golfdave
Autocross Champion
- Location
- Scotland (U.K.)
- Car(s)
- Mk7 Golf GT Estate
I've posted on here before about how the 1.4lt 140/150PS engines can adapt more to better fuel eg 98RON, as both camshafts are adjustable. However they will still hit the brick wall that is the pre-programmed limits written into the factory ECU software.
I notice this more now when I have my foot down when overtaking in the 40-70mph+ speed range. The car will be in 3rd gear & the torque is there low down, with the BHP peaking higher in the rev range. But instead of the torque plateauing as per the factory, the car now produces more, so it peaks early, & then tails off. The result is the car feels strong low down, then appears to run out of puff as you get high up say 5,000 to 6,000rpm, & with a bigger gap in the middle.
The engine is all ok, no fault codes, everything is well serviced by me, new timing belts fitted by vgood local dealer I know, etc., etc.,. So what is wrong? The car is basically producing circa 167bhp & 267Nm, & hitting the ECU software limits!
The ECU doesn't know what fuel you have put in it has no "fuel quality" sensor, so it relys 100% on two main factors:-
1. Knock (knock sensors) preignition of the fuel in the cylinder. Basically how late in the compression cycle of the air fuel mix in the cylinder, can the spark plug fire before the fuel self ignites causing detonation/pinking.
2. Lambda (two lambda sensors), one between the turbo & the first cat, the second sensor after the second cat. Basically the quality of the burn & % scrub of the exhaust gases by the two cats.
Basically it try's to keep the combustion of the fuel so that the exhaust gases register the correct Lambda reading for the best stochiometric (air fuel ratio) for that current load, altitude, fuel, speed etc..
The ECU will look at the accelerator position via its sensor, & determine the amount that the throttle flap should open. It will then alter the amount of boost provided by the turbo, by opening or closing the electronic waste gate to either increase into or dump boost pressure away from the cylinders. It will advance or retard the timing of the spark (how close the piston is to TDC when the spark fires), & opening & closing of the intake & exhaust valves using the variable camshafts. It will also control the amount of fuel injected & the timing of this by operating the fuel pump & injector nozzles.
Unfortunately, what is happening to me I have seen on other well looked after cars which only throw "lean fault" codes under high load high rev conditions. Basically the 98RON fuel & good condition engine hits the ECU limits & runs "just" lean at high revs! This is because the hard written end values in the ECU data will not allow more fuel to be pumped into the cylinders by the injectors at high revs! It might also not be able to advance the firing of the spark (timing) as much as it would like to, either as with a 98RON fuel you can advance the timing more than a 95RON fuel! (our cars are mainly programmed for 95RON) On our engines you also have to then balance this with more air into the engine "boost" & variable camshafts which might be hitting the end values!
When VAG write the ECU they programme it for the fuel it will mainly encounter in the countries of use. Mine has 95RON written on it as minimum. Therefore it might work on 91RON in emergencies, but mainly 95RON & make part use of 98RON. The "R/CS" engines have 98RON as the main fuel with 95RON for emergencies. So if you only want to use 98RON in our engine the existing map can only partially make use of the fuel, as it stands, so advancing the timing for 98RON mainly, with 95RON for emergencies like the R/CS would increase the power, & that's before you start tinkering with increasing boost etc.!
I notice this more now when I have my foot down when overtaking in the 40-70mph+ speed range. The car will be in 3rd gear & the torque is there low down, with the BHP peaking higher in the rev range. But instead of the torque plateauing as per the factory, the car now produces more, so it peaks early, & then tails off. The result is the car feels strong low down, then appears to run out of puff as you get high up say 5,000 to 6,000rpm, & with a bigger gap in the middle.
The engine is all ok, no fault codes, everything is well serviced by me, new timing belts fitted by vgood local dealer I know, etc., etc.,. So what is wrong? The car is basically producing circa 167bhp & 267Nm, & hitting the ECU software limits!
The ECU doesn't know what fuel you have put in it has no "fuel quality" sensor, so it relys 100% on two main factors:-
1. Knock (knock sensors) preignition of the fuel in the cylinder. Basically how late in the compression cycle of the air fuel mix in the cylinder, can the spark plug fire before the fuel self ignites causing detonation/pinking.
2. Lambda (two lambda sensors), one between the turbo & the first cat, the second sensor after the second cat. Basically the quality of the burn & % scrub of the exhaust gases by the two cats.
Basically it try's to keep the combustion of the fuel so that the exhaust gases register the correct Lambda reading for the best stochiometric (air fuel ratio) for that current load, altitude, fuel, speed etc..
The ECU will look at the accelerator position via its sensor, & determine the amount that the throttle flap should open. It will then alter the amount of boost provided by the turbo, by opening or closing the electronic waste gate to either increase into or dump boost pressure away from the cylinders. It will advance or retard the timing of the spark (how close the piston is to TDC when the spark fires), & opening & closing of the intake & exhaust valves using the variable camshafts. It will also control the amount of fuel injected & the timing of this by operating the fuel pump & injector nozzles.
Unfortunately, what is happening to me I have seen on other well looked after cars which only throw "lean fault" codes under high load high rev conditions. Basically the 98RON fuel & good condition engine hits the ECU limits & runs "just" lean at high revs! This is because the hard written end values in the ECU data will not allow more fuel to be pumped into the cylinders by the injectors at high revs! It might also not be able to advance the firing of the spark (timing) as much as it would like to, either as with a 98RON fuel you can advance the timing more than a 95RON fuel! (our cars are mainly programmed for 95RON) On our engines you also have to then balance this with more air into the engine "boost" & variable camshafts which might be hitting the end values!
When VAG write the ECU they programme it for the fuel it will mainly encounter in the countries of use. Mine has 95RON written on it as minimum. Therefore it might work on 91RON in emergencies, but mainly 95RON & make part use of 98RON. The "R/CS" engines have 98RON as the main fuel with 95RON for emergencies. So if you only want to use 98RON in our engine the existing map can only partially make use of the fuel, as it stands, so advancing the timing for 98RON mainly, with 95RON for emergencies like the R/CS would increase the power, & that's before you start tinkering with increasing boost etc.!
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