Boost Problem

[plebian]

All,

Hoping the forum can help me as I've exhausted many avenues?

Have a issue with my R33 GTST no delivering under boost, any boost that is.

Symptoms are:

-Very noisy when boost pressure becomes positive (induction type noise)

-No power (timing retarded)

-Struggles under load

-Have measured AFR while on dyno and mix drops to 10:1 before the fuel cut kicks in (boot pressure variable)

-Very poor fuel economy

Work done so far:

-Replace faulty coil packs with Spitfire coil pack

-Replaced air filter

-Cleaned AFM (though should be self cleaning)

-Replaced various vacuum hoses

-Wound down the aftermarket BOV to minimum

-Ran fuel injector cleaner

-Had mechnaical inspection

Any ideas much appreciated, thanks.

[paulr33]

could be a fault with the turbocharger or could be stock ecu taking out timing and dumping in stacks of fuel from picking up detonation. drop the exhaust and see if the exhaust wheel is ok. could try factory ecu reset.

[plebian]

Thanks for that.

I reset the ECU occasionally, have even done an ECU diag and get the all clear "55".

I'll have a poke at the exhaust on the weekend, have always wondered about the condition.

If the ECU is overcompensating for something, which sensor could be faulty and not register in the ECU diag?

The condition is intermittent, though strongly biased towards the bad. On nice cold mornings the 'behaves' itself, tourqey and responsive when the boost is wound down to factory. But crack it open a little and problem repeats. Anything load related sets it off, passengers, A/C, warm/hot day.

This is why I suspected the ext. BOV? Tightening it only gave me temporary relief.

A number of forum article say this is typical of BOV faults, something amount accounting for the air flow, but I don't understand what sensor is causing the overcompensation?

Frustrated....

[paulr33]

the factory ecu has excess airflow protection, when you turn the boost up you will hit the limit. it will retard itself and dump fuel to protect itself. keep below about 10psi. no sensors will be faulty, it could just be the knock sensor picking up lots of detonation, so the ecu retards and dumps fuel (again to protect itself)

it sounds like your hitting excess airflow protection

[plebian]

What I don't understand is this fuel cut will occur at or below stock levels (~2-5 psi).

I used to run 12psi quite comfortable until the last winter trasnitioned into summer and the boost limit slowly dropped, but again recovered on cold days.

What other symtoms would a worn turbine exhibit?

many thanks

[paulr33]

squealling

coughing n farting

jack all boost being made

usually nothing above 0 on the stock guage

[plebian]

hmmm, none of that. All audible noises are ok except when boost is positive, becomes loud as if boost was bleeding from the manifold. Also plenty of boost comes on quick, just doesn't translate to power but!?!?!

Is the turbine still worth a look?

You mentioned detonation before, isn't that rather nasty to happen? Could my knock sensor be faulty?

Can't help but feel there is a simple yet elusive answer. There is nothing obviously broken, as revealed by inspection.

Thanks again for the suggestions.

[plebian]

Okay, finally got to the inspection, and the turbine wheel spins freely. I tested and cleaned the O2 sensor at the same time. I manually pushed the swing valve actuater rod to check for resistance or play, I couldn't detect any, though an air gun would be better.

A test run proved interesting. Though 'nothing' had changed, and the O2 sensor would not affect performance under load, the behaviour was different. I'm getting the same retarded response under boost, but now I don't get the fuel cut anymore, it hits the factory boost limit (~7psi) and stays there.

According to the Nissan workshop manual says a faulty swing valve will be a 'high cause' or 'no power/accleleration'. There is no suggestion on how to fix it, except that the vacuum hose might have a leek.

[plebian]

Have discovered the fault to be a crack in a hose, that connected the intercooler to the inlet manifold. However given is was right on the frame, the crack was not visible until the intercooler was dismantled from the housing. Very simple in the end, and all the symptoms make sense in hindsight.

Thanks again everyone.