Jump to content
Ultimate Subaru Message Board

Flat spot when accelerating (around 3-4k, under load)


Recommended Posts

Torque spec on the knock sensor is something like only 12 ft lbs iirc. Not worth using a torque wrench unless it is a very accurate low scale wrench. A turn of the wrist once the bolt seats is really all it takes.

 

There are only 6 wires at the OBD2 diagnostic connector on the early Subarus. Nothing strange about that. It's possible the reader you got does not support the protocol used on the early models, but it's hard to say. I think it should be ISO 9141-2. I'm not sure if the AU spec cars had the same.

Link to comment
Share on other sites

I have heard nothing but bad things about the ebay obdII adapters. what software are you using? if you have an android phone try using an app called torque, its in the google play store with a free and paid version. it has never let me down and has many options to configure communication with your car. torque automatically selects the best protocol, and in test mode will give you a web link to any trouble code it finds. I'm also using a Kiwi PLX with bluetooth which is ironically made in AU and I would highly recommend.

 

I'm going to go re torque my knock sensor and tell a friend about this as he has had a knock sensor code for some time now but rarely looks up a torque spec on anything.

Link to comment
Share on other sites

Knock sensor arrived Friday and I put it in. The old one didn't have any visible damage at all (some have mentioned there is often cracks in the plastic covering) but it did had quite a bit of white corrosion on all the metal parts (between the senor and the engine, through the hole the bolt goes through and under the head of the bolt). And it was very tight (although perhaps that was because of the corrosion?)

 

I replaced it and when bolting the new one in, gave the ratchet about a 1/3 turn after it seated. And it has made a huge difference!! :clap: It's still not perfect, it has a slight hesitation for a moment around 3k-3.5k but the +/-500RPM flat spot is gone!! :headbang:

 

As it has a slightly unstable idle at times I am hoping that perhaps if I give the throttle body a good clean I can clear up that and the slight hesitation. I have sprayed carby cleaner through the throttle body before but my reading suggests that I need to get in there with a toothbrush and give it a good scrub out to do a proper job...

 

Over the weekend I gave it a pretty good workout. Myself and 3 mates went for a bushwalk which required about a 250km drive and it ran so sweet! It's never run that well carrying that much weight (probably equivalent to about 5 adults).

 

So I think we can safely say that the knock sensor was the main issue...

 

As for the OBDII adapter. I was using it with Torque (Android app) both on my phone and on my tablet. It connects fine (via bluetooth) and scans through all the protocols (and all the lights on the unit flash as it does it) but says that it can't connect to the ECU. My Dad has a later model Subaru Outback so I'll give it a try on that and see how that goes.

 

Thanks again for all your help guys!

Link to comment
Share on other sites

Might try a can of seafoam in the intake. It could also help to spray the idle control valve out really well with some intake cleaner. Carb cleaner doesn't work on FI intakes as well as it works on a carburetor. It just doesn't cut through the carbon/sludge buildup as well. Use Throttle body and Air intake cleaner if you can find it.

Link to comment
Share on other sites

  • 2 weeks later...

Just wanted to report back again. My Subi is going so well now! No doubt about it at all; that knock sensor was rooted! It still brings a smile to my face when I put my foot down and it takes off! It's just been a pleasure to drive over the last fortnight! :)

 

I still haven't hit it with a torque wrench yet, but the unstable idle seems to have fixed itself. Perhaps now it's running a bit better it has cleaned itself out a bit, although I still plan to give the throttle body a good go (when I get around to it).

 

Now it's going a bit better, I've been thinking about perhaps getting a higher flow air filter and perhaps squeeze a little more out of it... Any suggestions on good ones? Also if I do that are there any other considerations? Or can I just fit it and go? [Guess I should probably start a new thread...!? Or perhaps just have a good search...!!]

Link to comment
Share on other sites

High flow dry filters are OK. Actually the stock filter from Subaru has very good flow characteristics.

Try to stay away from wet filters as the oil can create problems with the MAF sensor signal.

Any filter that pulls air from inside the engine bay (exposed cone filter) will impede performance. The stock airbox pulls cool air from just behind the passenger headlight and through a water separator in the fender area before going into the filter.

Link to comment
Share on other sites

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
 Share

×
×
  • Create New...