AMF TDI low boost

Timmy2000

Member
Hi all, I'm having trouble figuring out what's going on with my wife's AMF TDI.

Since I bought it a couple of years ago it's always felt a bit down on power, used a bit more fuel than I'd expect (averages mid 50's mpg while my BHC averaged 70+ mpg) and has used a bit of oil (maybe 100ml ever 1k or so), VCDS shows boost is consistently about 10% below specified pressure, but I can't find a boost leak in the pipework (smoke tested), and there's no fault codes. I've already replaced the rocker cover, tandem pump and EGR since all were leaking oil, and whilst consumption has reduced a little, it's not that noticeable, though the engine appears dry apart from around the turbo inlet.... 😬 However, the intercooler doesn't seem to have much oil in it (a couple of drops came out), I've checked the hoses going to the N75 valve and all are good, but I have ordered a new N75 just in case that's not working properly. If that doesn't fix it, what should I check next?

Thanks!
 
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Take the outlet charge pipe off the turbo from underneath and inspect the fan blades and play in the shaft.
Try turbo cleaner.

Otherwise not sure.
 
Unless you are doing mid to long distance runs daily, for an AMF mid 50s mpg sounds pretty good to be honest. I only get properly good mpg with either car (AMF/BHC, both with 6-speed box) on country-length journeys overnight), and usually on those runs I am looking more at journey time so maybe 45 or thereabouts mpg but bang on 70 mph speed limit all the way with cruise control. All the rest of it sounds like good common sense maintenance, and the oil use sounds pretty normal.
 
@CrispyEdd that was going to be my next place to check but it got too cold on my drive and I wimped out for the day!

@Robin_Cox fuel and oil consumption wouldn't be such a concern if it had power and boost. The mpg comparison is direct: same journeys over a year or so, typically 50+ miles on a mix of road types. Both cars also have MZN boxes, the BHC was good but I really would expect more from the AMF, it's currently getting the same mpg as my ATL which has the standard gearbox, but a lot more power
 
I am running usually 25 km one trip to work with my AMF. About 65% highway and rest is mixed city and rural. I have long term 4,9l/100km (57 MPG). I am usually driving pretty dynamically.

I would assume it is not right. It may be caused by bad turbo. Check the vanes on the compressor side. Is it making different sound rather than usual turbo whistle?
 
Are all filters upto date?

I would check the coolant temp is reading correctly in the engine ecu as the sensor is a dual one meaning it could read correctly on the dash to what the engine receives.
Also worth seeing what the injector values are.
It might be worth unplugging the MAF to see if performance improves.
 
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@Howey good shout re. the MAF, I'll give that a try. Injector values looked OK from what I can remember, but I'll double check. I'm going to do the fuel filter ASAP: I've done all other filters recently and have the fuel filter to hand, just haven't got round to it and have no idea if it's ever been done previously. Coolant temp values looked good in VCDS, car gets to temperature really nicely (for a TDI) and stays there even in the cold weather.
 
@Howey good shout re. the MAF, I'll give that a try. Injector values looked OK from what I can remember, but I'll double check. I'm going to do the fuel filter ASAP: I've done all other filters recently and have the fuel filter to hand, just haven't got round to it and have no idea if it's ever been done previously. Coolant temp values looked good in VCDS, car gets to temperature really nicely (for a TDI) and stays there even in the cold weather.
Champion!!
Be sure to prime the filter (fill with fuel or additive) to be honest not a pleasant job on your back.
 
Unless you are doing mid to long distance runs daily, for an AMF mid 50s mpg sounds pretty good to be honest. I only get properly good mpg with either car (AMF/BHC, both with 6-speed box) on country-length journeys overnight), and usually on those runs I am looking more at journey time so maybe 45 or thereabouts mpg but bang on 70 mph speed limit all the way with cruise control. All the rest of it sounds like good common sense maintenance, and the oil use sounds pretty normal.
45mpg @ a constant 70mph for an AMF TDI 75? Something isn't right there!
To avoid anyone getting the wrong idea and the AMF getting a bad name i would like to state for the record that I've owned countless TDI's over many years and having owned multiples of all variants, AMF's (early with Webasto and later without) BHC's and ATL's, my go to TDI of choice and personal preference is the later AMF. I like it's simplicity, incredible reliability and unbelievable frugalness (if that's even a word) circa 70mpg @ 65mph in standard factory unmapped form the norm and mid 60's @ 70mph.
The things that I find effect economy most are binding rear brakes (handbrake adjustment not correct) the car not being serviced properly or frequently enough, failing to replace the fuel filter anywhere near often enough, or not running the correct (and best) 5w30 longlife 507 spec oil (Quantum only for me) which is changed at least annually regardless of mileage and is THE single most important thing to do for reliability and longevity (even if you do nothing else), running incorrect tyre pressures and poor quality budget tyres.
Obviously the earlier Webasto equipped AMF with use more fuel in the winter (which it is designed to do) so will have a significant effect on fuel consumption and mpg too.
This is just my two cents worth and my own opinion and not something I generally publicise but I read a few things recently which incorrectly and unfairly talked down the AMF, one person saying I would buy that car if it was a BHC not an AMF which puzzled me and someone else saying that the oil was changed 5 years ago but only 8k miles ago and seemed to think this was ok which amazed me too.
Anyway, this is meant as a positive not a negative with no wish or intent to cause any upset, just from experience that others haven't had the privilege of having. I currently have two late AMF' s (amongst others) and love them 👍
 
Hi all, I'm having trouble figuring out what's going on with my wife's AMF TDI.

Since I bought it a couple of years ago it's always felt a bit down on power, used a bit more fuel than I'd expect (averages mid 50's mpg while my BHC averaged 70+ mpg) and has used a bit of oil (maybe 100ml ever 1k or so), VCDS shows boost is consistently about 10% below specified pressure, but I can't find a boost leak in the pipework (smoke tested), and there's no fault codes. I've already replaced the rocker cover, tandem pump and EGR since all were leaking oil, and whilst consumption has reduced a little, it's not that noticeable, though the engine appears dry apart from around the turbo inlet.... 😬 However, the intercooler doesn't seem to have much oil in it (a couple of drops came out), I've checked the hoses going to the N75 valve and all are good, but I have ordered a new N75 just in case that's not working properly. If that doesn't fix it, what should I check next?

Thanks!
Are you looking at Group 011, when checking boost pressure?
Mac.
 
Did you log them, over a drive, or various rpms while stationary?
Mac.
Just while stationary, didn't log but kept a close watch at varying rpm. Pretty consistent 7-8% below specified boost.

N75 valve has arrived but weather has been awful so won't get out to do anything on the car until midweek
 
Just while stationary, didn't log but kept a close watch at varying rpm. Pretty consistent 7-8% below specified boost.

N75 valve has arrived but weather has been awful so won't get out to do anything on the car until midweek
You need a log that includes a period where the engine is under load, and boost demand is significant. That'll give you an idea of the turbo's condition, and what the N75 is doing.
Mac
 
So a quick update on this as it's been a while since I've had a chance to look at the car.

I've checked the inlet side of the turbo for any play and there's almost none, also not much oil considering the age and mileage. Confident there's no boost leaks and no issues with air getting to the turbo.

I've still to change the fuel filter, however I am starting to think the waste gate may be stuck open. There's quite a bit of oil coming out of the actuator hosetail that suggests to me the diaphragm may have split - any one have experience of something like this?
 
I’ve a similar enough issue with a 75hp BHC engine. Replaced bottom hose and fixed one small vac tube. Intercooler looks good. It’s got the combined n75 valve rather than single type and I swapped with another one but it had an electrical issue so waiting on another to arrive. Also intend to replace turbo as it’s oily. Will also probably change Intercooler given it seems to be a weakness. Here is what my issue looks like: it’s clear I get good boost and then it drops off. Green is specified and red actual. Mine however has fresh fuel filter and new tandem pump.
 

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@Needles73 you've reminded me that I've also tried the new N75 valve I bought, that didn't make any difference unfortunately, but I was expecting as much, just replaced it to try and narrow down the possibilities!

Tandem pump was replaced with a new Bosch one when I got the car a couple of years ago.
 
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