BMW 645CI Miss Fire But Only In 5th Gear?

BMW 645CI Miss Fire But Only In 5th Gear?

Author
Discussion

x111tom

Original Poster:

96 posts

112 months

Friday 5th December 2014
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Hi Guys my BMW runs like a dream until she goes into 5th gear. When in 5th between 30 - 40mph I get a feeling like the car is misfiring. I doubt it could be that as it would do it in every gear.

Any ideas?

Tom

Sump

5,484 posts

166 months

Friday 5th December 2014
quotequote all
Is it an auto?

TC?

x111tom

Original Poster:

96 posts

112 months

Saturday 6th December 2014
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Hi yes it's auto

Any ideas?

x111tom

Original Poster:

96 posts

112 months

Saturday 6th December 2014
quotequote all
Hi yes it's auto

Any ideas?

milu

2,346 posts

265 months

Saturday 6th December 2014
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Quite common this. Sort of a slight stutter under light throttle and cruising along.
Some say it's gearbox related...it may well be but Im more inclined to say fuel/ air mix. I cleaned my MAF and it seemed to go away.
I'm due to have my gearbox oil changed so it will ge interesting to see if it makes much difference .

Sump

5,484 posts

166 months

Saturday 6th December 2014
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Will be your torque converter.

May be solenoids if its a 6hp one which I think it is..

s4avant

196 posts

195 months

Monday 8th December 2014
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Is your 5th gear ratio maybe a little long to be pulling 30 to 40mph?

x111tom

Original Poster:

96 posts

112 months

Tuesday 9th December 2014
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Hi Guys,

When i researched it they said it could be the transmission oil which needs replacing but its supposed to have a lifetime guarantee?


RichardM5

1,733 posts

135 months

Tuesday 9th December 2014
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BMW 'Lifetime' is 10 years or 100,000 miles at most.

x111tom

Original Poster:

96 posts

112 months

Monday 15th December 2014
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Hi Richard they say that yes but I've heard people say you should change it every 50k?

RichardM5

1,733 posts

135 months

Tuesday 16th December 2014
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Yes, I'd agree, 50K is more than enough miles to do on one set of fluid.

mattman

3,174 posts

221 months

Thursday 18th December 2014
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i had a similar problem checked out by a gearbox specialist - they told me its the mechtronic system inside the gearbox starting to break down that was causing the issue. Replacement gearbox to fix

mine had a hard change under full throttle between 80-90 on hard accelerations and then would feel like it was missing between 30-40. Never found a proper fix before it was written off, but many had said when I was looking for solutions that a gearbox oil change can fix it.

you can try the 'reset' process - turn the key to 1 with your foot on the accelerator and hold it for 60 seconds - supposedly it resets the gearbox brain and when you start driving it learns your style again - think this is more placebo effect than anything tangible!

x111tom

Original Poster:

96 posts

112 months

Saturday 20th December 2014
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Hi Matt I tried that with the pedal but it didn't give me a sound that it had done anything but it has not done it in a while now!

x111tom

Original Poster:

96 posts

112 months

Saturday 20th December 2014
quotequote all
Also I have another issue which you may be able to help with.

There is also a slight power problem.

The headlights flicker when revving the engine along with the interior lights. Also the fan when it blows you can hear it speeding up and slowing down with every turn of the engine.

I replaced the Alternator & Battery and it is still doing the same thing.


8Tech

2,136 posts

197 months

Saturday 20th December 2014
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Thats not unusual. When you increase the engine rpm, your supply voltage from the alternator can go as high as 14.5V but when the car idles, the voltage will drop to around battery voltage of around 12.5V.
Those extra couple of volts will cause lights to brighten and fan speeds to increase.

x111tom

Original Poster:

96 posts

112 months

Wednesday 31st December 2014
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Ok cheers for the help guys