toasterknight

It will not change the afr because the computer uses the front o2 sensors to adjust. Yes. The injector will push more fuel at the same duty cycle, but the computer uses the duty cycle to adjust afr.

You could use an injector that pushes 5lbs more per hour and the computer could still adjust. It would be ridiculously rich to start with but give it 10 minutes running and the computer will have adjusted the short term trim and will continue to adjust the long term over time.

cruiser54

You are so misled/wrong. Thar's okay just so long as you mislead no others. Carry on.

toasterknight

I agree with you 100% cruiser. It seems like he is thinking they are jets on a carb rather than part of an intelligent fuel injection system.

Hopkins

But even though the computer is adjusting the AFR, it still is basing all of its internal calculations off the flow rate of the stock injectors. When the computer sends fuel, it only knows it is sending it at the stock rate of delivery; when in fact the fuel is being delivered at a higher rate than the computer is anticipating. Yes it will adjust when it realizes it is running rich, but you can't change the fact that the injectors themselves will be pushing more fuel than stock.

My logic may be wrong, but nearest I can figure it will have to run at least somewhat richer because of the higher flow rate. Maybe not a noticeable amount. The computer will continue to adjust, but you can't change the fact that the computer is basing its calculations off stock flow rate when in reality the flow rate is greater than being accounted for.

Tsaani97xj

This has been an interesting thread to follow which got me doing some reading and I found this article enlightening.

http://m.4wdmechanix.com/?url=http%3...referrer=#2724

It doesn't exactly apply to the original question but answers some important ones IMO. From what I understand the only time you will likely see a richer operation with the 703s is during open loop such as WOT. During normal driving the PCM is going to compensate for the higher flow based on sensor readings.

btz0

The data is in front of you. The 703 fuel trim readings are more negative across the board. Negative fuel trims = rich condition. It's really straightforward. If the 703 fuel trims are more negative than the stock injector fuel trims, it's pretty simple to conclude that it is pulling more fuel with 703 injectors. How can you even argue this? Well I guess you aren't other than just saying "you are wrong".

As I've said, the difference is mostly negligible. Maybe the pros outweigh the cons for majority of people, but this thread was made specifically to discuss alternatives to the 703 injectors because they flow slightly too much for my taste. There is information out there that these injectors still flow slightly too much for even stroked 4.0 motors. This information coming from people who actually analyzed engine data and work with performance oriented engines, ecus and fuel systems. I made it pretty clear in the OP that I didn't want to run 703s.

The whole point of this is that they flow more fuel than the stock injectors. Is this bad? No. Of course the computer will compensate to keep the AFR within a reasonably good operating mixture. That's not the point of the discussion. The point of this discussion is that the injectors flow more, and as a result the fuel trims are somewhat more negative. Especially evident at WOT, but even in normal operating conditions as well. You can say whatever you want about it but I've posted fuel trims comparing the two.

cruiser54

Still won't RUN richer.

Hopkins

@btz0 let us know if you find a better alternative out there than the 703s

toasterknight

The negative trims means it has realized there are bigger injectors and is pulling cycles. It's not running rich.

investinwaffles

I dont have any actual AFR measurements, but I change my plugs every 30K miles and my plugs looked just fine when I changed them in November. Definitely not running rich enough to tell by looking at the plugs.

I changed them at the exact same time as my injectors so it is a direct correlation (in my mind at least).

Plus I gained gas mileage and a smoother start/idle over 200+k mile old injectors, but not really sure if that can be compared to a stock baseline for the PCM.

DonDarko

I don't have a 98, I have a 2000. Picked up injectors from four cylinder caravan. Been running them about 2 weeks. Just plugged in the scanner and I'm running -9.4 long term fuel trim. Which means the computer is making an adjustment by removing 9.4% from factory settings to keep the engine running properly. The engine is not running rich because it's being adjusted. However I think the point trying to be made is that he wants injectors that will run without an adjustment by the computer.

toasterknight

That's an unattainable goal. My factory injectors run +7.

DonDarko

An unmodified vehicle with no issues runs on 0% long term fuel trim. Do you really think that's unattainable?

Krakker

Injector guru's: I got a set of 789 injectors from a vendor, (trust me, under the mag, they say 789) they are 4 hole and are supposed to work with my 99 XJ. Are these similar to the other 7** something injectors and if so does anyone have any info or comparison?


Didn't want to make another injector thread when this one is already rolling.

toasterknight

In a perfect world yes, but no injector is perfect.