Jump to content

rough idle help


Recommended Posts

hi guys i have a log attached of my car idleing. want some advice please. the car idles rough and jumps all over the place. mechanicalt it is fine i just cant seem to figure out why it wont idle smooth! the engine is a built cosworth yb engine. siemens dekka 875cc injectors. coil on plug conversion. bd14 inlet and exhaust cams 8.1 compression ratio. link monsoon ecu. just want it to idle smooth but its all over the place! help please!

rough idle.zip

Link to comment
Share on other sites

If youve got aftermarket cams you might be getting some overlap which makes your map signal unstable at idle. 

You could make a second fuel table that uses a virtual aux as a switch, so switches to an idle fuel map that's TPS based when you're below say 2% throttle and 1500rpm. 

Link to comment
Share on other sites

I've had a quick look over your log.  I think your MAP signal looks usable as is.  A couple of thoughts:

  1. Set up the CLL lockouts so it is disabled at idle, it looks like that is chasing its tail a bit.
  2. You only have 0° advance at idle, most engines would be happier with a bit more than that, try 10-15.
  3. Your injector timing is at 540°, that is a bit unusual, most engines with the injector close to the valve will work best around 380/400 at idle.  Try shifting it in say 30deg steps an see if it improves anything.
  4. Also, there are no indications of trigger issues in the log but just to confirm I would get a timing light on it, lock the ignition timing (open the set base timing screen) and just watch that the ignition timing is relatively stable at idle.  If for intnace the crank sensor was wired back to front it will bounce +/-10deg once every revolution when the gap goes past.
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...