Sudden problem

[akram]

Hi folks!! I have a 2004 M3 SMG convertible and to be honest it has seldom given me any problems in all these years. Lately it is doing this thing where (usually) in second gear it starts jumping/hopping. It is NOT the shifting of the transmission and I am absolutely sure about that. It is totally bizarre because no one can locate the source of the problem. On top of that, every technician keeps lecturing me on the SMG and I just can not seem to convince anybody it is not the shifting. The experts/visitors on this forum are my last hope. Any suggestions?

[cobbs]

Have you made sure that car is serviced regularly and spark plugs, wires, and coils are in absolutely healthy condition? If not get them checked to be 100% sure. After that you can look into relays and fuse are all fine, for sake of trouble shooting swap same power relays to each other and see if this problem goes away.

This may be an electronic issue, I had something like this with AC system and once electrician fiddling with relays it got corrected as accidentally electrician removed relays and fixed back and during the course AC relay got swapped with other one and it fixed the problem.

I changed that faulty relay and never had that same AC problem. Sometimes relays looks and work just fine but due to age and in this hot weather in Dubai resistance decreases and stops working intermittently and that's where you get these weird problems.

[charl]

Hey there mate. So basically it's the SMG A-mode right? You can avoid bucking by training yourself to keep constant pressure on the gas while it's revving up from low gears.

[kevin]

hi there,

The SMG is basically a manual transmission and in my opinion the behavior you describe is common in a manual car. The engine braking you describe after lifting off of the accelerator is actually considered a positive trait of manuals. Seems like you would have been happier with a true auto.

[dushyant]

The engine "bucking" and "out of control" aspects occur in all manuals when the engine RPMs are too low. So when you take your foot off the gas, what you should expect is a moderate amount of deceleration followed by 'bucking' if you fail to downshift/apply more gas before you reach the bottom end of the RPM range. Usually this happens around 500-700 RPM.

[akram]

@ charl Thanks for the tip bro!! Unfortunately, I seem to have a genuine problem.

@ kevin Interesting observation my friend but this is a pretty recent development and not something that I have been experiencing since the first day I bought the car.

[idris]

The traditional automatic car simply slows down smoothly after you lift your foot off the gas but the SMG does not. You feel like its shutting down its power altogether because a noticeable deacceleration immediately occurs. Instantly you apply pressure back on the gas pedal because you think the car is slowing down too much and too unexpectedly and then the car jerks. Now the mechanical reasoning behind that is something only a technician can explain, but i can assure you that this happens with all SMGs.

[anton]

Hey fella! hope i can help. firstly and fore-mostly, it does not sound like you are running low on gear-box oil. If this was an issue

related to the quantity of gear-box oil, your gear-box would most likely be equal to scrap by now. the SMG hydraulic fluid level

could be low due to a leak in the system but again, that would manifest itself in shifting problems in all gears most of the time.

you could still check it as a precaution anyways. so basically, the only realistic possibilities you are left with are a faulty SMG pump

unit, a faulty SMG control unit, a faulty SMG shift unit, faulty SMG gear position sensors, or an internal/mechanical fault in the

gear-box.

[mohan]

Just take it to AGMC try bartering with them for a fair price to run a diagnostic and identify the source of the problem. Look for a good deal regarding the software too.

[matt]

Not too hard. Try an independent. Just make sure he follows the list below:

- Replace the SMG relay

- Check that the SMG is priming

- Reset all fault codes

- Check SMG reservoir oil level

- Gearbox and clutch teach-in

Also, the SMG has loads of sensors so make sure they are all working fine - the scan tool can tell you if anything is faulty.