Weird Boost Occurences

[suwidji]

Hey all, i have a 1998 r34 gtt.

Today when i took it for a drive, i noticed that my boost gauge was reading that i was overboosting when i'm in 5th gear and go over 3.5-4k RPM. It never used to do this, and kinda feels like the boost has spiked up but no extra power is getting put down in the wheels. It doesn't always "overboost" but even when i hold down on max boost, it feels like the engine is working harder but getting power cuts.

I'm running max boost of 12psi on a std turbo and just change spark plugs about a month ago, gapped at 1.1

Any ideas to why this is happening is much appreciated.

cheers

[iruvyouskyrine]

How much boost is 'overboost'?

[suwidji]

It's about 1-2psi

Just had another drive, and yeh instead of holding power at boost, the engine sounds like it's working a lot more but there is no translation of power to the wheels.. sounds like the engine is going too fast or something it's ok at lower boost

[scotty nm35]

Are you on the stock ecu, no tune?

If the ecu isn't kept happy it will dump fuel and back out timing. The fuel will then burn in the manifold artificially raising the boost as the wastegate can't bypass enough gasses. My suggestion is to get a Nistune board installed.

[suwidji]

Yeh I'm running a Nistune board

[scotty nm35]

I would suggest you run it up on the dyno again, something isn't right. Perhaps a boost leak? Pressure test the intake before you go to make sure, it's not hard to make an 80mm bung.

I have had a few faulty Z32 afm's lately, they get dry solder joints inside, but that isnt a regular thing, the fault would come and go usually, randomly.

I have also had to replace a few Z32 afm plugs lately, as most guys buy old VL/300zx ones from the wreckers and the pins are bending/corroding. The new plugs I use are sealed unlike the old style Z32 plugs. If you have a Z32 afm it could be worth looking at...

[suwidji]

I don't have a z32 just the standard pink label AFM .

If it were a boost leak, i would expect to see it even in the lower boost ranges, no?

The RPM's seem to stop increasing at 4000 whereas before i could push it to 5 or even 6.

Very strange and frustrating - i may have to take it back on the dyno

How do I pressure test the intake?

[scotty nm35]

Bung in the intake, where the AFM goes, then fill it with compressed air. Should find any leaks at 10psi or so. Don't fill it too much you might pop something.

The same dry joints can occur on the factory afm, not hard to pull the lid off and resolder them, just in case. There is a how-to on here somewhere.

[suwidji]

oh, i don't have an air compressor

might just book it in and see what my tuner says.

[scotty nm35]

No point tuning it with a leak...

Get some PVC bunnings fittings and an old tyre valve, then head to the local servo.