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(Post Link) post #1 of 8 Old 05-01-09 Thread Starter
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No MCSF with same RPM on the different gear?

What is the real difference between 3000rpm in the 3rd gear and 4th or 5th gear according to possibility of MCSF appearing (remaped Alfa)? For example: I have MCSF (caused by overboost) on 3000rpm with 4th or 5th gear, but I have no MCSF on 3000rpm with 3rd gear? How ECU "calculates" overboost in 3rd gear and how in 4th or 5th gear on the same rpm?
Regards. Dusan.
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Re: No MCSF with same RPM on the different gear?

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Originally Posted by dusan View Post
What is the real difference between 3000rpm in the 3rd gear and 4th or 5th gear according to possibility of MCSF appearing (remaped Alfa)? For example: I have MCSF (caused by overboost) on 3000rpm with 4th or 5th gear, but I have no MCSF on 3000rpm with 3rd gear? How ECU "calculates" overboost in 3rd gear and how in 4th or 5th gear on the same rpm?
Regards. Dusan.
the engine is under more load in the higher gears, the more load the longer the engine will boost for, so maybe its not on boost long enough in the lower gears for it to recognise the problem
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Re: No MCSF with same RPM on the different gear?

I can achieve almost 4000rpm in 3rd gear without MCSF, but very rarely 3000rpm in 5th without MCSF. Sometimes in 4th I have MCSF even on 2200rpm. Very fast acceleration from 2000rpm to 4000rpm in 3rd don't caused MCSF, but acceleration from 1800rpm to 2500rpm in 4th is impossible without MCSF. What is reason for this phenomenon?
Cheers. Dusan.
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Re: No MCSF with same RPM on the different gear?

as soon as boost rises, the engine accellerates faster, and more air is needed. in low gears the engine accellerates faster than the boost can rise, and the peak pressure is most of the time not reached. try accellerating in 3rd with the handbrake on and/or uphill, bet it'll get the MSCF....
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Re: No MCSF with same RPM on the different gear?

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Originally Posted by Cuore_Sportivo_155 View Post
as soon as boost rises, the engine accellerates faster, and more air is needed. in low gears the engine accellerates faster than the boost can rise, and the peak pressure is most of the time not reached. try accellerating in 3rd with the handbrake on and/or uphill, bet it'll get the MSCF....
thats what iv just said
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Re: No MCSF with same RPM on the different gear?

the chaps here have answered your question, but you also have 'overboost', which allows a higher boost for a couple/three seconds, so 3rd gear with a remapped car will probably pull 2500-3500 mostly on overboost, then the ecu has to work out why it cn't control things.

modern ecu's know roughly what position the vnt's on the turbo should be in, reason being, garrett and the likes supply turbos with a maximum turbo rpm (not boost or anytrhing else), so its down to the manufacturer to keep within tolerance of this, so they rely on bosch ecu's to calculate this, hence the ecu having some idea of where vnt position should be in relation to amf, map voltage etc.

the edc15 is not very clever on the alfa, edc16 is loads better, but haven't you changed items on your turbo for things not alfa fitment?
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Re: No MCSF with same RPM on the different gear?

Thanks for your explanations.
I think that main reason for my MCSF is overboost caused by non adequate length of actuator rod and close-to-the-edge boost pressure in remap. I mean rod is too short. I was obtained one spare vacuum actuator from same Garret GT1749v turbocompressor and I will tomorrow re-adjust the actuator length according to spare actuator as one template.
Best regards. Dusan.

Last edited by dusanGT; 05-01-09 at 20:57.
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Re: No MCSF with same RPM on the different gear?

Good news from me: Length of the rod of my vacuum actuator (mounted a few months ago after one car accident) is approx. 2mm (1/12") shorter than standard... After the lengthening the rod to the proper length and mounting on the turbine Garrett GT1749v all MCSF errors gone in the past.
Now I will feel free to go in next tuning activities: One FMIC is first step...
Best regards and thanks for your support. Dusan.
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