Lumpy Misfire @ 2000 to 3000 rpm Under Load

[SilverBullet]

So I've had a look on here but can't spot the exact query.

Our Legacy starts fine every time which is great. But then when it's under load it starts missing between 2 to 3k, over three it then seems to be fine, which is good.

So far I've cleaned the O2 sensor swapped the plugs, but no joy. So I'm left thinking this is the a/f sensor or the knock sensor which might need replacing? Any thoughts?

SB

[tebbyj]

Hi,

Ive had the same sort of problem with my 96 GTB, very intermittent though. :-\

Usually after driving in 4th at 50-60kph the car will start coughing when you try to accelerate, power will all but disappear, even when pushed to full throttle car will not rev past around 3000 rpm. :-[

Then just as randomly it started it will disappear and car will drive completely normally.. no CEL displays at all.

Tried pulling codes later on and it comes out with 22 (knock sensor) so i assume that it might be retarting the timing extremely ? but surely that wouldn\'t cause symptoms this severe ?? ???

Hopefully someone will have a miracle cure ;D

[Jord]

Might be stating the obvious here but have you checked for any codes?

[titian]

 Jord said:

Might be stating the obvious here but have you checked for any codes?

Yep...First thing to do!

Could be AFM ...Sometimes there is no code but the AFM is "Slightly" faulty. But not enough to trigger the code.

Temp sensor for the ECU can also do this... Its a bit ??? for sure.

[titian]

 tebbyj said:

Hi,

Ive had the same sort of problem with my 96 GTB, very intermittent though. :-\

Usually after driving in 4th at 50-60kph the car will start coughing when you try to accelerate, power will all but disappear, even when pushed to full throttle car will not rev past around 3000 rpm. :-[

Then just as randomly it started it will disappear and car will drive completely normally.. no CEL displays at all.

Tried pulling codes later on and it comes out with 22 (knock sensor) so i assume that it might be retarting the timing extremely ? but surely that wouldn\'t cause symptoms this severe ?? ???

Hopefully someone will have a miracle cure ;D

Check Vacuum hose to fuel reg is air tight.

[tebbyj]

 titian said:

Check Vacuum hose to fuel reg is air tight.

Which hose is the fuel regulator hose? Better question is where is the fuel regulator?

Would this cause these problems? including the knock sensor fault code?

Im full of questions now ;D

[slystiguy]

cracked coil or vacuum leak ?

[rex-leggy]

have you tried coils ? that would be my bet

[slystiguy]

Could be a combination of a few faults but coils are the logical first step. It might only be one so just test it out before you spend $$ on a whole new set...

[rex-leggy]

ive had same symptoms twice and both times was dogy coils . on my rs i upgraded them to later ones because they stand the test of time better

[tebbyj]

I have just changed the coolant and a bit made it down the side of the engine, possibly got into and ruined the coil underneath?

It does feel like a misfire problem, but then it fixes itself and drives without misfire at all.

It happened a few times when driving home tonight (made for and interesting and frustrating trip lol) and i\'ve found that if you floor it, it does seem to minimize the effect so to say, almost pulls itself out of it??

Will try pulling off and testing coils tomorrow.

Its going in to a mates workshop on Thursday for a WOF might ask them to have a look.

[tebbyj]

KNOCK SENSOR replaced and all is well! have taken for a good drive and all symptoms have disappeared. Better power and fuel economy too. Amazing how much a little black circle can effect how your car runs. ;D

Thanks for all your help guys much appreciated.

EDIT:

Its back with vengeance! ??? , although a lot less violent, have changed plugs and tested coils, all seem to be okay, now seems to have no power low down... Hill starts don\'t really work anymore, have foot flat to the floor as soon as clutch comes out and struggles to gain speed, (mildly annoying when you live on a hill). But as soon as you get over 3k RPM its fine!!

Any suggestions?? (better than drving like a madman everywhere )