Forum » General Tuning Discussion » Need help getting my AFR at 14.1 at idle.

Need help getting my AFR at 14.1 at idle.

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I have a 90 supra with a 2JZGTE. Have bolt on parts precision 6766 turbo, 2200cc fuel injector, walbro 450 fuel pump and a haltech 2500 elite. When I try to make any adjustment it would go to 13.8 14.6 and ack like it want to cut off. While cruising the AFR stay between 10.8 and 11.7 most of the time. When I try to adjust it, it ack like it want to cut off. How can I get it to idle at 14.1 14.7 with out cutting off ? What the fuel pressure should be when using 2200cc injectors? Can somebody help me out please. I'm running 93 octane for now, I'm going to use E85 later on.

Hi Jahbless, Welcome to HPA.

Your base pressure should be whatever the information that you've entered into the software, usually 3 bar with the vac line off.

Has the ECU been tuned already or is it on a base map?

Could you post up a copy and a datalog for us to take a look?

I'm on a base map right now. When I get home I will make a data log. Make the data log at idle?

Idle is a good starting point.

Is the timing set right?

At 2200 cc, your injectors are oversized and operating in their non linear low end zone and and they are dropping into the "non-opening" state at very short pulswidths.

Swap the injector set to ID1700's or 1300's depending on your aim HP figure at 80% duty cycle.

Yes I am biased towards ID, take my statement for what it is worth.

Let's start with some basics - Which tuning method are you using? VE? Injection time?

Have you correctly adjusted your injector settings? Flow, dead time, current settings etc? In particular if the injector your using is a Siemens 2200, these are low impedance and need to be run with peak & hold current settings. I'll assume that's the injector your using?

It's important to make sure the basics are covered before trying to diagnose much further. It would also be worth noting the actual injector pulse width your seeing at idle. As Dynodom mentioned, if you're trying to drive the injectors at very low pulse widths then they can operate erratically.

You might want to start with a stock injector and get the car driving ok at low load, setup a reasonable VE MAP etc. and then move onto the bigger injectors. A lot of time can be wasted chasing your tail when doing many changes at one time and a car is far easier to tune on smaller injectors due to the low pulse width non-linear behaviour mentioned above.

I'm using the VE tuning method. Here can you get the information with the dead time etc. My goal is to make at lease 850 to 900 on e85. Hey Chris what do you want me put n the log?

The injector supplier should be able to supply the required data. If you haven't got anything I'd go back to the supplier and ask them to provide the data. Probably the most important distinction here though is if you're using the Siemens 2200 or a Bosch 2000 injector. The Siemens is low impedance while the Bosch is high impedance and both will require a different configuration in the Haltech. Failing to do this can result in damage to the injector drives.

I think the issue was raised in another thread that the Siemens exhibits quite pronounced non linearity at low pulse widths too and this can affect your ability to maintain a stable AFR.

Thank every body for your input. I finally got a chance look at the car. The injector dead time was all wrong, I got the right information and put it in the ecu and running a lot better. When it idle a 14.1 it sound like it has a slight missing. Do that comes from the car being to lean? I'm going log it and post the log here.

14.1 at idle isn't lean, it is slightly richer than stoich, you should be aiming for 14.7 on pump fuel.

What are the exact injectors that you have fitted? are they high or low impedance?

These are the injector I have in the car. I all so add a data log on the attach on the car at idle. When it do go any where 14.1 are more the car asks like it want to shut off.

That will likely be your problem right there, as it was mentioned, the Siemens low impedance injectors are 'operating in their non linear low end zone and and they are dropping into the "non-opening" state at very short pulse widths' at idle, you can try and combat this by increasing your idle speed or using your E85 as they will need to utilize longer opening times with this fuel.

As dynodom said, it might be worth swapping to a high impedance injector such as the ID range to give you better control at lower engine speeds.