Mark B

Hi,

I have a 95 WRX and have developed a stuttering effect in 5th gear ONLY when on boost. (half or full throttle). The rev needle jumps a bit and feel and hear this thudding noises.

But, if I accelerate in 5th without applying the boost everything is fine.

All other gears are fine with and without boost.

Any suggestions?

coolhand

Mark,
What speed are U travelling while in 5th gear? U could be using the wrong gear at the wrong RPM as there're few final drive ratios. Like 3.9, 4.1 or 4.44? I'm not too sure for a particular scooby but it's abt there. Yr final drive could be 3.9 n say maybe bcoz U didn't get the speed up to abt 70 or 80km/h, U couldn't go well in 5th. This is the usual problem...otherwise, nothing should b happening as other gears are running fine. There's also a veh speed sensor which might be sending signal to the ECU telling it's speed, gear n RPM. That's y U have this.

Happy driving.

Mark B

I am at around 3000 revs which should equate to around 60mph. Does not matter really. Even if I am at 3500 or 4000 revs as I soon as I engage some boost the car does what I can only describe as something like the gear slipping against the flywheel/clutch maybe?

I don't know. I only drive the thing..

sure is weird? and very concerning....

coolhand

As I've said, there are few final drive ratios available. Find out from the workshop manual on this as yrs is a 95MY. If it's a clutch or flywheel problem, I'll say it'll happen in all gear range unless yr car isn't moving. I still think it could be yr rpm range problem. By the way, have U fitted any extra stuffs like fuel controller or others? I've only experienced stutter in 5th for a Subaru when on flooring. The fuel cut got into action. Oh, there could be an air leak as well after the air flow sensor. Chk for leaks. If in doubt, chk with a mechanic.

Imago

Hi Mark

Could be the dreaded 'over boost' problem.

I have similar problem on my car. There has been a lot of info on this problem in this forum in the past, might be worth a look through the archives.

Basically what can happen is that over time oiling up of your pipes confuses a sensor into thinking there is too much boost and it cuts the ignition and fuel.

I know it is strange that this only occurs in fith geer at abot 3000 RPM but I am convinced this is what is wrong with my car.

A possible fix is to clean out the piping between the Turbo and the sensors, look in the FAQ 3.2.

Personally I just live with it, if it gets worse I will take it to the dealer.

Bob Rawle

Mark B ... do you have a boost guage fitted. If so at what boost does this happen ? If not then I would just say that it happening in 5th gear is logical as the car's produce more boost in 5th when accelerating than in the lower gears.

It could be a spark plug or coil pack problem. The earlier cars are susceptable to this. Check your plugs, the gaps should be 0.7/0.8 mm If they are not regap and test to see if its gone. If its still there then check to see if one plug is dirtier than the rest straight after the car has done this. The likleyhood is that the coil pack on that particular plug is faulty. They cost circa £47 each plus vat. If one is gone then its really best to change them all. I had this on my car, anything over 0.7 bar boost and the car misfired (not the boost cut) and felt just as you described.

Bob

Mark B

Thanks guys.

It happens when I engage any amount of boost above '0' on my guage.

I'm booked into PE for Thursday so hopefully they will be able to sort it for me.

I'll keep you informed

NeilR

I'll go along with Bob Rawle on this one.

Sounds like a loose spark plug lead - does the engine sound tappety on idle - or a spark plug breaking down (? cracked ceramic)

Ive had both on mine in the past and it can cause this stuttering under acceleration.

Cheers
NeilR

Mark B

So would a faulty coil or plug only show its ugly head in 5th gear only.

Why is 5th gear so different than the others on full boost.

Bob Rawle

Fifth is more searching because the revs rise more slowly and the boost has time to build up to a higher level. (on hard throttle) The engine works harder for longer.

firefox

Hi there,

When a fault is just showing its nasty head... they tend to appear first when the car is being stressed.. undernormal driving 5th puts the strain on the engine for the longest time.

Electrical faults (coil, lead and plugs) seem to appear first in 5th.

I know the coil packs have been an ever-seen problem with scoobs. I agree with Bob and Neil (knowledgable chaps)... check the plugs (gap and clean), wires and coil packs.

Cheers,

J.

[This message has been edited by firefox (edited 21-09-1999).]

Mark B

Just thought I'd push this back to the top.

I took the car in to be looked at about the 5th gear stutter/slip.

After leaving the car for a week, I picked it back up with a new STi clutch fitted and the flywheel had been skimmed (because it was blue and heavily scored!!)

Anyway, within 5 miles of driving away and getting into 5th gear - guess what? it still slips ! but only when I accelerate with some boost.

If I slowly creep up the rev range it does not slip.

HELP !!!

Do I need a new flywheel? Is the new clutch badly fitted?

Advice please people...

Mark.