Balancing the throttle bodies with the Carbtune tool - Page 2 - BMW M5 Forum and M6 Forums
E34 M5 Discussion 1988-1995 Sedan and Touring

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post #11 of 129 Old 23rd September 2011, 04:37 AM Thread Starter
mc hammered
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Originally Posted by 2man View Post
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?
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.

My 1991 M5... this is Veronica

My 1989 325i convertible (sold)... this is Nina
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post #12 of 129 Old 23rd September 2011, 03:48 PM
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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.

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post #13 of 129 Old 23rd September 2011, 08:10 PM
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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.

Raymond

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post #14 of 129 Old 24th September 2011, 06:52 AM
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Originally Posted by raymondw View Post
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.

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post #15 of 129 Old 24th September 2011, 07:58 AM
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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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Last edited by raymondw; 24th September 2011 at 07:58 AM.
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post #16 of 129 Old 24th September 2011, 08:29 AM Thread Starter
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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.
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.

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Originally Posted by raymondw View Post
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?

My 1991 M5... this is Veronica

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post #17 of 129 Old 24th September 2011, 09:49 AM
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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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post #18 of 129 Old 24th September 2011, 09:59 AM Thread Starter
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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.

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.

My 1991 M5... this is Veronica

My 1989 325i convertible (sold)... this is Nina
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post #19 of 129 Old 24th September 2011, 11:15 AM
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Originally Posted by mc hammered View Post
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

Raymond

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Last edited by raymondw; 24th September 2011 at 11:27 AM.
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post #20 of 129 Old 26th September 2011, 01:16 AM Thread Starter
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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.

My 1991 M5... this is Veronica

My 1989 325i convertible (sold)... this is Nina
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