Injectors replacement question...again

[Jeey-S]

Hi to every TJ's fan. I'm sorry if I make some mistakes in English, It's not my first language. As I read about injectors really helped me to take a decision for their replacement with Mopar 's ones on my 2003 6 cyl. 4.0L engine but ... when i changed one last tuesday because of misfire 0301 code cylinder 1 ; after changed all spark plugs, changed the coil rail, the crank sensor all from Mopar original parts. Finally solved it but when i did it, i found another one cracked, so I really think for a all new change of them.

My question is, I found the original Mopar injector, made by Siemens Deka model 04854181 with all the specs of it on Rockauto site... I decided to go on the Siemens Deka site to see them and found another high performance injector with the same specs BUT it throw de double of the fuel capacity at the same pressure !!! As Jerry said previously the air flow is really huge on this engine !!! ....

They are at the same size, the same connectors (EV6) and the same impedance (12 ohms).. Original one : 22.5lb/hour of fuel at 43 PSI
high flow one : 44.5lb/hour at the same pressure !!!

Here, I give the 2 sites for specs to compare them...

Original Siemens Deka mopar parts 04854181 (FI11333S) : https://www.injectorplanet.com/prod...2&_sid=6aaa3739c&_ss=r&variant=42597338218714

Siemens Deka high performance fuel flow ( FI114357): https://siemensdeka.com/product/44l...style-with-ev6-uscar-connector-fi114357-60mm/

Did anyone tried to make this fit ?

Now the final question: how the ECU will drive the high flow one ? Could it control the idle and adjust for an optimal combustion ? And how the engine will react with so much gaz ?

Please tell me your idea about this modification... Thanks for your feedback !

 

[Jerry Bransford]

Double the potential fuel flow from a fuel injector won't help or change performance. The O2 sensors and PCM keep tight control over how much fuel flows through the fuel injectors and both would flow precisely the same exact same amount of fuel into the engine.

 

[Jeey-S]

Double the potential fuel flow from a fuel injector won't help or change performance. The O2 sensors and PCM keep tight control over how much fuel flows through the fuel injectors and both would flow precisely the same exact same amount of fuel into the engine.

Thanks for your answer Jerry, The one I replaced last tuesday came from Rockauto, it s the original Mopar 04854181 made by Siemens Deka and made in USA, if you have other suggestion or better choice, i ll be happy to see it. May be another US manufacturer build them but don t know which one is...

 

[Jerry Bransford]

I know of no better quality or performing injector than the Mopar.

 

[IOwnCalculus]

Double the potential fuel flow from a fuel injector won't help or change performance. The O2 sensors and PCM keep tight control over how much fuel flows through the fuel injectors and both would flow precisely the same exact same amount of fuel into the engine.

The issue is that the computer can't pull enough fuel to adjust for injectors twice the size on a stock engine. You'd be deep into negative long term fuel trims on the order of -50% to make that work and most computers stop at +/- 25%. P0172 and P0175 should show up around -20%.

A tune with adjusted fueling tables would resolve that, but to your point there is absolutely no benefit to doubling injector sizing here.

 

[Pfarmer]

Double the potential fuel flow from a fuel injector won't help or change performance. The O2 sensors and PCM keep tight control over how much fuel flows through the fuel injectors and both would flow precisely the same exact same amount of fuel into the engine.

Yep! That’s the problem with “performance parts” on the TJ; the ones that actually make a difference get discovered my the computer, the Computer makes adjustment, and you’re right back to where you started.

 

[F13NGN]

Hi,
I wouldn’t recommend fitting the up graded ones without a full ECU remap. This is required as there are 2 factors which determines how much fuel is injected, fuel pressure and injection duration. Running a higher flow injector at the same fuel pressure and duration will cause massive over fueling and kill power. These values are stored in the engine ECU and although the system can adjust fuel trim, I will not be able to adjust to the extent require for such a change of injector flow.
Also without some serious power modification there really is no need to upgrade injectors on a naturally aspirated engine. Maybe if you we’re running high lift cams, fully flowed head, long tube headers ect, you”might” need an upgrade, but probably still not required as most stock injectors will allow for a +25-30% flow increase.
Hope this helps.

 

[CharlesHS]

The only changes I would consider in fuel injector design would be IF the fuel injectors require replacing then go from the 1 hole to the 4 hole fuel injector design which will provide better atomization of the fuel when sprayed into the combustion chamber. This would provide a slight bump in performance and a slight drop in combustion emissions.

 

[SkylinesSuck]

Double the potential fuel flow from a fuel injector won't help or change performance. The O2 sensors and PCM keep tight control over how much fuel flows through the fuel injectors and both would flow precisely the same exact same amount of fuel into the engine.

This isn't accurate at all. The PCM can pull a certain percentage of fuel in closed loop to get AFRs where they need to be, but it's not going to have a clue what to do with injectors that flow twice as much not to mention what's going to happen on open loop. However, your advice for OEM injectors is what I'd recommend as well--not because magical MOPAR branded parts, but because correct size.

OP--do not swap injector sizes without tuning the PCM to accommodate them, and that is only needed to feed the engine more fuel if you hit the limit of your current injectors which I'm sure you have not.

TL/DR--put the stock injector back in it.

 

[Jeey-S]

I know of no better quality or performing injector than the Mopar.

Ok. That s what i ll buy. Thanks a lot for your feedback. It' s always really appreciated ! Have a good day!

 

[Jerry Bransford]

This isn't accurate at all. The PCM can pull a certain percentage of fuel in closed loop to get AFRs where they need to be, but it's not going to have a clue what to do with injectors that flow twice as much not to mention what's going to happen on open loop.

The PCM controls the amount of fuel injected by varying its pulse width used to control the fuel injectors. It simply shortens or lengthens the pulse width to provide the correct amount of fuel whether it's a factory injector or one with a higher flow potential. Even the factory injectors can flow far more fuel than is necessary. It just generates shorter pulse widths for injectors with extra flow capacity.

 

[IOwnCalculus]

The PCM can do that, but only within a narrow range. It can't reduce it infinitely because it has logic built into it to say that if it has already reduced fuel by X percent and it still thinks the engine is rich, that something is wrong. Thus, it'll set P0172 and P0175 because even though it's reduced the fuel by as much as possible, the O2 sensors are still telling it the engine is running rich, and at that point the PCM doesn't know if that's because if the engine is actually running rich for reasons the PCM can't control (stuck-open injector, or an injector flowing double what the PCM was calibrated for) or if the O2 is lying and saying the engine is still running rich.

 

[SkylinesSuck]

@IOwnCalculus exactly.

@Jerry Bransford It can only control things inside of a relatively narrow set of parameters. An injector twice as big is well well outside of that. It would try adjusting to a point then the PCM will say "okay, WTF?!?" and throw a code. Slightly bigger injectors is exactly what many people do to "tune" their stroker without really knowing why it kinda sorta works. I can explain further and in more detail if you want reference the stroker injector thing. It's a good example to wrap your head around it actually. And also, you are absolutely right the factory injectors are more than big enough, even for a stroker (if you tuned for it though).

 

[IOwnCalculus]

@IOwnCalculus exactly.

@Jerry Bransford It can only control things inside of a relatively narrow set of parameters. An injector twice as big is well well outside of that. It would try adjusting to a point then the PCM will say "okay, WTF?!?" and throw a code. Slightly bigger injectors is exactly what many people do to "tune" their stroker without really knowing why it kinda sorta works. I can explain further and in more detail if you want reference the stroker injector thing. It's a good example to wrap your head around it actually. And also, you are absolutely right the factory injectors are more than big enough, even for a stroker (if you tuned for it though).

Funny enough, I decided to catch up on Youtube and SMA literally did a video fixing this exact issue last month. GM product but the basic logic is the same across everything OBD2.


P0172 and P0175, maxed out negative fuel trims, caused by unknown injectors flowing way more fuel than the PCM was calibrated for.