Fabia 1.9tdi - VCDS log help

[mbizzler]

Hi All,

Ive got a Hybrid PD150 turbo (Garrett GT1749VB) on my fabia, FMIC, standard injectors and a custom map. I recently got to use VCDS and thought id run some logs. I did a measuring block log for 011 and 003 and got the following:

https://dl.dropboxusercontent.com/u/22990413/LOG-01-011-003-xxxVRS.csv

Duty cycle peaks at 66, which seems low? Power seems to come on strong every time, but i thought it would spool quicker than it does - It doesnt meet requested until 2500ish from looking at the log? Peak flow also suggests a low BHP too, but i could be looking at this incorrectly?

Can someone please take a look at the logs and let me know what you think?

Thanks in advance

 

[A5INKY]

There is room to shorten the VNT actuator rod a bit. After that, your tuner might be able to help wake it up a bit sooner too. Have you sent them your log?

 

[devonutopia]

As above, I would say shortening the rod is called for, probably a turn and a half to 2 turns based on similar logs I have done on my fabia, and the resulting adjustment needed.

Maybe start with one turn first, then see what the duty cycle is @ 4000 revs. The target I believe is 75% duty cycle @ 4000 revs.

Oh, and also JUST log group 11 as you get better results with less gaps between the logs (which you get when logging 2 groups)

 

[mbizzler]

Great - Thanks for the quick replies guys. So shortening the rod then, which ive found a how-to here: ROD SHORTEN

I'm happy doing that - what will this mean the turbo does differently? spool quicker as the VNT actuates quicker?

Also, a quick one for my knowledge really - What does the stop screw effect in the real world? I know its a stop point for the VNT mechanism, but not what this effects in the running/power delivery.

Cheers so far, i appreciate your time in taking a look

 

[A5INKY]

Shorter rod will hold the VNT in a more efficient position for building boost at any given N75 duty cycle. Goal is to set the rod length as devonutopia suggests so that you have as much dynamic range as possible for the ECU to control boost. That is why 70-75% WOT at 4000 RPM is recommended, to allow room for the ECU to correct overshoot of actual boost.

Set-screw is a different animal, it only effects "tip-in" as any boost is requested. It is a finicky thing to set right, but when it is the set-screw holds the vanes in a slightly open position at the end of VNT travel to best balance the EMP to IMP at that critical point. Set-screw too short and the EMP will spike and the turbo will be slow to respond and low end power will be soft as the exhaust gasses try to find a way out, too long and the turbo will be a little laggy when trying to build boost. If yours came pre-set I wouldn't touch it unless you find a specific reason to. Too easy to mess up.

 

[mbizzler]

That's exactly what i was after thanks a lot.

So to set the rod length - is it accessible easiest from below with the undertray off?

The stop screw question was purely so i understand it really, i wasn't going to touch it. I have a mechanical mind and like to know how it all works

 

[faboka]

You can also carry out a duty cycle test. This shows pressure with the vanes open and closed. Can't remember of the top of my head how you do it.

 

[mbizzler]

Thanks guys - recognise a few names from Briskoda above

I'll carry out the rod adjust and get the duty cycle in the right region and report back after the weekend with more logs

 

[devonutopia]

Thanks guys - recognise a few names from Briskoda above

Hi!

 

[mbizzler]

Here is a decent log from last night of group 11 before I touch anything if anyone is interested (Its even got a fancy graph!)

https://www.dropbox.com/s/5er4o73vlv1v0hb/LOG-01-011-run2-GRAPH.xlsx

 

[A5INKY]

I'd go about a half turn on the rod at a time as you shorten it, and re log after each adjustment to see what it did. Once you get closer to 75% N75 duty cycle at 4K RPM any remaining improvement to earlier spool will be in your remapper's hands. I would expect it could get better with a little work though. Your rod is not so far out of whack to explain that lazy of spooling alone IMO.

 

[devonutopia]

Funny how duty cycle climbs to 64% odd at 2500 revs then actually drops back a bit before climbing a little to 62% ish at 4000 revs. Definitely at least one turn I reckon but I always thought duty cycle should increase progressively, not dip like that. Chances are thats in the mapping perhaps.

 

[mk3pd]

Could be a vacuum leak
Happened to me,the nipple on the vacuum pump was loose and the vacuum was going on and off causing very strange boost

 

[devonutopia]

Could be a vacuum leak
Happened to me,the nipple on the vacuum pump was loose and the vacuum was going on and off causing very strange boost

Hmm, yes - I remember mine coming loose from the clips and it was resting on the exhaust manifold, gradually melting a hole in it, so I got a very slow onset of funny turbo behaviour as a result.

 

[mk3pd]

That vacuum nipple gets wobbly after a while on all pumps it seems

 

[mbizzler]

Well, today i shortened the rod and ran a load of logging. Firstly, top marks to Devon, 1 1/2 turns got me in the right ball park!

I adjusted it twice and settled with a peak of 70% for now as i now peak at 29psi boost (on the in car gauge) when i stomp on the loud pedal which then settles back quickly, but i didnt want to take it any further as i know thats high for this turbo. If i feed the power on it barely spikes.

Here is the latest log, which still shows lag although i must say it does feel slightly sprightlier: LATEST LOG

I also spotted my vacuum pipe had freed itself from the clips and has be dangling onto the drive shaft, but definitely hasnt gone through to cause a leak.

Do we think this is in the mapping then?

 

[robnitro]

Check the output of the vacuum pump with a gauge connected directly and nothing else on it... (besides the brake booster). Wiggle it, if vac drops it is leaky. Also you want something like 28 or more vac.

Mine was loose, I sealed the rotating part with epoxy and put a bigger rubber hose over it and clamped it over the metal housing and the rubber hose to the split to the brake booster and vac system.

 

[devonutopia]

You really want to see what the EMP spikes are doing, but at least it sounds a lot better than it was.