Compare B4 standard turbo with a VNT turbo

[luceberg]

I am asking on this section because you folks are more likely to know.

I am troubleshooting a friends newly aquired Golf PD 100 Tdi. It came with an overboost condition, so we replaced all the vacuum lines, MAF sensor, N75 and EGR valve and fitted a reconditioned turbo, which has generally solved the issue, but my friend still complains that pulling away in 1st gear is lagging for a quite a bit, before the turbo kicks in. He is used to the A3 platform as his previous car was a Golf Mk 3.

What I need to know is whether this is just a characteristic of the VNT turbo, or whether there is another fault that we missed.

 

[Seatman]

Nope, probably need to tweak the actuator rod, very common on replacement turbos. Chances are it's struggling to get up to full boost very easily.

 

[greengeeker]

You also may still have a vacuum leak. It will seem like boost comes on very late if you have even a small leak.

 

[luceberg]

Thanks, I am going to try adjusting the actuator rod. I noticed the replacement turbo had a long travel, but assumed it had been set up correctly.

I replaced all the vacuum lines with silicone ones and the EGR diaphragm was leaking, now replaced, so hopefully there are no leaks.

 

[G60ING]

Vnt turbos are VERY responsive, they seam much more eager to boost than wastegate turbos.

 

[G60ING]

Are the vacuum lines routed properly?

 

[GTiTDi]

If you reused the vacuum check valve be certain that it isn't obstructed w carbon or other junk...

 

[Seatman]

Thanks, I am going to try adjusting the actuator rod. I noticed the replacement turbo had a long travel, but assumed it had been set up correctly.

Yep, me too, fitted a new one to a friends car and the car has been running sweet but we've been doing logs recently for the tuner and you can see the N75 is struggling to get the boost up. Need to shorten the rod a bit, we're going to try one turn then see how the boost does with vagcom. New vac pipes all done too.

 

[luceberg]

I am going to attempt this tomorrow or the next day. So one turn shorter would be a good starting point? The actuator rod is not exactly easy to reach. Will you gain access from the top or bottom?

 

[Seatman]

96 passat, I would say probably from the bottom, we're doing my friend one on the golf tomorrow too. Don't forget it check it with vagcom after to make sure it's not boosting to much and causing big spikes.

But yeh, half to one turn and test.

 

[Digital Corpus]

Vnt turbos are VERY responsive, they seam much more eager to boost than wastegate turbos.

I second that. A GTB1756 will respond at least as fast as the stock Garrett on a B4.

On my stock turbo, the wastgate cracked open at ~9 psi, and moved at ~10 psi.

 

[luceberg]

We adjusted the actuator rod 2 turns shorter, but it made no difference, also replaced the map sensor, to no effect.

There is an oil leak from the intercooler, although the pipe connectors are dry, suggesting the leak is from the intercooler body. Could this cause a boost leak and cause my symptoms?

I am fairly certain that I got the vacuum pipe routing correct, as I replaced one pipe at a time with silicone ones and I guess it should not be leaking now?

As for the non return valve, I tested it by sucking the ends and it seems clear one way. I could use a mityvac to make sure.

To recap, the acceleration is pathetic up to about 2500 rpm, when it eventually kicks in and accelerates well.

 

[greengeeker]

How much vacuum supply do you have to the n75?

 

[G60ING]

A small accumulator is required. I use the stock one used for gasser cars.

 

[luceberg]

I will do a vacuum test on it. Does the test need to be under load or stationary?

It does have a small accumulator.

I am going off for a few days camping, so will post back later.

 

[luceberg]

I quote myself, "Does the test need to be under load or stationary?"

Sorry, that's a daft question, forget it. I was thinking of boost.

 

[luceberg]

How much vacuum supply do you have to the n75?

I tested this and the vacuum slowly builds to 26 in Hg. I also tested the one way valve again. It works as it should, but on the suction side it is not exactly free flowing. It could be a bit obstructed, maybe?