www.tdiclub.com

Economy - Longevity - Performance
The #1 Source of TDI Information on the Web!
Forums Articles Links Meets
Orders TDI Club Cards TDIFest 2016 Gone, but not forgotten VAG-Com List Unit Conversions TDIClub Chat Thank You

Order your TDIClub merchandise and help support TDIClub


Go Back   TDIClub Forums > VW TDI Discussion Areas > TDI Conversions

TDI Conversions Discussions on converting non TDIs into TDIS. More general items can be answered better in other sections. This is ideal for issues that don't have an overlap and are very special to swaping engines.

Reply
 
Thread Tools
Old April 8th, 2019, 23:49   #1
jackfolstam
Veteran Member
 
jackfolstam's Avatar
 
Join Date: Oct 2016
Location: CA
Fuel Economy: 42mpg
Default AHU m tdi low boost

I have an uncontrolled VNT15 on a Mk1 Caddy swapped AHU mtdi and I am seeing about 7psi on the boost gauge. Previously I saw 14psi but I decided to tinker with it and I adjusted the rod to get 18psi. At least once I turned it too far and got 20psi but dialed it in to 18psi. Then, it seemed to be mis adjusted the next day and only had 7psi, and has been that way since regardless of rod length.


Diagnostics:
Pulled vacuum on gauge and reads correct with no leaks. Reality check: engine is low on power. There would normally be turbo lag, then suddenly acceleration, but now it's just, are we going yet?
Reset vnt rod to 3-5inHg.

Pulled all boost and intake hoses and checked for holes and cracks.
Pressure tested the intercooler and hoses together to 15psi and corrected a very minor leak.
Replaced turbo with known working unit (ran it on an etdi swap).
Pulled the glow plugs with a hot engine and found #4 to be wet. Pulled them again today after cruising around and none were wet.
Compression tested with GPs out: 500, 400, 500, 450. I want to check #2 again since the gauge relief valve was leaking badly during 1, 2, and 3 but it's probably true.
EGR was blocked off, tonight removed egr and blocked hole to intake manifold, no change.
Checked cam and crank timing, correct. WIll probably adjust the pump both ways tomorrow to see if ti changes anything.

I also changed out the main seal, crank sprocket that was wallowed, and bolt that was super loose and looked to be reused, but I forget if I messed with the boost or changed the sprocket first.

Can leaky injectors or failing IP cause low boost?
I'm hoping someone stuck a banana up my tailpipe (can't see any foul play) or there's a rag in my intercooler (which I will check tomorrow). Possible cause?
What kind(s) of internal damage can cause this? Cylinder head cracks or bad valve seats?

Last edited by jackfolstam; April 25th, 2019 at 10:09.
jackfolstam is offline   Reply With Quote
Old April 10th, 2019, 13:05   #2
CasaEd
Member
 
Join Date: Mar 2017
Location: Portugal
Default

Please can you just clarify something for me. Are you using Vacuum to control the VNT
turbo on your mTdi, or have you swapped the waste gate controller to a pressure one ?
CasaEd is offline   Reply With Quote
Old April 12th, 2019, 18:03   #3
jackfolstam
Veteran Member
 
jackfolstam's Avatar
 
Join Date: Oct 2016
Location: CA
Fuel Economy: 42mpg
Default

I bought the car without anything hooked up to the VNT control, and I haven't added anything, it just sits there with the vanes stuck in one position.

So I peeked inside the intercooler and didn't see any obstructions. I was also thinking about putting on an alh intake manifold (which I have) and race pipe (that I'd have to order). I guess I have a spare EGR that I could slap on, can I leave the lower port alone or do I need to block it somehow? I'd think that no vacuum means it is closed.

Also installed translucent fuel feed line, only one small bubble that doesn't move, and new fuel filter filled with LM Diesel Purge, no affect.

Last edited by jackfolstam; April 15th, 2019 at 15:49.
jackfolstam is offline   Reply With Quote
Old April 19th, 2019, 17:04   #4
jackfolstam
Veteran Member
 
jackfolstam's Avatar
 
Join Date: Oct 2016
Location: CA
Fuel Economy: 42mpg
Default

I put on the ALH manifold with a new gasket, an ALH EGR/ASV with a new gasket, and rerouted the intercooler hoses. Same measurement of 7psi on the gauge. I think I will try a VDO boost gauge that I just got for my other car, have to find the right fittings though. I was trying to feel the lag/boost and now I'm starting to doubt the boost ever went away, and that the gauge may just be faulty. if I could jam the boost gauge tube up a tire valve stem then I could use the compressor to see if the gauge matches the compressor.

If the gauge checks out I will drive it to the shop next week and try the leak down tester I just got. Either that or injector swap with the other car. Then, it's time to convert it to etdi using ALH sensors and ECU.
jackfolstam is offline   Reply With Quote
Old April 23rd, 2019, 11:25   #5
jackfolstam
Veteran Member
 
jackfolstam's Avatar
 
Join Date: Oct 2016
Location: CA
Fuel Economy: 42mpg
Default

The other gauge shows 9 psi tapering off to 7 at redline. I made the rod shorter by one turn and no change on the boost gauge. So not much progress. I think I'll try another run after disconnecting the downpipe. Also I could easily put a new gasket on the EGR delete and downpipe. Not as easily I could put new gaskets on the exhaust manifold.

Leakdown test showed 1%, 5%, and 4%. I couldn't get the fitting in the #4 glow plug because of the water outlet. I'll have to grind down the fitting or find a narrow one. Or make one out of a bad glow plug.
jackfolstam is offline   Reply With Quote
Old April 23rd, 2019, 13:03   #6
CasaEd
Member
 
Join Date: Mar 2017
Location: Portugal
Default

If the vanes are stuck only in one position then that is the reason for your low boost problems, the vanes are supposed to move to increase/decrease the boost pressure, if you're only getting between 7-9psi of boost I would assume the vanes are more fairly open. That is not an ideal way to use that turbo the vanes need some sort of control mechanism. I run an older 1.6td passat with a vnt turbo controlled by a pressure can and it will happily boost 1.5 bar all day every day, you need to free off the vanes and decide how you want to control them, going back to an ECU controlled engine is the safest option, although I have seen a stand alone controller for VNT turbos. Your choice.
CasaEd is offline   Reply With Quote
Old April 24th, 2019, 13:14   #7
jackfolstam
Veteran Member
 
jackfolstam's Avatar
 
Join Date: Oct 2016
Location: CA
Fuel Economy: 42mpg
Default

This is how I understand the VNT15 to work: If you decrease the length of the rod on the vacuum actuator, it's as if the computer has pulled the rod, which happens as you step on it, opening the vanes. So the maximum pressure the turbo can get to, will go up when the rod is pulled, no? As well as reduce lag.

However, if the rod is increased in length (or the rod moves out), the max pressure goes down and the vanes close, which the computer does when boost is built up or when cruising/idling.

myturbodieseldotcom explains it as I did in this video :https://www.youtube.com/watch?v=o1Hvt2b7PL0

So if this is correct, I should be able to decrease the length of the rod until I get to the max pressure I desire.

At the normal settings of 'starts to move at 3"-5" Hg' I've previously seen that at WOT from 3-4k RPM the uncontrolled VNT15 will push about 14psi.

I then decreased the length of the rod to try and get to 18psi, but even with a small movement of the rod it went over to about 22psi. So, I lengthened the rod to get it back to 18psi.

Then after a few days it is down to 9psi without having touched the rod.
Now when I decrease the length of the rod the max boost pressure does not change, so there is something else wrong that is limiting. Not a charge pipe leak, maybe an exhaust leak or plugged exhaust, maybe clogged oil feed line, etc etc.

Last edited by jackfolstam; April 24th, 2019 at 13:17.
jackfolstam is offline   Reply With Quote
Old April 24th, 2019, 15:32   #8
edjet
Veteran Member
 
edjet's Avatar
 
Join Date: Dec 2004
Location: GA
Fuel Economy: 43-47
Default

How many miles are on this turbo?
__________________
06 Jetta TDi DSG Silver, 165k,
00 Jetta Tdi 5spd Black 385k
edjet is offline   Reply With Quote
Old April 25th, 2019, 10:06   #9
jackfolstam
Veteran Member
 
jackfolstam's Avatar
 
Join Date: Oct 2016
Location: CA
Fuel Economy: 42mpg
Default

Previous turbo that worked and then suddenly low boost: unknown miles.
Current VNT15 that worked fine on my ALH etdi swap and now on the m-tdi, low boost: 203k
So I really don't think it's the turbo, since two have the same symptoms.

I took it out of the other car to swap with a junkyard GT1749V, which I read on here that the only difference is the 46 vs 49 dimension, and also more importantly more robust.

Last night took off the oil feed line and sprayed clear with brake cleaner. Have to remember to prime it tomorrow (as well as put new copper seals on).
Took off the EGR delete plate and didn't see soot past the seal, so probably wasn't leaking, at least not enough to cause a problem. Put a new gasket on it anyway, haven't driven it yet.

Last edited by jackfolstam; April 25th, 2019 at 10:12.
jackfolstam is offline   Reply With Quote
Old April 26th, 2019, 13:25   #10
CasaEd
Member
 
Join Date: Mar 2017
Location: Portugal
Default

VNT turbos with a vacuum can open the vanes when you take away the vacuum & close the vanes when there is vacuum, if you are making the rod longer or shorter you are changing when the boost occurs, either earlier or later. And looking at your 1st post i was under the impression you were running an mTdi ?
CasaEd is offline   Reply With Quote
Old April 27th, 2019, 10:10   #11
jackfolstam
Veteran Member
 
jackfolstam's Avatar
 
Join Date: Oct 2016
Location: CA
Fuel Economy: 42mpg
Default

Quote:
Originally Posted by CasaEd View Post
VNT turbos with a vacuum can open the vanes when you take away the vacuum & close the vanes when there is vacuum, if you are making the rod longer or shorter you are changing when the boost occurs, either earlier or later. And looking at your 1st post i was under the impression you were running an mTdi ?
Changing when boost occurs, and maximum pressure, yes?
Yes an m-tdi. See first post first sentence. It's a VNT15 with no vacuum hose on the rod actuator. To clarify about me changing the rod length, I change it when the car isn't running, then take it for a spin to look for changes. The rod/vanes just sit there at that same position I left it when I go for a drive. There's nothing at all actuating the vanes when driving.

Last edited by jackfolstam; April 27th, 2019 at 10:17.
jackfolstam is offline   Reply With Quote
Old April 27th, 2019, 17:37   #12
[486]
Veteran Member
 
Join Date: Mar 2014
Location: St.Paul, MN
TDI(s): 02 golf ALH
Fuel Economy: 42 stock, 47-49 now
Default

1749v's got a real slender shaft on them, so they're pretty easy to blow apart, so be careful

what is EGTs?
fuel supply to pump?

no fuel, no egt, no boost
too much vacuum on pump inlet, no timing advance, no power
[486] is offline   Reply With Quote
Old April 28th, 2019, 00:29   #13
jackfolstam
Veteran Member
 
jackfolstam's Avatar
 
Join Date: Oct 2016
Location: CA
Fuel Economy: 42mpg
Default

Quote:
Originally Posted by [486] View Post
1749v's got a real slender shaft on them, so they're pretty easy to blow apart, so be careful

what is EGTs?
fuel supply to pump?

no fuel, no egt, no boost
too much vacuum on pump inlet, no timing advance, no power
Ok thanks, another idea, a problem with fueling.
I don't have an EGT gauge.
Fuel supply to pump is non assisted.

I have an unmarked injection pump. Could be going out, has fuel leaks but very slow, after a few weeks pump will get wet in some areas. Truck has a puff of white smoke on start so may have leaking injectors. Have had these conditions before and after current problem.

My next idea with fueling troubleshooting is to swap out injectors. I have a few sets from manual Mk4s. The idea is to run them in the sonic cleaner/simple green, drop them in the etdi and see what happens, if good put in mtdi. Previous owner said that the previous owner put bigger nozzles in. That's all he knows. I guess I could take them out and inspect the nozzles, never occurred to me that they might have part #s on them.
jackfolstam is offline   Reply With Quote
Old April 28th, 2019, 09:28   #14
CasaEd
Member
 
Join Date: Mar 2017
Location: Portugal
Default

Until you sort out the control mechanism for that vnt turbo you're never going to get a decent level of power, all you are achieving is to move the power to a different part of the rev range, if you close the vanes too much the boost will be too high and if you open them too much you will have low boost.
CasaEd is offline   Reply With Quote
Old April 28th, 2019, 09:44   #15
Vince Waldon
Veteran Member
 
Vince Waldon's Avatar
 
Join Date: Apr 2009
Location: Edmonton Alberta Canada
Default

Quote:
Originally Posted by CasaEd View Post
Until you sort out the control mechanism for that vnt turbo you're never going to get a decent level of power, all you are achieving is to move the power to a different part of the rev range, if you close the vanes too much the boost will be too high and if you open them too much you will have low boost.
This, a thousand times this.

The vanes on an VNT turbo are not just an advanced wastegate to keep the turbo from overboosting... they are integral to how the turbo functions and develops boost in the first place.

The good news is that there are (fairly) easy mechanical systems you can use to drive the actuator in an mTDI setup... head on over to vwdiesel.net and you'll find a few examples of cable-driven systems that cue off the throttle lever position. Look for threads by member "libbydiesel"... his design specifically is generally thought to be one of the better ones.

Another option would be to fit a traditional waste-gate turbo.
__________________
Vince Waldon Edmonton AB Canada

Note: The above is to the best of my knowledge- but at the end of the day simply interweb opinion, worth EXACTLY what you paid for it, and if used done so at your own risk.
Vince Waldon is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
very low boost. Pressure deviation low. specific N75 question im confused johnsongti VW MKIV-A4 TDIs (VE and PD) 14 May 25th, 2018 01:25
🔴► Mk5 Jetta Tdi seem low on power, No CEL, I think low boost problem.. supak111 TDI 101 7 March 17th, 2015 19:22
BRM bobbles in low load low boost fueling conditions... ScratchRob13 VW MKV-A5 Golf/Jettas 3 September 15th, 2010 05:59
low boost, low mpg, low power koabi VW MKIII-A3/B4 TDIs 19 November 23rd, 2007 14:45
HELP! 03 Jetta with Low Boost code and low power 4vdubs TDI 101 1 October 18th, 2005 11:55


All times are GMT -7. The time now is 11:04.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright - TDIClub Online LTD - 2017
Contact Us | Privacy Statement | Forum Rules | Disclaimer
TDIClub Online Ltd (TDIClub.com) is not affiliated with the VWoA or VWAG and is supported by contributions from viewers like you.
1996 - 2017, All Rights Reserved
Page generated in 0.19588 seconds with 11 queries
[Output: 133.42 Kb. compressed to 111.73 Kb. by saving 21.69 Kb. (16.26%)]