Interesting info on stuttering / hesitation prob
03-02-2006, 09:22 AM
#1
Member
Thread Starter
Interesting info on stuttering / hesitation prob
Right,
Given the few threads about hesitation etc... I decided to replicate it on mine and do some data logging.
Sat in traffic for a while and watched the display on the logger (shows Air Fuel Ratio (AFR) and knock)
Pulled away and immidietely the car hesitiated and wouldnt pull away. The dispay showed an AFR of 18-19
and the car was actually showing signs of det / knock, even at bugger all speed / rpm. The levels of knock were about what you would get at 6000 rpm. Not dangerous by any means but very odd. AFR or 18 is very very lean. Stoich combustion is 14.7 (no air or fuel left after combustion) and you normally see that at idle. Foot flat on the floor is about 12.
Basically what is happening is that the car isn't putting barely any fuel in, and there is a lot of air going in. Ie, the throttle is open but injectors not giving enough fuel. Looking further, the voltage from the MAP is very low.
The MAP tells the ECU what pressure is in the intake tract, and assumes an engine load from this (combined with TPS etc) and fuels the car accordingly.
The fact its reading low means it doesnt think it needs to put much fuel in, because it thinks the engine load is low, meanwhile you have your foot down and nowt is happening. The reason it thinks it is low is probably because its just ingested a load of hot air and the AIT and MAP cant compensate that quickly.
The same would be true if the MAP was damaged, so could explain some other peoples problems?
Hope this makes sense, but its nice to see the facts right in front of my eyes on this one!
Will try any post a data log up at some point.
MB
Given the few threads about hesitation etc... I decided to replicate it on mine and do some data logging.
Sat in traffic for a while and watched the display on the logger (shows Air Fuel Ratio (AFR) and knock)
Pulled away and immidietely the car hesitiated and wouldnt pull away. The dispay showed an AFR of 18-19
and the car was actually showing signs of det / knock, even at bugger all speed / rpm. The levels of knock were about what you would get at 6000 rpm. Not dangerous by any means but very odd. AFR or 18 is very very lean. Stoich combustion is 14.7 (no air or fuel left after combustion) and you normally see that at idle. Foot flat on the floor is about 12.Basically what is happening is that the car isn't putting barely any fuel in, and there is a lot of air going in. Ie, the throttle is open but injectors not giving enough fuel. Looking further, the voltage from the MAP is very low.
The MAP tells the ECU what pressure is in the intake tract, and assumes an engine load from this (combined with TPS etc) and fuels the car accordingly.
The fact its reading low means it doesnt think it needs to put much fuel in, because it thinks the engine load is low, meanwhile you have your foot down and nowt is happening. The reason it thinks it is low is probably because its just ingested a load of hot air and the AIT and MAP cant compensate that quickly.
The same would be true if the MAP was damaged, so could explain some other peoples problems?
Hope this makes sense, but its nice to see the facts right in front of my eyes on this one!
Will try any post a data log up at some point.
MB
03-02-2006, 10:58 AM
#5
Member
Thread Starter
Hi Kobe
Not really kangeroo, but does lead to that - its more a good few seconds of really holding back when you pull away.
Cant be driver enhanced from what I saw. Foot down, all air, no fuel, and a fair bit of det.
MB
Not really kangeroo, but does lead to that - its more a good few seconds of really holding back when you pull away.
Cant be driver enhanced from what I saw. Foot down, all air, no fuel, and a fair bit of det.
MB
