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

Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

Thread Tools
Old December 10th, 2017, 15:14   #1
Veteran Member
Join Date: Mar 2013
Location: Ny state
Default ALH dropping MPG's

I have had my MKIV for 5 years now and have logged every tank of fuel in the car. In the last 12-15 months I have seen a steady dropoff in MPG's. I used to get high 40's consistently, and now have consistently been in the low 40's.

It is a stock ALH with EGR delete about 4 years back. Nothing has changed with maintenance or the way we drive. I do a can of diesel purge every 20K, just did fuel & air filter, no change. The only thing that is manifesting itself is some smoking on hard acceleration. Think on ramp and merging into traffic. It usually will smoke some, and never used to. There are no faults in the ECU.

Is this the early signs that the nozzles are getting worn? They are original and I now have 190K on it.
Thanks for any input you can offer!
atmarine is offline   Reply With Quote
Old December 10th, 2017, 15:23   #2
Veteran Member
jettawreck's Avatar
Join Date: Aug 2004
Location: Northern Minnesota-55744
Fuel Economy: 52+ average lifetime '01

Nozzles have probably had a good run and may benefit from new ones and injector refurbishing.
Thinking maybe the turbo actuator may be sticking and/or some minor vacuum issues. Hard to toss a good guess at it w/o more history and lack of obvious issues. Typical stuff even like a fail(ing) MAF can cause a smoke issue even w/o performance dropping off noticeably.
Any chance you made a tire change (new, different size, etc) about the time of the mileage drop??

2001 Jetta TDI GLS Silver-current driver (salvage)permanently vented-Panzer Plate-Sprint 520s-ScanGauge-CheckTemp III-ZeroStart heater-CAT 2 filter
2003 Jetta GLS Black w/leather (New Project Car) fixer-upper w/broken TB
2004 Cadillac SLS (wife's)
1999 GMC Suburban (It's MN-you need one)
197? Shibura 2cyl diesel 4WD tractor-loader/brushhog (very handy unit)
196? International TD340 Dozer-w/Drott 4-in-1 bucket/back ripper attachment
jettawreck is offline   Reply With Quote
Old December 10th, 2017, 15:56   #3
TDIClub Enthusiast
Principal IDParts
w/Business number
Join Date: Aug 2004
Location: South of Boston
Fuel Economy: 50/45/37

What jettawreck said. It's probably a combination of issues contributing to lower FE. MAF wearing out, vacuum leaks, actuator not providing as much boost or soon enough, deteriorating injector spray patterns...all kinds of things. Good news is that, with the exception of the injectors, none of these items are very expensive to address. First step would be to get access to VCDS and run some logs so you can narrow in on the problems.
2002 Jetta wagon, 373K, RC3+; 1993 Mercedes-Benz 300D 2.5, 197K; 1997 Passat, 286K; '99.5 Golf, 259K; 2011 335d, 56K; 2015 Golf Sportwagen, 10K. Principal, http://www.idparts.com
Kid's cars: 2002 Golf TDI, 2002 Jetta TDI
IndigoBlueWagon is offline   Reply With Quote
Old December 11th, 2017, 18:02   #4
Veteran Member
Join Date: Mar 2013
Location: Ny state

Thanks all.
I have made some tire changes, but still all seasons, and the FE has still created down since they have been installed. (check air pressure every 2 weeks as well)

I do have a VCDS but not totally up to speed on what logs would be needed.
I have all new vacuum hoses as of about 3 years back. I have a small pump and can leak check the system again, but think it is pretty tight. The MAF was also new about 50K ago. I do have a new turbo actuator but have never installed it as I believed the current one was ok. I can install it and see if anything changes.

I have also read up on the turbo vanes that can stick, causing only partial boost. Is this worthwhile check at this point?

Thanks for the help and point me in the right direction on this one-
atmarine is offline   Reply With Quote
Old December 11th, 2017, 21:02   #5
Veteran Member
UhOh's Avatar
Join Date: Dec 2014
Location: PNW

Do you have VCDS? Really no way of verifying the health of the MAF w/o it. A bad MAF will affect mileage. Sticking turbo vanes might also have an impact, but the MAF is the first place to look. However, why do you have a new actuator? Why did you think you needed to get a new one?

Where did you get the MAF (brand)? I'd agree that a MAF shouldn't crap out in only 50k miles, but stuff happens: w/o proper diagnosis you could chase your tail only to come back to finding out it really is a bad MAF.
UhOh is offline   Reply With Quote
Old December 12th, 2017, 08:39   #6
Veteran Member
Join Date: Oct 2011
Location: Monroe, NY, USA

Originally Posted by atmarine View Post
I do have a new turbo actuator but have never installed it as I believed the current one was ok. I can install it and see if anything changes.
Before you change it if you have a vacuum pump you could test it easily.
From the N75 valve carefully pull the hose off that goes to the turbo.
Should be the lower fitting on the 2 fitting side.
It should hold vacuum and the arm on the turbo should move smoothly.
Next, tee the gauge into the n75 with the hose going to the turbo.
With the car running you should get vacuum, less then 20 inches iIrc.
Last, the top hose should have at least 20 inches of vacuum to it. If less trace it back through a 1 way valve to the vacuum pump.
There's a nipple on the vacuum pump that is usually loose, too loose it could loose vacuum.
wonneber is offline   Reply With Quote
Old December 12th, 2017, 10:05   #7
Veteran Member
Join Date: Mar 2013
Location: Ny state

Wonneber, good comments, and I will check.

A while back I had some vacuum leaks, and went with the IDParts limp mode fix kit. I never did replace the actuator as I thought that was good. All other parts were new then, about 50K back. I will also check the MAF with the VCDC and report all this back. Thanks!
atmarine is offline   Reply With Quote

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
Mpg dropping 06 Jetta dsg... hip001 VW MKV-A5 Golf/Jettas 8 October 21st, 2013 22:05
Dropping MPG; Need Suggestions/Confirmation whyfish TDI Fuel Economy 9 April 30th, 2013 11:14
odo 300,000 mi; MPG dropping wrenching40plus TDI 101 7 April 2nd, 2013 04:09
Any one elses MPG Dropping?? quartermeter1999 VW MKV-A5 Golf/Jettas 111 August 7th, 2006 18:54
My MPG is dropping, could it be the heat? 2000jetta TDI TDI Fuel Economy 5 June 12th, 2001 10:21

All times are GMT -7. The time now is 22:20.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2018, 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 0.13851 seconds with 13 queries
[Output: 82.28 Kb. compressed to 71.86 Kb. by saving 10.42 Kb. (12.66%)]