dale_b_type_r

Hi all

I've just purchased a 1995 Impreza Wagon WRX 1995 to tow our trailer and race car to race meetings/shows etc Overal great car more than capable with the job in hand.

We have a slight problem with boost hesitation and sporadic boost pressures bare with me here are the main problems/questions:

1. Boost was supposedly set at 1.1 bar, not by the previous owner so can’t ask. I can’t find any type of manual or electronic boost controller. All I can think is that it’s either running 1.1 bar via the actuator without fuel mods (would this cause hesitation) or it’s running one of these chips that I have seen on group buys and ebay for £200.00 odd that raise boost to 1.1 bar and alter the ignition timing. I need to ascertain how it’s running this boost as it affects the problem and solutions!

2. She hesitates badly on boost, wasn’t too bad when we bought but has got worse. Boost used to go to 1.1 bar but not anymore. If you part throttle you can avoid the hesitation, over 5500rpm it’s not as bad seems to be lower down. It only happens when the boost goes over 0.6 bar, the car really stutters/misfires. Sometimes the boost is restricted to 0.5 bar (maybe a safety mode?), when this happen there is NO hesitation. Sometimes it boosts to 0.5 bar in all gears, slow but NO hesitation, sometimes only 1st is restricted to 0.5 bar when you are quick on the accelerator and in the other gears still tries to boost above 0.6 bar so it hesitates.

3. I’ve never really seen it running 1.1 bar apart from when the old owner took me out, wasn’t that bad only a slight stutter then and went well. Now the stutter is massive hesitation. Boost wise it’s either restricted to 0.5, or if you feather the throttle past 5500RPM it runs maybe 0.9 bar on WOT seems to be random and based on the hesitation.

4. We contemplated running less boost to see if it went away as we get no hesitation at low boost, this is why we need to know if there could be a chip in there. Running 0.7 (stock boost) with a chip would mean over fuelling as they are designed for 1.1 bar and won’t counteract the reduction on boost. We don’t know if it does have one purely speculation but seems to be too much of a coincidence that it’s running 1.1 bar and there are chips that let you run 1.1 bar for the classic scoobies. Unless it’s literally running 1.1 bar without fuel mods surely no one would be stupid enough to just raise the boost!?!

If it’s not the chip causing the problem then it may be boost related, is there a fuel cut? Don’t think it is fuel cut as you can still feather past 0.7 bar at times. If it wasn’t a dodgy chip then it could be a number of things: MAF Sensor, Idle Air Controller, Coil Packs, Plugs, Leads. I have heard of people changing plugs, re-gapping to 0.6mm with the problem going away for a week but coming back. Seems to be a million and one problems like this on the older scoobies. We’ve un-plugged the MAF while the car is running and it stalls which indicates the MAF is working. One thing I forgot to mention is that Idle sticks a little on start up at 1200RPM, when you touch the throttle it returns back to normal but this could possibly be an Idle Air Controller problem, could this cause the hesitation described? The car runs the stock BOV and an aftermarket filter, worth changing back to the stock OEM setup?

Rather than just throwing money at her I’m trying to research all common problems first so I can get it right from the word go. At £250.00 + VAT for a new MAF sensor parts are not that cheap so want to discuss all ins and outs on here first. I forgot to mention it also smells fuely when your put your foot down, as it's part throttle (full throttle causes hesitation) say 0.7 bar I think it's running rich due to this chip as it should be 1.1 bar but again all speculation I have no idea if it's running a chip!

We just really need to get this sorted before we start towing any help is really appreciated! Are their any Subaru ONLY specialists down south?

Best Regards,

T

bigdyl69

My 96 turbo wagon has a very similar problem that has been driving me crazy since I bought it, although the t**t I bought it from didn't warn me about any of the problems with it so I've been seriously stung.

Mine behaves the same way, I changed the silly aftermarket cone filter for a standard air intake setup using a green cotton filter (often referred to as a decent choice), I removed some nasty manual boost valve and replaced it with a new 3 port boost solenoid, changed teh plugs and oil, fitted a new thermostat, water pump and cam belt and also had a Walbro fuel pump fitted and none of it has really made much difference.

Other than taking it to a specialist, which I cannot afford now as the car has cost me a small fortune to do so far, I have no idea what else to do. I have thought about trying to adjust the turbo myself but I really cannot afford to do any more damage.

Is this sort of behaviour common on the pre facelift classics or are we both just terribly unlucky?

Clarkee

It might be your Knock sensor?? I had a similar problem about three years ago with mine, hesitating and misfiring - have you tried seeing if you've got any fault codes coming up?

bigdyl69

I tried putting mine into diagnostics mode using the wiring in the steering column but couldn't get it to do what it was supposed to

dale_b_type_r

@ bigdy - I can feel where you are coming from. What boost are you running mate and do you get the hesitation at the same boost? Before it was only a stutter now it feels a lot more agressive. Do you know if yours is running one of these "Scooby" chips or is the boost stock on yours? I can't believe someone would run 1.1 bar without modifying the fueling maybe it's best for us to get them on the dyno to see what is going on.

From what I can see this is a pretty common problem with the older models and not sure if diagnostics will through up the fault but worth a try. I've seen people replacing MAF Sensors, Idle Air Controllers, All Coil Packs, Plugs (seem to be short lived), leads etc. It's odd as at 0.5 bar it feels really good, granted not that quick but no hesitation an engine sounds good. Only after 0.6 - 0.7 bar really it hesitates and smells fuelly. Alsmost feels like a misfire.

@ Clarke - Thanks for the input mate. It's possible as if there was no fuel mods with 1.1 bar it would soon knock and detonate retarding the boost but it only seems to reduce it sometimes, would the engine light not come on if the knock sensor was triggered? I also can't believe that someone would do that, I stumbled across these chips that raise boost to 1.1 bar and sort fueling so it made me think that this could have one. Dyno would be a good idea at least we can see what the fuel maps look like and how consistent it is to stock levels.

Diagnostic test would be a good idea is there a tutorial somewhere? If anyone has any information on the above it would be great as it seems a few out there are suffering from this problem!

Cheers lads,

T


Edit: Jus found this thread:

https://www.scoobynet.com/general-te...der-boost.html

Doing as much searching as I can. Guy has a classic Wagon like us with a similar problem, thread didn't go far but I did spot he was running some sort of ECU chip wonder if it's related. The newer WRX's seem to have week MAF sensors but from what I can see the older ones seem to be good, worth checking regardless and the sensors are not too pricey cost wise.

bigdyl69

Mine seems to boost nicely, albeit not that aggressively, if I lift my foot up slightly when accelerating. If I keep my foot planted, as you would do if you wanted decent acceleration, my engine sounds like its getting choked up. I will be changing the coilpacks and plugs at the next service (ie as soon as I get paid) but I feel this is a silly problem as I have done nothing untoward to the engine. All I've done is put it back to standard as best as possible. But what I don't understand is how it chokes itself up, sounds like there is back pressure building in the exhaust but I have a 3" all the way through cat back on mine, when I put my foot down more.....very strange car

bigdyl69

Oh yeah, I have no chip on mine, standard ecu as far as I know and I have tested my MAF but that seems ok too

dale_b_type_r

Do you know what boost you are running do you have a boost gauge? Just trying to determine if it's happening around the same point as mine. Mine should be running 1.1 bar but need to ascertain how it is, I can only assume it has one of these chips as their is no mcb or ebc unless one of the previous owners has raised it via the actuator without fuel mods, I would like to think doubtful. If it is chipped and I reduce boost it could run pretty rich although for some reason under 0.6 bar ish there is no hesitation.

Like you I just want it to run standard boost without hesitation. If it is chipped then the problem is probably either the MAF, IAC, Coils, Leads or plugs. If it isn't chipped then it could be as simple as overboost, not enough fuel or fuel cut thats all I can think of really.

The ECU is stock, apart from chips and different fuel controllers/piggy backs which it doesn't have I can't see how else they would run 1.1 bar. A dyno will show if it has been chipped I guess.

Coilpacks are not that cheap though either I think around £500.00 for all four? I will check the obvious things first like plugs tomorrow hesitation is really nasty though.

T

bigdyl69

I think mine hits about 0.7 bar but not 100% sure on that, I'll try it out tomorrow on the way to work and let you know tomorrow afternoon. I think once it hits boost if I ease off the accelerator it will go ok but not as aggressive as it should be. I think I need new coilpacks but I've been looking at these ones on ebay as I was quoted 140+vat from my local subaru dealer for one!!!!

dale_b_type_r

After doing a lot of reading the coil packs on the older cars seem to be a big problem and often fail. Re-gapping the spark plugs seems to cure it for a while but the coil pack seems to be coming up again and again in old posts that I have searched.

Are those coilpacks aftermarket? You know how they say if you pay peantus you get monkies that would be the only thing holding me back really although OEM are not that cheap at least you know they are tried and tested.

I did see some uprated aftermarket ones in Banzai for around £400.00 but can't find the article. Are you going to replace coilpacks next, will more than likely do mine just not sure which ones to get at the moment.

Thanks,

T

bigdyl69

I think they are aftermarket but considering the price of originals and how much I've spent so far I'm gonna have to go for a cheaper option. The majority of the hesitation on mine seems to be when its boosting. The coilpacks are the next thing to go on mine but I need to get the money together to do it at the same time as oil and plugs