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

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post #1 of 131 Old 20th September 2011, 03:23 AM Thread Starter
mc hammered
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Balancing the throttle bodies with the Carbtune tool

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.

My 1991 M5... this is Veronica

My 1989 325i convertible (sold)... this is Nina
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post #2 of 131 Old 20th September 2011, 05:20 AM
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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.
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post #3 of 131 Old 20th September 2011, 12:09 PM
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post #4 of 131 Old 20th September 2011, 11:33 PM
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Marvellous thread , thanks for sharing .


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91 Sebring 3.6 | E28 UK RHD M5 | E34 UK RHD 3.8 | E34 M5 Touring | E24 M635CSi UK RHD
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post #5 of 131 Old 21st September 2011, 07:38 PM
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very good!

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You wash your car like it was your firstborn child, you tend to its needs like it was your own body, you rotect it like it's your family, then you drive it like you stole it.
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post #6 of 131 Old 22nd September 2011, 06:01 AM
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I am ordering the carbtune tool for the next few days...


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post #7 of 131 Old 22nd September 2011, 07:42 AM
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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?

Current Stable:
-91 E34 M5 with Dinan Chip & Cam sprockets + more
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post #8 of 131 Old 22nd September 2011, 06:34 PM
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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.

Euro M3'87 NogaroSilver/Euro E34 M5 '93/Porsche 993 TT 97' Euro/Porsche 993 Carrera 95' Euro/Skyline R33 GT-R
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post #9 of 131 Old 23rd September 2011, 04:16 AM
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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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post #10 of 131 Old 23rd September 2011, 04:26 AM Thread Starter
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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 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.

My 1991 M5... this is Veronica

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