Ford Focus ST Forum banner

1 - 5 of 5 Posts

·
Registered
Joined
·
255 Posts
Discussion Starter · #1 ·
So my exhaust is decently loud, when sitting at idle, it's definitely audible. I noticed my RPM was bouncing around a little. So I checked on my AP. For a minute it would jump from 850-930. Seem odd to anyone else?


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
255 Posts
Discussion Starter · #2 ·
Aaaand it's back to normal after driving a few blocks. Super odd


Sent from my iPhone using Tapatalk
 
  • Like
Reactions: shineboy and Zeek

·
Registered
Joined
·
408 Posts
Aaaand it's back to normal after driving a few blocks. Super odd


Sent from my iPhone using Tapatalk
New exhaust? That happened to me after my resonator delete. I went away after a couple days.

Sent from my SM-G935T using Tapatalk
 

·
Registered
Joined
·
255 Posts
Discussion Starter · #4 ·
New exhaust? That happened to me after my resonator delete. I went away after a couple days.

Sent from my SM-G935T using Tapatalk
Funny thing, I was in an exhaust shop today getting a quote. We put it on the rack but didn't do any work and I had driven since then for about 10 minutes. I figured maybe a vacuum line or something but it just went away.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
196 Posts
Funny thing, I was in an exhaust shop today getting a quote. We put it on the rack but didn't do any work and I had driven since then for about 10 minutes. I figured maybe a vacuum line or something but it just went away.


Sent from my iPhone using Tapatalk
Enable logging for STFT % (short term fuel trim) and LTFT % (long term fuel trim). STFT is the immediate adjustments the car is making to the A/F mixture to either make it more rich or more lean. LTFT is a long term adjustment for the same thing which is stored in KAM - short term is not.

Anyway, start logging while your AFR is bouncing around at idle. If your STFT is high, rev the engine to 2500 rpm and hold it for 30 seconds or so. If the STFT starts to fall to a normal range, you probably have a vacuum leak. Similarly, high LTFT could be an indicator as well. If I recall correctly, LTFT above 10% is considered pretty high. A faulty/dirty sensor, a fuel delivery issue or even a tune issue could also be the cause.
 
  • Like
Reactions: hanyolo44
1 - 5 of 5 Posts
Top