Running rich at idle and poor fuel economy after mods and tune

[aminoskee]

On 23/04/2023 at 1:27 AM, Puffwagon said:

Trims at 0 and O2 voltage pegged points to a stuffed O2 sensor.

 

See what it does at cruise too, maybe the idle fuelling is sh*t and it's ok at cruise. Watch the O2 readings for info.

 

A vacuum leak could be causing issues too. If the idle timing is very low, less than 10 degrees, you should look there.

 

The intank pump assembly gets modified to fit a 460. The sender will be at a slightly different level than it was before. Accustom yourself to the new fuel level readings and you'll be fine.

 

I took the car out today and drove it around with FORScan running live and monitoring both O2 sensor and STFT.

 

The O2 sensor live graph was mostly stuck at 0.92 volts and fluctuated slightly lower from time to time.

 

The STFT was mostly stuck at zero and moved slightly whenever the O2 sensor reading fluctuated.

 

The interesting thing is that the O2 sensor voltage drops below 0.92 volts whenever I press the accelerator a bit harder and wont change much during normal driving.

 

I don't know what to make of this!!!!

 

Also, I looked inside the engine bay and checked the O2 sensor and it looks pretty old and dirty.

 

I guess the tuner used the old O2 sensor of the stock factory exhaust system.

[aminoskee]

@Puffwagon I drove the car all week and on a few occasions had FORScan running and monitoring O2 sensor, STFT, LTFT, SPARKADV and Throttle Position.

 

Usually at idle the O2 sensor voltage is stuck at around 0.96 volts with STFT and LTFT stuck at zero and SPARKADV averages around 5.5 degrees.

 

Some other times at idle the the O2 sensor voltage is again stuck at around 0.96 volts with STFT ranging between 10% to 25%, LTFT stuck at zero and SPARKADV bouncing between 1 to 3.5 degrees.

 

However, O2 sensor voltage, STFT and LTFT and SPARKADV change as I drive the car.

 

O2 sensor voltage still wants to be around 0.96 volts even when the car is moving and only reduces when I push down the accelerator as if there is an inverse relationship between the O2 sensor voltage and Throttle Position.

[Puffwagon]

Go back to the tuner or any mechanic to confirm what you're telling me is what's actually happening. If it is the case you need to replace the O2 sensor.

[aminoskee]

@Puffwagon I'll do that and will report back.

[aminoskee]

@Puffwagon Called the tuner today and they didn't have time until Thursday. Me being me and very impatient, I decided to get a new O2 sensor from Fraud Stealership and installed it right away.

 

Unfortunately it didn't fix the problem.

 

Now the only difference is that the O2 sensor voltage signal rises to 1.0 volts and stays there at idle. However, it's more responsive whenever I push the accelerator pedal.

 

Both LTFT and STFT respond like before. Generally stuck at zero and only change when I push the accelerator pedal.

 

I don't know what to make of this.

 

Could it be a fueling issue caused by wrong injector parameters in the ECU???

 

Or maybe the fuel pressure in the fuel rail is too high due to improper/wrong FPR pressure adjustment causing injectors to spray more fuel???

 

I also looked at fuel pulse width and it was 0.39 ms at idle according to FORScan. I'm don't know if it is too high for 1650cc injectors at idle???!!!

[Puffwagon]

Wait until Thursday. I'm not going to speculate on everything you're asking, there isn't much point. I also think you might be interpreting the data you're seeing incorrectly, which further hampers remote diagnosis.

[BarraT]

Amin, Please confirm what was the issue in the end and what happen at the mechanic on " Thursday " Thanks

[aminoskee]

I had the car checked by my tuner on that "Thursday" and later we had a chat about the issue. The main problem was my lack of understanding on how larger injectors behave compared to smaller factory stock ones. Factory injectors are 440cc and I now have 1650cc injectors which are almost 4 times larger. The 1650cc injectors cannot be dialed down to match the flow rate of stock injectors at idle and naturally they'll spray more fuel at idle. It is just the way it is.

Later I spoke to a few guys who run the same injectors and they all confirmed that their fuel consumption at idle is around 2.4 L/Hour which is what I see on my dash cluster at idle.

The other thing that I noticed is that my average fuel economy is getting better as I drive the car more which is likely due to the ecu learning and adapting again. All adaptations were probably wiped out when the car was tuned. Initially When I picked the car up from my tuner right after the mods my fuel economy was around 24L/100km. Gradually it reduced to around 17 - 18L/100km and now I am getting 14 - 15 L/100km. I hope it gets even better over time.

I get much better fuel economy on the freeway and often the instant fuel consumption is somewhere between 6 - 7 L/100km or slightly more depending on the road inclination.