spoilr

Wondering if I can get some opinions on the following boost problem.

Car drives well and boosts to 16 - 17 psi most of the time, occasionally boost levels under full throttle drop to 10 psi.
This usually occurs after a short drive.

There is no pattern to the boost drop and when it happens it remains like this for a short time (1 - 5 mins) then boost returns to 16 - 17 psi.
Problem reoccurs every 10 mins or so, you can never tell what boost level will be achieved.

Mods are:
Ecutek 2 / Vf 34 / 3 inch turbo back / APS cold air.

Have tried the following so far with no success:

Cleaned air flow meter with contact cleaner
Cleaned air filter element
Replaced standard boost controller
Replaced ECU with another Tek 2 unit
Turbo is brand new and problem existed with std turbo as well.
Cleaned boost hoses with contact cleaner and compressed air.
Car has just completed 100,000 kms.MY00 wrx.

Appreciate any suggestions.

Thanks

nom

It's the APS cold air thing.

It causes the MAF to misread (the ECU thinks there's less air coming in than there actually is) and hence doesn't throw enough fuel into the mixture. This lean running then causes det. The ECU is panicking about the amount of det occuring. It's reducing boost for safety and is doing exactly what it should!

If I were you I'd remove the APS air filter ASAP before it does anything bad (and that can be really bad & expensive), then either not use it any more or get the ECU reprogrammed for the different airflow the filter creates. Looks like it might be an idea to get the ECE remapped anyway with that little lot!

In the mean time, try to not go over 7-10psi - should reduce any chance of bad things happening!

john banks

Agree with nom this is most likely. APS induction with 550 injectors produces sensible AFRs on a map designed for 440s. Your fuelling will be much leaner and the timing more advanced. With a bigger turbo you need to usually map in less advance if you are using it properly. You need to either remove the APS or get your ECU custom mapped, or your engine is likely to det itself to bits. A knocklink would tell all, and I would expect you should be able to hear it detting if you know what to listen for.

A bigger turbo is better suited to a standard ECU rather than a Tek 2. Having spent hours fiddling with similar components to those you have fitted I think your engine is in grave danger.

spoilr

Thanks for the replies so from what you have both said would you say this would be a sensible approach.

Source 550 injectors and turf the 440's
Have the car dyno tuned and go for a custom map on the Tek 2 turning it into a Tek 3.

Would you advise a fuel pump upgrade at the same time??
In regards to the aps cold air is it suitable once these extra mods are done or is there a better option?

nom

An upgrade to the fuel pump is always a good idea

The APS cold air kit is a good kit, it just changes the pattern of air flow over the MAF sensor meaning that it screws the mixture - if using the standard map. Once the map is adjusted for the kit, it's fine.

Jamesn

I seem to occasionally get a boost cut when the revs have been 3-4K for a fast roundabout in 2nd, then floored for the exit.

My car is a standard UK turbo wit ITG and Scoobysport back box.

I seem to get this when not paying attention to the revs, but i am sure taht i am not near the redline.

I have driven the car at full throttle a few time watching the RPM's, and it does not happen??

Any ideas?

There is like a small pop and the car feels like it hits a brick wall as far as the power is concerned?
I have also noticed that some times i do not appear to get full boost in 2nd if the RPM's have been fairy high prior to flooring it- just when you need the power to overtake


thanks,

James.

john banks

Fuel pump and Tek 3 is your best option. 550s will not sort out the excessive ignition advance on a Tek2 with a VF34!

spoilr

Ok, Tek 3 and fuel pump.

Appreciate the advise probably just saved my engine.


Thanks


Peter.....

john banks

And don't use any boost meantime IMHO.

James you are probably getting fuel surge. Happens just after a high g low speed right hand bend/roundabout usually.

Jamesn

How does one avoid this?

This is crap, how are you supposed to use the cars performance- how can you overcome this

James.

john banks

How much fuel was in it at the time?

Jamesn

Probably about 1/8 to 1/4 of a tank.

James.

Kempo

James

There have been similar threads to the problem you describe - holding revs in 2nd at 3 - 4k then flooring (like when overtaking a tractor / car scenario). Apparently the ECU believes the engine is being tested so goes into a mode that limits boost.

The suggestion is to change the revs / gear prior to the manouvre, although going round a roundabout kinda prevents this! Try search for overboost and you'll find some examples. I think mutant_matt put forward the diagnosis, but I could be wrong.

Paul

john banks

It may be that you are getting the half boost thing and/or fuel surge?

Fuel surge can be avoided by always keeping over 1/3 tank, this may be overkill. The half boost thing is at about 3000 RPM in second gear after steady throttle for a few seconds - this should just produce less boost boost but still be smooth and not feel like a fuel cut. A boost gauge would show 8 or so PSI or 0.5 bar during this.

Jamesn

John,

Thanks,

I have seen the half boost thing at time, is this normal operation?
The boost / fuel cut I will have to try and avoid with more fuel in the tank.

James.

john banks

Yes, for noise compliance. It triggers in this situation to meet legal requirements as these are the conditions for the test.