VNT17 Loader Conversion Problems: Troubleshooting Guide

Hi, I've been searching the archive for a while now, but unfortunately without success...
Last week, I installed a VNT 17 turbocharger in my AFN engine and also disabled the EGR system. After the first test drive, the vehicle went into limp mode immediately after shifting into 3rd gear. The error code was 'intercooler pressure regulation difference, intermittent.'
I checked the VTG shaft, and it moves freely. The turbocharger has 15,000 km on it and shows no play. After turning off the ignition, the error disappears, but the problem reappears when I demand full power in 3rd or 4th gear.

What could possibly not work? I have all the necessary tools and equipment available.
Vehicle information: Audi A4, 1996, 1.9 TDI AFN 4-motion. Automatic transmission, 214,000 km.

Thank you very much.

Hi,

'Why don't you log your boost pressure and the control of the vacuum valve for your VTG, then we'll be smarter... '

Hello,

'Could you please post a log showing the boost pressure behavior? Perform a diagnostic test on the actuator and check if the VTG (variable turbine geometry) is moving correctly. Does the vehicle run normally until it enters limp mode, or does the turbo boost feel stronger/weaker than usual?'

Regarding the error: Is the threshold limit being UNDERSHOT or EXCEEDED?

Hypothesis: The VTG rod needs to be adjusted in length.

EDIT: DocSnydor was faster...

Regards,
Private.

Hi,

Okay, try searching for 'intake manifold pressure control differential.' Also, use VAG-COM to check the target and actual boost pressure over a wider RPM range. It's very likely that the linkage between the turbocharger and the control valve is misadjusted.

I just took the 1551 for a test drive. The boost pressure was 2432 mbar at 3000 RPM when I floored it.
and I have a second error: short circuit in the mass airflow sensor, connected to the positive terminal.
'@private area, I can't say whether the turbo boost will be stronger or weaker, as it appeared immediately after the turbocharger modification. However, the boost is still enormous (even up to the emergency mode). It would be great if it stays that way...'
The actuator diagnosis has been performed and is in order.

I just finished a test drive with unit 1551. The boost pressure was 2432 mbar at 3000 RPM with full throttle.
That's about 1.4 bar of overpressure. Check the technical articles for the exact target values. One thing is certain: that's too much for an AFN in its standard configuration (assuming no modifications).

Adjust the VTG rod so that it creates less pressure.

EDIT: I just checked https://community.dieselschrauber.org/en/viewtopic.php?t=2992 something here. If you experience excessive throttle response or even limp mode issues at full load, you should adjust the rod longer.


and I have a second error: short circuit in the mass airflow sensor, connected to the positive terminal.
Is it an intermittent issue, or can it be deleted? What are the MAF sensor readings? Are they plausible? Compare them to the expected values, and check the wiring if necessary.

'If the boost pressure is excessively high, a significantly larger amount of air will be drawn in, which will result in a higher-than-expected output voltage from the mass airflow sensor. Whether the control unit interprets this as a short circuit to positive voltage is unknown. First, make sure to correct the boost pressure.'

Regards,
Private.

The LMM (lambda sensor) is working correctly, and the wiring also seems to be fine. I will now look into adjusting the VTG (vanos timing) rod and will report back.
Thank you very much in advance.

I just adjusted the VTG control rod; it's now at 2240 mbar. The LMM error is gone, but the intake manifold pressure/control difference error is still present... however, it's no longer going into emergency mode... Unfortunately, the performance has also decreased... Let's see, maybe the optimal setting hasn't been definitively found yet...

Without chip tuning to adjust the boost pressure, a VNT17 turbocharger is completely pointless.
So, increase the pressure in the engine map, and then the limp-home mode will be eliminated.
Find a tuner who can adapt your chip to your supercharger and who also knows how to hold a wrench properly.
Off-the-shelf tuning chips are useless in your case; you might as well have left the old charger in. Logically, all off-the-shelf tuning chips are designed for standard engine hardware.

I don't understand why you even installed the VNT17 without an adapted chip, and what the purpose of that is...

Best regards, Rainer.

Rainer K. wrote:

I don't understand why you even installed the VNT17 without an adapted chip, and what the purpose of that is...

I was just about to ask that.

Rainer K. wrote:

I don't understand why you even installed the VNT17 without an adapted chip, and what the point of that is...

Hi Rainer,

Thomas apparently installed a 17-inch rim on his AFN Golf at some point.

While the engine was already tuned, it seems it wasn't specifically optimized for the 17-inch wheels. As far as I recall, he didn't experience any problems using the 17-inch wheels instead of the 15-inch ones.

However, if the engine remains in its original condition, the 17-inch turbocharger generally doesn't make much sense (unless you want to build in some boost reserves for potential future tuning).

Since I replaced my G70 (which had a short circuit to ground), I haven't had any more intake manifold pressure difference errors!

While my boost pressure is high at 1.3 bar at around 4,000 RPM, even with the chip installed, it's still within an acceptable range.

In terms of performance, having the 17-inch model instead of the 15-inch model definitely makes a difference, improving the acceleration time in the benchmark test by at least 1.5 seconds!

'I'll get my chip customized when the big nozzles arrive!'

Regards,

Manuel.

Quote:

Since I replaced my G70 (short circuit to ground), I haven't had any more intake manifold pressure differential errors!

What is a G70?

Could it be that it's just a placebo effect, and he's only feeling better because he thinks he is?
Because, actually, he doesn't get more fuel according to the map!

ps.
I also have the big turbo sitting on my shelf and I'll install it when it gets warmer. Then, I'll put a 12mm piston in the ESP and a custom chip . You can always dream, maybe I'll be able to implement that someday.

@caravanatic: because of the too high boost pressure! Maybe the low-pressure side isn't sufficient to fully activate the VTG valve! Anything is possible...

Manuel Thomas wrote:

Since I replaced my G70 (short circuit to ground), I haven't had any more intake manifold pressure differential errors!

Hi Manuel,

*click* That makes sense somewhere.

If the values of the LMM (mass airflow sensor) and the boost pressure signal are no longer consistent with each other, the engine may enter a limp-home mode.

I know of a case where the hose connected to the pressure sensor (in the engine control unit) came loose on an AFN engine.
Starting at a boost pressure of 0.5 bar, the emergency mode would reliably activate – apparently because the air mass increased without a corresponding pressure being measured.

It could have been the other way around for you...

What is a G70?

G70 = Mass Air Flow Sensor.


Could it be that it's just a placebo effect, and he's only feeling better because he thinks he is?
Because, in reality, he's not actually getting more fuel according to the fuel map!

For me, it's a measurable delusion, but I also have a tuning kit in the engine control unit.


@caravanatic: because of the too high boost pressure! Maybe the boost pressure is not sufficient to fully engage the VTG valve! Anything is possible...

Then the boost pressure would be too low if the vacuum cannot pull the VTG adjustment to its maximum boost pressure setting.

@ ULF,
I hope it stays like this for now. I've only driven about 240 km, but I've been very careful to avoid situations where the engine might go into limp mode, like full throttle going uphill, etc.

Regards,

Manuel.

Quote:

Then the boost pressure would be too low if the vacuum cannot pull the VTG adjustment to the maximum boost pressure setting!

You are right, it was a mistake. Good thing it was noticed!