Idle progression hesitation/flat spot
Thread Starter
TECH Enthusiast
Joined: Jan 2004
Posts: 608
Likes: 0
From: New Zealand
Idle progression hesitation/flat spot Hi all,
Have just fitted a set of heads ,ported, bigger valves,11:1 comp.
already had TR224 /112 and all the boltons.
I have a very good idle - solid, no flaring ,comes back to idle well an no surge,
but has a bad flat spot just off idle, always felt a little week there with cam only but is much more pronounced with heads.
Which area should I be looking at ?
I get the impression its a lean condition (just sent my LM1 back for repair so can't verify)
May try increasing VE's and see if that helps
Have just fitted a set of heads ,ported, bigger valves,11:1 comp.
already had TR224 /112 and all the boltons.
I have a very good idle - solid, no flaring ,comes back to idle well an no surge,
but has a bad flat spot just off idle, always felt a little week there with cam only but is much more pronounced with heads.
Which area should I be looking at ?
I get the impression its a lean condition (just sent my LM1 back for repair so can't verify)
May try increasing VE's and see if that helps
Supposing you can log it, do some series of tip-in
throttle events off idle and watch the O2 sensors
and the knock retard. If you see a bad lean dip
then probably fatten up the VE (though you may
prefer to work with some of the transient fueling
things if you really believe the VE is right, for steady
state flow).
Another thing to watch is burst knock, don't know
your vehicle, but there is a lot of variation in what
the PCM setup is there. If you have "live" burst knock
tables you may see a lot of timing pull. Check the
spark advance delivered, vs the table + adders for
RPM*cylAir you are at, and see if you're getting less.
USA trucks have this set really badly, some years at
least. More airflow, more delta CyAir, easier to trip
the burst knock threshold.
throttle events off idle and watch the O2 sensors
and the knock retard. If you see a bad lean dip
then probably fatten up the VE (though you may
prefer to work with some of the transient fueling
things if you really believe the VE is right, for steady
state flow).
Another thing to watch is burst knock, don't know
your vehicle, but there is a lot of variation in what
the PCM setup is there. If you have "live" burst knock
tables you may see a lot of timing pull. Check the
spark advance delivered, vs the table + adders for
RPM*cylAir you are at, and see if you're getting less.
USA trucks have this set really badly, some years at
least. More airflow, more delta CyAir, easier to trip
the burst knock threshold.
Thread Starter
TECH Enthusiast
Joined: Jan 2004
Posts: 608
Likes: 0
From: New Zealand
Originally Posted by jimmyblue
Supposing you can log it, do some series of tip-in
throttle events off idle and watch the O2 sensors
and the knock retard. If you see a bad lean dip
then probably fatten up the VE (though you may
prefer to work with some of the transient fueling
things if you really believe the VE is right, for steady
state flow).
Another thing to watch is burst knock, don't know
your vehicle, but there is a lot of variation in what
the PCM setup is there. If you have "live" burst knock
tables you may see a lot of timing pull. Check the
spark advance delivered, vs the table + adders for
RPM*cylAir you are at, and see if you're getting less.
USA trucks have this set really badly, some years at
least. More airflow, more delta CyAir, easier to trip
the burst knock threshold.
throttle events off idle and watch the O2 sensors
and the knock retard. If you see a bad lean dip
then probably fatten up the VE (though you may
prefer to work with some of the transient fueling
things if you really believe the VE is right, for steady
state flow).
Another thing to watch is burst knock, don't know
your vehicle, but there is a lot of variation in what
the PCM setup is there. If you have "live" burst knock
tables you may see a lot of timing pull. Check the
spark advance delivered, vs the table + adders for
RPM*cylAir you are at, and see if you're getting less.
USA trucks have this set really badly, some years at
least. More airflow, more delta CyAir, easier to trip
the burst knock threshold.
Will do some logging tonight - normally don't see any knock , but the extra compression could have induced some.(probably need to revisit timing tables anyway)
What tables do we look at for transient fueling?
Car is an 02 Holden Commodore
