tom991981

Hi everyone,

Got a bit of a long standing problem that has failed to be diagnosed previously. Need some options to check ...

Car:
1994 Version 1 STi import
Sports Cat (Japspeed)
HKS Green air filter

Symptom:
Under WOT Boost peaks at a very steady 16psi according to my gauge. Fairly often however during acceleration between 9psi and 16 psi, it can suddenly drop back to 9psi and will not go any higher. If I drive on for a bit off boost, 50% of the time 16psi will be available again, other times not. Othertimes I don't have a problem. I have no other running issues at all.

So far I have checked my boost lines for any obvious leaks but not seen any. I did spot a leak between the lower end of the up-pipe and manifold which I have sorted, that did not fix this issue however.

I am at a loss as to what is causing it... is there a list of items in order to tackle to try and sort it or some likely sources of the issue?

I have Evoscan and a cable is on the way...what params are should I be looking to log?

Any ideas?

morandpeter

iTrader: (5)

i had the same sort of problems with mines, boosted fine at 1.1 bar then would drop to 0.5. tried looking for split hose etc. turned out it was detecting knock/det hence dropping to 0.5 bar.

turns out after a couple of tanks of optimax, then nothing but optimax boosted at 1.1 bar all day long.

what fuel do you use? hope that helps

P1Drifter

iTrader: (7)

try to clean the boost control solenoid, its on the drivers side suspension turret, have a search round for pics if you need them. one other thing is your ecu chipped ? just 16psi sounds a bit high for a stock ecu

tom991981

I did think this might be the case, I generally use V-Power. I used Esso 98 octane the other day on a long run to Belgium and noticed it was still happening. I *thought* using a lower octane had helped but to be honest I think my results are mixed.

How could I tell whether I am getting knock and what causes it? Too high an octane rating or too low? How did you diagnose the problem?

tom991981

I have one of MajorSarcasm (from here) ECU chips that is supposed to be mapped to this psi rating specifically for the STI V1. The issue did not coincide with the addition though. I ran the chip on Surrey Rolling road and the original SA jdm ECU and Charlie strongly recommended I go with the the chipped ECU as it gave 0.1bhp less performance but a much better A/F curve.

I will clean out the solenoid, I have done this a couple of years ago, it clicks freely in diag mode and does not throw a code.

I think its detecting knock or something similar and pulling boost but I am bu99ered if I can find out why...best way to diagnose if this is happening?

morandpeter

iTrader: (5)

all i did was put in a half tank of morrison crap and within 30miles the boost retarded. In basic terms low RON rated fuel is bad : )

see my thread from a few moons ago

https://www.scoobynet.com/scoobynet-...d-at-last.html

tom991981

Interesting. I actually thought it might be doing the opposite, i.e. too much octane after reading a few threads some people suggest 97RON on these only... I have pinged MajorSarcasm... wonder if he will see this with his ears burning! Lol! I have no issues with the chip BTW, safer than the crazy map that it came with... tested on RR as well.

Is anyone an Evoscan Pro as well? I might want to bend someones ear about how to use it and get the most out of it...

P1Drifter

iTrader: (7)

pretty sure the ecu pulls timing not boost when det is detected ?

westy94wrx

yeag P1DRIFTER im sure the ecu pulls the timing not the boost i dont think it can do anything to the boost itself

morandpeter

iTrader: (5)

if it helps the OP i have a polar performance chip on my car which is pretty much the original version of major sarcasms one. the pp chip was supposed to handle a lower RON rating i.e 97 but using 98 ron stuff just produced the 0.5 bar boost. I don't know why 1 ron makes the difference but it does.

try running a couple of tanks of v power then on a full tank use an octane booster, i found that the car was amazing when i did this, pulled smooth and hard all the way.

my friend has a MS chip and he's found no fault with it. when you get your rom raider just track the knock level on crap fuel, log it then track it on v power. What you'll see is a LOT less figures lol..