Boost level

[TieMyShoe]

A small fortune in parts and countless hours later Delilah has a fully rebuilt 4D56T sitting under her seats. I am curious though what kind of boost should I be seeing? I am reading a lot of conflicting info. Most of the Aussie/UK sites say 12PSI is stock, but I have seen many times on this site 8-9 PSI. Granted I am only seeing 6PSI on a brand new TD04 which seems exorbitantly low but probably sufficient for the break in period. Can anybody tell me with 100% absolute certainty what the stock boost should be? I don't want to blow my HG due to over boosting, however I don't want high EGT due to over fueling and low boost either.

[Growlerbearnz]

I can tell you with 100% certainty that *my* Delica, when stock, made 8 psi at full throttle with the occasional 10psi spike.

That increased to 10psi at full throttle with 12psi spikes when I blanked off the blowoff valve, which suggested the blowoff valve was a bit weak and had been leaking boost.

Does that help?

[yojimbo]

There is another question which is, how accurate is your boost gauge? Ive had a few, and none were terribly accurate. Good for a subjective look at boost level but off by several psi from what I could judge.

[TieMyShoe]

The gauge is an autometer so it should be fairly accurate. I have an exhaust leak at the turbo flange I need to fix as I'm pretty sure its robbing power, very annoying being that the gaskets are all new and the surface cleaned and smoothed... still leaks

[FalcoColumbarius]

The Miss Lil' Bitchi's boost pressure typically runs at a little under nine PSI under load, which suits me just fine. I have heard from more than one mechanic that eight or nine PSI would be the optimum, for if you set the PSI higher ~ it spins faster but the collection of air is less.

Falco.

[lrp374]

I think the boost level most people run is to low and results in excessive EGT values. I have been running a typical maximum of 15 psi and occasionally if I need it up to 18 or 19 for the last 50 000 km. I know some on this site have the boost maximum of over 20 psi. If I can maintain 15 psi the EGT values never go over 950 F, as soon as the boost starts to drop due to loss of RPM the EGT will climb quickly. I can't imagine going back to 12 psi boost.

[TieMyShoe]

hmmm... I can't get anything more then 6psi out of the thing.... The waste gate is not opening, exhaust colour is mildely black indicating I am not running lean... Turbo is new... No boost leaks... Why am I maxing out at 6psi?

[TieMyShoe]

Well as my engine hit 1000KM yesterday boost dropped down to 1PSI... lookin like my new turbo is faulty..

[TieMyShoe]

update. A while ago I posted a thread about a squeal that I couldn't find the source of. Every time boost came on the squeal would appear. I fixed all the exhaust and intake leaks, blocked the egr and even disables the pop off valve. No luck. So i figured it had to be the waste gate. After boost hit zero psi last night I decided it was time to pull the turbo and get it warrantied... However before doing that there was one more thing to try. I pulled the exhaust at the down pipe and fired the van up. Foot on the brake, loaded up the engine and low and behold the boost guage jumps to 8psi.... So turns out the exhaust was so restricted it was stopping the turbo from spoiling at all, and the squeal was due to the exsesive back pressure.

Van is now sporting a side exit 2.5 mandrel bent system with a magna flow 20" muffler. Still 4psi short of where it should be... But steps in the right direction.

[TieMyShoe]

and two steps back.... Back down to 3psi as of this morning... Since then I have replaced
Waste gate actuator
Fuel filter
Air filter
Fuel injectors

I loath throwing parts at a car but I can't for the life of my diagnose this!

I am pulling my hair out now... This doesn't make any sense! van has zero power, but hits max boost at 3/4 throttle... so if it were a fuel issue in theory it should still make more boost. Turbo is new less then 2000km on it... Actuator is used but known good... The old one was damaged... There are no exhaust leaks and no intake leaks... i starting to think the only good solution is pull the plates and insure my datsun....this is no longer fun...

[yojimbo]

Right so, I would check the wastegate is free to move, to rule out it being stuck open. Also, I would check the injector pump, because actually you could have a fuelling issue. The turbo makes more psi as a product of the fuel being turned into gas, so the amount of gas you can make dictates the amount of spin you can get out of the turbo. The turbo supplies boost to the top of the pump where it presses on a diaphragm to increase the fuelling as boost increases, for a given throttle position. A fault there could cause some problems, and so could a blocked fuel or air filter come to think of it.

[yojimbo]

Oops, just read you'd done the filters! Blocked fuel line?

[TieMyShoe]

what confuses me about the fuel is at 3/4 throttle the van hits 3psi and stops there... However if I pish the accelerator down more the van make more power meaning it must be injecting additional fuel... So why doesn't the turbo boost?

Waste gate moves free, I even tried to wire it shut... Here's another odd thing... I pinched off the waste gate "vac" line and boost climbed to 5 psi... Yet wired shut it still only made 3.

Fuel lines were blown through with compressed air, they seem clear.

[TieMyShoe]

what is the procedure to test the boost compensator??

[Growlerbearnz]

I'm sure there's an actual procedure to test it in situ, but if you remove the top cover the diaphragm is clearly visible. Look for any holes or splits.

(If you're going to remove the diaphragm, mark its position first- the cone shaped pushrod attached to it is eccentric, and replacing it in a new orientation will change your on-boost fuelling).

I once lost all boost when the small hose between the turbo and the compensator popped off, could it be that you've got a leak in that hose? Or if you've teed your boost gauge into that line, is there a leak in the boost gauge hose? Those hoses are often a push-on fit and can come loose- I now have cable ties acting as hose clamps to hold them in place.