Flat spot when cold
Discussion
Does anyone know how I can fix this?
Basically at tickover when cold, I try and move off with a few revs and the engine hits a flat/DEAD spot almost straight away, to get over it I dip the clutch, rev and off I go again, but I shouldn't really need to do this.
Any reason for it?
PS
Engine been tuned for Wortec Cat back and then again with headers and same problem there, so I'm thinking something else like MAF??
Basically at tickover when cold, I try and move off with a few revs and the engine hits a flat/DEAD spot almost straight away, to get over it I dip the clutch, rev and off I go again, but I shouldn't really need to do this.
Any reason for it?
PS
Engine been tuned for Wortec Cat back and then again with headers and same problem there, so I'm thinking something else like MAF??
wolfracer said:
Does anyone know how I can fix this?
Basically at tickover when cold, I try and move off with a few revs and the engine hits a flat/DEAD spot almost straight away, to get over it I dip the clutch, rev and off I go again, but I shouldn't really need to do this.
Any reason for it?
PS
Engine been tuned for Wortec Cat back and then again with headers and same problem there, so I'm thinking something else like MAF??
Basically at tickover when cold, I try and move off with a few revs and the engine hits a flat/DEAD spot almost straight away, to get over it I dip the clutch, rev and off I go again, but I shouldn't really need to do this.
Any reason for it?
PS
Engine been tuned for Wortec Cat back and then again with headers and same problem there, so I'm thinking something else like MAF??
Sounds like the open loop mode has you going into "limp" or "safe" mode....that is a program issue. Do you know if your tuner is using HP Tuners or LSEdit?
Edited by sargegto on Monday 23 March 23:49
Could also just be too cold and fuel is pooling rather than vapourising properly.
This can be addressed with more transient fueling under certain circumstances etc.
Anyway the bottom line is that if its not a phisical issue with narrow bands or sticky IAC motor etc, then its a tune tweak on the cards.
You should talk to the person who tuned it as I said before
This can be addressed with more transient fueling under certain circumstances etc.
Anyway the bottom line is that if its not a phisical issue with narrow bands or sticky IAC motor etc, then its a tune tweak on the cards.
You should talk to the person who tuned it as I said before
LawrenceF said:
Mine does it too. But only when it's first started and got ordinary petrol in rather than super.
Yes you are correct. What happens often times is when cold or in closed loop the ECM will protect itself until warmed up from knock (detonation). Some call it limp mode. This can be adjusted as not to over compensate thus causing a "dead spot"....
ringram said:
Check with Paul at Wortec.
Has it always done it? Could be loads of things, some mechanical.
Has it always done it? Could be loads of things, some mechanical.
Yes, its always done it - 50 thousand miles of doing it! probably 20k between the 2 tunes. Never been a massive issue, but now with "super loud mode" permanently selected I am more conscious of throttle openings....
sargegto said:
LawrenceF said:
Mine does it too. But only when it's first started and got ordinary petrol in rather than super.
Yes you are correct. What happens often times is when cold or in closed loop the ECM will protect itself until warmed up from knock (detonation). Some call it limp mode. This can be adjusted as not to over compensate thus causing a "dead spot"....
So can it be "adjusted" a little less to reduce the "dead spot" by the original tuner, and if so is it much work?
ringram said:
You are asking the wrong people unless you want idle speculation
We have seen exactly as the original poster describes being caused by a few things. The engine is "hunting" for the correct settings to send to the ECM for TPS/IAT/A/F etc. It is just a hesitation but is annoying as heck
as something is off and this causes the ECM to go "hunting" 1.MAP tuned incorrectly (is far and away the biggest culprit.)
2.MAP sensor has come loose at the manifold.
3. Small vacuum leak.
4. Throttle Body blade needing adjustment. You should see the throttle body opened around 10%-12% at idle. Many see much less and this condition causes the car to "putter"..when you drive away when cold also. Especially on the 05's and 06's!
If there were no modifications at all I would suspect the throttle body positioning sensor is out of whack and needs adjusted. But the original poster claims to have "tuned" for the exhaust which leads me to believe he may need to have his tuner recheck the MAP tuning.
sargegto said:
ringram said:
You are asking the wrong people unless you want idle speculation
We have seen exactly as the original poster describes being caused by a few things. The engine is "hunting" for the correct settings to send to the ECM for TPS/IAT/A/F etc. It is just a hesitation but is annoying as heck
as something is off and this causes the ECM to go "hunting" 1.MAP tuned incorrectly (is far and away the biggest culprit.)
2.MAP sensor has come loose at the manifold.
3. Small vacuum leak.
4. Throttle Body blade needing adjustment. You should see the throttle body opened around 10%-12% at idle. Many see much less and this condition causes the car to "putter"..when you drive away when cold also. Especially on the 05's and 06's!
If there were no modifications at all I would suspect the throttle body positioning sensor is out of whack and needs adjusted. But the original poster claims to have "tuned" for the exhaust which leads me to believe he may need to have his tuner recheck the MAP tuning.
Yes, its definitely hunting. Thanks for the advice both of you, will speak to the tuner.
Not really. Its almost never at zero. Cold start and idle is often around 20% etc. You can just check its working "about" right.
There are DTC codes that will trip if its too far out anyway, (ie) Airflow exceeds set parameters.
You can look in the tune and see what these are under the engine diagnostic section.
Idle transitions are the hardest things you have to tune. The rest is pretty easy. So many different conditions, brake vacuum, aircond load, alternator, power steering, hold and cold start, hot and cold air and engine temps etc. Plus any and all combinations of these.
Thats why Ive not done mine properly yet, Ive been messing for ages trying to get idle transitions and startup working nicely. Basically a reflash each time I drive it to try a small change or two.
There are DTC codes that will trip if its too far out anyway, (ie) Airflow exceeds set parameters.
You can look in the tune and see what these are under the engine diagnostic section.
Idle transitions are the hardest things you have to tune. The rest is pretty easy. So many different conditions, brake vacuum, aircond load, alternator, power steering, hold and cold start, hot and cold air and engine temps etc. Plus any and all combinations of these.
Thats why Ive not done mine properly yet, Ive been messing for ages trying to get idle transitions and startup working nicely. Basically a reflash each time I drive it to try a small change or two.
It's the same on an LT1, but here's my brand new throttle body (bought complete with sensors) stalling the car
http://www.youtube.com/watch?v=7uuZKDey_WU
Ten minutes with a voltmeter and some patience and it read 0% at 0 and 100% at WOT
http://www.youtube.com/watch?v=7uuZKDey_WU
Ten minutes with a voltmeter and some patience and it read 0% at 0 and 100% at WOT
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