Turbo mode kicks in at 3300rpm?
Discussion
Hijacked from another thread.
A few times now I have booted my car from a low speed down a straight road. At some point, when already moving quite fast and well up the rev range, there is an extra little surge forward that has me puzzled and slightly worried.
I thought maybe the clutch is slipping slightly and eventually biting fully, but there is no other evidence of clutch problems.
I wondered also if there is something programmed in the ECU to suddenly give more power if certain conditions are met (speed, revs, throttle, load) to put it into 'turbo' mode.
I only notice this effect when accelerating quite hard.
MA chiped and tuned this car about three years ago. Recently the air intake was changed for a more 'breathable' one. Maybe this has upset the mapping slightly? Or am I talking rubbish?
msg said:
Also like you that engine really does take off at around 3,300 rpm. Not sure if ECU is programmed to do something different at this point?
A few times now I have booted my car from a low speed down a straight road. At some point, when already moving quite fast and well up the rev range, there is an extra little surge forward that has me puzzled and slightly worried.
I thought maybe the clutch is slipping slightly and eventually biting fully, but there is no other evidence of clutch problems.
I wondered also if there is something programmed in the ECU to suddenly give more power if certain conditions are met (speed, revs, throttle, load) to put it into 'turbo' mode.
I only notice this effect when accelerating quite hard.
MA chiped and tuned this car about three years ago. Recently the air intake was changed for a more 'breathable' one. Maybe this has upset the mapping slightly? Or am I talking rubbish?
It could be a lambda reading dodgy. The ECU ignores the lambda reading from 3100rpm onwards, might be worth either diconnecting the lambdas altogether to see if that makes a difference, or test the lambda outputs using a multimeter
Disconnecting the lambdas will cause the ECU to slightly enrichen the fueling at low revs.
Regards
Iain
Disconnecting the lambdas will cause the ECU to slightly enrichen the fueling at low revs.
Regards
Iain
I would advise against running with the lambda disconnected. It damages the sensor and will push the ECU into 'limp home' mode. If you want to see whether the lambda sensors are working, put an analogue volt meter into the back of the plug and monitor the sensor output signal. If should cycle between rich and lean about once a second or faster. If it's slower, the sensor is getting old. If it isn't cycling, there's a fault in the closed loop operation. The fault could be that the lambda sensor has died, but it could be some a fault elsewhere. You can get an idea where the fault is by comparing the behaviour of the two banks, and checking the operation of the other sensors.
If you aren't sure what all that means, that's probably a hint that you should take it in to an expert. It's moderately complicated, and if you don't know what you're doing it's easy to waste money replacing things that don't need it, and possible to damage things. People who earn a living sorting out problems like this will have no trouble tracking it down.
If you aren't sure what all that means, that's probably a hint that you should take it in to an expert. It's moderately complicated, and if you don't know what you're doing it's easy to waste money replacing things that don't need it, and possible to damage things. People who earn a living sorting out problems like this will have no trouble tracking it down.
leadfootlydon said:
Fascinating.
Why would the output from the lambda sensor be oscilating?
Why would the output from the lambda sensor be oscilating?
It's a narrowband sensor that basically just says 'rich' or 'lean'. If it says rich the ECU reduces the fuel, if it says lean it increases it. This means the system normally settles close to lambda 1 and keeps cycling between rich and lean. This all relies on the lambda sensor reporting the lambda value accurately and promptly. If it's very slow to respond or doesn't respond at all then the ECU will keep adding more and more 'correction' and end up completely wrong.
The ECU goes into a predetermined fixed fuel map above 3000 rpm. It only ever used the sensors to get the emmissions down to pass the various Co2 and hydrocarbon tests at below this with a bit of tweeking of the fixed map. It was never done for power, purely emmisions and to prevent excess fuel burning the catalyst.
Doesn't have to be a problem necessarily. Depending on cam you can get a step change in your bhp line/curve as you go through the rev range. Mine's at 3,500 or so with a 218 cam, proved by the power chart from a Mark Adams RR session. On the open road it feels a little bit like a turbo cutting in.
Now that is interesting, because I do have a 218 cam, and several dyno charts. The 'turbo kick' at 3100rpm is not caused just by the 218 cam.
When my 218 cam was installed (and ECU chipped and mapped in Jun 2003), the dyno shows good torque coming in at 2000rpm and rising smoothly and steadily right through to 4500rpm. Very nice!
Two years and 11,000 miles later (May 2005), good torque was coming in later at 2500rpm and rising in not quite such a straight line to 4600rpm. The torque curve goes flat as it crosses 3100rpm then rises some more. Interestingly, this is the first time I have paid close attention to the curve. I didn't notice anything amiss at the time.
I have dropped some injector cleaner into the tank and am going for a power run in January, which will be very interesting. And I'll do the lambda tests as suggested.
When my 218 cam was installed (and ECU chipped and mapped in Jun 2003), the dyno shows good torque coming in at 2000rpm and rising smoothly and steadily right through to 4500rpm. Very nice!
Two years and 11,000 miles later (May 2005), good torque was coming in later at 2500rpm and rising in not quite such a straight line to 4600rpm. The torque curve goes flat as it crosses 3100rpm then rises some more. Interestingly, this is the first time I have paid close attention to the curve. I didn't notice anything amiss at the time.
I have dropped some injector cleaner into the tank and am going for a power run in January, which will be very interesting. And I'll do the lambda tests as suggested.
leadfootlydon said:
......... The torque curve goes flat as it crosses 3100rpm then rises some more. ........
Hence you have a(n) (appropraitely named) "flat-spot", which if it wasnt there on a previous dyno run suggests that something has changed and probably represents some malfunction. Its either going to be fuelling or ignition system, which I know isnt very helpful but the list of possibilties is pretty long. Try the tests suggested above initially or get expert help.
Was the flat-spot not commented on / investigated by the dyno people, since finding things like flat-spots is one of the primary objetcives of putting the car on the dyno in the first place?
Edited by tahiti450 on Thursday 14th December 19:24
tahiti450 said:
leadfootlydon said:
......... The torque curve goes flat as it crosses 3100rpm then rises some more. ........
Hence you have a(n) (appropraitely named) "flat-spot", which if it wasnt there on a previous dyno run suggests that something has changed and probably represents some malfunction. Its either going to be fuelling or ignition system, which I know isnt very helpful but the list of possibilties is pretty long. Try the tests suggested above initially or get expert help.
Was the flat-spot not commented on / investigated by the dyno people, since finding things like flat-spots is one of the primary objetcives of putting the car on the dyno in the first place?
Yup, something must have changed.
In defence of the dyno people, it was more of a BHP shoot-out than a serious tuning session. I was young and green and had no idea what I was looking at. Other people has worse things wrong with their cars.
tahiti450 said:
Hence you have a(n) (appropraitely named) "flat-spot",
The term "flat spot" to me implies that the engine isn't running well in some point, that's quite different to the power curve levelling off. If the engine has lost power compared to previous runs then there is probably a fault of some sort, but the torque/power curves can level off without indicating a fault.
I've just spotted this thread and thought I'd give my input.
Around a year ago I had the same problem in my Chim (also a 5ltr) which was remedied, where like as said above, it seamed to accelarate smoothly upto 3000 revs or so and then you'd feel the back end squat and you'd be pulled back into the seat in what can only be described like a turbo type boost in performance.
Being green at the time I thought that this was normal behaviour and drove the car like that for around a year, but upon messing around one day in the drivers footwell I noticed the ecu resistor was unplugged, obviously at the time I didn't know it was an ecu resistor, but was educated on the below thread with input by Mark Adams, and once plugged back in and resetting the ecu my turbo like acceleration went.
I think it's to do with because the ecu resistor was unplugged and running on an alternative 4 ltr fuel map which is not correct for a 5 ltr, it runs lean at low revs but as the revs increase it goes rich and I guess that's where the boost tends to come from.
Obviously I may have interpretated it wrong, but it's worth a check to make sure the resistor is plugged in or not broke.
Anyway, hope it helps.
Craig
www.pistonheads.co.uk/gassing/topic.asp?h=0&f=13&t=223687
Around a year ago I had the same problem in my Chim (also a 5ltr) which was remedied, where like as said above, it seamed to accelarate smoothly upto 3000 revs or so and then you'd feel the back end squat and you'd be pulled back into the seat in what can only be described like a turbo type boost in performance.
Being green at the time I thought that this was normal behaviour and drove the car like that for around a year, but upon messing around one day in the drivers footwell I noticed the ecu resistor was unplugged, obviously at the time I didn't know it was an ecu resistor, but was educated on the below thread with input by Mark Adams, and once plugged back in and resetting the ecu my turbo like acceleration went.
I think it's to do with because the ecu resistor was unplugged and running on an alternative 4 ltr fuel map which is not correct for a 5 ltr, it runs lean at low revs but as the revs increase it goes rich and I guess that's where the boost tends to come from.
Obviously I may have interpretated it wrong, but it's worth a check to make sure the resistor is plugged in or not broke.
Anyway, hope it helps.
Craig
www.pistonheads.co.uk/gassing/topic.asp?h=0&f=13&t=223687
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