2001 Bugeye WRX Engine stutter

[dnsn]

Hi Guys, This is a hard one to explain so bare with me...

Car is pretty standard apart from a STI Genome exhaust and a boost gauge, has done less than 100,000km and is in pretty good nick. It runs and boosts well, sounds like it should with no knocks or other suspect noises. I\'ve had the car for about 9 months now and it has just started to stutter when under load in 3rd, 4th, and 5th gear at around 3500-5000rpm. The stutter is hard to explain, the revs spike up and then drop down and then build again without changing throttle position (not always at WOT). It seems to be intermittent but has never happened in 1st or 2nd gear, The easiest way to get it to stutter seems to be to sit at a constant 50kmh in 4th gear and to open throttle from there without changing down (If I do a standing start and push it hard through all the gears it doesn\'t seem to do it). At first I thought it might have been clutch slip but it wont do it from a standstill when you push it hard and I have tried a steep hill start in 4th gear with plenty of revs and it stalled and wouldn\'t slip. It seems like it could be boost or vacuum related but I cant see any loose or perished hoses?

I\'ve been told by a mechanic that it\'s not a mechanical problem, and most likely a faulty sensor or some other electronic related problems. I haven\'t had a OBDII tool plugged in yet to see if it\'s throwing any fault codes, But that\'s my next step. I\'m waiting for it to arrive :-[

Any ideas?

[DacerX]

boost soldnoid? get it scanned would be the best bet

[boon]

Eek, tons of things to check... plugs, fuel pump, fuel filter, AFM, O2 sensor... if you can do a datalogging run that will probably tell you a lot.

[Marky]

description doesnt help

revs can not move up and down while in gear unless clutch is slipping

clutch slip can be worst when in higher gears, might be fine to take off but slip in 3 4 5 high load situations

is it a misfire, or is it the revs just going vroom upwards then back down all on their own

[dnsn]

 Marky said:

description doesnt help

revs can not move up and down while in gear unless clutch is slipping

clutch slip can be worst when in higher gears, might be fine to take off but slip in 3 4 5 high load situations

is it a misfire, or is it the revs just going vroom upwards then back down all on their own

It\'s hard to describe without Actually being in the car, I may have to get the GoPro on to get a video so you can get a clearer picture. Im pretty confident its not clutch slip, surely a hill start in a high gear with revs and boost up would make the clutch slip if it was weak. But in saying that im still open to any ideas.

As for a misfire it doesnt sound like it, There is no change in the audible tone of the engine other than the change in rpm.

I will be getting an OBD2 bluetooth unit (is it going to plug into my car?) in the next few weeks so can check for any error codes etc.

I will do a video and post the link tonight.

Thanks

[chappell943]

Where abouts are you located? If your in chch I could do some data logging with my tactrix cable to help you try find out the problem.

[DacerX]

hes in the north i think

[Marky]

ok, i just cant see any way that rpm can just change - without road speed changing - without something slipping - that said trying to explain something by typing it out is a mission at the best of times

[dnsn]

Yeah I\'m in Napier, hawkes bay. Its real hard to describe without actually being in the car! :\'(

[tebbyj]

Sounds very much like a Lazy O2 sensor to me,

Like a mild hesitation while cruising at a constant speed? its not violent but noticeable. and when you accelerate in the same gear it doesn\'t pick up strait away like it should?

The o2 Sensor will get stuck at a constant voltage, within specs so it wont throw a code, but the ECU will read it as incorrect for the engine conditions and pull timing or dump in more fuel etc.

[neodowd]

Is it happening at wot? if not it might be 02 sensor.

[dnsn]

It can han happen at any throttle postion as long as rev\'s can build and boost can build.

Shot this video last night on way home. Unfortunatley it doesn\'t do it as bad as it has been in the link.

I stayed in 4th gear after driving at 50-60km\'s (I did this on a quiet 100km/h zone road to play it safe ) All i did is gave it some gas, Dont think it was WOT, and let the boost and rev\'s build up to get to speed. After it made its fun with the rev\'s it build like normal, and will keep accelerating fine

And to top my bad luck off, after I stopped recoding, A car over took and flicked stones everywhere, Cracking my windscreen and Drivers side spotlight, So Does anyone know where to get one from to replace it??? :\'( It hasn\'t been my week.

[V2 378/555]

Clutch slip.

[dnsn]

 V2 378/555 said:

Clutch slip.

Clutch has been tested and it\'s fine. If im under full boost all through the rev range it\'s perfectly fine. And It doesn\'t do this all the time

[Marky]

Dont want to repeat myself

so ill go with an axle snapping then rewelding itself from friction

option b being clutch slipping

when the clutch starts to let go in trucks sometimes it behaves like this, wont slip in any situation but high load / low rpm - like heavy load, or uphill for example. I have had one behave exactly like this years back, it eventually started to show in the "normal" slipping clutch fashion

you could try adjusting the preload on it (via pedal adjustment under dash), that might give it a bit more clamp, could be juuust barely being disengaged at the moment

there is nothing engine related which can cause this to happen, you arent lighting the wheels up - if you were then speed would fly up - and its not a snapped axle cause that wouldnt behave like this, itd always slip

not trying to be a dick, its more a case of what else can cause this - the rpm is changing while you are in gear - the engine is "solidly" attached to the road via set gear ratios and the only thing which can change that relationship is wheel slip, clutch slip, or changing what gear you are in

edit - the point it is "letting go" is more or less where youd have peak torque on it too - basically the point where the clutch is having to work its hardest to maintain grip

[dnsn]

 Marky said:

Dont want to repeat myself

so ill go with an axle snapping then rewelding itself from friction

option b being clutch slipping

when the clutch starts to let go in trucks sometimes it behaves like this, wont slip in any situation but high load / low rpm - like heavy load, or uphill for example. I have had one behave exactly like this years back, it eventually started to show in the "normal" slipping clutch fashion

you could try adjusting the preload on it (via pedal adjustment under dash), that might give it a bit more clamp, could be juuust barely being disengaged at the moment

there is nothing engine related which can cause this to happen, you arent lighting the wheels up - if you were then speed would fly up - and its not a snapped axle cause that wouldnt behave like this, itd always slip

not trying to be a dick, its more a case of what else can cause this - the rpm is changing while you are in gear - the engine is "solidly" attached to the road via set gear ratios and the only thing which can change that relationship is wheel slip, clutch slip, or changing what gear you are in

edit - the point it is "letting go" is more or less where youd have peak torque on it too - basically the point where the clutch is having to work its hardest to maintain grip

I thought it was that originally too, But as I ain\'t so mechanically minded :-[. I got a mechanic to test it, He did a stall test and a hill start test and then said he reckon\'d the clutch is fine, and recommended that I Get it scanned as a sensor might be playing up.

I wasn\'t convinced by his answer hence why I posted it up here. ??? ???

[Kiwi_Fozze]

my clutch is fine for hill start and stall tests, first and second is fine, lets go at 4000 rpm in 3rd, slips everywhere higher gears.

can still get wheel spin using launch control, but it slips like no ones business.

[dnsn]

 kwi_fozze said:

my clutch is fine for hill start and stall tests, first and second is fine, lets go at 4000 rpm in 3rd, slips everywhere higher gears.

can still get wheel spin using launch control, but it slips like no ones business.

Is that a problem with yours? Did you end up replacing the clutch or leaving it?

[Kiwi_Fozze]

still in the car, have replacement clutch, will be getting changed. allow 800 for the plate and pressure plate and bearing, about that again for fitting. it will need doing, it only gets worse.

[dnsn]

 kwi_fozze said:

still in the car, have replacement clutch, will be getting changed. allow 800 for the plate and pressure plate and bearing, about that again for fitting. it will need doing, it only gets worse.

Yeah, I got told $1000 fitted. Not sure what type of clutch that is.

Any recommendations?

Ive got the cam belt to do soon too, So guess It\'s gonna come off trademe and stay in my Garage

[Kiwi_Fozze]

get genuine, i picked mine up for a song through wingers with clubsub paid member discount

get cam belt done at the same time, engine basically has to come out to do the clutch lol

[dnsn]

My Pocket sounds empty-er just thinking about all of this!

Go Genuine with all parts?? Or any aftermarket brand in particular for both cam belt/waterpump/clutch etc ????

[Kiwi_Fozze]

genuine genuine genuine..... aftermarket clutch is often more expensive, and from the accounts i\'ve heard about one "recommended" brand, not as good... but that\'s for the sti clutch, have a chat to your local supplier and see what they can do for you

[dnsn]

Yeah, Bit limited sometimes in Hawkes Bay. I travel to Auckland a bit at times So might get parts up there. I\'ll have a chat around down here and see what at I can source first! It\'s for just a plain non-STI wrx Wagon

[Kiwi_Fozze]

Wingers greenlane are good for parts, highbrook automotive for everything else