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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Sun, Jan-21-2018, 03:05:21 PM   #1
911Fiddler
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Default E46 M3 throttle balancing

In the past, with my multi pot motorcycles I'd regularly check for throttle flap balance, either mechanically -to equalise out the position of the flaps or with vacuum gauges at idle. Doing this usually produced some positive noticeable difference, eg smoother running.

On the E46 M3, last time I had the airbox off I spent a couple of hours figuring out how to then did this same equalisation. There was certainly some mechanical imbalance, so I felt at the time Id done something good. (method: use throttle #1 as the reference; take up the slack in the actuator using an adjustable/threaded stud; reset #2-6 for 0.002" clearance at the idle stop screw).

Soon I will revisit this job & repeat the check & reset. Ill be replacing the plastic links to the throttle flaps, they were worn last time.

It bugs me that the setting procedure will be imperfect because its a mechanical setting rather than one based on vacuum. So a less accurate balance, especially given I'm on a well used/worn throttle body. To set by vaccum of course, the manifold will need to be drilled/spotfaced/tapped so that measurement points are available for the gauges. That along with the purchase of decent gauges will make it a bigger investment. As I drive most of the time on the idle control valve (it does most of the throttling around town), I reckon the vacuum approach is going to make a difference.

Q:Has anyone done this vacuum conversion & setting approach already?
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Old Sun, Jan-21-2018, 06:36:40 PM   #2
bigjae1976
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Default Re: E46 M3 throttle balancing

I don’t think many people have had an issue that forced them to relook at the throttle body adjustments.

Those who have had an issue probably followed the BMW procedures.


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Old Fri, Feb-16-2018, 05:02:47 PM   #3
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Default Re: E46 M3 throttle balancing

my thinking has advanced on this...
The throttle bodies have a connecting tube in front of the butterfly providing the idle (& low load) air. Id think that this pipe, effectively operating a small secondary manifold and connecting all 6 throttles would balance off any mis alignment of the throttle valves. The throttles are not fully independent on air supply.
Project cancelled.
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Old Sat, Jun-02-2018, 03:49:50 AM   #4
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Default Re: E46 M3 throttle balancing

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Originally Posted by 911Fiddler View Post
my thinking has advanced on this...
The throttle bodies have a connecting tube in front of the butterfly providing the idle (& low load) air. Id think that this pipe, effectively operating a small secondary manifold and connecting all 6 throttles would balance off any mis alignment of the throttle valves. The throttles are not fully independent on air supply.
Project cancelled.
I just did this on my S54 for the hell of it, having recently had experience doing this successfully on Porsches at work.

I used a Redline-Weber synchrometer tool to measure actual airflow. Cylinders 1-5 were within ~1.0 kg/h of each other, but cylinder 6 was almost 3 times the others. (many say 0.5 kg/h maximum variance is acceptable).

I was surprised to find this considering that, as you said, the throttles are all connected via a common air rail. I suspect that the air rail does cause some improvement in balance but that significant variances can still show up. The engine of course wants to consume much more air than it is being “allowed” to by the throttles, even at idle, so a particular cylinder with a further-open throttle blade will consume more air. I also believe that the air rail is in a sense self-balancing, within itself, so that it will feed very close to equal air to each cylinder, regardless of individual throttle angles.

Anyway, I was able to get them all to within 0.2-0.3 kg/h without much trouble. As I have a stand-alone ECU, I temporarily disabled the IAC and ran the engine from the throttles only (about 1% opening required for 1000 RPM idle), although I did leave the air rail in place. While this wouldn’t be an acceptable condition to sync the throttles (as the individual throttle sync adjustments are essentially the throttle stops, and at this point the throttles would all be pulled off the stops), I was able to confirm that airflow stayed pretty well balanced even as the throttles open.
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Old Sat, Jun-02-2018, 09:59:18 AM   #5
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Default Re: E46 M3 throttle balancing

Hey, nice to hear back!
So you've tried it and found a bug then sorted it. Now I'm interested. Key thing is, was it worth doing? So how did she run beforehand and what was the effect post adjustment?
I've just Googled the tool and found it.
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Old Sun, Jun-03-2018, 08:10:58 AM   #6
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Default Re: E46 M3 throttle balancing

Subbing out of curiosity, but using a synchrometer is something pretty old school for tuning multi barrel carbs, I haven't heard of doing this on modern throttle bodies.

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Old Sun, Jun-10-2018, 11:33:09 PM   #7
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Default Re: E46 M3 throttle balancing

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Originally Posted by 911Fiddler View Post
Hey, nice to hear back!
So you've tried it and found a bug then sorted it. Now I'm interested. Key thing is, was it worth doing? So how did she run beforehand and what was the effect post adjustment?
I've just Googled the tool and found it.
To be honest I can’t tell any difference in driveability or idle quality etc. I did notice, before making adjustments, that when I ran the engine purely off the throttles with the IAC disabled, the idle did have a very slight lope in the exhaust note, a classic sign that the cylinders are running differently. This was gone once I synced the throttles. However, this was not present (not detectable at least) when running off the IAC as is standard.

I did see less bank to bank variation in fuel “trims” after syncing, although total change was under 2%. This has been very consistent on my car so I’m confident it’s due to the throttle sync. Technically, I will have improved the emissions of the car by doing this as cylinder 6 was certainly running leaner than the rest, which would cause higher NOx. Then, since the ECU (both stock and my standalone) only take a collective exhaust lambda measurement of 3 averaged cylinders, it would have added fuel to that entire “bank” to compensate for the lean cylinder, causing the others to run slightly too rich, increasing HC emissions.

Is it worth doing for everyone? Maybe not. I already had the tool, already had the car apart, and sync throttles regularly as part of my work, so why not? If you’ve ever removed the throttles and/or bolted them to a different head (engine swap, built head etc) then there’s likely more reason to re-sync as the torquing-down process can induce some variation.
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Old Mon, Jun-11-2018, 03:40:44 AM   #8
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Default Re: E46 M3 throttle balancing

Very interesting. So how would one do this on a stock ECU? Plug the IAC so it doesn't flow and manually actuate the throttle body linkage? I actually need to do this as my tuner mentioned my throttle bodies were definitely out of sync after a rebuild. Any special adapter required for the synchrometer to fit our ITBs?
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Old Tue, Jun-12-2018, 01:25:45 AM   #9
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Default Re: E46 M3 throttle balancing

I've done this a few times with the throttle bodies on my e30 m3's -- it makes a noticeable difference in how smooth the car idles -- after that when the throttles are open it's hardly noticeable. But, if the idle is jumpy synchronizing the throttle bodies is a project but time well spent.

I assume as e46's get older it will become more necessary. the e30 m3's I've had all needed it, although they didn't have computers that can compensate for differences as well as the e46 can.

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Old Tue, Jun-12-2018, 11:06:50 PM   #10
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Default Re: E46 M3 throttle balancing

Quote:
Originally Posted by ClutchKickChris View Post
Very interesting. So how would one do this on a stock ECU? Plug the IAC so it doesn't flow and manually actuate the throttle body linkage? I actually need to do this as my tuner mentioned my throttle bodies were definitely out of sync after a rebuild. Any special adapter required for the synchrometer to fit our ITBs?
Even on the stock DME you could do this, as I found that even running the car as standard (off the IAC with the throttles closed at idle) showed enough cylinder-to-cylinder variance to make it worth adjusting. You should be able to start up the car with the airbox removed on the stock DME; you'll probably want to unplug the MAF so the car runs in an "Alpha-N" mode so it will idle.

I bought the standard Redline-Weber synchrometer. The S54 throttles are 50mm ID so any tapered-shape synchrometer made for throttles in that size range should be fine.
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Discussing E46 M3 throttle balancing in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)