4.6is - Stutter/Misfire on part throttle - no fault codes(?)
 

Hi everyone,
Just bought a 4.6is Carbon Edition (my 3rd 4.6) after selling my E39 M5 :)

Unfortunately it has developed an intermittent multiple misfire on very light throttle (between 1700-2000rpm), and whats worse is that no fault codes are stored whatsoever. It doesnt happen every time, but does happen frequently enough for it to be irritating. The car performs perfectly in any other situation i.e. idle, full throttle, overrun e.t.c - no misfiring.

The car has just clicked onto 80,000 miles and has a full BMW service history and is in excellent overall shape, mechanically and cosmetically - no signs of neglect anywhere.

Any input would be greatly appreciated.

Thanks in advance
-Ben

Are you sure it is missfire? If vibration, might be Torque Convertor fault or something else.

All I can say is that it sure feels like a misfire. The car also suffers from the notorious 'thump' when shifting from 2nd to 1st gear when coming to a halt (dont know whether its linked).
Would there be any way of testing the transmission to identify a dodgy torque convertor?

-Ben

I do smell Torque Convertor! Mine had the same thing right before I sold it. Gives you missfire kind of feeling in certain RPM and when stoping it feels like it is slipping?

If this is your 3rd 4.6is you should be very, very, very familiar with the dreaded X5 transmission lurch, it affects all of us, not sure about the 3.0 models though. Do a search, you will find numerous threads about this subject, and BMW knew about it but never offered a fix, go figure...3rd X5, man you're a glutton for punishmment..lol!!:rofl:

Your symptoms don't seem related to torque converter failure...would throw oxygen sensor, possibly failing MAF ahead of TC failure. If you didn't perform a pre-purchase inspection i suggest a diagnosis...could be a number of things...ignition coils, crankcase valve, etc

Regarding the rough downshift, you'll simply have to compensate accordingly...in my experience, after 2 puma cases by the dealer on 2 separate 4.6iS', all they managed to come up with was to "top off trany oil". The Dinan engine/trany software was an improvement...however, it reappears from time to time.

Wouldn't O2 sensors throw fault codes? Not sure about MAF though, But MAF performance can be checked with GT1. Ign Coils and no Misfire fault codes stored either?:dunno:

Not quite sure where to start with this one then. The stealer wants £70 an hour labour just to investigate, which in my experience usually comes up blank if there are no fault codes - modern BMW technicians dont seem to want to fault find the old fashioned way. And I dont have any good independents around here either.

Help!

-Ben

UPDATE: Got the car diagnosed at a friendly local BMW indy rather than a stealer. Found just the one soft-code of 'clutch-slip, sporadic'.
Deleted the codes and test drove, only to find the same code returning.

So the car has just come back from the transmission specialists who have rebuilt the torque convertor, changed the fluid (and filter at my request) and re-fit it.
The mechanic said that I was lucky that I nipped it in the bud and got it done straight away. He said only the torque convertor seals had gone and the internal linings hadnt started to come away yet. Therefore the gearbox itself is in great shape, with no nasty filings e.t.c in the sump pan.

I've only done about 20 miles in the car up to now, but initial impressions are good so hopefully that has done the trick.

Time get my hands dirty now and tackle those damn valve cover gaskets!

-Ben

By the way, what is a 4.6is Carbon Edition?