Late turbo spool

[Matt_Stander]

Hi all. I recently did a bunch of work to my b6 a4 1.9tdi. This includes cam belt and water pump, cam and lifters as they were warn, intercooler because it had a hole on in and all filters. The problems is that before even though the car was down on power and had a slightly later spool than I was happy with I was expecting the new intercooler to fix that. Bower now even though it has slightly more power is spools wayy later. Before was around 2000-2100 now it’s closer to 2400rpm. The cam belt was previously done incorrectly and was a tooth out so they had adjusted the cam gear to compensate. I have triple checked that the timing is now definitely correct so it can’t be that. I have noticed that the vacuum line going to the brake booster does wiggle a little bit, more than I would assume to be an acceptable amount. Is this a sign that possibly my tandem pump is on its way out? I have also noticed that the anti shudder valve looks like it does not close all the way. I have replaced some of the vacuum lines that looked a little suspicious and that also made no difference.

[Matt_Stander]

The weirdest thing just happened. After parking the vehicle for the night, and going for a drive this morning, it seems that it is back to how it was before. I wonder if maybe because the battery was disconnected for a couple of days the ECU was a little bit confused. The car now spools around 2000 rpm in the lower gears and lower rpm in higher gears so I am happy with that but to me it still feels like it is lacking power. I am able to maintain 130km/h on the highway and even 100km/h in 6th gear on the country roads but that’s about all it has, overtaking is a hassle and don’t even think about trying to accelerate going uphill. The turbo and egr was replaced in November of 2023. The turbo still feels good with no shaft play and the vains move freely. The egr however seems to have a little bit of oil coming out of it. Is it possible that the egr is the problems here?

[willemml]

I would definitely do a complete boost leak test, not being able to accelerate uphill definitely sounds like you are losing boost, also 200kph shouldn't be difficult to reach. I would examine your diverter valve. Do you have a boost gauge? When you say spool do you mean hits peak boost or starts to spin audibly? When my DV failed I lost boost without any apparent leaks, and then eventually the turbo died from over speeding.

[Matt_Stander]

The car is completely standard, I have no boost gauge. I will only be able to check boost via a diagnostic tool. I can hear it audibly starting at around maybe 1800 depending on the gear but it only fully kicks in around 2k.

[willemml]

It should keep feeling more powerful until somewhere around 3000 to 4000 rpm (well it might be slightly lower as I assume you aren't tuned) but reaching max boost at 2000 definitely sounds like you either aren't making boost (boost leak, or maybe wastegate control issue) or the engine is not asking for more (limp mode, usually caused by a boost leak). Hearing it audibly means it's spinning fast, but spinning fast without producing much boost means there is likely a leak.

If your diverter valve (anti shudder/surge valve, connected to the n249) is not fully closing you will get exactly the symptoms you are describing, and in my case it led to the turbo grenading itself.

[Matt_Stander]

The car pulls the same from 2k rpm all the way till redline, there is no power fall off or or gain after 2k -2100 RPM. I have driven other 1.9tdis and this feels the same just with less power. s

[willemml]

I misread your post as being 1.8t rather than tdi, still sounds like a small boost leak somewhere to me but ignore everything else I've said. Especially about the (non existent on a diesel) diverter valve... Sorry, my bad.

[Matt_Stander]

haha thats alright. Im going to blank of the EGR sometime this week (there are no emissions laws in my country). If that does not work, the workshop next door to us has a smoke boost leak tester and I will see if I can use that quickly.

[Matt_Stander]

Hi all. Back to this thread as I’m still having the same issues. I have replaced so far the MAF, MAP, N75 valve and the intercooler (had a huge hole in it). I have checked the injector deviation which is no more than 0.30 mg so I’m not too worried about that yet. I have checked that it has the correct injectors in, it has AR injectors which I believe are correct. I have triple checked the timing after doing the belt and that is good. I did a smoke boost leak test which I am not entirely convinced as all the boost was just leaking through the breather pipe into the tappet cover but I don’t see any major oil sprays. My next thought is turbo. My issue is that the turbo does not assist below 1800rpm in 1-3rd but then there’s a higher load in 4-6th it spoils a little bit better but not entirely great. However it still just does not pull that well. It feels like a 100hp a4 not a 130hp. Can anyone agree that it sounds like the turbo because it’s starting to get a little bit frustrating.