Injector Change

[riderz4101]

I recently changed my injectors on my JDM Sti from 550 to 650 (Deatschwerk) and I have been having a problem.

I rescaled them in the Injector flow rate to 650. The car runs extremely rich. In fact on spool up I get a bad stutter between 3500-4000rpm.

I noticed that my WB is hitting low 9s. I started pulling fuel in this region and its not as bad but still there.

This only happens on WOT though. So I am assuming on WOT it delivers more fuel. How can I fix this.

[Freon]

Well, increase the injector size more if you are rich across the board. You always need to adjust injector scaling to fix these problems. You can't just pop in the number you think it should be. It is in fact unlikely you'll get it just right the first time.

You may need to fix the deadtime as well.

[riderz4101]

Did that. Once I lean out the injector by scaling it high, I was idling at an AFR of 16. When I came back down to 650cc I idled with little or no correction.

[Freon]

So you when you get it to idle good, it is rich elsewhere? When you get it ok under load, it is way lean on idle?

Set the injector value back to what you need for good fueling under load, then steadily increase your deadtime until you idle right.

Deadtime has the largest effect on idle or very light loads where the total injector pulse is very small. A small change to deadtime will have a large affect on the fueling. So increasing it will richen up your idle. Under load deadtime is only a fraction of the total injector pulse, thus it doesn't have much affect.

There is also a huge question of how the tune was before. Stock intake? Have you ever messed with the MAF scaling table? Either way, this should work out for you. You shouldn't need to increase the deadtime more than maybe 50%. Just multiple the whole table by 1.2 (or add 20%) to start, work from there.

[riderz4101]

Hey thanks, the thing is the term deadtime is new to me. Can you explain what map exactly I should manipulate.

[zlancerman]

Deadtime is also known as the Battery Voltage Injector Latency Compensation table/map. The table shows what the "deadtime" of the injector is in milliseconds to different values of voltage. The basics is that it takes the injector a certain amount of time, or deadtime, to open before it can start spraying fuel. This value is different for differing voltages. The higher the voltage, the shorter the "deadtime". At idle, your voltage is around 14 V, so start with that value.

[riderz4101]

thanks. I edited that map as well and tried different values but not much gains. I finally pulled fuel in the areas that were too rich and got considerable gains so far.

[bmorrisj]

it is my understanding that increasing the injector scale value actually scales the injectors to increase pulse width and flow more fuel into the engine.... while decreaseing the value would do the opposite...

oh i forget the calculation to determine new injector flow compared to old injector flow

but with the stock 550cc (legacy gt) the stock value was 529.49cc and after the calc i ended up with 510.27cc, thats still a 20cc difference from the safe 529cc factory tune and 550cc actual flow....


try going down to around 450cc~470cc



*this is just a suggestion to help point into the right direction... change the value gradually to see if you have positive effects....



**from the ST guide...

[Freon]

For the raw value in the ECU you are correct. Larger injectors require a smaller value.

But if you have it converted into CC, it works as expected. Larger value, larger injectors.

The factory values look like 3500-5500. The unit is not "CC".