shiftyoldscoob

Hi, my m8's 94 wrx wagon is jerking heavily under boost..

The car runs perfectly but jerks heavily when he reaches 4.5k revs???

I thought it could be the dump valve as it feels like when you take your foot off the accelerator with an aftermarket BOV fitted, but we're still unsure????

banny sti

iTrader: (68)

It sounds like you have a faulty coil pack, I eliminate them first before looking elsewhere.

Banny

WMS

iTrader: (2)

Has the speedo stopped working by any chance? Ive had the same effect when a speedo cable came adrift, it effectively brings the top speed limiter in at 4.5K revs

shiftyoldscoob

Just spoke to my m8, he says the coil packs are brand new...BUT he also said the speedo isnt working and as soon as the car starts to jerk, the engine management light comes on

We'll try the speedo cable and see what happens!

thanks for the help guys and if anyone else has any other suggestions keep em comin

happydude303

iTrader: (1)

its not over boosting is it

WMS

iTrader: (2)

It's the speedo then, if the ecu does'nt get a signal it brings top speed limiter in at exactly 4.5k rpm, had exactly the same on a 94 WRX a few years back
Good luck
Andy

joz8968

iTrader: (13)

Yes, seen JGM post about tis issue a few times too.

Speedo don't work/problematic = ECU sets rev limit to 4.5k (via a sensor on the gearbox, I think).

Glowplug

iTrader: (8)

Had the same thing last week, fitted new dawes device and hit fuel cut whilst setting it up, the 'jerk' from the cut dislocated the speedo cable and put me into 'limp' mode.

Ensure the cable is fully pushed home at the rear of the clock and also at both sides of the convertor if you have one fitted (mine is located on a 4" stem coming out of the gearbox) Hth

Natas

If the ecu light came on it will store a fault code,scoobypedia has a page about reading your fault codes, if it is the speedo it will list a speed sensor fault, or if it has hit fuel cut it will list an overboost fault.

Codes can been found here

shiftyoldscoob

been onto my m8, he's done the diagnostic. I cant remember the code but he said the ECU is saying that the speed sensor is at fault.

So he rang subaru and the guy on the end of the phone said that as his car is a 95 model it doesn't have a speed sensor???

Can anyone shed any light on this?

Thanks for everyones help so far!

WMS

iTrader: (2)

Has he got the speedo working? If it's still not working it will come up with speed sensor fault.

shiftyoldscoob

The speedo defos aint working..unsure weather its came adrift from the back of the speedo or the box

I'll get him to try fix it and see what happens! hopefully it'll solve the problem

W9LTN

iTrader: (1)

Check Spark plugs and Leads and if you have a boost guage check it's not hitting the fuel cut. when i bought my car it would jerk when on boost. think it had a missfire on boost. changed the Spark Plugs and it sorted it out instantly. Car was fine driving normaly but when you put your foot down it would jerk. i could get it to full revs if i was gentle with the pedal. I think fuel cut was 1 Bar on older (Pre 97) cars and 1.25bar for later cars.

WMS

iTrader: (2)

Tell him to fix the speedo, the ecu picks up a signal from the clocks, if it does'nt get a speed signal it goes into safe mode, and brings the rev limiter in at 4.5K, it's to stop people unplugging the cable to remove the top speed limiter.
I'll say it again, get the speedo working!
Andy