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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.

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Old December 10th, 2017, 15:14   #1
atmarine
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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!
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Old December 10th, 2017, 15:23   #2
jettawreck
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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??
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Old December 10th, 2017, 15:56   #3
IndigoBlueWagon
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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.
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Old December 11th, 2017, 18:02   #4
atmarine
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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-
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Old December 11th, 2017, 21:02   #5
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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.
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Old December 12th, 2017, 08:39   #6
wonneber
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Quote:
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.
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Old December 12th, 2017, 10:05   #7
atmarine
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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!
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