boost at high speed problems.
 

Posted a thread earlier but didnt get much of a response so here it goes again. Ive got a 94 wrx and it runs fine all day long, but when going fast top end doing about 120mph in 5th at around 5500-6000 revs the boost wont hold and drops off pulling back my car and throwing me forward, then builds up just to do it again! when i slow down its fine and the boost holds in any gear. I found this while going for a weekend drive out of town but like i said while driving at a steady 70-80 mph along the motorway (or any other speed steadilyfor that matter) it was fine and only does this when trying to achieve top speed. (which i dont do often but have just recently got the car and wanna see what it can do:rolleyes: )

please can anyone help as ive read alot of threads and it sounds like it could be a number of things of which im still no further forward! thanks for taking the time to read this.

fuel cut perhaps.

fuel cut

Mine did the same, did some searching on here and looked like it was the boost solenoid meaning it overboosted and the ecu cut the fuel.

I took the pipes off the boost solenoid and sprayed carb cleaner through them, did the same to the solenoid, i connected the green plug under the dash board first to make it start working and sprayed into the top holes until it ran out clear. Alowed to dry, sprayed a bit of WD40 in, replaced pipes, ecu reset, and its worked fine ever since. It doesn't overboost now.

Do a search on here and you'll find a more detailed instruction.
It was really easy to do as i have no mechanical knowledge.
Hope it helps
Matt

If it's surging rather then a violent cut, then it's not fuel-cut, but its due to the boost duty % being too high for the target boost.
this is most noticable in high gears at high speed.
The car tries to over-boost so the ECU pulls in the duty to drop the boost back down, but it pulls in too much then advances it again, hence giving the surge.

I suspect this may be due to a decat and/or the restrictor being missing from the boost control solenoid return pipe (maybe due to the fitment of an induction kit and some silicon boost hoses).

If the restrictor is still there, a solution would be to slightly reduce the hole size in the restricor (i.e fit another and re-drill smaller)
Or
Extend the actuator rod by a turn or 2.

but too be honest if it only does it at 120mph...that would be the least of my worries

Sounds like speed restrictor to me :wonder:

thanks for the input guys but done another top speed run (oops naughty me :D ) and it kept backing off at round 112mph so im guessing its still restricted??????:wonder:

yep, well i expect you did your run on a 'private track' though;)

very private indeed thats why i shall not and will not give out the directions or area code :lol1:

Yes that will be a import for ya... Buy a delimiter/convertor for about £50 on a well known auction...:thumb:
Jason.....

Thanks for that i'll get my friend to have a look as im an arm chair mechanic and only know what i read but dont acually know anything:cuckoo: if i had a small amount of your knowledge about my wrx i'd be dangerous:thumb: