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Discussion Starter · #1 ·
Hi there, I'd just really appreciate feedback from the experts as to my Block 11 graph;

Rectangle Slope Plot Font Parallel


Since getting the car back onto the road I'm progressively getting it to run better. It was off the road for years and the VNT vanes seized, requiring a strip and clean of the turbo housing some months ago. I then adjusted the VNT actuator rod, but I knew it wasn't running right. When I did a service recently and replaced the fuel filter that made a big difference - I then had dead spots in power and realised the VNT rod needed shortening again....so I think I might be getting there, but....
Is it normal that the duty cycle should drop off like it does as rpms go from 3500-4000? At 4000rpm the Duty Cycle is just over 70, should I be shortening the rod another turn? It's approaching 80 at around 3500rpm....?

I'm really no expert and have only a minimal understanding of what's going on here, so I'd really appreciate some guidance.

Many thanks
 

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VR6 GT35 4mo
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So these are controlled by a PID inside the ECU. Basically it has a target and it's programmed to know what duty it'll need to hit that target. They're almost always designed to overshoot - it makes the car appear faster when you get a big surge of torque, but the boost should then follow target. Sometimes it undershoots, which is what yours is doing. You're getting basically no deviation once it settles into steady state (note that req follows act).

Your RPM slams off when duty does - so you've lifted off the throttle. Remember that VCDS is aids for logging so you're seeing about 5 samples a second, useless for fine tuning.

Depending on how many samples you have between flooring it and actual meeting req, I'd be inclined to say you've got a leak - you're not hitting req and DC is low, so the vanes are asking for all she can give. Depends on sample count though, it might just be inaccurate.

Looks fine IMO - could tweak the vanes in an attempt to smooth out the undershoot.
 

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Hi there,
You mentioned a strip and clean of the VNT turbo over the vane mechanism.
I just wondered if this is something you had done professionally and if so you could give an indication of cost.
I've had a few episodes over the last year with intermittent dropping into limp mode that Im convinced are due to lack of use, short runs and sedate driving through changed circumstances during covid that clear when I get some longer higher speed runs with the engine working harder in.

Sent from my HRY-LX1T using Tapatalk
 

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Discussion Starter · #5 ·
Adam - many thanks for taking the time to reply with detail. Learning more about this all the time....
Looks fine IMO - could tweak the vanes in an attempt to smooth out the undershoot.
By tweaking the vanes do you mean further adjustment of the actuator rod?
I'm beginning to wonder whether I have a leak, which is only showing up at higher revs - God knows how I'm going to find that!
Gerry - I followed a couple of tutorials on the web to get the turbo cleaned out. I did it myself and it was fine in the end but the only thing I would say is to be very careful with the bolts which hold the vnt mechanism into the housing - they're small and break easily which can cause you a world of pain! Use plenty of heat, tighten/loosen movements to loosen them and good quality penetrator...
 

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VR6 GT35 4mo
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You don't have a leak at high revs, or the turbo is able to mask it with more duty, it's fine. It's that initial punch where act doesn't follow req even though DC is high, but there isn't enough data points for me to be able to say for definite.

I'd be trying to smooth out the undershoot so I'd tweak one way and see if it improves, if the deviation gets worse, go the other way. PIDs will NEVER be perfect, there's too much variation between motors and they don't calibrate them to be that accurate, so always expect some over/undershoot.
 

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Adam - many thanks for taking the time to reply with detail. Learning more about this all the time....

By tweaking the vanes do you mean further adjustment of the actuator rod?
I'm beginning to wonder whether I have a leak, which is only showing up at higher revs - God knows how I'm going to find that!
Gerry - I followed a couple of tutorials on the web to get the turbo cleaned out. I did it myself and it was fine in the end but the only thing I would say is to be very careful with the bolts which hold the vnt mechanism into the housing - they're small and break easily which can cause you a world of pain! Use plenty of heat, tighten/loosen movements to loosen them and good quality penetrator...
Thanks for the reply.
Ive had my 07 1.9 Tdi for 11year and its on nearly 97k but it"s only in the last 6 months or so that it's been playing up a few times and I'm just reviewing my options should it continue.
I've researched the DIY options over the years and with over 40 years of looking after my cars I am reasonably confident it's something I could tackle if needs must, but I was just after a rough idea how much it might cost if I needed to get someone to do it for me.

I'm very much hoping that as I get back to using my car in something like a more normal manner the issue will disappear as, touch wood, its been several weeks since it last happened.

Sent from my HRY-LX1T using Tapatalk
 

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Discussion Starter · #8 ·
I'm getting really frustrated with this - I just can't get the car to run right. I tweaked the VNT rod - shortened it a couple of turns and here's the result:
Human body Rectangle Slope Plot Parallel

Sorry - I've realised I've captured some of the 2nd gear run-up to the third gear run. The car doesn't have the oomph it should have - nowhere near, believe me, my foot is planted to the floor. It struggles and takes an age to get from 3500rpm to 4000rpm, almost ran out of road!

Actual pressure falls off at this stage as well.

Have I shortened the rod too far, would that make sense with these results? It's hitting over 80% duty cycle early - at about 3000rpm, which is too early isn't it?

Many thanks for any advice.
 

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VR6 GT35 4mo
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It's worse than the first time. PID can't regulate well and you have a huge hole at the start of the run. Request is following actual well in the first run.

Not sure what you're expecting between 3500 and 4000...
 

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Discussion Starter · #10 ·
Sorry to bother you all again....after tons of tweaking and then cleaning with Mr Muscle again, I took the car to a specialist to get it looked at. It turned out the MAF was dodgy and he replaced it - a massive improvement; night and day, the car now seems to want to go like when it was new.

But, I've found it now goes into limp mode if you're driving it hard. No problem I thought, I bet the VNT needs adjusting now that we've corrected the MAF. Mapping block 11 showed a duty cycle of 94.4 from 2800 revs so I thought I'd need to lengthen the VNT rod. Did that this evening by just 1 x 360º turn, only to find it now goes into limp mode even more readily - hitting a 94.4 duty cycle at 2100 rpm!

Any ideas what's going wrong? It's doing the opposite of what I'd expect when lengthening the rod. My plan now is to Mr Muscle it some more in case there's some sticking again, then re-test.
 

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ECU hard limit is 95% on 1.8ts - I'd have thought the diesels would have had a similar limit. It's to stop driving the solenoid at 100% duty which is hard on them. The 5% off time helps keep the coil cooler.

Anyway, 95% duty means the ECU is trying to open the vanes to reduce boost. Assuming the limp code is for overboost?

Adjust rod to bring it back inline. There's no real reason to deviate from stock.
 

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Discussion Starter · #12 ·
ECU hard limit is 95% on 1.8ts - I'd have thought the diesels would have had a similar limit. It's to stop driving the solenoid at 100% duty which is hard on them. The 5% off time helps keep the coil cooler.

Anyway, 95% duty means the ECU is trying to open the vanes to reduce boost. Assuming the limp code is for overboost?

Adjust rod to bring it back inline. There's no real reason to deviate from stock.
Hi Adam and many thanks for your reply. I've read that on Diesels it's 94.4% as a limit and yes it shouldn't be getting to that level and the vanes need to open to reduce boost. Yes I'm getting the code 17965 - Charge Pressure Control P1557 - 35 - 10 Positive Deviation - Intermittent. I've checked RossTech- website and yes it seems to be overboost.

My issue is that according to the threads on here about adjusting the VNT actuator rod, when you are hitting over 80 duty cycle you lengthen the rod and below 60 you shorten it. I've lengthened it and it's got worse, so that's what's confusing me.
 

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You're aiming for the ECU to control it. Trying to fixate yourself on a target duty number is not how the ECU works.

Put the rod to the factory setting and log it. All you want is that the requested boost matches the actual. The first over/undershoot doesn't matter unless it's massive.

Sample rates for VCDS are shit so they can easily make the graph look sloppy when it's not that bad.
 

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Discussion Starter · #14 ·
Thanks but I've no idea how to set the rod to factory setting. It's been adjusted loads, the turbo was replaced and later the actuator. Factory setting is lost. Hence chasing the numbers....
 

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Worth noting that an actuator is just a diaphram with a spring. Spring tension ultimately dictates actuator response which has to be correct for the ECU. If you put non-OEM actuators on a turbo that have a different spring rate, the ECU will need a recalibration on the dyno which takes hours/days.

Best checking actuator is OEM then compare against a built turbo and starting there. From memory your first graph was fine.
 
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