Aftermarket Fuel Injectors

[sixty7ss]

Wow... Okay. If you guys are going to have a pissing match on my thread, please use layman's terms. What does AFR mean? I figured out what WOT means after a while. The reason I'm asking questions on here is because I want to learn. I can't very well do that if y'all are speaking Greek.

You both make good points. Although, it does seem that there are quite a few XJ owners enjoying the benefits of the 784's. While the calculations presented made me have flashbacks of 9th grade algebra, they also made a little bit of sense - in a "clear as mud" sort of way.

Can my Jeep be damaged by using 784's? I suppose that question is more for Talyn, since I pretty much know Ben's answer.

 

[X E Ryder]

AFR is air to fuel ratio, usually shooting for around 14.7 parts air to 1 part fuel, adjusting for driving conditions yada yada

Yes I Want to learn more too! Can someone tell me which injector to put in a 91 XJ daily driver with chip, CAI and cat back?

Informative thread thanks!

 

[kndrewa]

For the 97+ 49psi fuel rail I would recommend the Ford YR3E-A4A or the XF2E-C4B.

Thanks Talyn! I've got a 97 XJ but never had a reason to investigate its manufacturing date. Since my model year was the cross-over year for the new body style, I know there might be some differences in some areas, but where/what I am not too sure. Every drop of information is another lead for research for me! I should get better at searching multiple forums, though - I spend *all* of my online XJ time here at .

 

[Frank Z]

Meant to post these here a few days ago...guess I put them in the wrong thread.

Interesting results here:

 

[Talyn]

The reason I'm asking questions on here is because I want to learn. I can't very well do that if y'all are speaking Greek.

AFR= Air fuel ratio, fuel trim numbers is how much the PCM reduced the injector duty cycle based on O2 feed back (how long its held open), and injector duty is the amount of time an injector is energized in percentage. The PCM wants a 14.7:1 AFR at cruise, idle and up to medium heavy throttle (aka closed loop). Under heavy throttle and WOT you will want a 12.5:1, but the PCM won't be able to control that via O2 sensor feed back. During that period (aka open loop)the PCM is deciding how much fuel to give it by relying heavily on the MAP sensor and referencing that reading to built in fuel look up tables.

Can my Jeep be damaged by using 784's? I suppose that question is more for Talyn, since I pretty much know Ben's answer.

No it won't be damaged. The PCM can pull enough fuel with out being limited to get the AFR it wants. But its not optimum especially in open loop.

Since my model year was the cross-over year for the new body style, I know there might be some differences in some areas, but where/what I am not too sure.

Pretty easy to tell. If you have the return less fuel system you will have the later style. ~49 PSI fuel pressure, later style, rounded injector sockets, later style.

I also should have been more specific in which fuel injector choice I disagree with. The Neon 703 is a good fit for the earlier years with a 39 psi fuel rail as it drops the flow down to close (mathematically) to what the factory injectors flow. Its the 784 or 703s on the later 49 psi fuel rail that I have an issue with.

Also, for those of you using the overhead console to get your fuel mileage, that number will be come junk when you change the stock injectors as the MPG number is based off injector pulse width.

 

[X E Ryder]

Just bought Bosch 0280155703 set for my '91

Well I hope I have not blown it, but I bought a set of refurb/built Bosch 0280155703 injectors for my '91 XJ.

With the other engine mods I have done I hope to see a good result so I can finish this dept and move on to suspension!

Regards,

 

[Talyn]

I wouldn't worry about your 91. Its more the later models with the 49psi fuel rail that I am disagreeing with.

 

[Programbo]

This "upgrade" has been used in literally 10's of thousands of 4.0 XJs over the years and every possible technical angle has been beaten to death in the discussions so whether it is "good" has already been decided long ago and proven over millions of miles of driving in 4.0's. Forget Wide Open Throttle. That`s not enough of a constant to figure into the equation for daily use.

If any of you guys still have questions about if the 703 or 784 injectors are a good upgrade for your stock 4.0 XJs (Forget "strokers" for the moment) I might suggest contacting the techs at companies like CS Perfomance, MotorMan, Injector ReHab, City Maker, etc etc and ask them. All they do for a living is re-build, test and sell injectors. See what they have to say and then decide.

 

[Talyn]

I haven't seen anything proven. And just because a company sells them doesn't mean they actually have done proper testing (which most haven't). One company sells the same injector for the 4.7 V8 and the I6 when they are clearly not the same flow rates.

 

[SolarBell]

Talyn - What is your opinion of the Precision Auto injectors? Looks like the same flow rate but much better atomization. A little expensive, but not unreasonably so. Up here at altitude even the stock injectors are dialed back.

 

[Programbo]

I haven't seen anything proven. And just because a company sells them doesn't mean they actually have done proper testing (which most haven't). One company sells the same injector for the 4.7 V8 and the I6 when they are clearly not the same flow rates.

Well obviously you know more about injectors than the guys who do it for a living and are the worlds leading authority on the subject so I guess I shall spread the word for everyone who did the swap and raves about the benefits to quickly yank the 703s and 784s they have been running for years from their smoothly functioning XJs before some disaster strikes.

 

[Ben824]

Well obviously you know more about injectors than the guys who do it for a living and are the worlds leading authority on the subject so I guess I shall spread the word for everyone who did the swap and raves about the benefits to quickly yank the 703s and 784s they have been running for years from their smoothly functioning XJs before some disaster strikes.

I like this guy! X2! Just run'em and be happy! I know I am!

 

[Talyn]

Just because someone does it for a living doesn't mean they know what the hell they are doing. Only need to find people that don't know any better. Obviously you two have no clue and no real data to back your claims up. Congrats.

Talyn - What is your opinion of the Precision Auto injectors?

Which ones?

 

[SolarBell]

Which ones?

The "1999-2004 Jeep 4.0L Upgrade" http://www.precisionautoinjectors.com/product.sc?productId=32&categoryId=3

 

[Customizer1000]

I've got a set of 703s for my 95, was leary of putting them in since ive heard it really doesn't do anything, now you say it does help a lot, so I'm back to wanting to put them in, only question is don't I have to reset the pcm? If so how?

 

[Talyn]

The "1999-2004 Jeep 4.0L Upgrade" http://www.precisionautoinjectors.com/product.sc?productId=32&categoryId=3

Unfortunately they list no specs and have removed the part numbers from the injectors.

I've got a set of 703s for my 95, was leary of putting them in since ive heard it really doesn't do anything, now you say it does help a lot, so I'm back to wanting to put them in, only question is don't I have to reset the pcm? If so how?

You should reset the PCM so it can relearn faster. Remove battery cables, wait for a few seconds then touch them together. This will drain the memory power from the PCM.

 

[Customizer1000]

Unfortunately they list no specs and have removed the part numbers from the injectors.


You should reset the PCM so it can relearn faster. Remove battery cables, wait for a few seconds then touch them together. This will drain the memory power from the PCM.

How long will it take to re learn?

 

[Ben824]

How long will it take to re learn?

You must also turn the headlight switch on and off 2 times while the the cables are disconnected to clear the computer's memory. It takes a certain amount of key cycles (turning the Jeep on and off so many times) before it can learn the new injectors. So the more you go out take it out to drive the faster it will learn them. Just a good excuse to take the Jeep to grocery store or to run errands haha

 

[CobraMarty]

What is the stock '98 injector rated at? is that at 43psi or 49psi?

 

[Ben824]

What is the stock '98 injector rated at? is that at 43psi or 49psi?

49 psi