Rob_f

Hi Phil,

I ran the car with a loose knock sensor to effectively deafen it to the knock and the car ran fine, full boost etc and I didn't hear anything bad, but another reply suggested I might not be able to hear the knock until it was too late so I tightened up the sensor and it slowed the car down to limp mode. I've also eliminated other vibration which may cause a det sound.

It is odd the check light does not come on but both myself and the subaru place I took it to had the same experience: reset ECU, run it, quite quickly go into 1/2 boost - safe mode, but with no light.

I have no misfire and have changed plugs but I am thinking incorrect fuelling like you say. I just had the lambda checked on an oscilloscope and it read .2V constant. The guy said it should be an square tooth reading with higher voltage. So either shagged or running very lean. Fitting a new one tomorrow so will post results.

Incidentally, when unplugged, I didn't get a check light for the lambda. Tomorrow I should know the problem, either lambda faulty or very lean mixture. How does cooling temp sensor react with ECU btw, assumed it's just a cold start signal.

Cheers

Rob

Rob_f

Jay, just read your post. I didn't know big end wear would register as knock, I suggested it to the subaru guy I went to and he said it wouldn't but I would think it would also.

Well if the mixture checks out then that would be my next thought. Don't suppose they can be done via the sump?

Butty

iTrader: (2)

Rob,
As well as the heat shield noise fooling the knocklink, it also picked up noise that turned out to be the start of big end damage.
This noise would show itself when putting the engine under load, but trickling along would show no problem.
The engine could just be heard to tap slightly when the KL lit up.

Nick

Rob_f

Did you change the bearings?

Butty

iTrader: (2)

A bit more than that - a new bottom end as it was under warranty!!

Rob_f

The chap at the garage tells me the lambda sensor is a constant voltage type and mine is probably ok. Reading 0.2v which I understand is a very lean mixture reading which would certainly give the sympoms i'm getting.

Can anyone suggest what could cause a lean mixture apart from the MAF?

Going to try Scoobytechnix tomorrow.

Turbotits

iTrader: (2)

Sorry but if its ready constant voltage it wont be telling the ecu anything except that the mixture is constant.

It should alter voltage. Id say it foobared

Rob_f

Can you elaborate, it was only tested at tickover and gave a constant .2v reading. Car warm. I agree it should be a higher voltage and increase further under boost and higher revs. If it is reading correctly, then it would indicate a lean mixture I think.

The diagnostic software this chap showed me suggested the items to check first for knock was MAF and MAP. I have checked out the MAF. I don't know where the MAP is - or even if it has one - and whether it has any effect on mixture.

I understand it will cut fuel if the pressure is too high but does it control mixture under normal conditions and where is it...

Cheers

Rob

Butty

iTrader: (2)

At Idle, the oxygen sensor voltage should be flicking around a couple of times per second.
A constant voltage indicates a problem - why doesn't your garage know this?
Quite a few recommendations have been to take the car to someone with det cans but you seem reluctant to do this or doesn't your garage have the ability to use them?
Perhaps it is also time to take it to another garage who can spot a problem with the oxygen sensor.

nick

jaytc2003

iTrader: (1)

To be honest if your subaru guy doesnt think that worn big ends can cause knock then I would change mechanics/garages
If the bearings are worn, then that means the crank wouldnt be seated correctly (or it is able to move under load), maybe only slightly but it could certainly cause knock.

Bearings cant be done via the sump unfortunately due to the design of the engine. Basically think of a conventional engine and how it is layed out, with a boxer engine you have in effect got 2 smaller engines that are lying on their sides 180 degrees from each other.
what this means is it is an engine out job and splitting the blocks

hopefully though, this isnt your problem as others have mentioned the lambada should change readings on tickover

Shark Man

A MY95WRX uses the old fashioned style Oxygen sensor; which as you stated switches very between full rich and full lean at a rate of 1 or 2 Hz or so at idle (about once a second) switching faster at high rpms.

If a digital voltmeter was used, or the value read off a plug-in diagnotics tool, it will be RMS or averaged voltage...and will show a somewhat steady voltage. The more basic the meter the more contstant the voltage will show (down to the sampling rate of the meter). These types of metre should read around 0.4 to 0.6v

So, if you see constant 0.2 volts using a scope, to me suggests its stuck on its full lean voltage and not switching at all. Generally, when these sensors fail, the switching rate slows down further and further until it stops switching entirely. Most notable at idle (always test with hot engine), whilst sometimes they spirng back to life during fast idle tests (constant 3000rpm for several minutes).


Now, just before you jump on the "thats the only fault" bandwagon, whilst it could be the case, its important to know that the OS sensor is only used for fueling adjustment during part throttle and idle conditions...The sensor is not used by the ECU during wide throttle openinngs and high boost. So if the symptoms exists under these conditions, there is still another problem somewhere.


MAP sensor for the Classic Impreza is located on the driver's side suspension turret/innerwing. This sensor is NOT used to adjust fueling (well, tell a lie, it adjusts via a switching solnoid to compensate for ambient pressure) and its prime use to to control and monitor boost levels. I'd be very suprised if this was causing any issues.


Sorry to be pedantic: Actually, you can get boost - a healthy TD04 should give 0.5bar on a full throttle blip to 6000rpm when measured at the manifold (presuming the guage reacts quick enough). A turbo is a passive device in that it is always spinning as long as exhaust gasses are going through it: Especially at high engine speed: Just its blowing against a nearly closed throttle plate - Disconnect the dump valve vacuum and Tee the gauge off the nipple on turbo outlet instead of the manifold and you'll see

Rob_f

Nick,
The chap said (after the part arrived) that this type of o2 sensor gives a constant reading and that therefore it's possible mine's ok. I would have bought it otherwise so trusted his opinion. The 3 wires did not match though so he may have just been being cautious. Still could be the lambda then.

Det cans - I keep asking if they can tell me the cause of the knock, but yes, my guy didn't check this, he just read what the knock sensor was telling the ECU to do.

I phoned Scoobytechniks today (my new garage) and they sound helpful and knowledgable - going to drop it in this week if I can arrange a lift so i'll ask them about det cans.

Jay,
The big end possibility worries me. Although it wouldn't cause det, it might sound like det to the sensor. But I also imagine det would cause big end damage eventually. So if my big ends were ok before then they might not be now. Engine sounds ok but i'm no longer loading it or revving it so can't tell.

When I know mixture is ok, i'll check it out. Perhaps the det cans can detect this.

Shark Man,
Symptoms do occur at full boost (at 3-4k revs) but the ECU has perhaps already learnt that it should retard timing at a rev range where knock was heard before. I'm not sure. If the o2 sensor is knacked and reading lean then shouldn't the ECU compensate by giving a richer mixture and therefore no det?
I'll forget about the MAP then for now.

I'll take it the scoobytecknix but i'm thinking low pressure air ingress somewhere or the lambda, or the big end.

Thanks for all your help I am leaning a lot.

Rob

jaytc2003

iTrader: (1)

im not convinced it is det. im sure scoobytexnic will have det cans, I know they use a guy called andrewc on here to map cars (or they used to) having met andrew I can tell you he is a very knowledgeable chap.

If your getting i imagine stuttering at full boost, I am gonna say coil packs are worn. Easy enough to check yourself, just remove them and then check the tips of them for cracks (will have to gently pull back the tip) keep us posted though

jasonius

iTrader: (1)

Yea ok, I should have said any meaningful boost..

Lol, never realised you could be pedantic..



OP when is it going to Scoobytechniks..? Let us know what they say..

Rob_f

Limping over to Fleetwood hopefully Thurs afternoon.

Rob_f

Still no joy.

Scoobytechnics couldn't test the lambda and didn't have det cans, but did put me in touch with someone local who does have det cans.

So more news on monday eve hopefully.

Rob_f

Finally found a chap who really knows his stuff. I have managed to get some det cans on the engine.

I hate to say 'I was told so' but it did answer quite a few questions. I also had the mixture checked.

Mixture is ok

Engine has 'real' det which occurs more at lower loads (yes I know, odd) but I assume higher boost will have a richer mixture which would reduce knock a bit.

So what's causing the knock???

I am going to clean / inspect the cam and crank sensors.

Most likely though is that the air system is quite oily, although the car doesn't use much oil or smoke at all, oil could have built up over time and be causing the det (very few explanations left).

If I find excess oil, this will be coming from the turbo or the piston rings.

Oh, the ECU was swapped to check ok - it was.

If anyone has experience of oil causing det please post.

Cheers

Rob

Triple X

iTrader: (1)

Hi Rob,

Saw you at Andrews last night, thought id say hi on here.

Hope the suggestions turn out to be solutions m8, best of luck.

John.

jasonius

iTrader: (1)

Check the intercooler and associated pipework from turbo to throttle body.

If you're running standard crankcase breather system (ie no catch can or VTA) then you may well have built up 0000's of miles worth of oil residue. Quite normal, but if it's never been done then it could be excessive and ultimately effect the octane rating of the fuel you're using..!

Can't remember if you've already done this, but have you tried adding some octane booster (NF of Millers Octane plus)..?

If it's oil residue in the intake adding OB should resolve it by upping the effective fuel octane rating. Either way it's worth cleaning out the IC etc: remove, bung and flush with petrol, leaving to soak for an hour or so. Drain then blow cool/warn air through for 20mins or so to dry out- wife's hairdryer on low is ideal..

Rob_f

Hi,
Good to hear from you John, and Andrew knows the cars well. He had my car wired up to register true stoik mixture through the exaust to a laptop and was listening to the electrical signal coming from a knock sensor on the manifold via headphones.

I am going to take apart / clean the air pipes / IC. If these get oily again over a week or so, i'll get the compession cheched, then look at the turbo.

I haven't worked out how the engine breaths back into the air supply. but if it's the turbo there will be oil in the blow off pipe, IC, everywhere. Where does an oil catch can fit in?

And what's a VTA?

Too risky to take apart before the weekend so will post then.

Cheers,

Rob

Rob_f

Finally got time to clean out the I/C and pipes. Put some Mobil 1 15/50 in (I was running 0/40).

The I/C was quite oilly and there was evidence of oil in the air intake to the turbo which can only come from the breather pipes above.

I also disconnected the breather pipes which are now venting to atmosphere. Blocked off the holes in the main air pipe. I'll get a catch can when I get round to it.

Now no sign of hesitation and have full boost.

This seems to have fixed the problem

Thanks for all your help.

Rob

jasonius

iTrader: (1)

Glad you seem to have got to the bottom of it..!

The 0/40 may have been a little too thin for your engine and exacerbated the blow by contamination.

Theoretically it should be better with the 15/50.

May be worth checking the IC every now and then to keep an eye on it..

Rob_f

Just wanted to end this thread properly.

Cleaning out the I/C didn't sort the problem...

Since last post relaced all 4 coil packs (two were cracked), no joy.

Eventually de-sensitized the knock sensor by moving it to a bracket further from the engine and been running on full boost for a couple of months now with no explosions. I hope it lasts.

Cheers for all your help

Rob

johngoulding

iTrader: (7)

i have exactly the same problem m8 , its weird ? chnged coolant temp sensor , maf sensor , boost solenoid , pressure sensor , actuator , fuel filter , plugs AND packs , multimetered evrey injector and wire also ditched the vta dv for a standard one and i also have the rattling noise that souns like a loose bolt at about 2000 rpm when driving and 1500 on idle i still cannot find the problem i even changed to the u8 ecu and still no change ? and the weirdest thing is mines s also a 95 wrx wagon import ? DEJAVU