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Discussion Starter #1
The previous owner told me he balanced the throttle bodies, however, in the interest of learning ow to do this myself I purchased a Carbtune tool to help with this maintenance step.




The Carbtune allows you to view 4 of the TBs at the same time which I think is a big bonus in doing this maintenance vs. doing each TB individually.



They include some small orifice tubing to make restrictors otherwise the rods bounce up and down too much to get a reading. Since I already designed an inline restrictor for the gauges I sell I chose to use that instead






Plugs on the vacuum ports removed, lines plumbed in and connected to the Carbtune




This is how the first 4 throttle bodies are adjusted. From left to right it is cylinders 4,3,2,1




According to the BMW service manual the TB should be adjusted to 300mbar or 22.5cmHg so using a 7mm socket you tweak the adjusters to even out the readings. Turn left to reduce, turn right to increase.



Plugs on cylinders 5 & 6 removed and put onto 1 & 2, lines from the carbtune plumbed in



So using cylinders 3 & 4 for reference we adjust 5 & 6. From left to right 4,3,6,5



After adjustment. The car does idle better and when I checked the tach the needle used to sit at 1000rpm, now it sits a bit below it.

 

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I always wondered why the M5s I've been in idle higher than usual and I've only been in and driven the 3.8 I myself own one and the idle seems to be fine not too high but still compared to my other BMWs. I guess they can all use some fine tuning? This is a good tool I should get one for myself. Great thread by the way! I don't understand where all the e34 guys are there's barely any threads. :eek7:
 

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very good!
 

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I am ordering the carbtune tool for the next few days...

Thanks
Anri
 

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i wonder if theres a place that i can rent one from? mc hammered, im not too far away from you. can i rent it from you?:Canada::deal:
 

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I purchased the SyncPro stuff (made for bikes and use glycol instead of mercury) and it works OK. I couldn't get consistent reading between some cylinder vs each other. Then I took the vac gauge that came in my craftman vacuum pistol and ran the vac line with the SyncPro super small restrictor and set the every cyl to 23inHg. I also synchronized the ITB's plates/arms and the whole idle of the car is more "solid" than before and it seat about 14.3 AFR according to my WB sensor.

You can see here the 1st cyl is not matching very well the rest, but with the vac guage I could set all the same, not sure why. I also checked my valve shims and were within specs.


 

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I have a question about using this tool. Actually more than 1 question.

First off, how do you know that the tool is calibrated properly? Meaning, how do you know that when it reads 23 it actually is reading 23?? Have you tested it or calibrated it on something that you know the exact reading of??

Secondly, how do you know that all 4 bars are calibrated to each other?? Meaning, how do you know that if connected to the same ITB all 4 would read the exact same value?? Have you tried it?

I am just thinking aloud here.
 

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Discussion Starter #10
Your question is valid for any tool like this, even dial gauges, unless you happen to have a reference vacuum source to test it against.

So in this case I do have to trust the manufacturer that they are selling a calibrated product and I do know that screwing up the calibration of a dial gauge is a much easier than 4 steel rods.

From the www.carbtune.com FAQ

Q. Is it as accurate as dial or clock type gauges?
A. Yes. Infact it is more accurate than any dial or clock type gauges that we have tested. It has better resolution than typical dial gauges and is also much easier to read. The four columns are right beside each other for easy comparison unlike the pointers in dial type gauges.

Q. My dial gauge pointers flicker up and down. Is the Carbtune II better damped?
A. Yes. The moving part in the Carbtune II is a solid rod. This is too heavy to flicker wildly up and down. It does flicker a bit without any damping but with the damping supplied with the Carbtune II the fluctuations are very small. In fact the Carbtune II needs a little fluctuation to work properly. We can supply stronger dampers if necessary.

Q. My dial gauges always need recalibrating, is this necessary on the Carbtune II?
A. No. The components of the Carbtune II are matched during assembly at the factory and will not need any recalibrating. They work on a different principle to dial gauges.
 

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Discussion Starter #11
i wonder if theres a place that i can rent one from? mc hammered, im not too far away from you. can i rent it from you?:Canada::deal:
I was trying to find one to rent as well but not too many people have this particular device, some motorcycle shops have the liquid mercury version and they don't rent those.

I have been renting it out locally. Person leaves me $150 which includes the $20 rental fee and $130 damage deposit. Upon return I refund the $130.

For the cost to rent it and then ship it to and back you are 1/2 way to buying one.
 

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mc hammered, does your tool has adjustable needles to balance the bars before attaching them to the ITB's? Mine does so you can calibrate the bars to egt them perfectly lined up each against other. :byebye:
 

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The problem that I have with this tool is that it doesn't read the pressure and I haven't found a manual with a conversion formula or chart; one might argue that equality prefers over absolute readings, but I for one disagree without setting valid boundries in which this applies.

I would say that as long as you apply the six-sigma rule over the initial readings you are safe, but without an absolute pressure reading, it is impossible to make a valid adjustment.
 

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The problem that I have with this tool is that it doesn't read the pressure and I haven't found a manual with a conversion formula or chart; one might argue that equality prefers over absolute readings, but I for one disagree without setting valid boundries in which this applies.

I would say that as long as you apply the six-sigma rule over the initial readings you are safe, but without an absolute pressure reading, it is impossible to make a valid adjustment.

What would you recommend as the most effective tool for performing this task ?

I too need to have such a tool for setting up the throttle bodies.

Cheers
 

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What would you recommend as the most effective tool for performing this task ?
Hi Erik,

A set of vacuum meters as we have used during the Dutch S38-M88 conference in may 2011.



Those for a four-cyll will do as weel since you can monitor and adjust 1-4 and 3-6 sequentially.

The advantage of these is that they have a larger bandwidth and thus a quicker response time. With the dampening-screw, the readings can be properly decimated for a reliable reading of the intake vacuum in bar's. This allows a comparison against manufacturers specifications and determine the mean and variance of the six cylinders before statistically calculating the range for the new setpoint for adjusting the intake vacuum too.

After adjustment, I raise the throttle to around 3k-4k RPM to check for the transition curve of the butterfly valves. These sould respond lineair and without stepping. If sudden changes occur, the linkages that operate the butterfly valves themselves have some wear and additional maintenance might be needed.
 

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Discussion Starter #16
mc hammered, does your tool has adjustable needles to balance the bars before attaching them to the ITB's? Mine does so you can calibrate the bars to egt them perfectly lined up each against other. :byebye:
I would have to assume that the bars are balanced before they are shipped. I am going to try and compare the readings of each bar to a vacuum gauge to see how accurate they are.

The problem that I have with this tool is that it doesn't read the pressure and I haven't found a manual with a conversion formula or chart; one might argue that equality prefers over absolute readings, but I for one disagree without setting valid boundries in which this applies.

I would say that as long as you apply the six-sigma rule over the initial readings you are safe, but without an absolute pressure reading, it is impossible to make a valid adjustment.
I am a bit confused. What pressure reading are you referring to that you would like to have read?
 

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I am a bit confused. What pressure reading are you referring to that you would like to have read?
Throttle body balancing on the S38 engine requires measurement of the intake vacuum, which unity is expressed in bars. The S38 specification mentiones 300mBar.

When I take a closer look at the carbtune website, it only describes the ease of operation, but not its principles. When I take a closer look at the carbtool display, it only states 'cmHg' as the unity of the reading. I haven't found a manual or description that explains its operation.

For the time being, I can only conclude that the 'carbtune pro' tool only returns a relative measurement with an unknown relation to the intake vacuum. With other words, when using the carbtune tool, I can only balance them, but not to the required specification for the S38-engine (300mbar) unless the relation is known. With other words, I am looking for a physical relation between the measurement of the 'carbtune pro' and the S38 specification of the 'intake vacuum'.
 

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Discussion Starter #18
My understanding of the Carbtune tool is the metal bars replaced the Mercury tubes as described on the website.

I converted the ccHg units of the Carbtune to mbar using this site: Barometric mbar (hPa) to psi, inHg, mmHg and Torr Pressure Conversion Table and 300mbar = 22.5ccHg which is what I used for my target value.

As I mentioned earlier I would like to test the tool against a calibrated vacuum source to determine how accurate each of the steel rods are.
 

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My understanding of the Carbtune tool is the metal bars replaced the Mercury tubes as described on the website.

I converted the ccHg units of the Carbtune to mbar using this site: Barometric mbar (hPa) to psi, inHg, mmHg and Torr Pressure Conversion Table and 300mbar = 22.5ccHg which is what I used for my target value.
Thanks; that is the answer I was looking for.

However, bear in mind that the conditions for carrying out the intake vacuum-sync is

1: Valve-lash within spec
2: Basic butterfly-valve setting (mechanical adjustment) corrrect.

I will add this article to teh FAQ's
 

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Discussion Starter #20
I took my car for a drive yesterday and the balancing of the throttle bodies did have an effect but I decided to redo the balancing again as I thought my process could be better as I did not compare all cylinders.

My original process was to balance cyl 1,2,3,4 and then use 1,2 as reference and balance 5,6 so

1,2,3,4
1,2,5,6

and then I left it at that assuming the setup was balanced.

So I took the M out for a drive to warm up the engine, hooked up the Carbtune and checked the settings.

With cylinders 1,2,3,4 I see that the readings were all slightly off so I balanced them all again to 22cmHg.

Then I measured cylinders 1,2,5,6 and adjusted all to 22cmHg.

I found that I was wrong to assume that they would be balanced. My oversight the first time is not understanding that adjusting one set of throttles would impact the vacuum of the others, I didn't think this would be the case but it is happening. Maybe my setup has a leak or something else needs to be replaced/adjusted, but when I measured 3,4,5,6 cylinders 3 & 4 were slightly off, so I adjusted them to 22cmHg.

Then I went back and checked 1,2,3,4 and needed to tweak 1,2 ever so slightly to match at 22cmHg.

I checked 1,2,5,6 and 3,4,5,6 and all readings were at 22cmHg.

I took the car out for a drive and the car drove even better than after the first adjustment. Throttle response was immediate and smooth vs. the jerky delivery of power the car initially exhibited prior to balancing.

Before balancing, when I was coasting in gear the car would have a tendency to lunge (feels like you stepped on the brakes hard for a split second) when the RPMs dropped to a certain point, so combined with the jerky acceleration make for a rough drive. These symptoms have been fixed and the car accelerates and coasts very smoothly now.

So I do suggest to everyone who is doing a throttle body balance to do the extra steps to make sure all of your throttles match up perfectly to get the best results.
 
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