs... indicating a rich mixture from the bad MAF... you may want to replace the plugs if that is the case... I cleaned mine... very carefully so as not to disrupt the platinum electrodes.

Hope this helps...

[zx6star]

nice post! I'm kinda having the same problem you are having and it really helped!

[calisupra2nr]

Thanks!

[quik96M3]

This site rocks! Jager561 rocks!

I just cancelled my BMW Service appointment and saved myself at least $120 diagnostic fee thanks to this thread. A site search on 'hesitation' resulted in finding this thread, and it just so happens my 2004 330i had exactly the same symptoms as Jager561 described in the initial post above. I decided to give it a shot - yesterday I bought a new coil/boot and swapped it into each cylinder, one by one, until I got to cylinder #5 (same location as Jager561 reported - coincidence?). Sure enough, the #5 coil/boot was bad, swapping it out fixed the problem, hesitation is gone.

No sign of arcing, damage, etc. on the bad coil/boot - it looks exactly the same as the others.

THANKS!

[xaxis360]

I have been battling this issue for a few months. I am glad I found this thread! I purchased 6 spark plugs and a coil with boot from BMW a few days ago. I was going to shell out $400 for 6 ignition modules and boots, but I am going to be patient and go one by one. I am now at cylinder 2.. 4 more to go!

[xaxis360]

Just wanted to say thank you to those who solved this issue. I have a '97 328is that I have been fighting this exact issue for about 2 years. it only happened after a warmed up and at low RPM with a sort of heavier throttle.

I wasted a lot of money on fuel system cleaners, premium gas, plugs and a coil I didn't need. I replaced all of my spark plug boots and my car drives like a dream! Thanks again!