fuel cut boost cut knock sensor bad rpm miss?

[gtlegacy]

ok so today the first lap i did on the track i got a real weird cut im not sure what it was it seemed to boost up and then just cut out and have 10psi and reset it and it would do it again a lap later im not sure if it was a miss or a cut as did it about 5500- or when the secondary turbo got going? (also a little whiney on boost but goes fine)

so i chnaged the knock sensor and it definetly made a difference but still had the problem but not as bad

it was about 23degrees when it first started to do it was cold later on in the day so it seems a bit weird

i have never had this problem before and i drive my legacy pretty hard it has a prova ecu vf20 vf27 rage downpipes and centre and 2.75" diff back desnorkled intake i also put a 2mm spacer to preload the wastegate a little to help the higher rpm boost drop off it usually runs about 12-13 and 18-19psi primary and secondary

the knock sensor i fitted was another used one should i buy another new one?

over the entire day i didnt get any check engine lights and was running 98 allday i have a walbro 500hp pump if it as dying would this happen?

[gtlegacy]

also should mention i gave it a boost on less than 1/4 of a tank the other day and it did the exact same thing

i was told that the higher pressure pumnps dont like to be run dry could this be the problem now its happening more and more and on the oad even

mainly happen around 17-18psi and above but never ever had a problem before even when constantly boosting 3-4minutes

[Durty-Sanchez]

Was it consistantly at 5500rpm? If not then check the error codes again using the under-dash connectors.. the AFM code might come up. If it was consistant then you're probably hitting the boost cut..

[gtlegacy]

it was more as the secondary spooled up around 17psi aye someone else has alos said this but i have previously hit 19pis and 20psi and never got boost cuts

[Durty-Sanchez]

One cut is load based, so if say your "load cut" is 90% then if the load on the engine (as calculated by the ECU) exceeds 90% it will cut out. You might be at 20psi in 2nd gear and the load will be at 70% - you're fine. But if you're at 15psi in 5th gear you might hit 92% load, and it will throw a cut in. In any case, I would say that if it is a cut then it's the ECU protecting the engine, so i'd leave it there..

[log1call]

That's an intersting bit of information Sanchez, about the load cut I mean.

Where did you get that information and do you have it in print that I could get off you? I'd like to have a read if possible.

Cheers.

[Durty-Sanchez]

It's all in the firmware.. it calculates the load based off rpm/airflow, then makes corrections for manifold pressure. The cuts/failsafes kick in if manifold pressure is too high, if the load values are too high (i.e. reach the limits of the map or the load limit), if rpm is too high, or speed is too high.. those are the only cuts I can remember finding but that's from the top of my head..

[log1call]

Oh Ok. I think I see. So it's not strictly a load limit but just when the MAP is too high for the fuel map and the fuel map is related to the load calculation. So it's a defacto load cut... makes sense.

I have read all the diagnostic charts and the trouble code setting criteia for heaps of models but I had never clicked to that connection(load to fuel maps).

There is always something new to learn!

Cheers.

[gtlegacy]

ok so what your saying is that it could be a load cut? as i would do it rear bad onto the straight at ruapuna but would also do it top of 2nd gear out of the dipper

i also did a battery reset and the car seams fine now but will back boost down a little bit

[gtlegacy]

has anyone had anything similar? it seems really weird to me that changing the knock sensor could make the problem different as first it seemed to almst go onto 3 cylinders when the cut came in but after then it was more just a miss or similar to cold hesitation might change back to factory n see if that makes a difference

4g rsb ecu and factory exhaust with cats no preload on wastegate and see how i go

[gtlegacy]

chnaged the fuel pump and it made no difference and it happens in any gear at around 16psi

[Guest boostin]

Close up the gap on your spark plugs. Mine had a miss like that, and it was too much boost blowing out the spark. I closed mine down to 0.65mm from 0.8mm.

[gtlegacy]

oh ok but the weird thing is that it never missed like that even when i raped it hard and its just getting worse and worse like down to 15-16psi when it was doin 19-20-psi easily

[gtlegacy]

i just took the 2mm spacers i had between the wastegate actuator and the housing to preload the wastegate out and it boosted to 16psi fine with no hesitation it is 21degrees at the moment in it position that when the boost comes up that the wastegate is trying to control it but cant so it puts a cuts the motor out?

i also should mention that i still have the factroy boost pill in

[gtlegacy]

still does the miss but about 17 psi will gap the plugs tonight