2.5 AKE loss of power - 00575 Intake Manifold Pressure Control Limit Not Reached - Intermittent[

[CharlesElliott]

I experienced significant (intermittent) loss of power today on my 130K, 2.5TDi AKE - whilst towing ~850Kg so a heavier right foot than normal. I've had the car for 10,000 miles and no issues so far.

On the first scan I got three codes:

00575 - Intake Manifold Pressure
11-10 - Control Limit Not Reached - Intermittent
01318 - Shareware Version. To Decode all DTCs
49-10 - Please Register/Activate - Intermittent
00777 - Shareware Version. To Decode all DTCs
28-00 - Please Register/Activate

I cleared them and then ran for another 15 mins, scanned again and just got the 00575. A lighter right foot definitely seems to avoid the issue.

The car has worked well all weekend including towing the same weight 200 miles on Thursday evening. I did fill it with diesel on Saturday and had driven ~15 miles since then not towing with no issues. It was a Texaco station but out of the way.....could a diesel problem be a likely cause?

What/how can I check where the issues lies? I see quite a few people with Control Limit Exceeded, but no so much on Control Limit Not Reached.

Thanks....

Charles

[ametlib]

Control limit exceeded or not reached, both is about the same stuff. Split vacuum hose, clogged turbo, bad n75, bad MAP sensor. A sticking EGR can also throw 00575 code, but will give other issues as well...

[CharlesElliott]

Thanks. What/how can I start checking to narrow it down?

[ametlib]

Check all the small vacuum hoses, especially around the t splitter next to the fuel filter, then check that the vnt actuator runs smooth, use adaptations in VCDS or simply pull and reconnect the hose on the VNT clock ( engine idle)

[CharlesElliott]

Thanks - I had a look at some things but don't have a baseline so need more help!

No obvious leaks in the hoses, but I don't have a vacuum pump/gauge so difficult to rule this out at this point.
The actuator does hit the stop at idle. But (with the engine off) it is very hard to move by hand. If I pull the vacuum hose off, the actuator springs back instantly. When I reconnect the hose, it takes about 5-7 seconds to get back to the stop and moves more slowly at the end.
I'm not sure how much vacuum should be generated, but putting a finger over the end of the hose doesn't create something particularly strong....I thought it would be trying to suck my skin off!

I drove about 20 miles around town without the trailer. The issue is most obvoius in second gear, particularly when accelerating from low revs. When it happens, I don't think I can hear the turbo spool up which I can normally. However, no fault was logged after the 20 miles so it didn't seem enough to trigger another 00575.

EDIT: I think it is the actuator that looks newer, the thing that the vacuum pipe goes onto that has the actuator rod to the turbo. I think this is separate from the N75? Where is that?
[WAS- I think the N75 might have been new at some point. It certainly looks shinier than most of the engine.]

MAF readings at idle are approx 180-200.

Does that provide any insight as to where the issue might be?

[ametlib]

I've never checked the time the actuator needs to pull the arm to the stop screw, but 5-7 sec MUST be far to slow ? When you pull the hose, the arm returns instantly, this could indicate that vanes in the turbo is ok and
your fault is a one of the following, VNT clock leaking, bad N75, a leaking hose or a bad vacuum pump.
Maf readings seems to be a little low, could you check the maf readings at idle with the EGR hose pulled off ?

[CharlesElliott]

Thank you.

Will do some more checks, and have ordered a vac pump/gauge. Would anyone be able to tell me the vac input going into the N75 and vac output to the actuator at idle?

[ametlib]

A bit hard to say, I dont know the spec. vacuum from the pump, try to google it. About the vac. to the actuator, the ecu will always try to get the right readings from the MAP sensor and will adjust the N75 related to that.
Since there are several components involved ( VNT-clock, N75, EGR, MAP sensor and even the MAF, since the ECU adjust the EGR to get the wanted MAF readings at idle) and due to tolerances in production and wear and tear this is
hard to answer. However if you pull the VNT hose and plug it on the vacuum gauge, I will expect the vac. going into the N75 and into the VNT clock to be about the same..
Are you sure the VNT clock isn't leaking ?

[CharlesElliott]

I found some specs on-line.

Are you sure the VNT clock isn't leaking ?

Not yet, still to be checked (when my vacuum pump arrives).

[CharlesElliott]

Well, the actuator holds a vacuum and doesn't have a leak.

The actuator moves from about 5 inHg to 20 inHg which seems about right from my searches.

The N75 has 16 ohm resistance across its contacts. Outputs around 22 inHg at idle - but it takes a while to get there (5-7 seconds) which lines up with what I see on the actuator. Problem is, I don't know what a 'good' car looks like so this might be normal or might not.

What I didn't check was the vac going into the N75 as I didn't want to pull the input off given how tight it is with the fuel filter (?). *If* the time taken for the pressure to rise is not normal, then it sounds like either the N75 moving slowly or a leak on the input to the N75. I wasn't sure how to test for a leak from the reservoir to the N75 input.