Does increasing the size of your injectors cause problems?

[surreybc]

1992 240sx

I think I went from around 270 cc to 370cc. I assume the computer would adjust by itself? I didnt reset the computer.

[adictd2b00st]

what do you mean you "think" you went from 270 to 370? If you changed the size of the fuel injectors, and have nothing to tune it with, then how do you expect the computer to know that you're running larger injectors?

[jiggs]

Hahah now thats a classic, anyways the comp wont adjust cuz the comp still thinks it 270cc injectors, if you dont tell the comp somethings different, its still gonna flow the same amount of fuel regardless

[surreybc]

Hahah now thats a classic, anyways the comp wont adjust cuz the comp still thinks it 270cc injectors, if you dont tell the comp somethings different, its still gonna flow the same amount of fuel regardless

The computer obviously adjusts the duty cycle. I'm just curious how long it takes the computer to adapt and if it has any problems during idle.

[[email protected]]

it will not adjust. if I'm thinking right, I could be wrong, let's just say that on idle, the stock injectors are flowing at 10% of 270cc injectors then with 370cc injectors, it will also flow the "10%" of 370cc which is much more rich. although this is just a example, not very accurate

[surreybc]

it will not adjust. if I'm thinking right, I could be wrong, let's just say that on idle, the stock injectors are flowing at 10% of 270cc injectors then with 370cc injectors, it will also flow the "10%" of 370cc which is much more rich. although this is just a example, not very accurate


It will definitely adjust. That's a given. I just worried that it wont adjust completely. I got some really bad smog results a few months after installing the new injectors. high hydrocarbons during idle and driving. Dumb mechanic replaced my computer which I tested to be good. However, I pass smog with these injectors now, but I do have trouble with high hydrocarbons during idle.

[singlecamslam]

Without a tune it will run "crappier." Why would you put bigger injectors in the first place? use your stock ones.

[surreybc]

Without a tune it will run "crappier." Why would you put bigger injectors in the first place? use your stock ones.


I was assured that they would not be a problem. at the time, deatchewerks didnt sell the stock size.

[HYPNOTIK]

Your car is NA?

[projectRDM]

It will definitely adjust. That's a given. I just worried that it wont adjust completely. I got some really bad smog results a few months after installing the new injectors. high hydrocarbons during idle and driving. Dumb mechanic replaced my computer which I tested to be good. However, I pass smog with these injectors now, but I do have trouble with high hydrocarbons during idle.

It will not adjust to the level you're hoping for. Although the ECU is self learning, it can't 'see' a larger injector. Just like plugging something into a wall outlet, the outlet doesn't know if you've plugged in a TV or a toaster, if it's a 20A circuit it will only know if the item is drawing more than 20A, anything less it's just another appliance. The ECU sends a signal to the injector to trigger it but can't establish what size it is from that, the extra fuel will trigger the O2 to send a signal that the car is running rich, forcing the ECU to lean out the mixture, but only within it's limits. You still need a piggyback to alter the signal so the ECU isn't trying to compensate for what it believes is a problem.

I'm surprised you'd even think this is possible, we've all known and been over the ECU's limits since before the internet, why do you think tuning equipment like the AFC exists? In your mind, none of that is required, just stick whatever size injector and MAF you want on the car and the ECU will do the rest. That's not how it works.

[adictd2b00st]

It will definitely adjust.

keep telling yourself that lol its not coincidence that so many people in here have already said it wont work....

[4x4le]

370cc injectors in place of the 270s will idle fine when in closed loop, but as soon as your in open loop your going to be dumping more fuel than necessary.

[surreybc]

370cc injectors in place of the 270s will idle fine when in closed loop, but as soon as your in open loop your going to be dumping more fuel than necessary.

I have passed two years of rigorous smog (including idle test) with good numbers. the computer does what it has to to maintain the target idle. i dont know if there is any mechanism during idle to reach an optimal air fuel mix. you could be right though because I do get a constant code during idle for too much fuel. I definitely failed at idle with my aiv disconnected and most people pass without aiv. other factors could be involed though. or you could be guessing like the rest of the pack. i will research this some more.

[murda-c]

Your injectors are too big.

That's your problem.

Get stock size injectors, or get some kind of tuning capability.

[adictd2b00st]

I have passed two years of rigorous smog (including idle test) with good numbers. the computer does what it has to to maintain the target idle. i dont know if there is any mechanism during idle to reach an optimal air fuel mix. you could be right though because I do get a constant code during idle for too much fuel. I definitely failed at idle with my aiv disconnected and most people pass without aiv. other factors could be involed though. or you could be guessing like the rest of the pack. i will research this some more.

you think you're the first one to ever put larger injectors in? we're not "guessing", its common knowledge lol

[projectRDM]

I have passed two years of rigorous smog (including idle test) with good numbers. the computer does what it has to to maintain the target idle. i dont know if there is any mechanism during idle to reach an optimal air fuel mix. you could be right though because I do get a constant code during idle for too much fuel. I definitely failed at idle with my aiv disconnected and most people pass without aiv. other factors could be involed though. or you could be guessing like the rest of the pack. i will research this some more.

Kid, you're fucking stupid. End of story. Since the dawn of fuel injection it's always been the same, anyone who builds or tunes a car will tell you the same thing.

The ECU does not 'see' the injectors at all. It measures pulse width from the injectors, after they're signaled, that's it. In your mind, the injectors are sending the ECU the signal, that's not even possible. The ECU begins the A/F graph with a measurement of air from the MAF, and with that measure it then signals the injectors to compensate for that airflow, making the correct A/F ratio. It then doublechecks that with the O2 sensor, so it can adjust accordingly (in very small parameters) so that the engine runs right where the ECU is programmed to run. You can have 100cc injectors or 1000cc injectors, the ECU does not know and cannot tell what they are, all it knows is X amount of airflow calls for X amount of fuel, period. By using larger injectors, X amount of fuel will always be more than the measured airflow, so the ECU attempts to lean the mixture out since it detects a problem, which is this case is too much fuel. Continued attempts force the ECU to go into open loop as it cannot adjust accordingly to meet the required A/F mixture, because from idle to redline it's seeing too much fuel. Nowhere can it detect the added fuel is coming from a larger injector, it's programmed one way and that way only, to supply fuel for the given injector that's prefitted. Anything larger has to have the signal modified from the MAF to the ECU so it reads a greater airflow to compensate for the increased fuel within the limits of the ECU.

50% duty cycle on a 370cc injector will always be more than a 270cc injector, so at 50% the ECU is seeing a rich fuel map. Always. There is no possible way for the ECU to relearn the increased injector size because it's not reading the size nor the volume, all it sees is what the signal is doing, in the case above, 50%. It will then try to recalibrate as the air and fuel numbers don't match, but there's no way it can learn a different curve just because you want it to.

[4x4le]

I have passed two years of rigorous smog (including idle test) with good numbers. the computer does what it has to to maintain the target idle. i dont know if there is any mechanism during idle to reach an optimal air fuel mix. you could be right though because I do get a constant code during idle for too much fuel. I definitely failed at idle with my aiv disconnected and most people pass without aiv. other factors could be involed though. or you could be guessing like the rest of the pack. i will research this some more.


Im not guessing man. My business is actually reprogramming nissan ecus for people that want to run larger injectors and different mafs and want to retune for more power.
We install daughter boards on the computers and sell the software and hardware needed so that you can tell your ecu you are using larger injectors so then it knows for sure.

That "mechanism" that allows it to meet the proper air fuel ratio at idle and cruise is called an o2 sensor. Since your injectors are not that much larger it will be able to correct for them that way enough to make it not run horrible. It can reduce enough pulsewidth that way but it sees that it is having to do that too often hince your ecu message.

With you having as many posts as you do have on here I am very supprised you have not heard of anyone that has done any tuning on here.... Do you think they call cars like this tuner cars for no reason?

You either need to buy a daughter board and some tuning equipment, the correct sized injectors, or an adjustible fuel pressure regulator. If you know for a fact that your running 370cc injectors you might be able to get away with a 30% decrease in fuel pressure but decreasing fuel pressure can be more dangerous than you probably think and without a wideband (which you most likely dont have) I would strongly advise against that rout.

Well I hope to have been able to provide you with enough info to get your problem fixed.

[surreybc]

I checked some sources and it seems the 370cc injectors might cause a rich idle. This shouldnt be a problem in california where it is closed loop during idle. if there is a jurisdiction outside of california that tests smog during idle you might have a problem with these injectors.

[surreybc]

Im not guessing man. My business is actually reprogramming nissan ecus for people that want to run larger injectors and different mafs and want to retune for more power.
We install daughter boards on the computers and sell the software and hardware needed so that you can tell your ecu you are using larger injectors so then it knows for sure.

That "mechanism" that allows it to meet the proper air fuel ratio at idle and cruise is called an o2 sensor. Since your injectors are not that much larger it will be able to correct for them that way enough to make it not run horrible. It can reduce enough pulsewidth that way but it sees that it is having to do that too often hince your ecu message.

With you having as many posts as you do have on here I am very supprised you have not heard of anyone that has done any tuning on here.... Do you think they call cars like this tuner cars for no reason?

You either need to buy a daughter board and some tuning equipment, the correct sized injectors, or an adjustible fuel pressure regulator. If you know for a fact that your running 370cc injectors you might be able to get away with a 30% decrease in fuel pressure but decreasing fuel pressure can be more dangerous than you probably think and without a wideband (which you most likely dont have) I would strongly advise against that rout.

Well I hope to have been able to provide you with enough info to get your problem fixed.

I know you are not guessing. I was referring to some of the shady tree mechanics who think they are geniuses. I appreciate your help.