Jaywalker

Hi guys I have a 1995 Import WRX wagon with boost problems and need some help diagnosing the problem, The cars standard with the 3 port boost solenoid, The only 2 things I've done is put a decat down pipe on it and a boost gauge, I use Tesco 99 ron fuel

The problem is that the boost keeps going down to .5bar, one minute i start my journey its on .7 bar (standard for my car) boosting fine, the next its dropped down to .5 bar with no check engine light or stored faults on the ECU,

According to the research I've done on here the things I have tried are,

I have tried resetting the ECU and driving around for a couple of days with no boost so the ECU can do its learning bit and after that its fine, boosting .7 bar no hesitation spools up lovely, a couple of days later it drops down to .5 bar with no check engine light, Then the next day i'd start the car drive till warm then its back on .7 bar for a couple of minutes then goes back down to .5 bar,

I have also checked a few things in the engine bay,

The boost control solenoid has been checked by using the green plug under the steering clicks away happily and has been cleaned,

All the pipes from and too the boost control solenoid have been checked to make sure they are in the right places,

The restriction pill is in place in the bottom pipe from the BCS and all the pipes are original subaru pipes with correct length,

The ECU has been checked for faults and reset several times,

The MAF sensor has been cleaned and put back on,

Can't seem to solve the problem, its still doing it, any help from you guys would be very very helpful and will help me to stop scratching my head,

Thanks in advance.

Glowplug

iTrader: (8)

Possibly one of the 3 sensors on the BCS bracket on the way out. The BCS its self which you have cleaned, could try it again by squirting the brake cleaner through whilst in test mode.

The Pressure Exchange Solenoid, on the top, a brown sensor with a black cylinder on the left end, pull off the black cylinder (a filter) and check the pipe is not blocked.

Or the MAP sensor, a black unit on the left of the bracket, has a hose connecting upto the PES. Not alot you can do with the MAP.

Problem with the ECU on the early cars is the parameter settings for the sensors. It usually will not show a fault code until the sensor in question has all but failed. If you can get hold of another bracket with all the sensors on it would ne worth swapping them to see if things get any better. Keep checking the fault codes.

Give all the pipes a squirt through with carb cleaner too.

Jaywalker

Hi and thanks for the quick reply, I have already squirted the BCS while it was in test mode thanks to one of the guides i found on here but I will try it again, I will also give the PES a good clean and the pipe from the map sensor a good squirt of carb cleaner to see if it does improve,

I forgot to mention a few things, when the car does sit on .5 bar the engine seems slow to respond to throttle as if it was holding back and much slower accelerating, so I think you might be on the right line of thought some things on its way out but not enough to register on the fault codes its just finding it and not spending to much money in the process,

I will keep an eye out for a PES and a map sensor or wait until one of my friends buys a scooby and ask if i can try there's lol, is there no way of testing the PES or the MAP sensor?

I also have replaced all 4 coil packs, plugs were gapped correctly and installed and I have also temporarily installed a MBC (now removed just for checking purposes) to check the actuator and it holds .7bar all day long but with that holding back when throttled problem I mentioned earlier,

Thanks again for any help

Glowplug

iTrader: (8)

Not quite so relivent now you have mentioned the holding back.

Trottle Position Sensor (TPS) would be the obvious culprit with those symtoms. But as you say, with out a fault code, it's just geuss work. And can be expensive.

There is always 1 or 2 on ebay, or mattyrb5 on here may have one for sale. £15-£25.
I know of no way of testing the PES or the MAP.


Good, so you can rule those out. It also boost fine with a MBC so it's not a direct fault.
If i was you and i was taking a punt, the first thing i would try is the TPS. Although you might like to try matty again for that as they aren't cheap if not needed. See here.

Jaywalker

HMM thats changed a few things lol, would the TPS be intermitant IE if i reset the ECU it boosts fine .7bar and drives fine with no holding back at all in fact it seems like the car is purfect for a couple of days and then it just goes to .5 and stays there, if it was the TPS wouldnt it be either working or not? or like the other bits intermitant.

PS I just thought the holding back or hesitation was a result of the low boost lol shows how much i know,

Once again thanks for the reply

Glowplug

iTrader: (8)

Like i said earlier mate, it's all geuss work. A fault on any one of the 3 gzillion sensors can cause the ECU to pull the timing or flip into limp mode and cause cr@p running. The sensors in my experience seem to degrade over time, rather that just completly fail in one foul swoop. A rolling road or diagnostic session would help determine the fault. But even these can be inconclusive some times. Bad dog scooby!

Jaywalker

Hi again,

I've taken the pipes off from the PES both sides and sprayed with carb cleaner both appeared clear and clean and will test the car a little later,

My question today is lol, I checked the TPS reading from the multi plug on the TPS I have 4 wires Brown, Black, Red and white didn't know what wires to check so I check them all listed below,

With the earth taken from the brown wire ignition on engine off:

red: closed throttle 5.09v open throttle 0.00v
white: closed throttle 4.73v open throttle 3.86v and fluctuated between open and closed

With the earth taken from the black wire ignition on engine off:

red: closed throttle 5.09v open throttle 5.09v
white: closed throttle 4.73v open throttle 0.85v and fluctuated between open and closed

I have just found after doing all that a diagram and info on checking these values from the ECU plugs, so I'm just having a cup of tea then I'm outside again checking the readings from the switch wire at the ECU, I also noticed on the info from JGM pin-out diagram that there's a reading for the Pressure Exchange Solenoid Valve so while I am there I will grab a reading from that as well just unsure what on and off means in the diagram as those values are in the ignition on engine off box lol

http://www.jollygreenmonster.com/pinouts.htm

thanks again for your help you have at least started me on a journey to fix my scooby and pointed me in the right direction lol

Jaywalker

Right from the ECU pins for the TPS

Closed throttle 4.72v
Open throttle 1.77v

But I worked out that the throttle cable had stretched so after adjusting the throttle cable and moving the mat over I got 0.85v which isn't a mile off the set figures

I also tested the Pressure Exchange Solenoid Valve pin outs from the ECU

Ignition on engine off 11.97v
engine on 13.64

which according to JGM pinout diagram are all within tolerances

So I will try to get hold of a used Map Sensor and PES valve and maybe even the BCS although I have tested my one and try them out.

Glowplug

iTrader: (8)

Nice to see someone using their noodle, makes a refreshing change.

You could also check the Knock Sensor whilst your down there.

bmposer

iTrader: (3)

My friend has a problem like this on a 1996 wrx, we have tested all the sensors and all within limits, changed a few pipes that looked a bit dodgy and tried other bits off of mine but still no closer to finding whats causing it.

bigfarlz

iTrader: (9)

I've had problems like this from day one with my Uk 2000 classic my00 turbo. I tried everything I could think of. Finally got it sorted this week, don't know what sorted it as I tried loads of things at once. I'd already changed plugs, leads, bcs, checked vacuum hoses, maf, got the correct restrictor pill, tested actuator, it was none of these.
Anyhow this week I looked at my lambda sensor and the electrical plug had a lot of oily residue in and around so I unplugged and cleaned with brake cleaner. Then I did the brake cleaner through the bcs while in test mode, took off intercooler and noticed the y pipe underneath was loose as jubilee clip wasn't tight, and also cleaned out the y pipe as it had lots of oily residue inside. Now everything seems fine, I'm awaiting an oem reirc valve to replace vta one just for good measure, and think might buy a Walbro fuel pump for good measure!

Jaywalker

One thing I wanted to ask, when I do aquire the BCS, PES and the map sensor if I change them one at at time will the effect be instant or will I have to reset the ECU after changing each part, The reason I ask is that I would like to change them one at a time just to find out which part has caused this problem lol been annoying me for a while.

thanks again guys for the help

Glowplug

iTrader: (8)

No real need to reset at every change. Just make sure you do after you have sorted it as unpluging may cause a fault to be stored.

Jaywalker

Right guys, I bought a second hand BCS,PES and map sensor off a breakers, I changed them all one by one and took the car for a spin after changing each one and on all three of them still boosting .5bar , I also checked all the part numbers on the parts I was replacing and they were all the same gonna check that 4th one now,

The breakers sent me the whole bracket and I noticed on the back of the bracket that's pictured above there is a 4th sensor with 2 grey multi plugs one going into each side of it does anybody know what that is? I'm going to swap it over now and give it a try to see if it works,

I also did like you said and checked the knock sensor voltage from the ECU multi plug and it said,

Ignition on engine off 2.00v
Engine on 1.99v

On JGM pinout sheet it say 3 to 4 volt on both engine on and off, but I did do this with the engine cold just started it up if that makes a difference (I don't think it should lol) so does that mean a new knock sensor and could the knock sensor cause the low boost?

Once again guy thanks for your patience and help.

Glowplug

iTrader: (8)

OK, i'm not 100% on this, but i think the unit on the rear of the bracket is the 'ignitor'.

Yeah, the KS seems well out of range. If the KS is faulty, it is possible that it thinks knock is occuring and is therefor instucting the ECU to pull the timing which will reduce power and could also limit the boost.

Might be worth doing a reset and code check at this point.

Jaywalker

Just finished swapping the ignitor over but this was the only sensor which had different part numbers on it, not sure if its OK to drive with the other part on but I,m gonna go for a quick test, On closer inspection of the part numbers at the bottom its got i1 i2 G i3 i4 on it looks like some thing to do with the spark so you may be correct lol,

My one had
E1 E2 E3 E4
D05 5717
PBT-GF30
DIAMOND
J714 5206 A
i1 i2 G i3 i4

The spare on had
E1 E2 E3 E4
D05 4Z08 <<<<<<(Different)
PBT-GF30
DIAMOND
J714 4703 A <<<<<<(Different)
i1 i2 G i3 i4

I did do a code check just before fitting the ignitor but after the test drive I will do another code check and then reset,

I will let you know what happens when I get back from the drive, do you know where the knock sensor is located in the engine bay?, If this doesn't work I will buy one thanks again

Jaywalker

just got back no difference so going to put my ignitor back on code check and then reset, I'll let you know what happens next lol

Glowplug

iTrader: (8)

Location of KS:

Jaywalker

Thanks for that, just a quick question I have searched on here but cant find anything that relates to my question,

The ECU reset procedure I've found and done but after you have reset the ECU do you

Drive normally IE: under load, boosting, accelerating fast ETC or do you drive slow no boost for a couple of day?

How exactly do you drive the car after the ECU has been reset?

I do remember reading it some where but for the life of me I cant find it now when I need the Info lol

thanks

Jaywalker

Hi again, I have an up date after replacing the BCS,PES and the MAP and reseting the ecu, drove the car round for the day first few times I put my foot down boosted straight to .7bar and then back down to .5bar lol I'm starting to go a bit grey now lol

So this morning I bit the bullet and bought a Knock sensor from the main dealers £110. lighter, first I checked the voltage on the old sensor then put then new one in and checked the voltage again spot the difference ,

Old sensor
Ignition on engine off 2.00v
Engine on 1.99v

New sensor
Ignition on engine off 2.00v
Engine on 1.99v

So after scratching my head for several minutes I decided to unplug the sensor and check the voltage that was being suplied to the sensor which is 3.3volts (engine off ignition on)with in tolerances but when i connect the sensor to the plug it drops down to 2.0volts,

so the 3 to 4 volts is being supplied to the sensor but it drops to 2 volts when I plug the sensor in

So I have reset the ECU again and I'll have to wait and see what happens in a couple of days,

I did find a thread with a similar symptoms to mine but the problem appears to be the fuel, so I just don't know what to do next I'm lost.

https://www.scoobynet.com/general-te...ecu-reset.html

Any more help would be very very appreciated

Glowplug

iTrader: (8)

Just drive it as normal mate.

Very strange volts on ks, will check mine tomorrow or Monday.

Jaywalker

Hi again,

The car has been ok up until yesterday, thats roughly 13 days boosting correctly at 0.7bar and then it went back to 0.5bar and it wont budge,

One of my friends said it sounds like the ECU is restricting something, so I was wondering if there were any sensors on the car that if they failed the check engine light would not report it,

Sorry I'm grabbing at straws now I've tried loads of things and I dont know what to do now, I dont really want to take it to a dealer as they will charge the earth and not to sure they could fix it,

Any one out there with an Idea what I could try next??

thanks in advance

madscoob

iTrader: (3)

week actuator spring maybe . there is a way of piping it up to run on actuator pressure only , then adjust up on actuator arm until desired boost is reached then pipe back to boost solonoid and see what happens

f4la k

iTrader: (1)

What dump valve is on your car, If its standard, try another standard one, if its not standard take it off and get a standard one to try, I would check all the hoses for a pin hole...

burbling1

iTrader: (1)

I have the same problem o the same car.
So far I havechanged the BCS and MAF but still no joy.
I cleaned the old MAF and it was ok for a few mile same when I changed it. Also if I disconnect it or reset the ecu its ok for a bit.
If you get to the bottom of it please post it on here and I will do the same.
Good luck.

burbling1

iTrader: (1)

I personly dont think its the actuator as it can hold full boost the ecu is telling it not to.
As for dumpvalves I have used the standard one a vent one and even tried it without one.
All have the same results.

Glowplug

iTrader: (8)

Jay and Burbling, what fuel are you both using??

burbling1

iTrader: (1)

V power.

burbling1

iTrader: (1)

Update on mine.
Lastnight it was running 7psi, I kicked its **** which I dont normally do when Its running that boost and it started running full boost again, it was about 5 mile until home. I got in it again today and it was running full boost until I came off a roundabout quite quickly and the boost dropped off again. Now I dont know if thrashing it made the boost come back or the fast exit on the roundabout made it loose it again. Just posting as it may help in the diagnostics.
The tank was full of fuel when exiting the roundabout.

Jaywalker

Sorry i havent replied sooner guys been a bit busy at work,

I have tried this already but for the life of me I cant remember the result lol does any one know the standard pressure for my car for the actuator is it 0.7bar? I will give it a check and let you guys know, because it was holding boost straight after the reset I didn't think it could be the actuator but who knows maybe the second hand BCS is faulty as-well lol just my luck,


I have tried it with a forge VTA dump valve with the same results but thats to be expected I think with a VTA but just thought I would try it lol, I do have the standard recirc valve on the car,

I did check all the relevant pipes with my air compressor but with the air leak theory wouldn't the car be the same before and after a reset? If I reset the ECU now I'm 100% sure it will boost 0.7bar for a while and then go down to 0.5 bar it still feels like the ECU pulling some thing back

I will do, good luck to you too


Tesco 99 ron

Could this have something to do with a faulty ECU maybe? Its not like the ECU is going to tell you its on its way out lol