Malone Stage 3; boost spikes then plummets

Just chipped my TDI ('97 1Z) with a Malone Stage 3 (with EGR delete) tune. Sprint 520 nozzles, upgraded intercooler, catless downpipe, VR6 clutch.

The car seems to build and hold boost pretty decent in the lower gears, but in 4th and 5th primarily, I notice the boost spiking to 25psi and then dropping to 12 or so. I've tried multiple scenarios, starting at different RPMs and under partial throttle and such, however it seems to always return to the same symptoms. It may very well do it in the lower gears, but since it's in a MK2 chassis, it roasts through the revs in 1st 2nd and 3rd pretty quickly. It might not have enough time to plummet before having to up-shift.

Before anyone asks, the car is properly timed with VAGCOM, the IQ is set to 3.5, and the N75 and vacuum lines are brand new. The turbo was also replaced recently (with a low mileage unit).

***This isn't boost falling off as I approach redline, like expected with a baby-sized turbo, this is a steep spike to 25psi, and a very quick drop to 12psi and staying there

Threw in my spare manual boost controller in place of the N75 and it's showing the same symptoms. Faulty N75 is off the list of culprits. I noticed that if I ease into the throttle as opposed to going wide open throttle quickly, it'll hold boost. If I get on the throttle quickly and initiate the sudden boost drop, followed by an upshift, it carries the low boost into the next gear until 10 or 15 seconds pass and then it's all back to normal. Similar to what I would expect of an "over-boost" type safe mode, or limp mode. Some research showed that limp mode due to over-boost is normal, however others seem to have to restart the car to clear the limp mode. Mine goes away quickly on it's own. Also, I've been driving it for three days and it has yet to throw a single code. A sticky wastegate has also been discussed in other threads, but I ran the car off wastegate pressure and it held 10psi through the rev range under all conditions, so that is no longer a culprit either.

As you mentioned it looks like the n75 is at fault here.Some "chipped" ecu's tend to ignore massive overboost situations!

andy2 said:

As you mentioned it looks like the n75 is at fault here.Some "chipped" ecu's tend to ignore massive overboost situations!

Click to expand...

I'm pretty sure I ruled OUT the N75, as the same symptoms were occurring with a manual boost controller. For some reason, the computer is drastically cutting power after an over-boost (25ish PSI) but then returning to normal in quick fashion. It's cutting power like an over-boost response, however it isn't storing a code, or requiring a restart to reset the limp mode. It's odd and I can't seem to pinpoint the cause.

I wonder if running a good manual boost controller parallel to the N75 would help. Just to open the wastegate faster than the N75 can, to avoid the slight over boost all together.

Wastegate actuator binding? Sure sounds like it might be if its stuck closed it'll spike, then pops open, boost drops then can't close enough again so it holds low boost?

Sounds like that to me as well, a sticky wastegate actuator or wastegate. I've lubed them with graphite and actuated a bunch and it usually comes out of it. I've seen it before when people hypermile their car everywhere and things get gunked up. It's why I recommend shifting at 2,500-3,000 rpm's and not lower, so things will stay working fine.

JFettig said:

Wastegate actuator binding? Sure sounds like it might be if its stuck closed it'll spike, then pops open, boost drops then can't close enough again so it holds low boost?

Click to expand...

Abacus said:

Sounds like that to me as well, a sticky wastegate actuator or wastegate. I've lubed them with graphite and actuated a bunch and it usually comes out of it. I've seen it before when people hypermile their car everywhere and things get gunked up. It's why I recommend shifting at 2,500-3,000 rpm's and not lower, so things will stay working fine.

Click to expand...

Thanks to the both of you for the input! I never really thought about it being an issue, since it runs 10psi without any issue off of waste gate pressure, but then again I've never ran more than that until now. I will investigate a bit more tonight or tomorrow and report back!

I replaced the rubber line inside the ECU, and disconnected and blew out all of the other lines on the car with an air compressor to clear out any condensation or oil. This made no difference. I will be getting the car in the air this afternoon to mess around with the wastegate. I fed pressurized air into the wastegate line from the engine bay and I did hear noticeable movement, but obviously that tells me nothing (except that it isn't completely frozen). Any other notorious problems worth checking while I'm in there?

Well JFettig & Abacus, I got underneath the car to get a good view of the wastegate actuator, and fed it 15psi, 20psi, and 25psi. All three times it opened right up all the way instantly, and when the pressure source was removed, it slammed back closed. It was moving very freely and consistently when pressure was added, and it didn't take much. I did clean off a bit of the gunk and lubed it up regardless.

Side Note: I scanned the ECU again for codes via VAGCOM after trying to put some miles on the car and it still is throwing no codes (aside from the 00750 code for the cluster).

Back to square 1 =(

Did it open at 8-10 psi and hold it as long as you supplied pressure (left the pump hooked up, and it didn't bleed closed)?

Abacus said:

Did it open at 8-10 psi and hold it as long as you supplied pressure (left the pump hooked up, and it didn't bleed closed)?

Click to expand...

Yes, it opened as it should at 10-12psi. I was using my 33 gallon compressor so the gauge isn't super accurate. It held the pressure as long as I had the waste gate line hooked up to the source. As soon as it was removed it closed. However, I did decide to clean and grease it as best I could from under the car. And after a bit of driving with it greased, I noticed it holding pressure much better than before, and the boost spikes are now less dramatic. Instead of spiking to 25+psi, it now is only spiking to about 22, and will hold 19-20psi about half of the time. The other half of the time, it'll get stuck at 5-10psi (at any amount of throttle), until I coast for a bit and then it seems to return to normal.

For example: Last night I took it out for a quick hot lap of town and it demonstrated this scenario...

This is a 2nd gear to 5th gear pull for diagnostic purposes only. On a closed track of course

2nd gear, WOT 22psi spike, held 19psi (lots of wheel spin), shifted at 4000-4200rpm
3rd gear, WOT 22psi spike, held 20psi, shifted around 4000 rpm.
4rd gear, WOT 4psi. I let off for a second, and went WOT again, same thing.
5th gear, WOT 4psi, no change. At this point I downshifted...
4th gear, WOT 22psi spike, held 20psi, pulled hard and healthy.

Maybe there is something to this sticky actuator theory. Prior to this, I couldn't get anything above 3rd gear to hold boost. The fact that it was temporarily stuck at exactly 4psi in both 4th and 5th gear makes me think that this actuator is getting hung up. Is it worth dismantling the turbo to clean and regrease the entire wastegate actuator unit? Is the actuator still available to purchase new? Is it worth it to upgrade to a TIAL (or equivalent external wastegate) and plumb it off of the (now blocked off) EGR port in the exhaust manifold?

You guys are awesome for all the input, I really appreciate the help with this new-fangled diesel thing

When I had a similar issue in my B4, my issues were:

Sticky N75 (replaced)
Oil in the vacuum lines (blew out with compressed air)
Oil in the WG actuator (suctioned via tiny tube and vacuum pump)

Windex said:

When I had a similar issue in my B4, my issues were:

Sticky N75 (replaced)
Oil in the vacuum lines (blew out with compressed air)
Oil in the WG actuator (suctioned via tiny tube and vacuum pump)

Click to expand...

The N75 I replaced, as mine was known to be bad. I blew out all my vacuum lines as well, though they're only 2 years old. However, I have not heard of oil in the actuator. That's something I will investigate. Thanks!