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1998 Forester S turbo AT Auto 4eat
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4 Posts
Discussion Starter #1
Hi Folks , hope someone can help . hopefully not bumping an old thread . I have looked but carnt find one .

I have the following problem with my 98 Forester S turbo ( european model) with 4eat trans. pre OBDI . km stand at 198.000
for about the last four weeks : prior to the problem below i had a fuel pump go dead on me whilst driving , this was replaced .

Car randomly looses power under acceleration & or a trailing throttle , this can be whilst overtaking , pulling a way from lights , junctions or under hard full throttle conditions , it some times happens under part or trailing throttle , no CEL given . some times its a full stall , other times its a drop in power , not matter what you do with the throttle it dies for a few seconds then sorts its self out .

engine starts fine , idels fine and runs good both cold and hot . problem seems to be in open loop only , once warmed up ??

the following have been replaced with in last two weeks to try to sort the problem : new fuel pump , new fuel filter , new Mafs , new TPS, New Cam & Crank postion sensor , new air idel valve , new fuel pressure regulator , new coil , new plugs and leads , new air filter .
ecu has been reset also .

had complet oil change in trans , both diffs & engine oil and new filter 1000km a go .

due a cam belt change at 210.000km

i am at a loss as to the cause of the problem , might have to call in on the local (50km away ) subaru dealer to plug their subaru select monitor.
hope some one on here can help??
 

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2000 SF5 Automatic
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446 Posts
You've covered most of the quick things to check. How are your vacuum tubes and clamps?
Maybe do that cam belt change early?
Sent from my SM-J700F using Tapatalk
 

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1998 Forester S turbo AT Auto 4eat
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4 Posts
Discussion Starter #3
Hi thanks for your reply ,
sorry for the delayed answer ,
I have checked the vac pipes and there appears to be no leakes or split hoses .
No leaks at inter cooler or Y pipe ( running complet alloy Y pipe + silicon hose .
no leaks at throttle body or intake from air filter housing to turbo .
no leaks from turbo to intercooler .
No leak at BOV either . but the BOV is original so now done nearly 200,000km but seems to be working ok .
no leaks between turbo and OEM boost controler / and or intake manifold

no build up of carbon or deposits in throttle body, inter cooler shows on very fine film of oil on inside fines , also very clean too.

The foz shows an indicated boost of max 0.5 to 0.55 bar at wot , pulls well , holds boost .

At trailing or closed throttle shows vaccum of -0.6 to -0.8 bar again constant , no loss .
same bar at idle .

when the stumble ocures there is no loss of boost if under wot , just no throttle responce for a few seconds , if under trailing or closed throttle no loss of vaccum , again this causes stumble or complet stall if slowing down at lights ect .

But Foz starts . idls and warms up normally , once warm idles at 7 to 800 rpm , nice and steady .
looks like i will be starting at the fuel pump and working my way forewards again ,
but Im still at a loss to what is causing it .
 

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1998 Forester S turbo AT Auto 4eat
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4 Posts
Discussion Starter #5
Up Date , to day i carried out the following checks :

the vac pipes/ hoses and there appears to be no leakes or split hoses .
No leaks at inter cooler or Y pipe ( running complet alloy Y pipe + silicon hose .
no leaks at throttle body or intake from air filter housing to turbo .
no leaks from turbo to intercooler .
No leak at BOV either . but the BOV is original so now done nearly 200,000km but seems to be working ok .
no leaks between turbo and OEM boost controler / and or intake manifold

no build up of carbon or deposits in throttle body, inter cooler shows on very fine film of oil on inside fines , also very clean too.

The foz shows an indicated boost of max 0.5 to 0.55 bar at wot , pulls well , holds boost .

At trailing or closed throttle shows vaccum of -0.6 to -0.8 bar again constant , no loss .
same bar at idle .

when the stumble ocures there is no loss of boost if under wot , just no throttle responce for a few seconds , if under trailing or closed throttle no loss of vaccum , again this causes stumble or complet stall if slowing down at lights ect .

But Foz starts . idls and warms up normally , once warm idles at 7 to 800 rpm , nice and steady .
looks like i will be starting at the fuel pump and working my way forewards again ,
but Im still at a loss to what is causing it .
 

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MY05 Forester 2.5 XT 5MT
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2,740 Posts
I would be looking at getting the injectors ultrasonically cleaned and flow tested. Then checking electrical connections to the pump, injectors etc
 

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04 FSTi Manual
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681 Posts
I had a similar issue recently although it did give me a check engine light and code (can't remember what it was, but it was saying to check the throttle body). Turned out it was a faulty sensor on the accelerator pedal. the garage cleaned it up and reconnected it and it seemed to work well afterwards but I got a new assembly fitted to be on the safe side because i didn't like the idea of the problem coming back halfway through an overtake.
 

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1998 Forester S turbo AT Auto 4eat
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4 Posts
Discussion Starter #8
Thanks for all those who took the time to reply and offer advice , great .
Good news traced the problem to the kick down switch mounted on the accelerater pedal , it had stuck open giving false signals , so causing the problem as reported .
New one ordered and fitted . a 15min job , unbolt complet throttle pedal .
release throttle cable , disconect elec conections , measure old kick down switch fixing bolt distance on threads . set distance on new kick down switch and remount in reverse order of disasembly. check kick down switch is operating with in tolerance as per service manual . start car and check throttle works . test drive .
So fingers crossed , took car for 30km test drive over various types of roads , including a blast on the local autobahn , then a slow cool down run home , so far good , no sign of the problem and the foz now drives a lot better , more responsive to throttle inputs at all speeds and goes like a scolded cat at WOT .
 
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