Understanding primary and secondary injectors
 

I have searched all over and could not find a good explanation for the injectors set up on a 13b. Can someone please explain it to me? I know that there is primary and secondary injectors, and i have noticed that people use different sized injectors for both, i just want to understand how the fuel injection works on a 13b?

Well basically and this is skipping what causes all this to happen, under light acceleration which includes all rpm below about 3800 your car only runs on the primary injectors, the secondary are effectively off, under harder acceleration and some sensors doing there job above 3800ish rpm the secondary injectors kick on with the primary injectors giving you more fuel. On a non turbo car this happens at the same time as the auxiliary ports open to add more fuel to compensate for the extra air. Larger secondary injectors are used when people modify there intake and exhaust systems to make up for the extra air this let's flow through your motor, more power basically.

That is exactly what i was looking for, thanks. Can you have it tuned to increase/decrease the rpm range, for when the secondary injectors kick in?

RX-7fetish nailed it. The stock ecu cannot be adjusted. Modified rtek ECU's have a lower switchover rpm. Standalone EMS's should have an adjustable setting. I believe only 2 injectors are used because it would be difficult to control 4 injectors to deliver such a small amount of fuel.

FYI, Lowering the rpm won't add power unless you are running lean below the switchover rpm.

Ok, thanks guys that is what i was looking for

Not trying to thread jack but does increasing the primary injectors instead of the secondaries have the same effect in the end as to more fuel but will might suffer idle and low rpm problems?

Much easier/cheaper to get larger secondary injectors. it would seem to me larger primary would bog you down a lot in lower rpms unless you have some crazy porting/giant turbo. Just seems that larger primary isnt a great idea.

And getting them clean is a good bonus

Just asking because I'm running 820/720 right now and wanted to know if I would get more or less fuel than if I would've kept it at 720/820. Im guess it would be the same though.

720/820, on the rteks 720/720, would be best. otherwise you're wasting fuel.

when I used the 720/720 setting in the rtek with the 720/820 setup the car smoked like crazy at idle and was bucking everywhere with afrs bouncing from 14 to 17. I swapped in the 820's to the primary spot and it did the same thing but only minor adjustments were need. Now it is working perfectly but I want to know if it still supplies the same amount of fuel as with the 820's being in the primary position. Sorry if I'm being difficult....

One thing to think about a bit is........................when your engine is under LOAD and you hit the 3800 rpm mark and the secondarys come online, there is another thing to remember and it's the following.

The primarys might be hitting, as an example, a 80% duty cycle just prior to 3800 rpm. When you hit the 3800 rpm and the secondarys come online, the primary duty cycle gets cut waaaay back and now both primary and secondary injector duty cycles will match each other.

Mabe that was not clear. Say you have a digital meter attached to one of the primary injector wires. You stomp the gass and are headed for 3800 rpm. The meter might read 6vdc just prior to 3800 rpm and when 3800 rpm is past, the voltage on the meter will now read ? maybe 10 vdc.

The six vdc indicates a heavy load on the injector and the 10vdc represents a lesser load now that your past 3800 rpm and have the secondary injectors online helping out. Make sense???.

Maybe not too clear. Say you have a meter that has a duty cycle feature and your attached to a primary injector. You see a duty cycle of 80% just prior to 3800 rpm and once past 3800 rpm you now see ???? a 50% duty cycle on the primary injectors..........'cause the secondary injectors are no helping out now that their online. Once past 3800 and under LOAD, both primary and secondarys will have the identical duty cycle. That might help a bit or might confuse. I'm outta here and won't return to this thread.

If you don't mind me asking, where did you get that pdf file from?

From the free online training manual that can be found in the FAQ thread on this site.

EDIT: Well maybe not. Try this thread and read it. There is a link there: https://www.rx7club.com/showthread.p...raining+manual

Once upon a time NZCONVERTIBLE was on this site and he made it available to this site and I downloaded it yrs ago but not lately. So I'm not that sure where you can download it if it's not on the thread above.

Also a fellow named HENRIK on the RTEK forum has made a lot of threads on how the ECU works on a series four car. Years ago though.

manual, along with most of the others is @ www.foxed.ca

Thanks guys, that is going to be really helpfull.